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Luminescence properties of defects in GaN
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10.1063/1.1868059
/content/aip/journal/jap/97/6/10.1063/1.1868059
http://aip.metastore.ingenta.com/content/aip/journal/jap/97/6/10.1063/1.1868059

Figures

Image of FIG. 1.
FIG. 1.

Radiative transitions associated with major doping impurities (see Sec. V) and unintentionally introduced defects (Sec. IV) in GaN. For the complex, two charge states are shown (Sec. IV B). Transitions resulting in the GL2 and RL2 bands are assumed to be internal and the related defect levels are unknown (Sec. IV F).

Image of FIG. 2.
FIG. 2.

Formation energies as a function of Fermi level for native point defects in GaN. Ga-rich conditions are assumed. The zero of Fermi level corresponds to the top of the valence band. Only segments corresponding to the lowest-energy charge states are shown. Adapted with permission from Limpijumnong and Van de Walle, Phys. Rev. B69, 035207 (2004). Copyright (2004) by the American Physical Society.

Image of FIG. 3.
FIG. 3.

Transition levels for native defects in GaN, determined from formation energies displayed in Fig. 2. Adapted with permission from Limpijumnong and Van de Walle, Phys. Rev. B69, 035207 (2004). Copyright (2004) by the American Physical Society.

Image of FIG. 4.
FIG. 4.

Calculated formation energies and ionization levels for the defects in GaN in the Ga-rich case. The dashed lines correspond to isolated point defects and the solid lines to defect complexes, respectively. Reprinted with permission from Mattila and Nieminen, Phys. Rev. B55, 9571 (1997). Copyright (1997) by the American Physical Society.

Image of FIG. 5.
FIG. 5.

Calculated formation energies as a function of Fermi level for shallow donors and acceptors in GaN grown in the most favorable for these dopants conditions (except for which should have even lower formation energy in Ga-rich conditions). Solid lines—Ga-rich case, dashed lines—N-rich case. The zero of Fermi level corresponds to the top of the valence band. The data for Ca, Zn, Mg, and Be are taken from Ref. 30, C—from Ref. 36, and O and Si—from Ref. 53 with kind permission from the authors.

Image of FIG. 6.
FIG. 6.

Calculated formation energy of interstitial hydrogen in wurtzite GaN as a function of Fermi level. corresponds to the valence-band maximum, and formation energies are referenced to the energy of a molecule. Reprinted with permission from Van de Walle, Phys. Status Solidi B235, 89 (2003).

Image of FIG. 7.
FIG. 7.

Calculated formation energies of hydrogenated Ga vacancies in GaN as a function of Fermi energy. The formation energies of the isolated vacancy , of interstitial and , and of the Si donor are also included. Reprinted with permission from Van de Walle, Phys. Rev. B56, 10020 (1997). Copyright (1997) by the American Physical Society.

Image of FIG. 8.
FIG. 8.

Schematic of the main transitions in -type GaN in conditions of PL. Electron-hole pairs are created with the rate by optical excitation. The photogenerated holes are captured by radiative acceptors (one acceptor level is shown), nonradiative defects , and form excitons (Ex). The level for excitons is conventional, meaning only that some energy is required to dissociate the excitons. The solid and dotted lines show the transitions of electrons and holes, respectively. Optical transitions are shown by the straight solid lines; recombination of holes at nonradiative centers with free electrons is shown with a dashed line. Rates for all the transitions are noted.

Image of FIG. 9.
FIG. 9.

Calculated temperature dependencies of the PL QE for three radiative recombination channels in GaN: excitonic (ex) and via two acceptors ( and ). The dependences were calculated using Eqs. (6)–(10) with the following parameters: ; ; ; , , , , , , . Reprinted with permission from Reshchikov and Korotkov, Phys. Rev. B64, 115205 (2001). Copyright (2001) by the American Physical Society.

Image of FIG. 10.
FIG. 10.

Schematic representation of a recombination of the localized hole with a free electron, resulting in emission of a photon and several phonons.

Image of FIG. 11.
FIG. 11.

An example of the CC diagram and resulting PL spectrum.

Image of FIG. 12.
FIG. 12.

An example of the CC diagram and resulting PLE spectrum.

Image of FIG. 13.
FIG. 13.

PL spectra from undoped GaN at 15 K. The spectra are plotted in logarithmic scale and displaced vertically for better viewing.

Image of FIG. 14.
FIG. 14.

Normalized room-temperature PL spectra of the MOCVD-grown sample (mo76) and three representative MBE-grown GaN layers. All the spectra were measured in identical conditions with an excitation density of . Weak oscillations of intensity are caused by light interferences.

Image of FIG. 15.
FIG. 15.

Temperature dependencies of QE of the YL, BL, and exciton emission at excitation density of . Reprinted with permission from Reshchikov and Korotkov, Phys. Rev. B64, 115205 (2001). Copyright (2001) by the American Physical Society.

Image of FIG. 16.
FIG. 16.

Temperature-induced variation of the intensity of the YL band in the region of its quenching. The solid curves demonstrate fits by using Eqs. (5)–(7). Reprinted with permission from Reshchikov and Korotkov, Phys. Rev. B64, 115205 (2001). Copyright (2001) by the American Physical Society.

Image of FIG. 17.
FIG. 17.

Intensity of the YL, BL, and UVL bands at 15 K in undoped GaN grown by MOCVD. The curves are calculated using Eq. (17). Reprinted with permission from Korotkov et al., Physica B273, 80 (1999). Copyright (1999) by Elsevier.

Image of FIG. 18.
FIG. 18.

Steady-state PL spectrum (solid curve) and time-resolved PL spectra (points) at time delays of , , and for undoped GaN sample grown by MOCVD. Reprinted with permission from Korotkov et al., Physica B273, 80 (1999). Copyright (1999) by Elsevier.

Image of FIG. 19.
FIG. 19.

Temperature dependence of the effective lifetime of the YL (2.2 eV), BL (2.9 eV), and UVL (3.27 eV) bands in undoped GaN grown by MOCVD. Reprinted with permission from Korotkov et al., Physica B325, 1 (2003). Copyright (2003) by Elsevier.

Image of FIG. 20.
FIG. 20.

PLE spectra for the YL in the 2.5-μm-thick MBE-grown GaN layer at 15 and 295 K. The solid curve is a Gaussian fit with maximum at 3.32 eV and FWHM of 0.52 eV. The broken line is a Gaussian fit with maximum at 3.19 eV and FWHM of 0.40 eV. Reprinted with permission from Reshchikov et al., Mater. Res. Soc. Symp. Proc.693, I6–19 (2002).

Image of FIG. 21.
FIG. 21.

One-dimensional CC diagram for the YL in GaN.

Image of FIG. 22.
FIG. 22.

PL spectra from a freestanding GaN template at 15 and 295 K. Exciton part at 15 K is cut in order to present better the defect-related bands. See Ref. 222 for details of the exciton part.

Image of FIG. 23.
FIG. 23.

Room-temperature PL spectrum of a freestanding GaN template (Ga face) at different excitation densities. Points are experimental data (only every tenth point is shown for clarity); solid curves - fit using modeled YL and GL bands with their relative contribution given in Fig. 24. Reprinted with permission from Reshchikov et al., Appl. Phys. Lett.81, 4970 (2002). Copyright (2002) by the American Institute of Physics.

Image of FIG. 24.
FIG. 24.

Dependence of the integrated intensity of the YL and GL bands on excitation intensity. The points are experimental data obtained from deconvolution of the spectra shown in Fig. 23 onto two bands (YL and GL). The solid lines represent a fit with the following parameters: , , , , , , . Also shown are the FWHM and position of maximum (after deduction of 2 eV for appearance) of the experimentally observed broad band (points) and the same values simulated by using the modeled shapes of the YL and GL bands and their relative contributions. Reprinted with permission from Reshchikov et al., Appl. Phys. Lett.81, 4970 (2002). Copyright (2002) by the American Institute of Physics.

Image of FIG. 25.
FIG. 25.

PL spectrum in the defect range taken for below-band excitation at different photon energies. The excitation density is about . Reprinted with permission from Reshchikov et al., Appl. Phys. Lett.78, 3041 (2001). Copyright (2001) by the American Institute of Physics.

Image of FIG. 26.
FIG. 26.

Position of the broad band maximum, FWHM, and sample transparency for the freestanding GaN template as a function of the incident light energy at room temperature. The excitation density is about . The full squares and triangles are for the Ga face. The open squares and triangles are for the N face. The solid lines are guides to the eye. Reprinted with permission from Reshchikov et al., Appl. Phys. Lett.78, 3041 (2001). Copyright (2001) by the American Institute of Physics.

Image of FIG. 27.
FIG. 27.

PLE spectra for the YL in the freestanding GaN template at different temperatures. The solid curve is a Gaussian fit with maximum at 3.32 eV and FWHM of 0.52 eV. Reprinted with permission from Reshchikov et al., Mater Res. Soc. Symp. Proc.693, I6–19 (2002).

Image of FIG. 28.
FIG. 28.

PL spectrum from the freestanding GaN template excited with below-band-gap energy (3.44 eV) at 50 K. Points—experiment. Dashed lines—Gaussians peaking at 1.86 and 2.27 eV and having FWHM of 390 meV. The solid curve is the sum of two Gaussians.

Image of FIG. 29.
FIG. 29.

Steady-state PL spectra (solid curves) obtained from a freestanding GaN under excitation with pulsed nitrogen (SS-N) and cw He–Cd (SS-HeCd) lasers, and time-resolved PL spectra at different time delays (points). . Reprinted with permission from Reshchikov et al., Appl. Phys. Lett.83, 266 (2003). Copyright (2003) by the American Institute of Physics.

Image of FIG. 30.
FIG. 30.

PL intensity decay of the UVL (3.25 eV), BL (2.9 eV), and GL–YL (at 2.2 eV) in freestanding GaN grown by HVPE. The curves are calculated using Eq. (17) with the following parameters: , , and , , and , as shown in the figure. Reprinted with permission from Reshchikov et al., Physica B340–342, 444 (2003). Copyright (2003) by Elsevier.

Image of FIG. 31.
FIG. 31.

Population of an acceptor with holes after excitation pulse in the DAP model (Ref. 79) with the same parameters as in Fig. 30. Note that covers the range estimated for different acceptors in GaN. Reprinted with permission from Reshchikov et al., Physica B340–342, 444 (2003). Copyright (2003) by Elsevier.

Image of FIG. 32.
FIG. 32.

Steady-state (SS) PL spectrum (solid line) and PL spectrum at time delays of , , , and (open points) in freestanding GaN at 100 K. Effective lifetime is also shown (closed points). Reprinted with permission from Reshchikov et al., Physica B340–342, 448 (2003). Copyright (2003) by Elsevier.

Image of FIG. 33.
FIG. 33.

PL lifetime (points) as a function of inverse temperature for the main PL bands in freestanding GaN: UVL band (at 3.28 eV), BL band (2.9 eV), GL band (2.43 eV), and YL band (2.21 eV). Variation of the inverse free-electron concentration (solid line) is also shown for comparison. Reprinted with permission from Reshchikov et al., Physica B340–342, 448 (2003). Copyright (2003) by Elsevier.

Image of FIG. 34.
FIG. 34.

Schematic of transitions responsible for the GL band in high-purity GaN. e.s. is the excited state of the acceptor, therefore the transition is of intracenter type. SD stands for the shallow donors, and the transitions involved are distant DAP transitions. The dashed lines correspond to less probable transitions, whereas the solid lines show the dominant transitions.

Image of FIG. 35.
FIG. 35.

UVL band in undoped GaN at 15 K. Points are from experiment. The dashed line is a modeled shape of the zero-phonon line (ZPL). The solid line is a fit accounting for LO phonon replicas having intensities of 0.4, 0.097, 0.022, and 0.004 with the shapes identical to the modeled shape of the ZPL. The ZPL and donor-bound-exciton peaks are located respectively at 3.286 and 3.475 eV in this undoped GaN layer grown by MBE on sapphire.

Image of FIG. 36.
FIG. 36.

Transformation of the UVL band (e-A related) in GaN with temperature.

Image of FIG. 37.
FIG. 37.

PL spectrum of the UVL band at different temperatures in freestanding GaN (empty squares) and in the GaN overgrown on the freestanding GaN template by MBE (filled circles). Excitation density is . Reprinted with permission from Reshchikov et al., Appl. Phys. Lett.79, 3779 (2001). Copyright (2001) by the American Institute of Physics.

Image of FIG. 38.
FIG. 38.

Positions of the ZPL of the UVL band in undoped GaN as a function of excitation intensity in the steady-state PL (filled points, bottom scale) and time delay after excitation pulse (open points, top scale). Squares–30-μm-thick GaN layer on sapphire substrate, triangles—200-μm-thick freestanding GaN template, both grown by HVPE. The e-A line is detected at while the DAP line position varies from 3.253 to 3.269 eV depending on experimental conditions. Reprinted with permission from Reshchikov et al., Physica B340–342, 444 (2003). Copyright (2003) by Elsevier.

Image of FIG. 39.
FIG. 39.

PL decay for the DAP transitions (filled points) and e-A transitions (empty points) of the UVL band in freestanding GaN template. Reprinted with permission from Reshchikov et al., Physica B340–342, 444 (2003). Copyright (2003) by Elsevier.

Image of FIG. 40.
FIG. 40.

ODMR spectra at 24 GHz detected on the UVL band (at 3.27 eV) for several orientations of the applied magnetic field in the (11-20) plane (0° refers to the axis). The thick black curves (displaced vertically for clarity) are simulations of the low-field line shapes for resonance SA. Reprinted with permission from Glaser et al., Phys. Rev. B68, 195201 (2003). Copyright (2003) by the American Physical Society.

Image of FIG. 41.
FIG. 41.

values of ODMR signal SA in homoepitaxial Si-doped GaN layer (circles) and those found previously for Mg shallow acceptors in Mg-doped GaN heteroepitaxial layers (squares) as a function of the angle between magnetic-field vector and the axis. The dashed curves are fits to the data [see Eq. (30)]. Reprinted with permission from Glaser et al., Phys. Rev. B68, 195201 (2003). Copyright (2003) by the American Physical Society.

Image of FIG. 42.
FIG. 42.

PL spectrum of the BL band in undoped GaN sample at 13 K and excitation density of . Two sets of sharp peaks with energy separations of 36 and 91 meV are seen. The zero-phonon line (ZPL) energy is 3.098 eV. The solid curve is the fit using Eq. (31) with and and simulated shape of the no-phonon transition (dashed curve). The inset shows the shift of the peaks with excitation intensity for the BL and shallow DAP bands. Reprinted with permission from Reshchikov et al., J. Appl. Phys.87, 3351 (2000). Copyright (2000) by the American Institute of Physics.

Image of FIG. 43.
FIG. 43.

Temperature-induced variation of the intensity of the BL band in MOCVD-grown GaN. The solid curves are the best fit for the samples RK93 (1) and RK120 (2) by using Eqs. (6)–(10). Reprinted with permission from Reshchikov and Korotkov, Phys. Rev. B64, 115205 (2001). Copyright (2001) by the American Physical Society.

Image of FIG. 44.
FIG. 44.

Shift of the BL band maximum (triangles) with temperature. The shifts of the YL (2.2 eV) and GL3 (2.5 eV) bands in GaN grown by MOCVD are shown for comparison. Reprinted with permission from Reshchikov et al., Physica B273–274, 105 (1999). Copyright (1999) by Elsevier.

Image of FIG. 45.
FIG. 45.

Temperature dependence of FWHM of the BL band (triangles) in comparison with the dependences for the YL (2.2 eV) and GL3 (2.5 eV) bands in GaN grown by MOCVD. The solid curves are fit by Eq. (26) with the following parameters: (1); 390 (2); 340 (3) meV. (1); 40 (2); 43 (3) meV. Reprinted with permission from Reshchikov et al., Physica B273–274, 105 (1999). Copyright (1999) by Elsevier.

Image of FIG. 46.
FIG. 46.

Room-temperature PL spectrum of GaN layer grown by HVPE on sapphire (H966 for us) excited at . The points are experimental data taken at (1) and (2). The curves are self-consistent deconvolution of the experimental curves into two bands (a RL with a maximum at 1.92 eV and a GL with the maximum at 2.39 eV). Reprinted with permission from Reshchikov et al., Mater. Res. Soc. Symp. Proc.680, E5–6 (2001).

Image of FIG. 47.
FIG. 47.

Room-temperature PL spectra of GaN layers grown by MBE on sapphire. Oscillations with a period of 100–150 meV are caused by interference from the 1.5–2.5-μm-thick films. Sample svtl703 is a representative sample with a strong YL band in the PL spectrum.

Image of FIG. 48.
FIG. 48.

PL spectra from Ga-rich GaN layers grown by MBE on sapphire. .

Image of FIG. 49.
FIG. 49.

Effect of excitation density, , on low-temperature PL spectrum of the Ga-rich GaN layer. Position and shape of the bands are independent of excitation density with accuracy of ± (5–10) meV. The curves are shifted arbitrarily in the vertical direction (log scale).

Image of FIG. 50.
FIG. 50.

Variation of quantum efficiency of the RL2, GL2, and exciton emission bands in the Ga-rich GaN layer with an excitation density at 15 K.

Image of FIG. 51.
FIG. 51.

PL spectra of the Ga-rich GaN layer (sample svt591) at different temperatures.

Image of FIG. 52.
FIG. 52.

PL intensity (in log scale) vs inverse temperature for the RL2 and GL2 bands. The solid lines are calculated curves using Eq. (32) with the activation energy of 115 meV (1) and l00 meV (2) for the RL2 and GL2 bands, respectively.

Image of FIG. 53.
FIG. 53.

Temperature dependence of the peak position of the RL2 and GL2 bands in Ga-rich GaN.

Image of FIG. 54.
FIG. 54.

Temperature dependence of the FWHM of the RL2 and GL2 bands in Ga-rich GaN. The curves are fit by Eq. (26) with the following parameters: and (GL2); and (RL2).

Image of FIG. 55.
FIG. 55.

PLE spectra at 15 K for the RL2 and GL2 bands in Ga-rich GaN. The points are experimental data. Curve 1 represents a part of the PLE spectrum for the RL2 band in the sample svt591 measured with excitation by Xe lamp. Curve 2 is the PLE spectrum of the sample svt369 at 295 K and represents the noise signal. Curves 3 and 4 are calculated Gaussians with maxima at 3.10 eV (3) and 3.38 eV (4) and FWHM of 372 meV (3), and 204 meV (4). Reprinted with permission from Reshchikov et al., Mater. Res. Soc. Symp. Proc.680, E5–6 (2001).

Image of FIG. 56.
FIG. 56.

An example of the CC diagram for the GL2 and RL2 bands in Ga-rich GaN. Transition 1 corresponds to excitation of the e-h pair; transition 2 corresponds to capture of carrier by defect in its excited state and relaxation of the lattice around the defect; PL involves emission of a photon (vertical transition 3) and relaxation of the lattice followed by emission of phonons (transition 4); thermal excitation of the defect up to crossover point (transition 5) results in nonradiative recombination with emission of many phonons (transitions 6 and 4). is the barrier height for the nonradiative recombination. Zero-phonon energy is .

Image of FIG. 57.
FIG. 57.

PL spectra of undoped GaN samples grown by MOCVD on sapphire. .

Image of FIG. 58.
FIG. 58.

Normalized AL band in GaN films grown by MBE on 10-μm HVPE layer (sample svt857) and on 200-μm HVPE freestanding template (sample svt844) at 15 and 295 K.

Image of FIG. 59.
FIG. 59.

Low-temperature PL spectrum of undoped and Zn-doped GaN layers grown by HVPE on sapphire. The intensity is normalized at maximum of the BL band.

Image of FIG. 60.
FIG. 60.

Excitonic region of the low-temperature PL spectrum of undoped and Zn-doped GaN layers grown by HVPE on sapphire. The intensity is normalized at maximum of the ABE line.

Image of FIG. 61.
FIG. 61.

PL spectra of high-resistivity Zn-doped GaN grown on sapphire (front side) at different temperatures. Excitation density is . Reprinted with permission from Reshchikov et al., Mater. Res. Soc. Symp. Proc.693, I2–10 (2002).

Image of FIG. 62.
FIG. 62.

Low-temperature PL spectra at different excitation intensities from high-resistivity GaN:Zn layer grown by HVPE on sapphire (front side).

Image of FIG. 63.
FIG. 63.

PL intensity decay of the BL (at 2.9 eV) in undoped (1011), Si-doped (1721), and two Zn-doped (560 and 1394) GaN layers grown by HVPE on sapphire. Note the logarithmic scales. Reprinted with permission from Reshchikov et al., Mater. Res. Soc. Symp. Proc.693, I2–10 (2002).

Image of FIG. 64.
FIG. 64.

Room-temperature concentration of free holes in Mg-doped GaN as determined from the Hall effect vs concentration of Mg obtained from SIMS measurements. The solid line is a guide to the eye. Reprinted with permission from Obloh et al., J. Cryst. Growth195, 270 (1998). Copyright (1998) by Elsevier.

Image of FIG. 65.
FIG. 65.

Low-temperature (4.2 K) PL spectrum of a Mg-doped GaN sample. Reprinted with permission from R. Stepniewski et al., Phys. Status Solidi B210, 373 (1998).

Image of FIG. 66.
FIG. 66.

Variation of the energy of the DAP transitions vs the reciprocal DAP separation for the acceptor in GaN. Reprinted with permission from R. Stepniewski et al., Phys. Status Solidi B210, 373 (1998).

Image of FIG. 67.
FIG. 67.

Expected typical amplitude of potential fluctuations in -type GaN:Mg with the combined concentration of donors and acceptors , , and .

Image of FIG. 68.
FIG. 68.

Schematic representation of bands and defect levels in the presence of long-range potential fluctuations under conditions of PL. The arrows indicate diagonal transitions resulting in redshifted PL bands. Photogenerated electrons and holes are shown as filled and empty circles, respectively.

Image of FIG. 69.
FIG. 69.

Estimated average slope of potentials in compensated -type GaN:Mg with the combined concentration of donors and acceptors , , and .

Image of FIG. 70.
FIG. 70.

Low-temperature PL spectrum of GaN:Mg grown by MBE at different excitation intensities. Note the gradual shift of the BL from 2.85 to with increasing excitation density up to above which the UVL band and the line at 3.45 eV emerge with roughly quadratic dependence of their intensities on the excitation density.

Image of FIG. 71.
FIG. 71.

Low-temperature PL spectra of semi-insulating GaN:Mg sample at different excitation intensities. Reprinted with permission from Reshchikov et al., Phys. Rev. B59, 13176 (1999). Copyright (1999) by the American Physical Society.

Image of FIG. 72.
FIG. 72.

Low-temperature PL spectra of semi-insulating GaN:Mg sample at different excitation intensities. Reprinted with permission from Reshchikov et al., Phys. Rev. B59, 13176 (1999). Copyright (1999) by the American Physical Society.

Image of FIG. 73.
FIG. 73.

Intensity dependence of the PL spectra in -type GaN:Mg (a) measured with a cw-HeCd laser at up to , (b) measured with the third harmonic of a pulsed Nd:YAG (yttrium aluminum garnet) laser with pulse intensities up to . Reprinted with permission from Eckey et al., J. Appl. Phys.84, 5828 (1998). Copyright (1998) by the American Institute of Physics.

Image of FIG. 74.
FIG. 74.

Variation of the BL peak shifts with temperature at low and high excitation intensities. Variation of the band-gap width is also shown, shifted by 0.7 eV for convenience. Reprinted with permission from Reshchikov et al., MRS Internet J. Nitride Semicond. Res.4S1, G11–8 (1999).

Image of FIG. 75.
FIG. 75.

Low-temperature PL from two Be-doped GaN grown by MBE. Reprinted with permission from Ptak et al., Mater. Res. Soc. Symp. Proc.639, G3–3 (2001).

Image of FIG. 76.
FIG. 76.

Low-temperature PL spectrum of the As-implanted GaN, showing the no-phonon (NP) line and its phonon replicas. Reprinted with permission from Chen and Skromme, Mater. Res. Soc. Symp. Proc.743, L11–35 (2003).

Image of FIG. 77.
FIG. 77.

Low-temperature PL spectrum of the P-implanted GaN, showing the no-phonon (NP) line and its phonon replicas. Reprinted with permission from Chen and Skromme, Mater. Res. Soc. Symp. Proc.743, L11–35 (2003).

Image of FIG. 78.
FIG. 78.

CL spectra of a cubic GaN crystal at 5 K. (a) and (b) correspond to different points on the same crystal. The solid lines in the insets are fits to the data points, using Gaussians. The FWHM of the exciton line amounts to 8 meV (a) and 11 meV (b). Reprinted with permission from Menniger et al., Phys. Rev. B53, 1881 (1996). Copyright (1996) by the American Physical Society.

Image of FIG. 79.
FIG. 79.

PL spectra of C-doped cubic GaN layers grown with different fluxes of C. The topmost spectrum has been multiplied by a factor of 25. Reprinted with permission from As et al., Mater. Res. Soc. Symp. Proc.693, I2–3 (2002).

Image of FIG. 80.
FIG. 80.

A schematic of the exciton energy levels in wurtzite GaN in (a) an uncoupled hydrogenlike isotropic model, (b) including the effect of anisotropy, (c) including the effects both of anisotropy and intersubband coupling, and (d) including anisotropy, intersubband coupling, and polaron corrections. Reprinted with permission from Rodina et al., Phys. Rev. B64, 115204 (2001). Copyright (2001) by the American Physical Society.

Image of FIG. 81.
FIG. 81.

Schematic diagram of the internal structure of and excitons in a wurtzite GaN. The allowed polarizations are given in parentheses. The thin lines correspond to dipole-forbidden states. Reprinted with permission from Paskov et al., Phys. Rev. B64, 115201 (2001). Copyright (2001) by the American Physical Society.

Image of FIG. 82.
FIG. 82.

PL spectra of the 80-μm-thick GaN layer for polarization (solid line) and polarization (dotted line). The intensities of the donor-bound excitons (double peak at about 3.477 eV) and acceptor-bound excitons (at about 3.473 eV) are substantially lower in the -polarized spectrum compared to the polarization because the bound excitons are dipole-forbidden in the geometry. Note that due to biaxial compressive stress in GaN grown on sapphire all peaks in this sample are shifted to higher energy by 7 meV as compared to homoepitaxial GaN layers. Reprinted with permission from Paskov et al., Phys. Status Solidi B228, 467 (2001).

Image of FIG. 83.
FIG. 83.

A high-resolution PL spectrum of a homoepitaxial MOCVD-grown GaN. Reprinted with permission from Kornitzer et al., Phys. Rev. B60, 1471 (1999). Copyright (1999) by the American Physical Society.

Image of FIG. 84.
FIG. 84.

Low-temperature PL spectrum of freestanding GaN template. Reprinted with permission from Wysmolek et al., Phys. Status Solidi B235, 36 (2003).

Image of FIG. 85.
FIG. 85.

PL spectra taken at 5, 15, and 25 K in the two-electron satellite region. The dotted line overlapping the 5-K spectrum represents the best fit. Emission-peak assignments apply to the indicated spectrum only except for emission peaks connected by a dotted line. The spectrum intensities measured at 15 and 25 K were divided by 4 and 6, respectively, to minimize overlapping. Reprinted with permission from Freitas, Jr.et al., Phys. Rev. B66, 233311 (2002). Copyright (2002) by the American Physical Society.

Image of FIG. 86.
FIG. 86.

Low-temperature PL spectra measured with the excitation power densities, from top to bottom, 61.1, 8.4, 0.80, and . The inset represents the linear dependence of the excitons’ binding energy with the neutral-donor binding energy. Reprinted with permission from Freitas, Jr.et al., Phys. Rev. B66, 233311 (2002). Copyright (2002) by the American Physical Society.

Image of FIG. 87.
FIG. 87.

PL spectra of the exciton bound to a neutral acceptor in GaN recorded at different values of magnetic field oriented at 35° to the axis. The inset shows PL spectrum of GaN in the range of excitonic transitions. Reprinted with permission from Stepniewski et al., Phys. Rev. Lett.91, 226404 (2003). Copyright (2003) by the American Physical Society.

Image of FIG. 88.
FIG. 88.

Time-resolved PL spectrum of GaN:Zn at 9 K. Two lines of excitons bound to Mg acceptor and Zn acceptor are at 3.467 and 3.456 eV, respectively. Inset: comparison of time-integrated spectra of GaN:Zn at 8 and 31 K. Reprinted with permission from Korona et al., Phys. Status Solidi B235, 40 (2003).

Image of FIG. 89.
FIG. 89.

Dependence of the ionization energies of donors and acceptors on binding energies of the related bound excitons in GaN. The dashed lines show the slope of 0.21 for donors and 0.057 for acceptors.

Image of FIG. 90.
FIG. 90.

Low-temperature PL spectra from different GaN layers grown on sapphire by MBE. The spectra are normalized at maximum and shifted along the energy axis (from 1 to 7 meV) so that the DBE peak position is the same for all samples (3.470 eV). Reprinted with permission from Reshchikov et al., J. Appl. Phys.94, 5623 (2003). Copyright (2003) by the American Institute of Physics.

Image of FIG. 91.
FIG. 91.

Positions of the DBE and peaks in different samples. The samples, including etched ones, are numbered l,2,3…, on this figure. For example, numbers 23, 24, and 25 correspond to the same sample 605: as-grown, etched in phosphoric acid, and PEC etched, respectively. Note that , , and on this figure when the doublets are resolved.

Image of FIG. 92.
FIG. 92.

AFM images of the GaN sample 426. (a)—as-grown; (b)—after etching in boiled aqua regia for 5 min; (c), (d), (e), (f)—after etching in at 160 °C for 5 s, 15 s, l min, and 30 min, respectively. The vertical scale is 30 nm for all images. Density of the etch pits is about in (c) and (d). Note that the depth of the pits did not increase with increasing etching time, remaining under 30 nm, and we could not detect any reduction of the layer thickness even after 1 h or longer etching time.

Image of FIG. 93.
FIG. 93.

Effect of etching of Ga-polar GaN in boiled aqua regia for 6 min and in at 160 °C for 5 s and 30 min. . See the surface morphologies for this sample in Fig. 92.

Image of FIG. 94.
FIG. 94.

Low-temperature PL spectrum of the N-polar GaN layer grown by MBE on sapphire substrate, . A piece of the sample was etched in at 100 °C for 10 s and another piece of the sample was etched by PEC method.

Image of FIG. 95.
FIG. 95.

Transformation of PL spectrum with time of exposure by HeCd laser at 15 K. . The sample was etched in at 160 °C for 1 min and subsequently exposed to air for 20 days. Reprinted with permission from Reshchikov et al., Mater. Res. Soc. Symp. Proc.743, L11–3 (2003).

Image of FIG. 96.
FIG. 96.

Evolution of PL intensity at 3.36 eV with time of HeCd laser exposure. . .

Image of FIG. 97.
FIG. 97.

Low-temperature PL spectrum of Ga-polar GaN layer grown by MBE on top of the HVPE-grown 10-μm-thick GaN on sapphire substrate. Excitation density was attenuated from 100 to by neutral density filters. The spectra are shifted arbitrary along the vertical axis for better viewing. Reprinted with permission from Reshchikov et al., Mater. Res. Soc. Symp. Proc.693, I6–28 (2002).

Image of FIG. 98.
FIG. 98.

Low-temperature PL spectrum of N-polar GaN layer grown by MBE on sapphire substrate. The spectra are normalized at maximum. Reprinted with permission from Reshchikov et al., Mater. Res. Soc. Symp. Proc.743, L11–3 (2003).

Image of FIG. 99.
FIG. 99.

Dependence of the PL peak shift on excitation density at 15 K.

Image of FIG. 100.
FIG. 100.

Temperature dependence of PL spectrum at for as-grown Ga-polar GaN layer by MBE on top of the HVPE-grown 10-μm-thick GaN on sapphire substrate. Temperatures are 15, 35, 60, 100, 140, 195 K (solid curves), 25, 50, 80, 120, 160 K (dashed curves), and 240 K (dotted curve). Reprinted with permission from Reshchikov et al., Mater. Res. Soc. Symp. Proc.693, I6–28 (2002).

Image of FIG. 101.
FIG. 101.

Temperature dependence of positions of the FE (DBE) and peaks in GaN samples. For the sample 605 the DBE and FE peaks were unresolved and the position of their common maximum is plotted. The solid curves show the shift of the GaN band gap (Ref. 473) corrected to the following positions of lines at : 3.479 eV (FE); 3.459 eV ; 3.410 eV ; 3.35l eV ; 3.363 eV ; 3.305 eV ; 3.195 eV, 3.210, and 3.225 eV ( and ). Reprinted with permission from Reshchikov et al., J. Appl. Phys.94, 5623 (2003). Copyright (2003) by the American Institute of Physics.

Image of FIG. 102.
FIG. 102.

Low-temperature PL spectrum from GaN layers grown by MBE on sapphire substrate.

Image of FIG. 103.
FIG. 103.

Low-temperature PL spectrum of Ga-polar GaN layers grown by MBE on sapphire substrate subjected to different treatments [rapid thermal annealing (RTA), etching in hot and PEC etching].

Image of FIG. 104.
FIG. 104.

Low-temperature (15 K) PL spectra of five GaN layers grown by MBE on sapphire. All the spectra are measured under identical conditions. Excitation density is . The spectra have been shifted by up to l0 meV to compensate different strain-related shifts and align the DAP peaks. See characteristics of these samples in Table VI. Reprinted with permission from Reshchikov et al., Mater Res. Soc. Symp. Proc.798, Y5–66 (2004).

Image of FIG. 105.
FIG. 105.

PL spectra of oil from mechanical pump. Phonon replicas of the peaks are separated by 70 meV.

Image of FIG. 106.
FIG. 106.

PL spectrum of a high-resistive MBE-grown GaN sample. The sample was etched in 160 °C for 2 mins and then repeatedly exposed to air at room temperature for various times. Two broad bands with maxima at about 1.8 and 2.4 eV are related to point defects in bulk layer. Broad blue band emerging after etching is attributed to the surface states. The multiple peaks with separation of about 0.2 eV are due to interference effect.

Image of FIG. 107.
FIG. 107.

Variation of the blue band intensity with time (recorded at 2.8 eV). The intensity at “zero time” is normalized to 100% for all excitation densities. The bleaching with time has fast and slow components. The latter is nearly independent of the excitation density. Reprinted with permission from Reshchikov et al., Appl. Phys. Lett.78, 177 (2001). Copyright (2001) by the American Institute of Physics.

Image of FIG. 108.
FIG. 108.

Low-temperature PL spectrum of undoped GaN before and after UV illumination during 150 min with . Excitation density during the PL scan is .

Image of FIG. 109.
FIG. 109.

Evolution of PL intensity at 15 K with UV exposure time for unstable YL and BL bands (YL-u and BL-u, respectively) and stable PL bands (YL and BL) in undoped GaN layers. .

Image of FIG. 110.
FIG. 110.

Variation of PL spectrum with temperature for the GaN layer exhibiting unstable BL and YL bands. Excitation density is (at such low-excitation density the bleaching caused by UV exposure was negligible). The spectra were taken without high-intensity UV exposure.

Image of FIG. 111.
FIG. 111.

Schematic diagram showing the band bending and the vacuum level near the surface of GaN in vicinity of the metal tip.

Image of FIG. 112.
FIG. 112.

Schematic diagram showing the band bending near the surface of GaN in dark (a) and after UV light pulse (b). Electrons are shown with solid circles and holes—with empty circles. The Fermi level is shown as the same for electrons and holes in nonequilibrium case (b) in assumption that recombination in bulk is much faster than recombination over the barrier, and concentration of traps in the depletion region is much less than density of the surface states.

Image of FIG. 113.
FIG. 113.

Evolution of the YL intensity at room temperature in changing ambient for the MBE-grown GaN layer.

Image of FIG. 114.
FIG. 114.

Evolution of the near-band-edge emission intensity at room temperature under different ambient conditions for the MBE-grown GaN. Reprinted with permission from Reshchikov et al., Mater Res. Soc. Symp. Proc.743, L11–2 (2003).

Tables

Generic image for table
Table I.

List of main luminescence lines and bands in GaN.

Generic image for table
Table II.

Calculated acceptor ionization energies (in meV) for wurtzite (wz) and zinc-blende (zb) GaN.

Generic image for table
Table III.

Parameters of the PL bands in undoped GaN analyzed in our laboratory.

Generic image for table
Table IV.

Low-temperature parameters of the PL bands and related defects in doped GaN.

Generic image for table
Table V.

Classification and typical characteristics of the lines in GaN. Reprinted with permission from Reshchikov et al., Physica B 340–342, 440 (2003). Copyright (2003) by Elsevier.

Generic image for table
Table VI.

Comparison of dislocation densities (from TEM data) and relative intensities of the and DBE lines (from PL spectrum) in GaN layers grown by MBE on sapphire substrate

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2005-03-15
2014-04-21
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Luminescence properties of defects in GaN
http://aip.metastore.ingenta.com/content/aip/journal/jap/97/6/10.1063/1.1868059
10.1063/1.1868059
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