Calculations of the inter-subband scattering rates of electrons in GaAs/AlGaAs quantum wells (original) (raw)
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Electron scattering by optical phonons in AlxGa1-xAs/GaAs/AlxGa1-xAs quantum wells
Physical Review B, 1997
The scattering of a quasi two-dimensional electron gas by optical phonons in selectively doped Al x Ga 1Ϫx As/GaAs/Al x Ga 1Ϫx As quantum wells is systematically studied in order to determine the effect of phonon confinement. The electron states are calculated solving self-consistently Schrödinger and Poisson equations to obtain an accurate dependence upon the structure parameters and the temperature. We study the way the scattering is affected by the form of the phonons calculating the mobility using three models for the phonons. They are considered: ͑a͒ as three dimensional ͑3D͒, ͑b͒ as a set of confined and interface phonons, and ͑c͒ as the normal modes of the heterostructure. The relaxation times for the electron energy subbands are calculated solving the system of Boltzmann equations. The effect of the temperature and the well width variation is also investigated. The results are in a good agreement with experimental measurements. The agreement is only slightly dependent on the model used for the phonons and becomes best when the effect of the heterostructure on the phonon modes is taken into account. ͓S0163-1829͑97͒07624-8͔
Superlattices and Microstructures, 1996
The problem of intersubband relaxation in GaAs/GaAs quantum wells, where the energy separation of the two lowest subbands is smaller than the optical phonon energy, is considered. Time resolved pump-and-probe measurements are performed with a far-infrared free-electron laser on two multiquantum well samples with similar thicknesses ( 300 Å ), but different doping and mobilities. The measured lifetimes are shorter than could be explained by acoustic phonon emission alone. Monte-Carlo calculations show the importance of electron-electron scattering for thermalization of the hot electron distribution function and subsequent optical phonon emission from the long thermal tail.
Microscopic calculation of the electron-phonon interaction in quantum wells
Physical Review B, 1992
The electron-optica1-phonon scattering rates in GaAs/AlAs quantum wells are calculated on the basis of a fully microscopic description of the phonon spectra. The results indicate the great importance of confined as we11 as GaAs-like and A1As-like interface phonons. By comparing our results with those of several macroscopic models, we resolve a long-standing controversy on their ability to describe the relevant vibrations.
Superlattices and Microstructures, 1997
Using luminescence upconversion with 100 fs resolution, we have investigated the intersubband scattering of electrons in GaAs quantum wells (QWs). The energy separations between the first and second confined electron subband (E 12 ) were more or less than the LO phonon energy (E LO ). In narrow QWs (E 12 > E LO ) the intrinsic LO phonon scattering rate is found to be 1.6 × 10 12 s −1 . A Monte Carlo simulation allows us to reproduce the experimental data with high accuracy. In wide QWs (E 12 < E LO ) we find a very fast thermalization of the carrier population in the QW within times shorter than 300 fs. The intersubband relaxation rate for electrons in the n = 2 subband can be estimated to be shorter than 1.5 ps.
Electron-phonon scattering rates in GaAs/AlGaAs 2DEG samples below 0.5 K
Surface Science, 1996
We have studied electron heating in a 2DEG in GaAs/AIGaAs heterojunctions below 0.5 IC The electron temperature was raised above the lattice temperature using Joule heat/n& Weak localiT~tion and the temperature-dependent sample resistance were used as thermometers for the electrons. The electron-phonon energy relaxation rate was found to be proportional to T s. We find that the relaxation rate increases with disorder in the system.
Influence of interface phonons on intersubband scattering in asymmetric coupled quantum wells
Physical Review B, 1993
A theoretical investigation of intersubband transitions in asymmetric coupled GaAs-Al, Ga& "As quantum wells is presented in order to understand the role of interface phonons on intersubband scattering times estimated from photoluminescence up-conversion. Photoexcited carrier behavior is analyzed in relation to recent measurements and shows time constants for electron relaxation in agreement with experimental data. We show that interface modes are vital to intersubband relaxation in these structures.
Physical Review B, 1995
We have calculated electronoptical-phonon scattering rates in ultrathin GaAs/Al Gai As alloy quantum-well systems of Rnite depth, based on a fully microscopic lattice dynamics approach for the phonon spectra. A pseudo-unit-cell model is utilized to calculate the lattice-dynamical properties of the Al Gaz As alloy system together with the two-parameter Keating potential and the long-range Coulomb potential between ions. The polar interactions of quantum-confined electrons with GaAsand AlAs-like optical modes are presented for both intrasubband and intersubband transitions, and the comparison with other theoretical calculations made. Good agreement is obtained for the 1~1 and 2-+1 transition rates between the microscopic pseudo-unit-cell model and a macroscopic two-pole dielectric continuum model.