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Type-II CdSZnSe strained layer superlattice (SLS) grown on a CdS buffer on (1 1 1)A GaAs provide evidence for the intrinsic Stark effect at visible wavelengths. Shifts in photoluminescence (PL) peak energies are expected when photoexcited carriers screen the internally generated piezoelectric fields. Characteristic PL blue shifts under increasing excitation for CdSZnSe samples are observed. Transmission electron micrographs show that a superlattice, grown at 400°C, is mostly hexagonal in structure but a similar sample, grown at 300°C, adopts a cubic habit. However, both samples show similar shift factors, 70 meV per decade of excitation intensity, in the range of power densities from 50 mW cm −2 to 20 kW cm −2 . These shift factors are only slightly smaller than that found in CdSCdSe hexagonal superlattices of similar period. This result is not expected since the bulk piezoelectric coefficients of cubic ZnSe are thought to be much smaller than those for wurtzite phase II–VI semiconductors. A resolution of these apparent contradictions may be found by involving the recently reported nonlinearity of cubic piezoelectric coefficients as a function of strain by Andre et al. [Phys. Rev. B 53 (1996) 6951].

The low-temperature photoluminescence (PL) spectra of a range of CdS-CdSe and CdS-ZnSe type-II superlattices was measured under both cw and quasi-cw excitation over the excitation range from mW cm −2 to MW cm −2 . In all cases, a single PL band due to the recombination of separated electrons and holes in the type-II bandstructure was observed. As the excitation density increases from a low value, the PL peak shifts logarithmically towards the blue. Total shifts of up to 200 meV for a CdS-CdSe sample of 10 nm period are observed, with a corresponding shift-factor of 30 meV per decade of excitation density. The shift factor increases in a regular fashion with the superlattice period. A comparison with the literature shows that a logarithmic dependance of the blue shift with increasing excitation density appears to be a universal feature of type-II SL, even in the absence of strain.

The first evidence of the intrinsic Stark effect at visible wavelengths (∼ 600 nm) is reported for a CdSZnSe strained layer superlattice (SLS) grown on a (111)A GaAs substrate. At the same time, smaller but significant exciton peak shifts with excitation power occur for similar samples that were grown on (100)GaAs substrates and thus predicted not to exhibit the effect. We attribute these shifts to band filling in a relaxed type-II SLS. We also report the largest light-induced exciton peak shift ever observed, 600 meV, in a CdSCdSe piezoelectric type-II strained layer superlattice. A shift of 150 meV per decade of excitation power occurs in a superlattice of period 16 nm under both pulsed and CW excitation at low temperature. Finally we mention the prospect of producing optically activated modulators that work in the visible and near infrared spectral region (500–1100 nm) from such structures.

Implants of arsenic and gallium ions have been made into InGaAs/GaAs and GaAs/AlGaAs single quantum wells to a dose of 10 13 atoms/cm 2 . In each case the implantation energies are varied so as to get the peak of the implantation profile at the centre of the well. Using repetitive anneals and photoluminescence from the n = 1 electron to heavy hole transition, it has been possible to follow the evolution of the diffusion coefficients for the interdiffusion with anneal time. Following gallium implantation no effect was observed on the diffusion coefficient for intermixing in either material system. However, a region of very rapid intermixing which occurred either during implantation or the first anneal was seen in both materials. This is attributed to either radiation enhanced diffusion or the movement of interstitials created by the ion beam. Following arsenic implantation, the GaAs/AlGaAs material behaved identically to the gallium implanted samples. The InGaAs/GaAs materials, however, showed a region of intermixing where the diffusion coefficient was enhanced by an order of magnitude before returning to approximately the unimplanted control value.

We report on verification of the proposed energy transfer mechanism responsible for photoluminescence of rare earth (RE) ions in semiconductors. Using two-color spectroscopy in the visible and the midinfrared regions (with a free-electron laser) we demonstrate reversal of the most important step in the excitation process. In that way, formation of the intermediate state bridging atomic states of the RE ion core and extended orbitals of a semiconducting host is explicitly confirmed and its characteristic energy spectroscopically determined. The study is performed for InP:Yb. It is argued, however, that the conclusions are valid for all semiconductor:RE systems, including the notorious Si:Er.

Electron intersubband lifetimes of 1.8 ps and 2.5 ps were measured in GaAs/AlGaAs asymmetric stepped quantum well samples by using a pump–probe three-beam technique at 4 K to room temperature. At high pump intensities, an absorptive signal of sub-nanosecond lifetime was detected following a normal positive transmissive signal of picosecond lifetime. This absorptive signal is believed to be caused by the absorption from the free electrons pumped from the ground subband to the continuum conduction band in the barrier layers associated with incoherent multi-photon process. The intersubband lifetimes and free carrier effects play an important role in optically pumped multiple-quantum-well far infrared lasers. A three-level electron transition model is built to simulate the process, which agrees very well with the experimental data.

We report the photoluminescence study of low‐energy, low‐dose oxygen implantation induced compositional disordering of AlGaAs/GaAs quantum well structures. Significant disordering of both single and multiple AlGaAs/GaAs quantum wells has been achieved using low‐energy (155 keV) oxygen ion implantation with doses as small as 5 × 1013 cm−2 after a moderate annealing step. These doses are significantly lower than those reported previously (500 keV and 1016 cm−2).

The intermixing of InGaAs/GaAs strained quantum wells following gallium ion implantation was characterised using photoluminescence. It was found that the implanted atoms had no effect of the diffusion coefficient for intermixing when compared to an unimplanted control sample. However, it was seen that the well was broadened by a diffusion length of approximately 37A during the first anneal, before a photoluminescence measurement could be made. A simulation of the implantation process shows that cascade mixing is not sufficient to account for this and it is suggested that we are observing the diffusion of interstitials created by the implantation.