We present the results of our experimental and theoretical studies concerning the temperature dependence of electron mobility in a two-dimensional electron gas (2DEG) confined at the GaN/AlGaN interface. Experimental mobility of 2912 cm 2 (V s) −1 at 4.2 K, remains almost constant up to lattice temperature T L = 150 K, it then decreases rapidly down to 1067 cm 2 (V s) −1 at T L = 300 K. In order to compare the experimental results with the theory we use a simple analytical formula for low-field electron mobility based on 2D degenerate statistics for a 2DEG confined in a triangular well. We consider acoustic phonon, polar-optical phonon, dislocation and interface-roughness (IFR) scattering. The polar-optical phonon scattering is the dominant mechanism at high temperatures. At low temperatures, however, both the IFR and dislocation scattering explain, equally well, the observed mobility. In reality, however, a mixture of the two mechanisms together with the deformation potential and piezoelectric scattering will determine the low temperature mobility. The experimental results are discussed in the light of the calculations.
We report on the energy and momentum relaxation of hot electrons in n-type epilayer InN grown on sapphire substrate using molecular beam epitaxy (MBE). Hall and pulsed I -V measurements are carried out in the temperature range between 77 and 300 K. Drift velocity versus electric field characteristics show that, at 77 K, the drift velocity saturates just above v d ∼ 8 × 10 6 cm s −1 at electric fields in excess of E ∼ 12 kV cm −1 . The mobility comparison method together with the power balance equation is used to obtain the electron temperature as a function of applied electric field and the electron energy loss rate as a function of electron temperature. Our results show conclusively that the effective energy relaxation time constant in InN is 200 fs. This is about six times slower than the theoretical value for the e-LO phonon scattering time of 31 fs. The effects of non-equilibrium phonon generation on slowing down of the energy relaxation and increasing the momentum relaxation processes are discussed using a theoretical model first developed for GaAs and then adapted to the III-N material systems.
The electronic properties of modulation-doped GaAs/Ga 1−x Al x As multiple quantum wells (MWQ) with well width (L z ) in the range between 51 and 145 Å have been investigated by using the Shubnikov-de Haas (SdH) oscillations technique. The carrier density and the Fermi energy have been determined from the period of the SdH oscillations. The in-plane effective mass (m * ) and the quantum lifetime (τ q ) of 2D electrons have been obtained from the temperature and magnetic field dependences of the SdH amplitude. For narrow MQW samples (L z = 51, 75 and 78 Å), m * increases with decreasing L z ; for the samples with L z = 106 and 145 Å, m * is approximately equal to that of electrons in bulk GaAs. The values obtained for τ q show no clear well-width dependence and suggest that interface roughness is the dominating scattering mechanism in GaAs/Ga 1−x Al x As MQWs.
We present an overview of our optical characterization work on dilute nitride quantum
well (QW) samples. A simple model for calculating interband transition energies is
constructed, tested against published results and used to model experimental data. Steady state photoluminescence (PL),
time-resolved PL and photomodulated reflectance measurements are utilized to characterize
GaNAs/GaAs, GaInNAs/GaAs and InGaAs/GaAs QWs. The effects of carrier
localization, hot-carrier relaxation, non-radiative recombination and the reduced
bandgap temperature dependence of dilute nitrides are investigated. Emission
from recombining hot carriers in a GaInNAs/GaAs QW is recorded and used to
estimate the LO-phonon scattering energy. The addition of small fractions of N is
found to have little effect on phonon energy, which is found to be meV.
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