The detailed characterization of metal organic vapour phase epitaxy grown ZnS layers on GaAs is the first step towards the study of their different non-linear optical properties performed with nanosecond lasers. Biexciton phenomena (with a binding energy of about 10 meV) are observed in photoluminescence-excitation and optical-gain spectra.
Lightly compensated epitactic n-type GaAs is obtained by metal-organic vapour-phase epitaxy (MOVPE) with free-carrier concentration in the low 1015 cm−3 range and with good uniformity of both thickness and impurity concentrations over a 2-in.-diameter area (1 in. = 2.54 cm). Detailed Hall-effect and photoluminescence measurements are reported. At temperatures below 8 K, the conductivity is governed by variable-range hopping, clearly indicating a band of localized donor states. At higher impurity concentrations, a metallic contribution to the conductivity suggests a buildup of extended states near the middle of this band. These results are consistent with the observed photoluminescence.
Undoped and doped layers of gallium arsenide and aluminium gallium arsenide have been grown on gallium arsenide by low-pressure metal organic vapour-phase epitaxy (MOVPE). Delta doping and growth on silicon substrates have also been attempted. Of particular interest in the present study has been the influence of growth parameters, such as growth temperature, group III mole fraction and dopant flow, on the electrical and physical properties of gallium arsenide layers. An increase in growth temperature leads to increased doping efficiency in the case of silicon, whereas the opposite is true in the case of zinc. Deep level transient spectroscopy (DTLS) studies on undoped GaAs layers showed two levels, the expected EL2 level and a carbon-related level. The determination of optimum growth conditions has allowed good quality GaAs and AlGaAs epitaxial layers to be produced for a range of applications.`
Abstract
Growth of AlxGa1−xN layers (0 ≤ x ≤ 1) simultaneously on polar (0001), semipolar ($$10\bar{{\rm{1}}}$$
10
1
¯
3) and ($$11\bar{{\rm{2}}}2$$
11
2
¯
2
), as well as nonpolar ($$10\bar{{\rm{1}}}0$$
10
1
¯
0
) and ($$11\bar{{\rm{2}}}0$$
11
2
¯
0
) AlN templates, which were grown on planar sapphire substrates, has been investigated by metal-organic vapour phase epitaxy. By taking into account anisotropic in-plane strain of semi- and non-polar layers, their aluminium incorporation has been determined by x-ray diffraction analysis. Optical emission energy of the layers was obtained from room-temperature photoluminescence spectra, and their effective bandgap energy was estimated from room-temperature pseudo-dielectric functions. Both x-ray diffraction and optical data consistently show that aluminium incorporation is comparable on the polar, semi- and non-polar planes.
Adduct purification of metal alkyls for use in metal-organic vapour-phase epitaxy is described and shown to give high purity alkyls of Al, Ga, In, Cd, Zn and Te. In most cases involatile Lewis bases are used to form dissociable adducts, but for tellurium alkyls, halides of mercury or cadmium are used. Alternative source materials such as higher alkyls, volatile adducts and mixed alkyls are discussed and new results on the stability of mixed alkyls of tellurium are presented.
We have analyzed the structural and optical properties of GaxIn1−xAs–GaAs strained-layer superlattices (SLS) grown by low-pressure metal-organic vapour-phase epitaxy. Sample uniformity over 2.5 cm × 2.5 cm has been studied by X-ray diffraction and low-temperature photoluminescence. The sample composition and period are uniform in the longitudinal direction (gas-flow direction in the reactor) and in the central portion (1.5 cm) in the transverse direction. On each side, the In composition decreases slightly towards the edges, as shown by an energy shift of the photoluminescence excitonic recombinations. Comparison of experimental and calculated transition energies in a series of samples, taking into account strain and quantization, shows clearly that SLS grown on mismatched buffer layers arc under additional strain. This additional strain is not present when the layer or whole SLS thicknesses exceed a critical value beyond which the mismatch is partially accommodated by misfit dislocations.
Characterisation of III?V Multilayers Grown by Low-pressure Metal Organic Vapour-phase Epitaxy