Energy position of near-band-edge emission spectra of InN epitaxial layers with different doping levels (original) (raw)
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Dynamics of free carrier absorption in InN layers
Applied Physics Letters, 2009
Carrier dynamics in highly excited InN epitaxial layers was investigated in the 1550-2440 nm ͑0.8-0.51 eV͒ spectral range by using a femtosecond differential transmission technique. A transition from induced bleaching to induced absorption was observed for probing energy of 90 meV below the bandgap of the samples. The decay of the induced free carrier absorption provided the averaged lifetime of the total nonequilibrium carriers. In the carrier density range of ⌬n =10 18 -10 20 cm −3 , the density-dependent recombination mechanism was attributed to trap-assisted Auger recombination with decay rate 1 / = B TAAR ⌬n, with B TAAR in the range ͑4-30͒ ϫ 10 −10 cm 3 s −1 for layers with different defect densities.
Influence of defects on the absorption edge of InN thin films: The band gap value
We investigate the optical-absorption spectra of InN thin films whose electron density varies from ϳ10 17 to ϳ 10 21 cm −3 . The low-density films are grown by molecular-beam-epitaxy deposition while highly degenerate films are grown by plasma-source molecular-beam epitaxy. The optical-absorption edge is found to increase from 0.61 to 1.90 eV as the carrier density of the films is increased from low to high density. Since films are polycrystalline and contain various types of defects, we discuss the band gap values by studying the influence of electron degeneracy, electron-electron, electron-ionized impurities, and electron-LO-phonon interaction self-energies on the spectral absorption coefficients of these films. The quasiparticle self-energies of the valence and conduction bands are calculated using dielectric screening within the random-phase approximation. Using one-particle Green's function analysis, we self-consistently determine the chemical potential for films by coupling equations for the chemical potential and the single-particle scattering rate calculated within the effective-mass approximation for the electron scatterings from ionized impurities and LO phonons. By subtracting the influence of self-energies and chemical potential from the optical-absorption edge energy, we estimate the intrinsic band gap values for the films. We also determine the variations in the calculated band gap values due to the variations in the electron effective mass and static dielectric constant. For the lowest-density film, the estimated band gap energy is ϳ0.59 eV, while for the highest-density film, it varies from ϳ0.60 to ϳ 0.68 eV depending on the values of electron effective mass and dielectric constant.
Physical Review Letters, 2000
The highest equilibrium free-carrier doping concentration possible in a given material is limited by the "pinning energy" which shows a remarkable universal alignment in each class of semiconductors. Our first-principles total energy calculations reveal that equilibrium n-type doping is ultimately limited by the spontaneous formation of close-shell acceptor defects: the ͑32͒-charged cation vacancy in AlN, GaN, InP, and GaAs and the ͑12͒-charged DX center in AlAs, AlP, and GaP. This explains the alignment of the pinning energies and predicts the maximum equilibrium doping levels in different materials.
Direct Auger recombination and density-dependent hole diffusion in InN
Scientific Reports, 2018
Indium nitride has a good potential for infrared optoelectronics, yet it suffers from fast nonradiative recombination, the true origin of which has not been established with certainty. The diffusion length of free carriers at high densities is not well investigated either. Here, we study carrier recombination and diffusion using the light-induced transient grating technique in InN epilayers grown by pulsed MOCVD on c-plane sapphire. We show that direct Auger recombination governs the lifetime of carriers at densities above ~10 18 cm −3. The measured Auger recombination coefficient is (8 ± 1) × 10 −29 cm −3. At carrier densities above ~5 × 10 19 cm −3 , we observe the saturation of Auger recombination rate due to phase space filling. The diffusion coefficient of holes scales linearly with carrier density, increasing from 1 cm 2 /s in low-doped layers at low excitations and up to ~40 cm 2 /s at highest carrier densities. The resulting carrier diffusion length remains within 100-300 nm range, which is comparable to the light absorption depth. This feature is required for efficient carrier extraction in bipolar devices, thus suggesting MOCVD-grown InN as the material fit for photovoltaic and photonic applications. Indium nitride with a direct band gap of 0.7 eV 1 is an attractive material for infrared optoelectronics. However, InN layers of high quality are difficult to obtain. In addition to structural problems, InN suffers from high residual electron density (n 0) caused by abundant point defects. n 0 can be diminished by growing thick InN layers using molecular beam epitaxy (MBE) 2 , but this is an expensive and hardly scalable approach. Other growth techniques were also employed, including metalorganic chemical vapor deposition (MOCVD) 3 , chemical vapor deposition 4 , sputtering 5 , or even sol-gel spin coating 6. The typical n 0 values, however, remain in the range from 10 18 cm −3 to mid-10 19 cm −3. It is likely that InN-based devices will have to operate at high electron densities, thus, it is essential to understand the impact of high carrier density on carrier dynamics. Carrier lifetime dependence on their density τ(n) is a powerful tool to reveal the dominating recombination mechanisms. Mainly linear or sublinear dependences were observed in InN layers by using the time-resolved photoluminescence, differential reflectance, or light-induced transient gratings (LITG) techniques. Based on these results, it was argued that Shockley-Read-Hall (SRH) 7-9 , Auger recombination in degenerate plasma 10 , or trap-assisted Auger recombination 11 were the dominant recombination mechanisms in InN. Carrier transport, especially that of minority holes, is less investigated. It was theoretically predicted that the room temperature hole mobility μ h can reach 220 cm 2 /Vs in low-doped InN, but should drop rapidly with n 0 above 10 17 cm −3 12. Experimentally, several techniques were used to measure μ h at fixed hole density. μ h = 17-36 cm 2 /Vs was estimated from sheet conductivity against sample thickness in Mg-doped layers at (1.4-3.0) × 10 18 cm −3 13. Variable magnetic field Hall measurements provided the mobility of heavy and light holes of 50 cm 2 /Vs and 600 cm 2 /Vs, respectively, in a sample with Mg doping at 3 × 10 20 cm −3 14. Hall measurements in InN layers Mg doped in a wide range from 10 18 to 10 20 cm −3 revealed p-type conductivity with similar μ h of 20-30 cm 2 /Vs 15. Application of LITG technique allowed for measuring the mobility of minority holes, which was ~40 cm 2 /Vs in high-quality MBE layers with n 0 in the mid-10 17 cm −3 16,17. This work is focused on the study of carrier dynamics in a wide range of carrier densities. Epilayers with different residual carrier densities were fabricated, while the increasing photoexcited carrier densities were generated using femtosecond laser pulses to ensure high time resolution. LITG technique is exploited to simultaneously extract the carrier lifetimes and their diffusion coefficients at different stages of the decay of nonequilibrium
Physical Review B, 2005
The temperature dependence of the resistivity of InN was investigated as a function of carrier density. The carrier density was changed from n e = 1.8ϫ 10 18 cm −3 to 1.5ϫ 10 19 cm −3 by Si doping. The InN investigated showed metallic conduction above 20 K. At lower temperatures there was a resistivity anomaly originating from carrier localization in the a-b plane, which was confirmed by the magnetoresistance at 0.5 K. The Shubnikov-de Haas oscillation showed that InN had a spherical Fermi surface and its radius increased according to the increase of n e when n e Ͻ 5 ϫ 10 18 cm −3. In addition, an oscillation corresponding to the constant carrier density of 4.5ϫ 10 12 cm −2 was observed in the field applied perpendicular to the a-b plane. This oscillation showed an anomalous angle dependence on the magnetic field. Taking into account this density, we determined the critical carrier density of the Mott transition to be 2 ϫ 10 17 cm −3. Anisotropy of localization was observed within the a-b plane, which indicates that the distribution of the electrons was not uniform in the a-b plane. The n e dependence of the magnetoresistance revealed an electronic structure change around 5 ϫ 10 18 cm −3. From these results, an electronic structure at the fundamental absorption edge of InN grown on sapphire ͑0001͒ was presented.
Spectral distribution of excitation-dependent recombination rate in an In0. 13Ga0. 87N epilayer
Generalized model of the dielectric function of AlInGaP alloys J. Appl. Phys. 113, 093103 (2013) Correlations between the morphology and emission properties of trench defects in InGaN/GaN quantum wells J. Appl. Phys. 113, 073505 (2013) Optical characterization of free electron concentration in heteroepitaxial InN layers using Fourier transform infrared spectroscopy and a 2×2 transfer-matrix algebra J. Appl. Phys. 113, 073502 (2013) Influence of structural anisotropy to anisotropic electron mobility in a-plane InN Appl. Phys. Lett. 102, 061904 (2013) Temperature dependent carrier dynamics in telecommunication band InAs quantum dots and dashes grown on InP substrates
Applied Physics Letters, 2007
Nearly defect-free InN microcrystals grown on Si͑111͒ substrates have been realized by plasma-assisted molecular beam epitaxy. High-resolution transmission electron microscope images reveal that these microcrystals exhibit single-crystalline wurtzite structure. Low temperature photoluminescence ͑PL͒ shows a strong emission peak at 0.679 eV with a very narrow linewidth of 17 meV at excitation power density of 3.4 W / cm 2 . Temperature-dependent PL spectra follow the Varshni equation well, and peak energy blueshifts by ϳ45 meV from 300 to 15 K. Power-densitydependent PL spectroscopy manifests direct near-band-edge transition. A low carrier density of 3 ϫ 10 17 cm −3 has been estimated from PL empirical relation, which is close to the critical carrier density of the Mott transition of 2 ϫ 10 17 cm −3 .
Photoluminescence of n‐InN with low electron concentrations
… status solidi (a), 2006
Photoluminescence (PL) of n-InN grown by molecular beam epitaxy with Hall concentrations from 3.6 × 10 17 to 1.0 × 10 18 cm-3 demonstrates new features as compared with that of the samples of previous generation which are characterized by a higher carrier concentration. The striking dependences of PL spectra on carrier concentration, temperature, and excitation density give evidences of a fast energy relaxation rate of photoholes and their equilibrium distribution over localized states. The well resolved structure consisting of three peaks was observed in the PL spectra of these samples in the energy interval from 0.50 to 0.67 eV at liquid helium and nitrogen temperatures. We attributed one of two low-energy features of the spectra to the recombination of degenerate electrons with the holes trapped by deep acceptors with a binding energy of E da = 0.050-0.055 eV and the other one is attributable to the LO-phonon replica of this band. The higher-energy PL peak is considered as a complex band formed by two mechanisms. The first one is related to the transitions of electrons to the states of shallow acceptors with a binding energy of E sh = 0.005-0.010 eV and/or to the states of Urbach tail populated by photoholes. The second mechanism contributing to this band is the band-to-band recombination of free holes and electrons. Relative intensities of two higher-energy PL peaks were found to be strongly dependent on temperature and excitation power. At room temperature, the band-to-band recombination of free holes and electrons dominates in PL. Experimental results on PL and absorption are described by the model calculations under the assumptions of the band gap equal to 0.665-0.670 eV at zero temperature and zero carrier concentration and the non-parabolic conduction band with the effective mass at Γ-point equal to 0.07 of free electron mass.
Influence of high electron concentration on band gap and effective electron mass of InN
physica status solidi (b), 2011
Effects of high electron concentration on the band gap energy of InN films having different layer thicknesses as 600 and 800 nm are investigated experimentally and theoretically. Electron concentrations of the samples are obtained through the Hall measurements accomplished between 77 K and room temperature. Optical characterization of the samples is carried out using the photoluminescence (PL) measurements and the observed PL spectra are explained considering the high electron concentration related effects, i.e. Burstein-Moss shift, band renormalization and band tailing in non-parabolic k Á p model. Extracted PL results indicate that the samples have approximately 0.685 eV band gap energy at 77 K. Effective mass of the carriers, which is calculated as 0.097 m 0 for electron concentration of $10 19 cm À3 , are also observed to be influenced by the high carrier concentration.