Low-pressure MOCVD has been used to grow layers of inP, InGaAs, GalnAsP and quantum weii material on planar substrates patterned with silica masks. The thicknesses and, where relevant, the compositions of these selectively grown layers were investigated by optical and scanning electron microscopy, surface profiling, energy dispersive x-ray analysis, secondary-ion mass spectroscopy and spatially resolved photoluminescence. The epitaxial layers were found to be both thicker and richer in indium in the vicinity of a mask. The perturbations in the thickness and composition of material grown around a given mask pattern were independent of the orientation of the pattern with respect to the gas flow and the crystallographic axes of the substrate. Lateral movement of material from the masked regions to the surrounding areas was found to take place in the gas above the wafer surface. A gas-phase diffusion model based on Laplace's equation was used to analyse the thickness and compositional variations caused by selective growth. The emission wavelength of selectively grown InGaAsl GalnAsP MOW material was shifted by over 100 nm without degradation in emission efficiency. The lasing wavelength of Fabry-Pbrot lasers fabricated on such material was increased by a similar amount without degradation of threshold current.

No abstract

Magneto-optical experiments have been used to study a range of InoaAsP-based multiple-quantumwell (MQW) structures containing biaxial strains, ranging from 1.6% tensile to 1.0% compressive. The observed excitonic transitions, involving both heavy and light holes, are studied in fields up to 15 T. Estimates of the hole effective masses are made, providing details of the valence-band nonparabolicities, and electronlike behavior is demonstrated for both heavy and light holes with different amounts of tensile strain. This is related to band crossings within the valence band and enables an estimate of 0.68+0. 10 to be made of the heterojunction band offset in a strained In, "Ga"AsilnGaAsP MQW, with approximately 1.25%%uo tensile strain in the well region. The experimental data are compared to the results of k. p Hamiltonian calculations of the in-plane valence-band dispersion.

The application of image intensification techniques to the study of the spatial, temporal and spectral characteristics of the light emitted during the crystallisation of sodium chloride is described. The crystallisation is induced by adding concentrated hydrochloric acid to a saturated aqueous solution of sodium chloride. It is found that during an early stage of its growth a homogeneously nucleated crystal emits a burst of some 105 photons (measured in the range 390 to 570 nm). Assuming that this light emission accompanies an amorphous-to-crystalline transition in the growing 'crystal', simple thermodynamic arguments indicate that it occurs when the crystal diameter is of order 10-7 m. Comparisons of the crystalloluminescent spectrum with the photoluminescent spectra of the crystalline and dissolved salt suggest that the light emission occurs from crystalline sodium chloride. Temporal studies revealed some long-lived crystalloluminescent emission (lasting up to several seconds) that are consistent with local high levels of supersaturation. Overall, the results broadly support the conclusions reached in earlier photomultiplier-based work by Garten and Head (1963). Unlike photomultipliers, image intensifier allow the spatial behaviour of crystalloluminescence to be studied and provide a sensitive and accurate way of recording the spectra of these transient and low-level light emissions.

No abstract