R. Dingle

Electron mobilities in modulation‐doped semiconductor heterojunction superlattices

GaAs‐AlxGa1−xAs superlattice structures in which electron mobilities exceed those of otherwise equivalent epitaxial GaAs as well as the Brooks‐Herring predictions near room temperature and at very low temperatures are reported. This new behavior is achieved via a modulation‐doping technique that spatially separates conduction electrons and their parent donor impurity atoms, thereby reducing the influence of ionized and neutral impurity scattering on the electron motion.

Optical characterization of interface disorder in GaAs-Ga1-xAlxAs multi-quantum well structures

Abstract We report a systematic increase of the linewidth of luminescence, absorption and excitation spectra of undoped GaAs-Ga 1-x A l x As Multi-Quantum structures with decreasing layer thickness. This broadening is interpreted as due to the island-like structure of the interfaces. A very simple model assuming islands with a one monolayer height and a lateral size ≳ 300 A gives very good agreement with the reported linewidths.

Quantum States of Confined Carriers in Very Thin Al x Ga 1-x As-GaAs-Al x Ga 1-x As Heterostructures

Quantum levels associated with the confinement of carriers in very thin, molecular-beam—grown AlxGa1−xAs−GaAs-Alx Ga1−xAs heterostructures result in pronounced structure in the GaAs optical absorption spectrum. Up to eight resolved exciton transitions, associated with different bound-electron and bound-hole states, have been observed. The heterostructure behaves as a simple rectangular potential well with a depth of ≈0.88ΔE g , for confining electrons and ≈0.12ΔE g for confining holes, where ΔE g is the difference in the semiconductor energy gaps.

Epitaxial structures with alternate‐atomic‐layer composition modulation

Epitaxial structures grown by alternate monolayer depositions of GaAs and AlAs are reported. As many as 104 alternate (100) layers of GaAs and AlAs as thin as 1.0±0.1 and 1.0±0.1 monolayers, respectively, were deposited by sequential molecular beam epitaxial growth on a (100)GaAs substrate. Transmission electron microscopy showed the resultant films to be perfectly epitaxial with layered composition modulation of the expected periodicity. Their electronic properties were studied by optical absorption and luminescence.

Current injection GaAs‐AlxGa1−xAs multi‐quantum‐well heterostructure lasers prepared by molecular beam epitaxy

Low‐current‐threshold room‐temperature injection GaAs‐AlxGa1−xAs multi‐quantum‐well (MQW) lasers have been prepared by molecular beam epitaxy. Under pulsed current injection, lasing emission attributed to the n=1 electron‐to‐light‐hole (1 e‐lh) confined‐particle transition was observed at threshold. Above threshold, lasing emission involving the n=1 electron‐to‐heavy‐hole transition (1 e−hh) became dominant. Single longitudinal mode operation has also been observed for these broad‐area MQW lasers. For heat‐sink temperatures between 8 and 100 °C, the lasing current threshold Ith for the 1 e−hh transition has an exponential variation with temperature of the form Ith∝ exp(T/T0), where T0=230 °K.

Observation of intersubband excitations in a multilayer two dimensional electron gas

Abstract We report the observation, by resonant inelastic light scattering, of intersubband excitations of the multilayer two dimensional electron gas, in modulation doped GaAsAlGaAs heterojunction superlattices. These are the first measurements of these transitions by any technique, and furnish intersubband energies in good agreement with calculated values. The spectral bands are broad, and nearly Lorentzian in shape: the implied relaxation rates scale linearly with band energy and are significantly faster than transport relaxation rates. Finally, the polarized spectra reveal differences between spin-flip and non spin-flip excitations which are unique to multilayer two dimensional electron gases.

Dependence of the structural and optical properties of GaAs‐Ga1−xAlxAs multiquantum‐well structures on growth temperature

The structural and optical properties of multiquantum‐well (MQW) structures grown by molecular beam epitaxy are strongly dependent on the substrate temperature Ts during the growth. A study of the optimization of MQW structures as a function of Ts is carried out using optical and electron microscopy and photoluminescence characterization. Optimal temperatures in the range 670–730 °C are shown to yield smooth free surfaces and interfaces and high quantum efficiencies.

Two‐dimensional electron gas at a molecular beam epitaxial‐grown, selectively doped, In0.53Ga0.47As‐In0.48Al0.52As interface

We report the observation of a high‐mobility, two‐dimensional electron gas (2DEG) at the interface between a molecular beam epitaxial (MBE)‐grown undoped In0.53Ga0.47As layer and a subsequent layer of MBE‐grown, Si‐doped In0.48Al0.52As . Peak mobilities of ∼92 000 cm2 V−1 s−1 have been observed at 4.2 K. From Hall and Shubnikov‐de Haas studies we have found that the 2DEG can be characterized by nch = 6–8×1011 cm−2. In all cases we found two subbands to be occupied at Nch≳4.5×1011 cm−2.

Two-dimensional electron gas at a semiconductor-semiconductor interface

Abstract We report the first observation of a two-dimensional electron gas at a semiconductor-semiconductor (GaAs-AlGaAs) interface. A novel, high-mobility, persistent-photoconductive effect allows one to vary the two-dimensional carrier concentration continuously from 1.1 × 10 12 cm -1 to 1.6 × 10 12 cm -2 , as obtained by Shubnikov-deHaas measurements. Cyclotron resonance data establish an effective mass of 1.11 m ∗ b , where m ∗ b is the mass at the conduction- band edge of GaAs. Hall data and cyclotron resonance yield a mobility of μ ≈ 5000 cm 2 /Vsec.

Intersubband spectroscopy of two dimensional electron gases: Coulomb interactions

Abstract We have made a direct determination of resonant screening (the depolarization field effect) in the collective intersubband excitations of a dense two dimensional electron gas. The effect was observed, for both odd and even parity transitions, in polarized inelastic light scattering spectra of a modulation-doped GaAs-AlGaAs superlattice. We offer a quantitative interpretation in terms of the Coulomb matrix elements for the transitions. Final state, or exciton-like, many-body effects are considered briefly.