Cyclotron resonance and interband measurements are reported in magnetic fields up to 160 T for InAs/InAs_{1-x}Sb_{x} superlattices, one of which is a "self-organised" or "natural" superlattice, and InAs_{1-x}Sb_{x} epilayers. The samples were grown by MBE at temperatures between 370°C to 500°C. No dependence of the band gap, effective masses or g-values on the growth temperature was detected. Anomalous tilt behaviour was observed for the superlattices. Inversion asymmetry induced spin-splitting of the subbands in gated InAs quantum wells is investigated by means of the Shubnikov-de Haas effect and cyclotron resonance. The non-parabolicity was well fitted by Kane theory, although the measured values of effective mass were substantially higher than predictions. Infrared life time measurements at wavelengths between 6 and 85 microns are undertaken with free electron lasers on InAs/InAs_{1-x}Sb_{x} superlattices and InAs/AlSb quantum wells. Suppression of the Auger recombination times is demonstrated with the superlattices.
The diamond anvil cell technique is applied for magneto-optical far-infrared transmission experiments with LPE grown GaAs:Sn. The 1s-2p(+) intra-shallow-Γ-donor transition is investigated as a function of high hydrostatic pressure for Sn and residual S donors. Both donors are shallow up to 30 kbar. Above this pressure both donors become deep and shallow donor absorption is persistently bleached due to deep non-metastable (non DX-like) states of the donors entering the gap of GaAs.
Variable-pressure Dunstan-type diamond anvil high pressure cell and a low temperature photoluminescence technique are used to observe the shallow-deep A_{1} transition for Sn donors in highly Sn doped n-type (≈ 10^{18} cm^{-3}) GaAs. Fermi level pinning to the position of the deep Sn donor state entering the gap close to 30 kbar pressure is observed. Drastic narrowing of the near-band-edge luminescence is observed in the transition region. The deep-donor pressure coefficient of 2 meV/kbar with respect to the valence band is deduced from the energy position of the deep donor-acceptor transitions.
The dependence of the energy position of the deep defect-related photoluminescence line Y-1.2 eV in Ge-doped GaAs on high hydrostatic pressure is investigated using a Dunstan-like diamond anvil cell. The observation that the energy position of the line follows that of the Γ-conduction band minimum in the 1 bar-30 kbar pressure range demonstrates that the line has Γ-(free or shallow bound)-to-deep acceptor character. This fact confirms the deep-acceptor character of the deep defect, most likely a donor impurity-Ga vacancy complex, which contributes to the Y:-1.2 eV photoluminescence line.
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