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January 5, 1998

Volume 72, Issue 1,  pp. 1-133

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OPTICS

Advantages of ultraviolet Raman scattering for high temperature investigations

E. Zouboulis, D. Renusch, and M. Grimsditch

Appl. Phys. Lett. 72, 1 (1998) (3 pages)

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We show that UV Raman spectroscopy is eminently well suited for the in situ investigation of samples at high temperatures. Using sapphire as a test material, we have recorded Raman spectra from ambient temperature to 1700 K using different excitation wavelengths, both in the visible and near UV region of the spectrum. These spectra show that, because of the very rapid decrease of blackbody radiation in the short wavelength region, Raman spectra recorded in the near UV region of the spectrum are free from the blackbody radiation background, which typically hampers experiments in the visible. With 266 nm exciting radiation, we observe no thermal background even at 1700 K. We foresee that the method will become a powerful tool for in situ investigations of high-temperature materials. ©1998 American Institute of Physics.
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78.40.Ha, 78.30.Am

6.1 W continuous wave front-facet power from Al-free active-region (lambda =805 nm) diode lasers

J. K. Wade, L. J. Mawst, D. Botez, R. F. Nabiev, M. Jansen, and J. A. Morris

Appl. Phys. Lett. 72, 4 (1998) (3 pages)

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Al-free active-region diode lasers grown by low-pressure, metal-organic chemical vapor deposition and emitting at lambda =805 nm have been optimized for high continuous wave output power. The 1-mm-long devices consisting of an InGaAsP/In0.5Ga0.5P/In0.5(Ga0.5Al0.5)0.5P laser structure have a threshold-current density, Jth, of 310 A/cm2 and relatively high values for the characteristic temperatures of the threshold current, T0 (135 K), and differential quantum efficiency, T1 (900 K). Lasers with 10%/90% coatings and a 100-µm-wide stripe provide a maximum cw output power of 6.1 W at a heatsink temperature of 10 °C. The devices fail due to catastrophic optical mirror damage (COMD), where the internal power density, P-barCOMD, is 17.4 MW/cm2; that is, twice that for conventionally facet-coated, 810 nm emitting, AlGaAs active-region diode lasers. ©1998 American Institute of Physics.
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42.55.Px, 42.60.By

Two-color corrugated quantum-well infrared photodetector for remote temperature sensing

C. J. Chen, K. K. Choi, W. H. Chang, and D. C. Tsui

Appl. Phys. Lett. 72, 7 (1998) (3 pages)

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A quantum-well infrared photodetector (QWIP) based on the corrugated light-coupling scheme has been fabricated and tested for remote temperature sensing. The QWIP consists of two stacks of multiple quantum wells (MQWs), each sensitive in one of the atmospheric infrared transmission windows and each with a separate readout circuit. High optical coupling efficiency is obtained in both wavelength ranges, demonstrating the use of the corrugated structure for two-color detection. By monitoring the ratio of the photocurrent generated simultaneously in each MQW stack, the temperature of the object emitting the radiation can be determined, regardless of its emissivity and the geometrical factors. This temperature sensing ability is tested by using a blackbody radiator with precision temperature control as the target. The agreement between the measured and the preset temperatures indicates that the corrugated QWIP is capable of precision thermometric measurements. ©1998 American Institute of Physics.
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85.30.Vw, 07.57.Kp, 85.60.Gz, 07.07.Df, 42.79.Qx, 95.75.Rs, 93.85.+q

Simultaneous optimization of membrane reflectance and tuning voltage for tunable vertical cavity lasers

F. Sugihwo, M. C. Larson, and J. S. Harris, Jr.

Appl. Phys. Lett. 72, 10 (1998) (3 pages)

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Micromachined wavelength tunable vertical cavity lasers are attractive for applications ranging from wavelength division multiplexing to spectroscopy. An improved tunable structure that incorporates a partial anti-reflection coating to increase coupling between the air gap and the semiconductor cavity, and a more flexible micromachine process that enables independent optimization of the central reflector region and deformable membrane structure are described. This combination of structural and process modifications enables decoupling the tradeoffs between wavelength tuning rate and threshold current, as well as the tradeoffs between top mirror reflectance and tuning voltage. With these improved approaches, a 2.5 pair dielectric distributed Bragg reflector hybrid membrane top mirror produced singlemode devices with a 23 nm wavelength tuning range and multi-transverse-mode devices with a 30 nm wavelength tuning range. Threshold current, differential quantum efficiency, and lasing mode are characterized as a function of membrane bias. ©1998 American Institute of Physics.
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42.60.By, 42.55.Px, 42.86.+b, 42.60.Da, 42.60.Fc, 42.79.Wc

Red–green–blue light emission from hydrogenated amorphous silicon carbide films prepared by using organic compound xylene as carbon source

Tianfu Ma, Jun Xu, Kunji Chen, Jiafang Du, Wei Li, and Xinfan Huang

Appl. Phys. Lett. 72, 13 (1998) (3 pages)

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We fabricated hydrogenated amorphous silicon carbide (a-Si1-XCX:H) films by the plasma-enhanced chemical vapor deposition technique using organic compound xylene (C8H10) as the carbon source, which was initially attempted by W. A. Nevin H. Yamagishi, M. Yamaguchi, and Y. Tawada, Nature 368, 529 (1994). Here we used different preparation conditions from those authors to produce xylene-based a-Si1-XCX:H films, and a different light emission behavior of the films has been observed at room temperature. The light emission wavelength can be shifted from 630 nm to 450 nm by changing the optical band gap (Eopt) of the films from 2.3 eV to 3.5 eV, nearly covering the whole visible light range, which was never reported previously. Fourier transform infrared spectra showed that the configuration of the material was a combination of organic aromatic rings and inorganic SiC networks. ©1998 American Institute of Physics.
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78.66.Jg, 78.55.Hx, 78.20.Ci, 81.05.Gc, 81.15.Gh, 63.50.+x, 78.30.Ly, 52.75.Rx
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FLUIDS, PLASMAS, AND ELECTRICAL DISCHARGES

Effect of gravitational acceleration on temperature wave propagation in a critical fluid

Koji Ishii, Toru Maekawa, Hisao Azuma, Shoichi Yoshihara, and Mitsuru Onishi

Appl. Phys. Lett. 72, 16 (1998) (3 pages)

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Temperature propagation near the critical point of a classical fluid is investigated theoretically. The governing equations of thermal energy transfer near the critical point are introduced and a linear analysis is carried out. The dispersion relation between the angular frequency and the wave number is obtained and the wave characteristics are discussed. The effect of gravitational acceleration on the temperature wave propagation is made clear. Through this analysis, the following results were obtained; (1) The propagation speed of temperature waves is sqrt( gamma/(rho[sub 0] kappa[sub T])),where gamma, rho0, and kappaT are, respectively, the ratio of specific heats, the density, and the isothermal compressibility, with or without gravity if the wavelength is larger than 10–3.(2) The amplitude of wave increases with time in the antigravitational direction and decreases in the gravitational direction but the decay time is long if the wave number is small. (3) Waves decay quickly if the wave number is larger than 104. ©1998 American Institute of Physics.
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65.20.+w, 51.30.+i, 44.50.+f, 62.10.+s

Generation of ultrashort, discrete spectrum microwave pulses using the dc to ac radiation converter

P. Muggli, R. Liou, J. Hoffman, T. Katsouleas, and C. Joshi

Appl. Phys. Lett. 72, 19 (1998) (3 pages)

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The output radiation of a dc to ac radiation converter is characterized. A relativistic ionization front passing through a capacitor array of period d = 1 cm produces short pulses of tunable radiation between 39 and 84 GHz with a gas pressure between 0 and 30 mT. The frequency spectra of the produced pulses are discrete and exhibit full widths at half maximum between 12% and 28%, consistent with the expected width for six cycles' pulses. An upper bound of 750 ps (detection bandwidth limited) is placed on the pulse widths. These are the shortest pulses produced by a source of coherent radiation in this frequency range. ©1998 American Institute of Physics.
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52.75.Va, 52.25.Sw, 07.57.Hm, 52.50.Jm, 52.40.Db, 52.40.Fd

Emission of excimer radiation from direct current, high-pressure hollow cathode discharges

Ahmed El-Habachi and Karl H. Schoenbach

Appl. Phys. Lett. 72, 22 (1998) (3 pages)

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A novel, nonequilibrium, high-pressure, direct current discharge, the microhollow cathode discharge, has been found to be an intense source of xenon and argon excimer radiation peaking at wavelengths of 170 and 130 nm, respectively. In argon discharges with a 100 µm diam hollow cathode, the intensity of the excimer radiation increased by a factor of 5 over the pressure range from 100 to 800 mbar. In xenon discharges, the intensity at 170 nm increased by two orders of magnitude when the pressure was raised from 250 mbar to 1 bar. Sustaining voltages were 200 V for argon and 400 V for xenon discharges, at current levels on the order of mA. The resistive current–voltage characteristics of the microdischarges indicate the possibility to form arrays for direct current, flat panel excimer lamps. ©1998 American Institute of Physics.
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52.80.Hc, 42.72.Bj
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CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

Fuzzy controlled feedback applied to a combined scanning tunneling and force microscope

F. M. Battiston, M. Bammerlin, C. Loppacher, R. Lüthi, E. Meyer, H.-J. Güntherodt, and F. Eggimann

Appl. Phys. Lett. 72, 25 (1998) (3 pages)

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A feedback mechanism based on fuzzy logic has been applied to operate a combined atomic force microscope (AFM)/scanning tunneling microscope (STM), which is able to measure the resonance frequency shift Delta f of the cantilever-type spring and the mean tunneling current I-bart simultaneously. Using a decision making logic, the microscope can be scanned over a heterogeneous surface without tip crash. On the conductive parts of the sample, the STM mode is preferred, whereas the noncontact (nc)-AFM mode is used on the poorly conductive parts of the surface. The transition from the STM mode to nc-AFM mode is performed smoothly with the fuzzy logic feedback. ©1998 American Institute of Physics.
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07.79.Cz, 07.79.Lh, 61.16.Ch, 07.05.Mh

Thermally activated electron capture by mobile protons in SiO2 thin films

K. Vanheusden, S. P. Karna, R. D. Pugh, W. L. Warren, D. M. Fleetwood, R. A. B. Devine, and A. H. Edwards

Appl. Phys. Lett. 72, 28 (1998) (3 pages)

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The annihilation of mobile protons in thin SiO2 films by capture of ultraviolet-excited electrons has been analyzed for temperatures between 77 and 500 K. We observe a strong increase in proton annihilation with increasing temperature, and derive an activation energy for electron capture of about 0.2 eV. Based on quantum chemical [(OH)3Si]2[Single Bond]O[Single Bond]H + cluster calculations, we suggest photoexcitation of electrons from excited vibrational states of the ground electronic (valence band) state to a nearby excited electronic (SiO2 gap) state. It is argued that the latter excitation can result in H0 formation at elevated temperatures. ©1998 American Institute of Physics.
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73.61.Ng, 73.50.Gr, 72.20.Jv, 71.55.Ht

X-ray photoelectron spectroscopy study of excimer laser treated alumina films

D. G. Georgiev, K. Kolev, L. D. Laude, B. Mednikarov, and N. Starbov

Appl. Phys. Lett. 72, 31 (1998) (3 pages)

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Amorphous alumina layers are deposited on a single crystal Si substrate by a e-gun evaporation technique. These films are then thermally annealed in oxygen to be crystallized and, further, irradiated with an excimer laser beam. At each stage of the film preparation, an x-ray photoelectron spectroscopy analysis is performed at the film surface and in depth, upon ion beam grinding. Results give evidence for the formation of an aluminosilicate upon thermal annealing of the film in oxygen. At the surface itself, this compound is observed to decompose upon excimer laser irradiation at energy densities exceeding 1.75 J/cm2, giving rise to free Si atoms and SiO2, however with complete disappearance of Al atoms. Model photochemical reactions are proposed to explain such transformations. ©1998 American Institute of Physics.
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79.60.Bm, 61.72.Cc, 82.50.-m

Mesoscopic caverns and nucleation twins formed in the growth of Co on Cu

G. L. Zhou and C. P. Flynn

Appl. Phys. Lett. 72, 34 (1998) (3 pages)

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Mesoscopic caverns in the form of facetted voids are observed to form when Cu pumps through pinholes to the outer surface during the epitaxial growth of fcc Co(111) on Cu(111) near 500 °C. We prove that the pinholes are located mainly at boundaries between fcc twin domains that occur with ABC and ACB stacking. ©1998 American Institute of Physics.
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68.55.Jk, 81.15.-z, 61.72.Mm, 61.72.Qq

Scanning Joule expansion microscopy at nanometer scales

J. Varesi and A. Majumdar

Appl. Phys. Lett. 72, 37 (1998) (3 pages)

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We report a new technique called scanning Joule expansion microscopy that can simultaneously image surface topography and material expansion due to Joule heating with vertical resolution in the 1 pm range and lateral resolution similar to that of an atomic force microscope. By coating the sample with a polymer film, we demonstrate that sample temperature distribution can be directly measured without the need of fabricating temperature-sensing scanning probes.©1998 American Institute of Physics.
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07.79.-v, 61.16.Ch, 07.20.Dt, 68.35.Bs

Phase separation in InGaN grown by metalorganic chemical vapor deposition

N. A. El-Masry, E. L. Piner, S. X. Liu, and S. M. Bedair

Appl. Phys. Lett. 72, 40 (1998) (3 pages)

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We report on phase separation in thick InGaN films with up to 50% InN grown by metalorganic chemical vapor deposition from 690 to 780 °C. InGaN films with thicknesses of 0.5 µm were analyzed by theta–2 theta x-ray diffraction, transmission electron microscopy (TEM), and selected area diffraction (SAD). Single phase InGaN was obtained for the as-grown films with < 28% InN. However, for films with higher than 28% InN, the samples showed a spinodally decomposed microstructure as confirmed by TEM and extra spots in SAD patterns that corresponded to multiphase InGaN. ©1998 American Institute of Physics.
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68.55.Nq, 81.15.Gh, 81.05.Ea, 64.75.+g, 81.30.Mh

Nanocrystalline-silicon superlattice produced by controlled recrystallization

L. Tsybeskov, K. D. Hirschman, S. P. Duttagupta, M. Zacharias, P. M. Fauchet, J. P. McCaffrey, and D. J. Lockwood

Appl. Phys. Lett. 72, 43 (1998) (3 pages)

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Nanocrystalline-silicon superlattices are produced by controlled recrystallization of amorphous-Si/SiO2 multilayers. The recrystallization is performed by a two-step procedure: rapid thermal annealing at 600–1000 °C, and furnace annealing at 1050 °C. Transmission electron microscopy, Raman scattering, x-ray and electron diffraction, and photoluminescence spectroscopy show an ordered structure with Si nanocrystals confined between SiO2 layers. The size of the Si nanocrystals is limited by the thickness of the a-Si layer, the shape is nearly spherical, and the orientation is random. The luminescence from the nc-Si superlattices is demonstrated and studied. ©1998 American Institute of Physics.
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68.65.+g, 61.72.Cc, 61.80.Ba, 78.66.Db, 78.30.Am, 78.55.Ap

The role of second-neighbor effects in photoemission: Are silicon surfaces and interfaces special?

K. Z. Zhang, K. E. Litz, M. M. Banaszak Holl, and F. R. McFeely

Appl. Phys. Lett. 72, 46 (1998) (3 pages)

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A widely used assignment scheme for Si 2p core-level photoemission studies of silicon oxidation relies solely on the formal oxidation state of the silicon. The tacit assumption of this assignment methodology is that second-neighbor effects have no measurable effect on observed Si 2p binding energies. In this letter, new experiments are combined with literature precedents to make the case that the second-neighbor effects play an important role in determining binding energy shifts. ©1998 American Institute of Physics.
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79.60.Jv, 81.65.Mq, 73.20.At, 79.60.Dp, 79.60.Bm, 81.05.Cy, 73.20.Hb
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SEMICONDUCTORS

A "smarter-cut" approach to low temperature silicon layer transfer

Q.-Y. Tong, R. Scholz, U. Gösele, T.-H. Lee, L.-J. Huang, Y.-L. Chao, and T. Y. Tan

Appl. Phys. Lett. 72, 49 (1998) (3 pages)

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Silicon wafers were first implanted at room temperature by B+ with 5.0 × 1012 to 5.0 × 1015 ions/ cm2 at 180 keV, and subsequently implanted by H2+ with 5.0 × 1016 ions/cm2 at an energy which locates the H-peak concentration in the silicon wafers at the same position as that of the implanted boron peak. Compared to the H-only implanted samples, the temperature for a B+H coimplanted silicon layer to split from its substrate after wafer bonding during a heat treatment for a given time is reduced significantly. Further reduction of the splitting temperature is accomplished by appropriate prebonding annealing of the B+H coimplanted wafers. Combination of these two effects allows the transfer of a silicon layer from a silicon wafer onto a severely thermally mismatched substrate such as quartz at a temperature as low as 200 °C. ©1998 American Institute of Physics.
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61.72.Tt, 81.05.Cy, 85.40.Ry, 61.72.Cc

Estimation of doping density in HgCdTe p-n junctions using scanning laser microscopy

J. F. Siliquini, J. M. Dell, C. A. Musca, E. P. G. Smith, L. Faraone, and J. Piotrowski

Appl. Phys. Lett. 72, 52 (1998) (3 pages)

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Quantitative assessment of p- to n- type conversion due to reactive ion etching (RIE) of p-type Hg0.71Cd0.29Te is presented using laser-beam-induced-current (LBIC) measurements. For the RIE processing conditions used (390 mT, CH4/H2, 0.4 W/cm2), n-type conversion was observed in extrinsic arsenic-doped p-type Hg0.71Cd0.29Te which had previously undergone a Hg anneal to eliminate Hg vacancies. Effective doping density of the n-type converted region is determined by fitting a theoretically determined LBIC signature to the measured LBIC signal over a temperature range 80–300 K. Effective n-type doping density is the only fitting parameter used in the simulation, which was carried out using a commercial semiconductor device modeling package (SEMICADTM DEVICE). This noncontact experimental technique promises to be a useful tool in the characterization of p-n junction diodes in HgCdTe, and for studying the precise nature of p to n conversion in p-type HgCdTe. ©1998 American Institute of Physics.
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68.55.Ln, 85.40.Ry, 73.40.Lq, 73.61.Ga, 72.60.+g, 61.72.Vv, 61.72.Ss, 72.40.+w, 52.75.Rx, 81.65.Cf, 61.72.Ji, 73.20.Hb

An optical method for studying carrier diffusion in strained (InP)2/(GaP)2 quantum wires

Y. Tang, D. H. Rich, A. M. Moy, and K. Y. Cheng

Appl. Phys. Lett. 72, 55 (1998) (3 pages)

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The carrier transport in strain-induced laterally ordered (InP)2/(GaP)2 quantum wire (QWR) samples was examined with a noncontact Haynes–Shockley diffusion measurement which utilized time-resolved scanning cathodoluminescence. An anisotropy in ambipolar diffusion along the [110] and [11-bar 0] directions (perpendicular and parallel to the QWRs, respectively) was observed. The temperature dependence of this anisotropy was measured, revealing that carrier diffusion along the QWR direction is thermally activated. ©1998 American Institute of Physics.
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85.30.Vw, 78.60.Hk, 78.47.+p, 78.66.Fd

Auger carrier capture kinetics in self-assembled quantum dot structures

A. V. Uskov, J. McInerney, F. Adler, H. Schweizer, and M. H. Pilkuhn

Appl. Phys. Lett. 72, 58 (1998) (3 pages)

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We establish rate equations to describe Auger carrier capture kinetics in quantum dot structures, calculate Auger capture coefficients for self-assembled quantum dots, and analyze Auger capture kinetics using these equations. We show that Auger capture times can be of the order of 1–100 ps depending on barrier carrier and dot densities. Auger capture rates depend strongly on dot diameters and are greatest at dot diameters of about 10–20 nm. ©1998 American Institute of Physics.
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73.20.Dx, 72.20.Jv, 73.61.Ey, 73.40.Kp

Multiple-junction single-electron transistors for digital applications

R. H. Chen and K. K. Likharev

Appl. Phys. Lett. 72, 61 (1998) (3 pages)

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The concept of the capacitively coupled single-electron transistor (CSET) is generalized to a device based on a linear array of N tunnel junctions. The basic characteristics of such multiple-junction CSETs are calculated for several distributions of tunnel junction and coupling capacitances. The results indicate that for optimized parameters, the operating temperature and parameter tolerances increase appreciably with N, with the most striking gains for N <~ 5. For example, a five-junction transistor may provide a 2.5-fold increase of the maximum operating temperature, for the same minimum feature size. ©1998 American Institute of Physics.
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85.30.Wx, 85.30.St, 84.30.Sk, 85.30.Tv

The influence of the deformation on the two-dimensional electron gas density in GaN–AlGaN heterostructures

R. Gaska, J. W. Yang, A. D. Bykhovski, M. S. Shur, V. V. Kaminski, and S. M. Soloviov

Appl. Phys. Lett. 72, 64 (1998) (3 pages)

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We report on the effect of external strain on the two-dimensional electron gas density in AlGaN/GaN heterostructures grown on sapphire by low pressure metalorganic chemical vapor deposition. The electron sheet concentration in the studied samples was 4 × 1012–2 × 1013 cm – 2 and decreased with compressive strain. Lower doped heterostructures had a higher sensitivity to applied strain. The comparison between the experimental data and our model shows that the GaN layers are primarily nitrogen terminated at the heterointerface. ©1998 American Institute of Physics.
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73.40.Kp, 73.20.Dx

Capture of vacancies by extrinsic dislocation loops in silicon

S. B. Herner, H.-J. Gossmann, F. H. Baumann, G. H. Gilmer, D. C. Jacobson, and K. S. Jones

Appl. Phys. Lett. 72, 67 (1998) (3 pages)

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The capture of a flux of vacancies in Si by a band of extrinsic dislocation loops has been observed in Sb doping superlattices. Annealing Sb doping superlattices containing a band of dislocation loops in NH3 results in an injection of vacancies, which enhances the diffusion of Sb spikes located between the surface and loop band. By extracting the diffusivity in the Sb spikes on either side of the loop band, we conclude that over 90% of the injected vacancies are captured by the loops. ©1998 American Institute of Physics.
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61.72.Yx, 61.72.Ff, 68.65.+g, 66.30.Jt

Excitation density dependence of photoluminescence in GaN:Mg

Eunsoon Oh, Hyeongsoo Park, and Yongjo Park

Appl. Phys. Lett. 72, 70 (1998) (3 pages)

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Continuous redshift of an emission from 3.23 to 2.85 eV with decreasing excitation density is observed in the photoluminescence spectra of highly doped GaN:Mg. It has been explained by the formation of minibands originating from the overlap of deep levels and shallow acceptor levels. For nominally undoped samples the intensity ratio of a donor-bound exciton line and a donor–acceptor pair line changes dramatically with excitation density due to the limited number of acceptors. ©1998 American Institute of Physics.
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78.55.Cr, 71.55.Eq, 71.35.Cc

Phonon confinement effects in the Raman scattering by TiO2 nanocrystals

D. Bersani, P. P. Lottici, and Xing-Zhao Ding

Appl. Phys. Lett. 72, 73 (1998) (3 pages)

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Nanocrystalline TiO2 has been obtained by a sol-gel process by controlling the crystal size through the water/alkoxide ratio. Raman spectra of anatase nanocrystals with average sizes of 9.5–13.4 nm are reported and the correlation between the Raman band shape (peak position and linewidth) of the main feature at 144 cm – 1 and the crystals dimension is discussed. While in this system a minor role is played by nonstoichiometry and pressure effects, a model based on the phonon confinement, which takes into account the size distribution as determined by the transmission electron microscopy images, correctly reproduces the Raman band shape change. ©1998 American Institute of Physics.
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78.30.Hv, 61.46.+w, 61.50.Nw, 63.20.Dj

Temperature dependence of mobility in n-type short-period Si–Ge superlattices

T. P. Pearsall, A. DiVergilio, Pierre Gassot, Duncan Maude, Hartmut Presting, Erich Kasper, W. Jäger, and Dirk Stenkamp

Appl. Phys. Lett. 72, 76 (1998) (3 pages)

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We have studied the mobility and carrier concentration as a function of temperature between 4 and 300 K in n-type Si–Ge short-period superlattices. In the parallel transport configuration, we have measured a mobility ratio µ77/µ300 > 50 in an n-type strained-layer superlattice with a carrier concentration in the mid 1016 cm – 3 range. The peak mobility measured was 17 000 cm2/V s – 1 at 70 K. Carrier freeze-out effects frustrated transport measurements below 60 K. Above 80 K the mobility is limited by optical phonon scattering with a characteristic phonon energy of 60 meV. These characteristics indicate electron transport via extended states. ©1998 American Institute of Physics.
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73.61.Cw, 73.50.Lw

Positive charging of thermal SiO2/(100)Si interface by hydrogen annealing

V. V. Afanas'ev and A. Stesmans

Appl. Phys. Lett. 72, 79 (1998) (3 pages)

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Annealing of SiO2/(100)Si interfaces in hydrogen in the temperature range of 500–800 °C is found to introduce a considerable density of fixed positive charge. The charge is diamagnetic, and shows no correlation with any kind of dangling bond defects at the Si surface or in the oxide. The observed charged state is attributed to hydrogen bonding to a bridging oxygen atom at the interface (threefold coordinated oxygen center), which may account for the well-known oxidation-induced charge at the Si/SiO2 interfaces. ©1998 American Institute of Physics.
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61.72.Cc, 81.65.Mq, 41.20.Cv

Ultraviolet GaN light-emitting diodes grown by molecular beam epitaxy using NH3

N. Grandjean, J. Massies, M. Leroux, and P. Lorenzini

Appl. Phys. Lett. 72, 82 (1998) (3 pages)

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Si- and Mg-doped GaN layers were grown on c-plane sapphire substrates by molecular beam epitaxy with NH3 as the nitrogen precursor. Their optical and electrical properties were investigated by photoluminescence experiments and Hall measurements, respectively. P-type conductivity, with a net acceptor concentration of 3 × 1017 cm – 3 and a mobility of 8 cm2/V s, was obtained. Mesa-etched light-emitting diodes were processed from p–n junctions. The turn-on voltage is 3 V and the forward current reaches 20 mA at 3.5 V. The room-temperature electroluminescence exhibits a strong emission at 390 nm. ©1998 American Institute of Physics.
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85.60.Jb, 81.05.Ea, 81.15.Hi, 78.66.Fd, 78.55.Cr, 78.60.Fi, 73.61.Ey, 73.50.Jt, 73.50.Dn, 71.55.Eq

The effect of Al on Ga desorption during gas source-molecular beam epitaxial growth of AlGaN

J. R. Jenny, J. E. Van Nostrand, and R. Kaspi

Appl. Phys. Lett. 72, 85 (1998) (3 pages)

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In this letter, we report on the impact aluminum has on gallium desorption kinetics in AlGaN alloys grown by gas source-molecular beam epitaxy. Aluminum is found to preferentially incorporate into the AlGaN films over the range of fluxes and temperatures investigated [0.05 <= Ji(Ga) <= 0.5 ML/s; 0.1 <= Ji(Al) <= 0.2 ML/s; 700 °C <= Ts <= 775 °C]. As a result, Ga is not observed to incorporate into the film until the NH3 flux exceeds that required to grow stoichiometric AlN. This preferential incorporation stems from two facts: (a) Al has an ammonia cracking efficiency ~ 2.5 times greater than that of Ga, and (b) Al participates in a Al-for-Ga exchange. As a result of these factors and under NH3 limited growth conditions, the aluminum mole fraction in a layer can be controlled by changing the incident NH3 flux. ©1998 American Institute of Physics.
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81.15.Hi, 68.55.-a, 68.45.Da, 81.05.Ea

Mechanism of the photochemically induced reaction between Ga(CH3)3 and HN3 and the deposition of GaN films

C. J. Linnen and R. D. Coombe

Appl. Phys. Lett. 72, 88 (1998) (3 pages)

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Gaseous HN3 reacts with surface-bound Ga(CH3)x species slowly at 300 K to produce thin films containing azide-substituted gallium compounds. When mixtures of HN3 and Ga(CH3)3 over the surface are irradiated at 253.7 nm, the reaction is dramatically accelerated, and films containing GaN and complexed N2 are produced. Heating of these films to 400 K drives off the N2 leaving GaN. The mechanism of the reaction is thought to involve photodissociation of HN3 to produce excited NH(a1 Delta) and N2, followed by insertion of the NH(a1 Delta) into the Ga–C bond of surface-bound Ga(CH3)x molecules. The insertion product eliminates CH4 to leave GaN. ©1998 American Institute of Physics.
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81.15.Gh, 81.05.Ea, 82.50.Fv, 82.65.Pa
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ELECTRONIC TRANSPORT AND SEMICONDUCTORS

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High stability amorphous-silicon–nitride thin-film diode ring switch

M. T. Johnson, G. Oversluizen, A. A. van der Put, and W. H. M. Lodders

Appl. Phys. Lett. 72, 91 (1998) (3 pages)

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Hydrogenated amorphous-silicon–nitride thin-film diode (TFD) switches have been shown to degrade electrically at both the cathode (electron injection contact) and anode (noninjection contact) due, respectively, to electron–hole recombination and hot-electron-induced-state creation mechanisms. An antiparallel configuration of two asymmetric TFDs provides an elegant method to minimize the cathodic degradation and avoid the consequences of anodic defect state creation. In this way, extremely stable TFDs may be prepared. ©1998 American Institute of Physics.
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85.30.Kk, 85.30.Hi, 84.32.Dd
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SEMICONDUCTORS

Excitonic transitions in (GaAs)1 – x(Ge2)x/GaAs multilayers grown by magnetron sputtering

B. Salazar-Hernández, M. A. Vidal, H. Navarro-Contreras, R. Asomoza, and A. Merkulov

Appl. Phys. Lett. 72, 94 (1998) (3 pages)

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We report on excitonic transitions observed at room temperature in multilayers of (GaAs)1 – x(Ge2)x/GaAs grown by magnetron sputtering. We attribute the observation of the exciton absorption at room temperature to confinement effects on the bound electron–hole pairs inside the Ge-rich layers of the (GaAs)1 – x(Ge2)x alloys. From secondary ions mass spectroscopy these layers are measured to be 50, 33, and 30 nm in full width at half maximum (FWHM), for three different samples. These layers alternate with (GaAs)1 – x(Ge2)x alloy layers of very low Ge concentration that can be considered of plain GaAs, ~ 360 nm in thickness for two samples and 240 nm for a third one. The observed transition energies of the exciton are very close to [approximate] 1 eV both at 300 and 4 K. A calculation of exciton energy-level spacing and transition probabilities provides acceptable values for the exciton transition energies observed, considering a triangular quantum well as an approximation to the Ge profile in the confinement layers. The observed excitonic FWHM remain nearly constant at all temperatures examined (300–4 K). ©1998 American Institute of Physics.
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73.20.Dx, 81.05.Ea, 81.05.Cy, 81.15.Cd, 73.61.Ey, 68.65.+g, 78.66.Fd, 78.66.Db, 71.35.Cc, 79.20.Rf, 78.20.Ci

Effect of interface roughness and well width on differential reflection dynamics in InGaAs/InP quantum wells

Y.-G. Zhao, Y.-H. Zou, J.-J. Wang, Y.-D. Qin, X.-L. Huang, R. A. Masut, and A. Bensaada

Appl. Phys. Lett. 72, 97 (1998) (3 pages)

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We have observed differential reflection dynamics in In0.518Ga0.492As/InP multiple quantum wells, using the pump–probe technique, and examined the photoluminescence spectra to determine the interface quality for the samples studied. Our results show that the interface quality and well width of the quantum wells (QWs) strongly influence the differential reflection dynamics. The experimental results provide a direct evidence to demonstrate that photoexcited carrier diffusion in cap layer and barriers along the direction perpendicular to sample surface plays a dominant role in determining the differential reflection dynamics of the QWs. ©1998 American Institute of Physics.
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78.66.Fd, 78.55.Cr, 78.47.+p, 73.20.Dx, 68.65.+g

Signal strength enhancement and bandwidth tuning in moving space charge field photodetectors using alternating bias field

Chen-Chia Wang, Richard A. Linke, David D. Nolte, Michael R. Melloch, and Sudhir Trivedi

Appl. Phys. Lett. 72, 100 (1998) (3 pages)

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Enhancement of the photocurrent density generated by internal moving space charge electric fields in semi-insulating GaAs multiple quantum wells is observed when the sample is biased with a high speed, zero-mean square wave electric field which increases the internal space charge electric field strength. Tunability of the space charge field formation time is also demonstrated by adjusting the amplitude of the bias signal. This technique can be used to enhance the sensitivity of optical doppler frequency measurements based on moving space charge field effects in photoconductive semiconductors. Electronic tunability of the space charge field formation time also adds versatility in optical power spectrum analysis applications. ©1998 American Institute of Physics.
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85.60.Gz, 85.30.Vw, 77.22.Jp

Sensitization of the minority carrier lifetime in hydrogenated amorphous silicon

R. Rapaport, Y. Lubianiker, I. Balberg, and L. Fonseca

Appl. Phys. Lett. 72, 103 (1998) (3 pages)

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While sensitization of the photoconductivity, i.e., the increase of the majority carrier lifetime by the addition of recombination centers, is known for many years, there was no evidence or suggestion for the corresponding sensitization of the minority carrier lifetime. In this letter, we present experimental evidence for the existence of such an effect in device quality undoped hydrogenated amorphous silicon films. We propose possible scenarios that can yield the observed effect and mention the possible benefits of the minority carrier sensitization for the improvement of bipolar optoelectronic devices made of this material. ©1998 American Institute of Physics.
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73.61.Jc, 73.50.Gr, 72.40.+w, 73.50.Pz, 72.80.Cw

Boron-doped amorphous diamondlike carbon as a new p-type window material in amorphous silicon p-i-n solar cells

Chang Hyun Lee and Koeng Su Lim

Appl. Phys. Lett. 72, 106 (1998) (3 pages)

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A boron-doped hydrogenated amorphous diamondlike carbon (a-DLC:H) was prepared using a mercury-sensitized photochemical vapor deposition (photo-CVD) method. The source gases were B2H6 and C2H4. By increasing the boron doping ratio (B2H6/C2H4) from 0 to 12 000 ppm, the dark conductivity increased from ~ 10–9 to ~ 10–7 S/cm. A boron-doped a-DLC:H with an energy band gap of 3.8 eV and a dark conductivity of 1.3 × 10–8 S/cm was obtained at a doping ratio of 3600 ppm. By using this film, amorphous silicon (a-Si) solar cells with a novel p-a-DLC:H/p-a-SiC double p-layer structure were fabricated using the photo-CVD method and the cell photovoltaic characteristics were investigated as a function of a-DLC:H layer thickness. The open circuit voltage increased from 0.766 V for the conventional cell with a 40-Å-thick p-a-SiC to 0.865 V for the cell with a p-a-DLC:H (15 Å)/p-a-SiC (40 Å) double p-layer structure. The thin (< 15 Å) p-a-DLC:H layer proved to be an excellent hole emitter as a wide band gap window layer. ©1998 American Institute of Physics.
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84.60.Jt, 81.15.Gh, 73.61.Jc, 68.55.-a, 72.40.+w, 81.05.Gc, 72.80.Cw, 81.05.Cy, 72.80.Ng

Wurtzite GaN epitaxial growth on a Si(001) substrate using gamma-Al2O3 as an intermediate layer

Lianshan Wang, Xianglin Liu, Yude Zan, Jun Wang, Du Wang, Da-cheng Lu, and Zhanguo Wang

Appl. Phys. Lett. 72, 109 (1998) (3 pages)

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Wurtzite GaN films have been grown on (001) Si substrates using gamma-Al2O3 as an intermediate layer by low pressure (~ 76 Torr) metalorganic chemical vapor deposition. Reflection high energy electron diffraction and double crystal x-ray diffraction measurements revealed that the thin gamma-Al2O3 layer of "compliant" character was an effective intermediate layer for the GaN film grown epitaxially on Si. The narrowest linewidth of the x-ray rocking curve for (0002) diffraction of the 1.3 µm GaN sample was 54 arcmin. The orientation relationship of GaN/gamma-Al2O3/Si was (0001) GaN||(001) gamma-Al2O3||(001) Si, [11–20] GaN||[110] gamma-Al2O3||[110] Si. The photoluminescence measurement for GaN at room temperature exhibited a near band-edge peak of 365 nm (3.4 eV). ©1998 American Institute of Physics.
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81.05.Ea, 68.55.Jk, 81.15.Kk, 78.66.Fd, 71.20.Nr, 78.55.Cr, 73.20.At, 68.35.Ct
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SUPERCONDUCTORS

Reduction of flux creep by heat pulses

G. A. Levin, C. C. Almasan, D. A. Gajewski, and M. B. Maple

Appl. Phys. Lett. 72, 112 (1998) (3 pages)

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We investigated the possibility of reducing the giant flux creep in high-temperature superconductors by temporarily increasing the temperature T above the operating temperature T0, after the critical state is created at T0. This T increase leads to a supercritical state which decays rapidly so that, when T is decreased back to T0, the superconductor is in the subcritical state. We have found that both the maximum persistent current and the relaxation rate are hysteretic and differ substantially from the corresponding quantities measured after flux annealing. ©1998 American Institute of Physics.
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74.72.Bk, 74.60.Ge, 61.72.Cc

Low noise multiwasher superconducting interferometer

P. Carelli, M. G. Castellano, G. Torrioli, and R. Leoni

Appl. Phys. Lett. 72, 115 (1998) (3 pages)

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The dc-superconducting quantum interference device (SQUID) is a low-noise converter from magnetic flux to voltage which can have, in principle, an energy sensitivity near the quantum limit of [h-bar]/2. A critical parameter for the ideal performance is the device inductance, which must be kept as small as possible. Minimizing the SQUID inductance, however, is a major concern for a practical device; this requirement implies a small SQUID ring and hence magnetic coupling with an external signal is more difficult to achieve. Here we present an original scheme (called multiwasher) to circumvent this problem, and its implementation in an all-refractory thin-film device. Our scheme not only provides good magnetic coupling with a large input coil (0.5 µH) and very low SQUID inductance, but also shielding from outside uniform fields, such as those generated by ambient disturbances. The measured coupled spectral energy sensitivity in the white region at about 1 kHz is 28[h-bar] at 4.2 K and 5.5[h-bar] in a pumped helium bath at 0.9 K. The flux noise spectral density at 0.1 Hz and 0.9 K is Phin = 1 × 10–6 Phi0/sqrt(Hz). ©1998 American Institute of Physics.
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85.25.Dq
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MAGNETISM

A microstructural study of annealed Ti/Co/Cu/Co/MnFe/Ti spin-valve films

X. Portier, A. K. Petford-Long, P. Bayle-Guillemaud, T. C. Anthony, and J. A. Brug

Appl. Phys. Lett. 72, 118 (1998) (3 pages)

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Spin-valve properties are adversely affected by heat treatments and in order to study this effect, microstructural analyses of Ti/Co/Cu/Co/MnFe/Ti spin-valve films annealed at 225 and at 290 °C have been performed. Whereas the lower temperature tends to optimize the giant magnetoresistance (GMR) ratio, the higher temperature induces a significant decrease in the GMR ratio (from 7.5% to 5.2%). High resolution electron microscopy studies have explained this result as being due to the formation of a TiCo alloy at the Ti/Co interface and to a decrease in the thickness of the sense layer. No significant modification of either the Co/Cu or the Cu/Co interfaces has been observed. ©1998 American Institute of Physics.
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75.70.Cn, 73.61.At, 75.70.Pa, 81.40.Rs, 81.40.Gh, 73.50.Jt, 81.40.Ef, 68.55.Jk, 68.35.Ct

High performance alpha-Fe/Nd2Fe14B-type nanocomposites

W. C. Chang, D. Y. Chiou, S. H. Wu, B. M. Ma, and C. O. Bounds

Appl. Phys. Lett. 72, 121 (1998) (3 pages)

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The alpha-Fe/R2Fe14B-type exchange-coupled NdFeB nanocomposites with a coercivity (iHc) of more than 11 kOe and energy product, (BH)max, of more than 16 MGOe have been successfully obtained on melt spun (Nd0.95La0.05)7.5 + xFebalCr2B10 alloy powders, where x ranged from 3 to 3.5. It was found that a slight substitution of Cr for Fe suppresses the formation of the R2Fe23B3 and Fe3B phases during crystallization and results in the formation of an alpha-Fe/R2Fe14B mixture. Increasing the total rare earth content was found to enhance the remanence, and the iHc of (Nd0.95La0.05)7.5 + xFe80.5 – xCr2B10 ribbons was also increased drastically with increasing values of x. A Br of 9.2–9.7 kG, iHc of 11.1–13.2 kOe, and (BH)max of 16.5–18.0 MGOe have been obtained on (Nd0.95La0.05)7.5 + xFe80.5 – xCr2B10 (x = 3–3.5). ©1998 American Institute of Physics.
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75.50.Vv, 75.50.Ww, 75.50.Bb, 75.50.Kj, 81.05.Ys, 75.30.Et, 75.60.Ej

The spin-polarized scanning electron microscope observation of 0.1 µm marks recorded by magnetic field modulation on a magneto-optical recording disk

Teruo Kohashi, Hideo Matsuyama, Kazuyuki Koike, Yoshiteru Murakami, Yasuhito Tanaka, and Hiroyuki Awano

Appl. Phys. Lett. 72, 124 (1998) (3 pages)

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The magneto-optically recorded marks with magnetic field modulation method were studied using spin-polarized scanning electron microscopy. We confirmed that marks with as short a length as 0.1 µm could be written repeatedly even with laser spot sizes about 1.2 µm. This mark length is less than (1/6) that of present commercial products. ©1998 American Institute of Physics.
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85.70.Li, 42.79.Vb, 85.70.Sq, 75.60.Ej, 61.16.Bg
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PAPERS IN OTHER FIELDS

Enhanced cluster mobilities on Pt(111) during film growth from the vapor phase

V. Chirita, E. P. Münger, J.-E. Sundgren, and J. E. Greene

Appl. Phys. Lett. 72, 127 (1998) (3 pages)

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We use molecular dynamics simulations to follow the dynamics of small two-dimensional Pt clusters on Pt(111) at 1000 K. While close-packed Pt7 heptamers are extremely stable structures, the addition of a single cluster vacancy or an on-top adatom immediately results in intracluster bond breaking, reconfigurations, rotations, the introduction of stacking faults, and greatly enhanced cluster diffusion rates. Mapping center-of-mass motion for total simulation times > 145 ns revealed increases in cluster velocities by more than an order of magnitude with cluster migration occurring primarily by concerted motion and a novel diffusion mechanism involving double shearing of dimers/trimers. Contrary to some previous reports, edge-atom diffusion plays only a minor role. ©1998 American Institute of Physics.
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68.35.Fx, 61.72.Nn, 61.46.+w, 61.72.Ji, 68.45.Ws, 68.55.-a

Transient photocurrents in lead zirconate titanate thin films

A. Kholkin, O. Boiarkine, and N. Setter

Appl. Phys. Lett. 72, 130 (1998) (3 pages)

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Transient photocurrents are investigated in ferroelectric lead zirconate titanate (PZT) films illuminated by laser pulses in the spectral range of 340–380 nm. At low electric fields, the photocurrent is sensitive to the ferroelectric polarization state and changes sign upon the polarization switching. At higher fields, the polarization-independent current proportional to the applied electric field is dominant. The spectral dependence of polarization-dependent current is controlled by the excitation of charge carriers over the forbidden band of PZT having a maximum near 3.5 eV. Possible mechanisms of the observed effect are discussed and the possibilities of a nondestructive read out of polarization state in the ultraviolet spectral range are demonstrated. ©1998 American Institute of Physics.
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77.84.Dy, 77.55.+f, 73.50.Pz, 77.80.Fm, 77.22.Ej
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ERRATA

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Erratum: "Etch-pit initiation by dissolved oxygen on terraces of H–Si(111)" [Appl. Phys. Lett. 71, 1679 (1997)]

Christopher P. Wade and Christopher E. D. Chidsey

Appl. Phys. Lett. 72, 133 (1998) (1 page)

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+
 Abstract Unavailable
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99.10.+g, 81.05.Cy, 81.65.Cf, 68.35.Bs, 68.45.Da

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