Volume 18, Issue 6, November 2000
- regular articles
- brief reports and comments
- rapid communications
- papers from the 44th international conference on electron, ion, and photon beam technology and nanofabrication
- extreme ultraviolet (euv) lithography
- x-ray lithography and microscopy
- charged particle and photon optics
- electron beam lithography
- ion beams, lithography, and beam induced processing
- dry etching
- nanofabrication and nanodevices
- nano-mems, bio-nano, molecular electronic and atomic beam
Index of content:
- REGULAR ARTICLES
18(2000); http://dx.doi.org/10.1116/1.1322040View Description Hide Description
The growth parameters of grown on GaAs by molecular beam epitaxy were investigated. Low substrate temperatures coupled with lower growth rates and low arsenic overpressures were explored and the corresponding threading dislocation densities were determined using transmission electron microscopy. Threading dislocation densities in layers much thicker than the critical thickness were found to be as low as using optimal growth conditions. In addition, the critical thickness of the ternary alloy was estimated. The evolution of the misfit dislocations and threading dislocations was also examined as a function of epilayer thickness.
Investigation of mesa-sidewall effects on direct current and radio frequency characteristics of pseudomorphic high electron mobility transistors18(2000); http://dx.doi.org/10.1116/1.1322047View Description Hide Description
The influences and improved methods for mesa-sidewall effects of GaInP/InGaAs/GaInP pseudomorphic high electron mobility transistors are investigated and demonstrated. The mesa-sidewall effects of gate leakage current path and parasitic capacitance seriously degrade the device characteristics. For instance, the excessive gate leakage current, reduced breakdown voltage and transconductance, variation of threshold voltage, increased sidegating effect, and degraded radio frequency response are found when the number of the mesa sidewall is increased. In the work, a simple and low-cost technique of the selective removal of mesa-sidewall materials is introduced. This selective etching method can substantially eliminate the mesa-sidewall contact problems of heterostructure field-effect transistor devices.
Diode structures based on for optoelectronic applications in the near-ultraviolet range of the spectrum18(2000); http://dx.doi.org/10.1116/1.1326943View Description Hide Description
It was previously reported that spectrally matched and MIS Schottky barrierdiodestructures exhibited optical emission and photosensitivity in the near-ultraviolet (UV) range of the spectrum and rectification at elevated temperatures. However, such structures were not practical due to the low mechanical and thermal stability of the semitransparent Au contacts. In addition, we experienced difficulties in achieving stable optical emission from the structures. In this work various Schottky barrierdiodestructures based on p-type GaN layers grown on sapphire with silicon (Si), boron nitride (BN), and silicon dioxide interfacial layers were investigated. Blue and wide-spectrum optical emissions at forward and reverse bias, respectively, and photosensitivity were observed from these structures. A spectral match in the range of 365–400 nm between the light emitting diode(LED) and photodetector structures fabricated on the same substrate was achieved. A total Lambertian radiant UV power of ∼466 μW was measured from a blue/UV LED at 22 V. UV-transparent and electrically conductive layers were fabricated, characterized, and employed for fabrication of photodiode structures.
18(2000); http://dx.doi.org/10.1116/1.1319693View Description Hide Description
The current leakages of InAs photodiodes have been systematically studied by adding undoped layers having thicknesses of 0, 0.30, and 0.72 μm between the junction. At reverse bias V, the dark currents of the InAs p–i–n diodes with undoped layer thicknesses of 0, 0.30, and 0.72 μm are about and A, respectively, at 77 K. The leakage current of the InAs p–n diode was successfully reduced by adding 0.72-μm-thick undoped layer between the p–n junction.
18(2000); http://dx.doi.org/10.1116/1.1320802View Description Hide Description
Thin metal films are of considerable interest for optoelectronic device fabrication. The high resistivity of thin metal films results in drawbacks of their application in the devices. The low Schottky barrier height for certain important material such as InGaAs blocks its application in optoelectronic device at long wavelength. Recent studies have been conducted in low temperature (LT) deposition of thin metal films. The LT thin films showed 4–5 orders lower resistivity compared to those formed at room temperature. The LT process also results in increased Schottky barrier height for most III–V semiconductor materials. Therefore, the LT processed thin films show superior properties for optoelectronic devices applications. In this work, computer simulation was conducted by partially implementing the LT results in device parameters. The optimum design for the high performance metal–semiconductor–metal photodetector was obtained by simulation. The results show that the LT processing is of convenient, cost-effective, and could be implemented in more optoelectronic device fabrications.
Effect of growth interruption and the introduction of on the growth of InGaN/GaN multiple quantum wells18(2000); http://dx.doi.org/10.1116/1.1327298View Description Hide Description
The effects of the growth interruption and the introduction of during interruption time on the optical and structural properties of InGaN/GaN multiquantum wells (MQWs), grown by metalorganic chemical vapor deposition, were investigated. When the growth was interrupted during the formation of interfaces in the MQWs, the intensity of photoluminescence (PL) was greatly increased and the formation of InN-rich regions near the surface of the InGaN well layer was suppressed. As the interruption time increased, however, the PL intensity decreased and the average In composition of InGaN/GaN MQWs decreased. When was introduced during the growth interruption, the intensity of the PL was significantly enhanced by eliminating the impurities at the interface and the PL peaks were blueshifted due to the reduction in the thickness of the InGaN well layers, as a result of etching of well and barrier layers.
18(2000); http://dx.doi.org/10.1116/1.1322039View Description Hide Description
We studied a site-control technique for InAsquantum dots(QDs) on GaAs substrates using a combination of in situ electron-beam (EB) lithography and self-organizedmolecular-beam epitaxy. On prepatterned square-mesa structures with a dimension of several tens of microns, we were able to control the average density of Stranski–Krastanow QDs. On these mesa structures, submicron holes in an array were formed as preferential growth sites of QDs by EB writing and gas etching. By supplying 1.8 monolayer (ML) of InAs,QDs were formed in the patterned holes without any formation on the flat region between them. The QD concentration in each hole was dependent on the hole depth, that is, on the density of atomic steps inside holes. In the holes deeper than 50 Å, QDs were so densely formed that carrier tunneling occurred between them. In the shallow holes with 5–6 ML steps, on the other hand, single QDs were formed.
Fabrication technology of a Si nanowire memory transistor using an inorganic electron beam resist process18(2000); http://dx.doi.org/10.1116/1.1314373View Description Hide Description
We report on a novel fabricationtechnology of a Si nanowire memory transistor using an inorganic electron beam (EB) resist process. The inorganic EB resist process technique was put to practical use in Si nanodevice fabrication for the first time. We have successfully demonstrated the 15-nm-wide and 20-nm-thick Si nanowire memory transistor with a Si nanodot less than 10 nm in diameter. In the fabricated Si nanowirenanodot memory transistor, we have observed a large electron memory effect, i.e., a threshold voltage shift of 2.2 V at room temperature. It is experimentally shown that the inorganic EB resist process is promising for fabricating various Si nanodevices.
18(2000); http://dx.doi.org/10.1116/1.1320808View Description Hide Description
We have used an ultrahigh vacuum scanning tunneling microscope to investigate the deposition of mesoscopic ironclusters from a gas aggregation source. The size of the clusters was found to be in the range 1–7 nm. The effect of exposure of the ironclusters to the atmosphere results in a significant increase in cluster size, which we believe is consistent with total oxidation of the clusters. A specially designed quadrupole mass filter is incorporated inside the cluster source. We have investigated the sizes of the clusters deposited using different quadrupole settings and find that it is possible to size select the clusters prior to deposition. Finally we have studied the effect of sample surface reactivity and annealing on cluster distribution.
18(2000); http://dx.doi.org/10.1116/1.1319697View Description Hide Description
and capped on cerium oxide were observed in x-ray photoemission spectroscopy. Since the ceriumoxide surface is partially covered with hydroxide before Si deposition, the Si layer is expected to have a poor crystal quality at the initial Si growing stage. Cross-sectional transmission electron microscopyanalysis verified that there was not but amorphous Si and between the Si overlayer and The reason why is not formed is explained. The transition of the growth mode for the Si overlayer was observed in atomic force microscopyimages. It is confirmed that the growth mode of Si on is step flow at the low deposition rate and island growth at the high deposition rate.
18(2000); http://dx.doi.org/10.1116/1.1318190View Description Hide Description
In this article, we present the fabrication and electrical characterization of nanostructures made of alkanethiol-encapsulated gold particles. We fabricated ordered close-packed monolayer and multilayer structures of encapsulated gold particles using a self-organization process. Room-temperature electrical properties of these nanostructures were studied by using a conductive atomic force microscope. In both cases of monolayer and multilayer structures, the current suppression around zero bias was observed for 9-nm-diameter gold particles. However, it was not observed for 20-nm-diameter particles. This suggests that the Coulomb blockade has occurred in the case of 9-nm-diameter particles. Moreover, the current–voltage properties of multilayer structures demonstrate a nearly linear relation between the Coulomb gap and the number of layers which is in good agreement with the theory of single-electron tunneling in a tunnel-junction array. These electrical properties suggest that an alkanethiol shell on gold particles can serve as a stable tunnel barrier. As a consequence, the proposed method for fabricating quantum dot structures is very useful for developing nanoelectronic devices.
18(2000); http://dx.doi.org/10.1116/1.1314372View Description Hide Description
Regular nanostructures are formed by chemical reaction of ammonia gas with crystalline substituted benzoic acid such as p-bromobenzoic (1a), p-toluic (1b), p-aminobenzoic (1c), and p-nitrobenzoic acid (1d). Their size and shape are determined and depicted by atomic force microscopy(AFM).AFM reveals that the crystal main face (100) of 1a, (100) of 1b, (100) of 1c, and (001) of 1d exhibits craters and volcanoes, craters and volcanoes, volcanoes, and volcanoes, respectively, whereas the long side face (100) of 1d gives rise to craters and volcanoes. All the experimental results are correlated with the crystal structures. Molecular interpretations of the AFM features of 1a, 1b, 1c, and 1d are given.
Effect of photoenhanced minority carriers in metal-oxide-semiconductor capacitor studied by scanning capacitance microscopy18(2000); http://dx.doi.org/10.1116/1.1326947View Description Hide Description
A scanning capacitance microscope was used to study the photoenhanced minority-carrier contribution to the capacitance of the metal-oxide-semiconductor(MOS)capacitor at high frequencies. When a light is induced over the semiconductor surface, electron-hole pairs are generated and recombined. This steady-state generation-recombination process yields the temporary source of minority carriers, and the inversion layer underneath the oxide layer can respond to very fast-varying ac bias. We measured the differential capacitance (dC/dV) of the MOS capacitor under various light intensities, and observed a peak at the inversion region where the amplitude increased as the irradiation intensity increased. By integrating dC/dV with respect to V, we obtained C–V curves in which the capacitance of the depletion region recovered its value up to that of the accumulation region as the light intensity increased. We also observed that the C–V curves shifted in one direction under irradiation which we believe is due to the surface photovoltaiceffect.
Integrated atomic force microscopy array probe with metal–oxide–semiconductor field effect transistor stress sensor, thermal bimorph actuator, and on-chip complementary metal–oxide–semiconductor electronics18(2000); http://dx.doi.org/10.1116/1.1327299View Description Hide Description
A microfabricated 2×1 array of active and self-detecting cantilevers is presented for applications in atomic force microscopy(AFM). The integrated deflection sensor is based on a stress sensing metal–oxide–semiconductor transistor. Full custom complementary metal–oxide–semiconductor amplifiers for signal readout are combined on the same chip. A sensor sensitivity of 2.25 mV/nm, or a change in current was obtained at the final output stage. Three Al–Si thermal bimorph actuators are integrated on each cantilever for self-excitation and feedback actuation. The efficiencies of the heaters are 2.4–4.7 K/mW. In the experimental setup, a maximum displacement of 8 μm was achieved at 45 mW input. A pair of parallel AFM images in the constant height mode, a typical tapping mode image, and a constant force image with 1.3 μm high features have been successfully taken with the array probe.
18(2000); http://dx.doi.org/10.1116/1.1318189View Description Hide Description
An ultrahigh-vacuum scanning tunneling microscope (UHV-STM) combined with an x-ray source has been developed. STM samples were irradiated with an x-ray beam and an x-ray induced photoemission current was detected with the tip. By using the system, apparent height increases due to the x-ray induced current were successfully observed in STM images of Cr/Cu(111), Au/Cu(111), Si(111)7×7, and Si(111)-5×1 Ausurfaces. A bias voltage applied to the tip enhances collection of the x-ray induced current and increases the apparent height. The relative height increase of the Au overlayer to the Cu substrate in the STM images of the Au/Cu(111) surface was found to depend on the x-ray irradiation, suggesting that it may be a promising tool for elemental analysis in a STM.
18(2000); http://dx.doi.org/10.1116/1.1318191View Description Hide Description
We introduce the principle on a new high resolution thermal field emission microscope (HRTFEM). The crystalline structures of W(111), W(100), and W(110) tips have been observed. Both theoretical analyses and experiments show that HRTFEM has high resolving power with which atoms can be distinguished clearly. By using this HRTFEM, the states of atoms on tip surface can be studied easily.
Dual tunneling-unit scanning tunneling microscope for practical length measurement based on reference scales18(2000); http://dx.doi.org/10.1116/1.1319696View Description Hide Description
A new setup of dual tunneling-unit scanning tunneling microscope (DTU STM) has been developed that can realize simultaneous calibration between test sample images and standard reference scales. The crystalline lattices and periodic grating features are employed as such scales for practical length measurements, respectively, in the nanometer and the micron orders. The DTU STM consists of a reference unit and a test unit horizontally set in parallel to eliminate Abbe’s errors. Their probe tips are attached to one single scanner on the same surface, while the reference and test sample holders are open. As the tips scan over the sample surfaces, two images with the same lateral size are simultaneously acquired. Line lengths in the test image could be measured by counting the number of crystalline lattices or grating patterns in the reference side. Two vertical impact drive mechanisms were applied to coarsely positioned samples in the direction. Another two impact drive mechanisms were employed to the horizontal drive sample holders as to automatically position the samples in the lateral plane. We present a brief discussion about the concept and setup of the DTU STM. Some comparison results using crystalline lattices and grating patterns, respectively, as reference scales for length calibration are provided. Experiments show a satisfactory matching between the two tunneling units when covering a wide scan range from 5 nm to 10 μm. With its new setup, the DTU STM is confirmed to be a more accurate device for practical length measurement even when measuring comparatively large and heavy samples.
Effect of metal–insulator–semiconductor structure derived space charge field on the tip vibration signal in electrostatic force microscopy18(2000); http://dx.doi.org/10.1116/1.1323968View Description Hide Description
The role of metal–insulator–semiconductor structure derived space charge field in the tip vibration signal of electrostatic force microscopy was studied using borondoped Si tip and Pt filmsputtered on Si substrate. The ohmic contact between the tip and the film was confirmed by current–voltage characterization. Then the tip was held at a position so that an air gap of 100 nm existed between the tip and the film. The tip deflection and the tip vibration signals were examined by applying dc voltage to the film and ac voltage to the tip. The asymmetry in both signals supports the existence of the space charge field, and the direction of the field at zero dc bias field is from the tip to the sample as expected from the band bending theory.
18(2000); http://dx.doi.org/10.1116/1.1320807View Description Hide Description
A wide dynamic range silicon diaphragm vacuum sensor by an electrostaticservo system and an electrical circuit for servo control have been made. In nonservo mode, i.e., when the sensor was used as a capacitive vacuum sensor, a linear characteristic between pressure and output voltage was obtained in the pressure range from 0.1 to 100 Pa. On the other hand, the square root of the servo voltage was proportional to the pressure in a wide pressure range from 0.1 to 530 Pa in servo mode. The servo mechanism is effective for widening the dynamic range of vacuum sensors.
18(2000); http://dx.doi.org/10.1116/1.1322043View Description Hide Description
A modified cathodic arc technique has been used to deposit carbon nitride thin films directly on Si substrates. Transmission electron microscopy showed that clusters of fullerene-like nanoparticles are embedded in the deposited material. Field emission in vacuum from as-grown films starts at an electric field strength of 3.8 V/μm. When the films were etched in an solution for 10 min, the threshold field decreased to 2.6 V/μm. The role of the carbon nanoparticles in the field emission process and the influence of the chemical etching treatment are discussed.