I. Introduction (Preface, Nanostructures in Si Inversion Layers, Nanostructures in GaAs-AlGaAs Heterostructures, Basic Properties). 
II. Diffusive and Quasi-Ballistic Transport (Classical Size Effects, Weak Localization, Conductance Fluctuations, Aharonov-Bohm Effect, Electron-Electron Interactions, Quantum Size Effects, Periodic Potential). 
III. Ballistic Transport (Conduction as a Transmission Problem, Quantum Point Contacts, Coherent Electron Focusing, Collimation, Junction Scattering, Tunneling). 
IV. Adiabatic Transport (Edge Channels and the Quantum Hall Effect, Selective Population and Detection of Edge Channels, Fractional Quantum Hall Effect, Aharonov-Bohm Effect in Strong Magnetic Fields, Magnetically Induced Band Structure).

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Quantum Transport in Semiconductor Nanostructures

Publisher Summary Quantum transport is conveniently studied in a two-dimensional electron gas (2DEG) because of the combination of a large Fermi wavelength and large mean free path. Semiconductor nanostructures are unique in offering the possibility of studying quantum transport in an artificial potential landscape. This is the regime of ballistic transport in which scattering with impurities are neglected. The chapter presents a self-contained account of these three novel transport regimes in semiconductor nanostructures. The study of quantum transport in semiconductor nanostructures is motivated by more than scientific interest. The fabrication of nanostructures relies on sophisticated crystal growth and lithographic techniques that exist because of the industrial effort toward the miniaturization of transistors. Conventional transistors operate in the regime of classical diffusive transport, which breaks down on short length scales. The discovery of novel transport regimes in semiconductor nanostructures provides options for the development of innovative future devices.

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Dislocations in strained-layer epitaxy : theory, experiment, and applications

The rate equations for a microcavity semiconductor laser are solved and the steady-state behavior of the laser and some of its dynamic characteristics are investigated. It is shown that by manipulating the mode density and the spontaneous decay rates of the cavity modes, the threshold gain can be decreased and the modulation speed can be improved. However, in order to fully exploit the possibilities which the modification of the spontaneous decay opens up, the active material volume in the cavity must be smaller than a certain value. Threshold current using different definitions, population inversion factor, L-I curves, linewidth, and modulation response are discussed. >

Analysis of semiconductor microcavity lasers using rate equations

The band‐gap energy (Eg) of metalorganic vapor phase epitaxially (MOVPE) grown Ga0.5In0.5P lattice matched to (001) GaAs is presented as a function of a wide range of V/III ratios and growth temperatures. Photoluminescence, Raman scattering spectroscopy, transmission electron microscopy, and impurity diffusion were used to investigate this functional relationship. Two pieces of evidence are shown which demonstrate that MOVPE Ga0.5In0.5P epitaxial layers with ‘‘abnormal’’ Eg∼1.85 eV and ‘‘normal’’ Eg∼1.9 eV correspond to an ordered and a random (Ga,In) distribution on column III sublattices, respectively. In an ordered state, a sequence of (110) planes...GaGaInInGaGaInIn...in the [110] direction is the most probable distribution.

Evidence for the existence of an ordered state in Ga0.5In0.5P grown by metalorganic vapor phase epitaxy and its relation to band‐gap energy

It is demonstrated that the energy band gap in epitaxial layers is changed by biaxial elastic strains which are produced by lattice mismatches in heterostructures. The epitaxial layers used in this work were Gax In1−xP layers grown on (001) GaAs substrates by liquid phase epitaxy. The energy band‐gap shifts were determined by comparing the photoluminescence peak energies of the as‐grown GaxIn1−xP layers with those from free‐standing layers removed from the GaAs substrates. It was experimentally found that the energy band gap shifts linearly with the elastic strain in the layer. Assuming that the lattice mismatch was accommodated only by the elastic distortion, the energy band‐gap shifts in Ga0.5In0.5P alloys were also calculated. The calculated results are 6.0 eV or 4.9×10−12 eV/dyn cm−2 per unit strain or stress, respectively, for the [100] and [010] biaxial elastic stress. These values are in quite good agreement with the experimental results.

Energy band‐gap shift with elastic strain in GaxIn1−xP epitaxial layers on (001) GaAs substrates

Anisotropic lateral growth in GaAs MOCVD layers on (001) substrates

An In0.53Ga0.47As/In0.52Al0.48As superlattice avalanche photodiode is fabricated by molecular beam epitaxy, and ionization rates are measured. The electron ionization rate is enhanced by a factor of 20 over hole ionization rate. This is the first time that such a remarkable increase has been observed for a superlattice. The increase is attributed to the large conduction‐band offset.

Impact ionization rates in an InGaAs/InAlAs superlattice

We have performed Gax In1−xP liquid phase epitaxial (LPE) growth on (100) GaAs substrates at a growth temperature of 785 °C. The P atom fraction in the growth melts was kept constant every LPE growth run. The lattice mismatch Δa⊥/a0 between the Gax In1−xP layer and GaAs substrate normal to the wafer surface and photoluminescence (PL) of the alloy layer were measured. It was found that Δa⊥/a0 and the PL peak energy vary linearly from +0.47 to −0.13% and from 1.869 to 1.921 eV at room temperature, depending on the Ga atom fraction in the growth melts, respectively. This means that the so‐called composition pulling phenomenon does not occur in LPE growth of Gax In1−xP on (100) GaAs substrates.

GaxIn1−xP liquid phase epitaxial growth on (100) GaAs substrates

Narrow two‐dimensional electron gas (2DEG) channels have been fabricated for the first time on GaAs/Al0.3Ga0.7As sidewall interfaces by selective growth using metalorganic chemical vapor deposition (MOCVD). The 4‐μm‐wide 2DEG channels are formed on the {111}A facets by controlling the facet formation in the selective growth layers only through MOCVD growth conditions. The angular dependence of Shubnikov–de Haas oscillations has confirmed the existence of 2DEG on the {111}A facets.

Hiromitsu Asai

Papers

Energy band‐gap shift with elastic strain in GaxIn1−xP epitaxial layers on (001) GaAs substrates

Anisotropic lateral growth in GaAs MOCVD layers on (001) substrates

Impact ionization rates in an InGaAs/InAlAs superlattice

GaxIn1−xP liquid phase epitaxial growth on (100) GaAs substrates

Narrow two‐dimensional electron gas channels in GaAs/AlGaAs sidewall interfaces by selective growth