Monte Carlo simulations of electron transport in seven semiconductors of the diamond and zinc-blende structure (Ge, Si, GaAs, InP, AlAs, InAs, GaP) and some of their alloys (Al/sub x/Ga/sub 1-x/As, In/sub x/Ga/sub 1-x/As, Ga/sub x/In/sub 1-x/P) and hole transport in Si were performed at two lattice temperatures (77 and 300 K). The model uses band structures obtained from local empirical pseudopotential calculations and particle-lattice scattering rates computed from the Fermi golden rule to account for band-structure effects. Intervalley deformation potentials significantly lower than those which have been previously reported are needed to reproduce available experimental data. This is attributed to the more complicated band structures, particularly around the L- and X-symmetry points in most materials. Satisfactory agreement is obtained between Monte Carlo results and some experiments. >

Monte Carlo simulation of transport in technologically significant semiconductors of the diamond and zinc-blende structures. I. Homogeneous transport

By increasing the quantum well barrier width, we have dramatically reduced the tunneling dark current by an order of magnitude and thereby significantly increased the blackbody detectivity D*BB. For a GaAs quantum well infrared detector having a cutoff wavelength of λc=10.7 μm, we have achieved D*BB =1.0×1010 cm (Hz)1/2/W at T=68 K, a temperature which is readily achievable with a cryogenic cooler.

High sensitivity low dark current 10 μm GaAs quantum well infrared photodetectors

The properties of hot electrons in systems where electrons and phonons experience quantum confinement are reviewed. The modifications to the behaviour of electrons and phonons brought about by confinement are described, particularly with reference to the principal scattering mechanism. The latter include the interaction with longitudinal optical phonons and plasmons, along with carrier-carrier effects. Some conflict in the literature concerning Fuchs-Kliewer polaritons is discussed. Low-temperature interactions with acoustic phonons are described. A central topic is that of energy relaxation, and the experimental and theoretical data relating to this form a large part of the review. Energy relaxation mechanisms in the femtosecond to nanosecond regimes, including intersubband and well-capture processes, are eventually summarized. An equally large section deals with hot-electron transport; in which negative differential resistance and other instabilities associated with parallel transport are discussed before turning to ballistic transport and impact ionization.

https://iopscience.iop.org/article/10.1088/0034-4885/54/2/001/pdf

Hot electrons in low-dimensional structures

A critical review of the different theoretical models proposed for explaining the metal-semiconductor and semiconductor-semiconductor interfaces is presented. Although no attempt to present a thorough review of the experimental evidence is made, the authors discuss the most relevant information concerning those interfaces. Their discussion concentrates mainly on the models that have received more widespread acceptance: the induced density of interface states model and the defect model. A few comments on other cases are also made, and a critical evaluation of the different models is presented.

https://iopscience.iop.org/article/10.1088/0022-3719/20/2/001/pdf

On the formation of semiconductor interfaces

The experimental and theoretical work on carrier dynamics and recombination mechanisms in semiconductor heterostructures with staggered type II alignments is reviewed. Examples from the literature are discussed for each of the III-V, II-VI, and IV-VI systems, as well as cross-column examples, with a focus on AlGaAs structures. The key optical properties which have been identified as signatures of staggered-alignment behavior are summarized. A discussion of other epitaxial systems likely to exhibit staggered lineups is presented, and additional experimental and theoretical work is suggested, which could increase understanding of staggered-system behavior. >

Carrier dynamics and recombination mechanisms in staggered-alignment heterostructures

We have measured the electron velocity in low‐doped GaAs and in AlGaAs/GaAs modulation‐doped heterostructures at electric fields up to 8000 V/cm at both 300 and 77 K. In order to avoid the charge domain formation which occurs in dc measurements at these fields, this measurement uses 35 GHz radiation to supply the electric field. These measurements indicate that the peak velocity for electrons in the heterostructures is lower than for electrons in bulk low‐doped GaAs. This result is explained in terms of modified intervalley transfer, real space transfer, and an enhanced scattering with polar optical phonons.

Electron velocity and negative differential mobility in AlGaAs/GaAs modulation‐doped heterostructures

Recent experimental and theoretical results on band offsets in AlGaAs/GaAs heterostructures are discussed. A charge transfer dipole stabilization model is proposed to explain the long-range order in AlGaAs alloys. The connection between the large valence band offset of AlAs/GaAs and AlGaAs alloy ordering is pointed out. The role of band symmetry in quantum confinement is discussed.

On the band offsets of AlGaAs/GaAs and beyond

We have measured the electron velocity in low-doped GaAs and in AlGaAs/GaAs modulation-doped heterostructures at electric fields up to 8000 V/cm at both 300 and 77 K. In order to avoid the charge domain formation which occurs in DC measurements at these fields, this measurement uses 35 GHz radiation to supply the electric field. These measurements indicate that the peak velocity for electrons in the heterostructures is lower than for electrons in bulk low-doped GaAs. This result is explained in terms of modified intervalley transfer, real space transfer, and an enhanced scattering with polar optical phonons.

Electron velocity at high electric fields in AlGaAs/GaAs modulation-doped heterostructures

We have measured the energy relaxation of carriers in p- and n-type GaAs quantum wells using time-resolved photoluminescence. At low excitation densities (low carrier temperatures) the energy loss rate for holes is greater than for electrons, but it is not observed to depend on well width for values greater than 60A. At high excitation densities the rate is found to increase significantly for narrow wells (25A).

Energy relaxation in p- and n-GaAs quantum wells: Confinement effects

The energy relaxation of photoexcited hot electrons and holes in quantum well structures has been studied extensively using time resolved photoluminescence techniques. The energy loss rates (ELR) for both types of carrier have been systematically measured using undoped and modulation doped structures for a wide range of well widths. It is now well established that the ELR is reduced in low dimensional structures, especially for intense photoexcitation, and this effect has been explained, at least in part, by invoking the presence of nonequilibrium phonons which are generated in the relaxation process. Our measurements show that the ELR is not a strong function of well width for either low or high excitation densities, although in the former case the electron rate is substantially lower than that for holes. For intermediate excitation densities we find a substantial increase in the ELR both in GaAs and GaInAs structures for decreasing well width. Theoretical calculations of the ELR of electrons and holes have been made using a model in which carriers confined to a single subband interact with bulk optical phonons. In wide wells the wavevector to which the carriers couple lies within the plane of confinement. For narrower wells there is an increased coupling to out of plane modes due to the relaxation of momentum conservation. Under these conditions the carriers then couple to a larger number of phonon modes which reduces the nonequilibrium phonon population.

W.I. Wang

Papers

Electron velocity and negative differential mobility in AlGaAs/GaAs modulation‐doped heterostructures

On the band offsets of AlGaAs/GaAs and beyond

Electron velocity at high electric fields in AlGaAs/GaAs modulation-doped heterostructures

Energy relaxation in p- and n-GaAs quantum wells: Confinement effects

Nonequilibrium Phonon Effects In The Energy Relaxation Of Hot Carriers In Quantum Wells