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

We report the first high‐detectivity (D*=1.0×1010 cm (Hz)1/2/W), high‐responsivity (Rv =30 000 V/W) GaAs/AlxGa1−xAs multiquantum well detector, sensitive in the long‐wavelength infrared band at λ=8.3 μm (operating at a temperature of T= 77 K). Because of the mature GaAs growth and processing technologies as well as the potential for monolithic integration with high‐speed GaAs field‐effect transistors, large focal plane arrays of these detectors should be possible.

High‐detectivity D*=1.0×1010 cm √H̄z̄/W GaAs/AlGaAs multiquantum well λ=8.3 μm infrared detector

Publisher Summary This chapter focuses on the basic aspects of intersubband transitions, with the main emphasis on linear absorption. An expression for the intersubband absorption coefficient is based on Fermi's golden rule for induced transition rate in the framework of the one-band effective mass approximation. The chapter discusses several experimental geometries that enable the coupling of electromagnetic waves to the intersubband transition, which in most cases requires a polarization component perpendicular to quantum well (QW) layers. The chapter discusses asymmetrically-shaped QW potentials, such as those induced by a vertical electric field or by the variation of alloy composition. A main feature of intersubband transitions is their δ-function-like density of states, which is a consequence of the same curvature of the initial and final subband. It is generally advisable to work with the dielectric function ɛ(ω) or the conductivity σ(ω) instead of the absorption coefficient, whenever the electromagnetic properties of a sample are to be calculated consistently or many-body effects in the absorption are to be taken into account.

Chapter 1 The Basic Physics of Intersubband Transitions

A long-wavelength infrared imaging camera that uses a GaAs/Al/sub x/Ga/sub 1-x/As quantum-well infrared photodetector (QWIP) array is demonstrated. Excellent noise equivalent temperature difference sensitivity (NE Delta T >

10- mu m GaAs/AlGaAs multiquantum well scanned array infrared imaging camera

Ultrafast laser spectroscopy with time resolution down to 6 femtoseconds has been applied to study optical dephasing, relaxation, and recombination in various semiconductors and semiconductor microstructures. We report some applications of ultrafast laser spectroscopy to bulk and quantum well III–V and II–VI semiconductors in order to illustrate the potential. The characteristics time scales for dephasing, relaxation and recombination are discussed and determined experimentally.

M. Wörner

Papers

INTERSUBBAND RELAXATION IN GaAs/Al x Ga 1-x As QUANTUM WELL STRUCTURES