Acceptor-bound exciton recombination dynamics in p-type GaN (original) (raw)
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Applied Physics Letters, 1995
Neutral-donor-bound exciton recombination (I2) dynamics have been studied by photoluminescence in an unintentionally doped n-type GaN epitaxial layer grown by metalorganic chemical vapor deposition. The luminescence emission line shape, peak position, and intensity as functions of temperature have been measured. In particular, time-resolved emission spectroscopy has been employed to study the dynamic processes of the bound exciton recombination, from which the temperature and the emission energy dependencies of the recombination lifetime of this transition have been obtained.
Analysis of Time-Resolved Donor-Acceptor-Pair Recombination in MBE and MOVPE Grown GaN : Mg
physica status solidi (b), 2001
We have investigated the dynamics of the donor-acceptor-pair (DAP) recombination in Mg-doped GaN layers grown by MOVPE as well as MBE. The observed nonexponential decay curves are perfectly described if all parallel decay channels for each donor impurity surrounded by the acceptor impurities are included. Best fits have been obtained with a donor binding energy of 32 AE 2 meV. Additionally, under resonant excitation of the donor-bound-exciton complex the excited state of the donor could be clearly identified. From these data a donor binding energy of 29:9 AE 1:0 meV has been estimated, in good agreement with the value obtained from the DAP decay. We emphasize that the analysis of the DAP decay yields an accurate estimate for the neutral acceptor concentration in GaN : Mg without any need for further electrical measurements.
Impact of doping on carrier recombination and stimulated emission in highly excited GaN:Mg
Physica B: Condensed Matter, 2011
Light-induced transient grating and photoluminescence measurements were employed for carrier recombination studies in variously Mg doped GaN layers. Carrier lifetime and ambipolar diffusion coefficient were found to decrease with doping from 210 to 20 ps and from 2.0 to 0.9 cm 2 /s,respectively, which proved the degradation of electrical quality of the layers. A threshold of stimulated emission was found to depend non-monotonously on doping and had the lowest value of 0.19 mJ/cm 2 in the most doped layer. This dependence was explained in terms of degeneracy of the hole system.
Photoluminescence Excitation Studies of the Optical Transitions in GaN
MRS Proceedings, 1996
ABSTRACTWe present a detailed photoluminescence excitation study of the optical transitions in GaN. This technique is employed to distinguish between band-to-band excitation and exciton contribution to the formation of the free exciton, bound exciton, violet and yellow photoluminescence bands. We show the dominant role of the Fröhlich polar intraband scattering in the formation of the free exciton states. We demonstrate that bound exciton states in a large extent are created by the capture of the free excitons by shallow impurities as well as by phononassisted resonant excitation of the bound exciton states. The capture of the free carriers excited in the band continuum is a main excitation source for the violet and yellow bands. However, distinct A- and C-exciton resonances are detected in the excitation spectra of the violet and yellow emission bands.
Role of the V/III precursor ratio on exciton dynamics in GaN MOCVD epilayers
Materials Science and Engineering: B, 1997
Time-resolved photoluminescence spectroscopy is performed on strained epilayers of GaN, grown by MOVPE on Al 2 O 3 substrates. As the V/III precursor ratio R is increased, the decay time of the donor -accepter pair (DAP) recombinations at 3.22 and 3.29 eV is changed from 1 ns to much more than 20 ns. Coherently with this change, the X A and X B free excitons and a donor-bound exciton D o X lying 5.7 meV below X A are subject to significant variations. For R 8000, DAP transitions are fast and the D o X recombination dominates the spectrum at T = 8 K, with decay times of 35 -45 ps, while free excitons decay on a 25 ps time scale. For R 10000, the DAP transitions are very slow and all excitonic recombinations become faster: times of up to 280 ps are obtained for D o X and 35 ps for the X A line, which now dominates the time-integrated spectrum. Exciton dynamics in GaN epilayers can thus be controlled by the V/III precursor ratio, which affects both the density of vacancies and extrinsic impurity incorporation. © 1997 Elsevier Science S.A.
Applied Physics Letters, 2000
We have studied the As doping effects on the optical characteristics of GaN films by time-integrated photoluminescence and time-resolved photoluminescence. When As is incorporated into the film, the localized defect levels and donor–acceptor pair transition become less resolved. The recombination lifetime of neutral-donor-bound exciton (I2) transition in undoped GaN increases with temperature as T1.5. However, the I2 recombination lifetime in As-doped GaN first decreases exponentially from 98 to 41 ps between 12 and 75 K, then increases gradually to 72 ps at 250 K. Such a difference is related to the isoelectronic As impurities in GaN, which generate nearby shallow levels that dominate the recombination process.
Applied Physics Letters, 2006
Carrier recombination and diffusion dynamics in a 100-m-thick GaN grown by hydride vapor phase epitaxy on semi-insulating GaN:Mg substrate have been studied by means of transient photoluminescence under one-photon ͑1P͒ and two-photon ͑2P͒ excitations. For 2P bulk excitation the luminescence transients featured an exponential decay with the time constant of 1100 ps, which was mainly due to carrier capture to nonradiative deep traps. Meanwhile for 1P surface excitation, the luminescence transients showed a nonexponential decay with the mean time constant of 440 ps, which was shown to be due to both carrier in-depth diffusion and recombination.
Optical Spectroscopy of Mg- and C-Related Donor and Acceptor Levels in GaN Grown by MBE
physica status solidi (b), 1999
We present photoreflectance (PR) in combination with temperature and density dependent photoluminescence (PL) on undoped as well as on Mg-and C-doped GaN grown by molecular beam epitaxy (MBE). We determined the binding energy of the free A-exciton, the residual donorbound exciton and the Mg-acceptor-bound exciton to (26 AE 1), (5 AE 1) and (18 AE 1) meV, respectively. In n-type GaN a residual DAP band appears independent of the particular type of dopant. Free-hole concentrations up to 10 18 cm ± ±3 in MBE grown p-GaN:Mg were achieved without generation of deep compensating donors. Moreover, we found evidence for a second DAP series involving a shallow compensating donor level built in along with Mg doping. The correlation of different DAP bands to the respective type of conductivity opens an alternative way to control the p-type doping in GaN:Mg without the need for electrical contacting.
Exciton-related photoluminescence in homoepitaxial GaN of Ga and N polarities
Applied Physics Letters, 2000
A photoluminescence ͑PL͒ study of GaN homoepitaxial layers grown by metal-organic chemical-vapor deposition demonstrates the high optical quality of N-face layers deposited on vicinal (0001 ) GaN substrates. In contrast to broad PL emission in exact (0001 ) layers, narrow-bound ͑0.9 meV͒ and free-͑A and B͒ excitonic transitions are observed. By following the PL spectra as a function of temperature and excitation power, the main optical transitions in the Ga-and the misoriented N-face layers are found to be the same. Observed differences are related to the distinct creation of donor and acceptor states in the samples of different polarities.