P.E. Oliver

Control of prereaction in the metalorganic chemical vapour deposition of zinc- and cadmium-based chalcogenides

Abstract It is shown that pyridine, when introduced into the gas phase, is effective in controlling the prereaction between the group II alkyl precursur and the group VI hydride during the metalorganic chemical vapour deposition (MOCVD) of ZnSe. During the corresponding growth of CdSe, pyridine induces a greatly reduced effect. Possible reaction mechanisms to account for prereaction control are proposed.

Growth of AlxGa1-xAs by MOVPE using alternative alkylaluminium precursors

Epitaxial layers of AlxGa1−xAs have been grown using a variety of different aluminium alkyls, in conjunction with trimethylgallium and arsine. These compounds, precursors based on trimethyl and triethylaluminium, have been made, purified, characterised and analysed for residual impurities. Most have vapour pressures suitable for use in MOVPE. Atmospheric pressure MOVPE has then been used to grow layers of AlxGa1–xAs, with compositions 0 ⩽ x ⩽ 0.4, at temperatures between 700 and 800°C. The layers were characterised both electrically and optically. Low temperature photoluminescence (PL) indicated that carbon, the major impurity in high quality AlxGa1–xAs layers grown by MOVPE, remained the dominant impurity in layers grown using these precursors.

Metalorganic chemical vapour deposition of manganese arsenide for thin film magnetic applications

Abstract Thin films of the ferromagnetic material manganese arsenide (MnAs) have been grown for the first time by atmospheric pressure metalorganic chemical vapour deposition (MOCVD), using tricarbonylmethylcyclopentadienyl manganese (TCM) and arsine. A detailed study of the MnAs growth characteristics are presented together with the resulting magnetic and structural properties.

Diffusion lengths in p-type MOCVD GaAs

Abstract In developing MOCVD GaAs/GaAlAs technology for photocathode applications, the minority carrier diffusion length ( L ) of p-type GaAs has been studied. Homo- and heteroepitaxial GaAs with hole concentrations in the range 1 × 10 15 −8 × 10 19 cm -3 has been compared with similar liquid phase epitaxial material. L was assessed using two techniques which were in substantial agreement: (1) the spectral response of an electrolytic barrier (“Water Drop”) applied to the sample surface, and (2) EBIC measurements using a scanning electron microscope. The diffusion length data show a high doping region where L is controlled by the free hole concentration, and a low doping region where L attains a value of about 10 μm, independent of the hole concentration. This low doping limit could be interpreted as the result of bulk lifetime limitation due to a concentration of residual recombination centres, but analysis show that the surface recombination could also produce an artificial limitation in both the assessment techniques used. Direct minority carrier lifetime measurements were used to resolve the position and show that the surface recombination effects are indeed compromising the L data at low hole concentrations. A value of 100 cm 2 s -1 for the electron diffusion coefficient at a hole concentration of 2.2 × 10 18 cm -3 is directly deduced from the lifetime data.

Growth of AlxGa1−xAs by MOVPE using a new alkylaluminium precursor

Abstract Epitaxial Al x Ga 1- x As has been grown using tertiarybutyldimethylaluminium (Bu t AlMe 2 ) 2 as an alternative to Me 3 Al. The grown layers are of good optical quality although low temperature PL data indicates that carbon is a contaminant in the layers. (Bu t AlMe 2 ) 2 has proved suitable for the growth of high quality GaAs/AlGaAs MQW structures at low substrate temperatures.

Magnetic and electrical characteristics of MnAs films grown by metalorganic chemical vapour deposition

Abstract The magnetic and electrical property of changes associated with the phase transition in MnAs have been measured in uncracked material by using thin films grown on to sapphire substrates by metal organic chemical vapour deposition. The films exhibited a first-order transition with Curie points in the range 35–47±1°C. An increase of approximately 60% in the electrical resistivity of the films was measured on heating through the phase transition. The Curie temperature of the films increased with an applied magnetic field by approximately 1.2°C in a field of 600 kA m −1 . This shift in Curie temperature with applied magnetic field also produced a magnetoresistance effect with a maximum value of 2.24% at 600 kA m −1 . The values of these parameters are shown to be dependent upon the growth conditions of the films.

The fabrication and assessment of high speed MOCVD GaAlAs pin detectors

Abstract High speed MOCVD grown PIN photodiodes are described. Growth, fabrication, packaging and testing details are presented. It is shown that the frequency response of large area devices is accurately described by a simple RC model. Smaller geometry devices display 3 dB frequencies up to 7.0 GHz with responsivities of 0.24 A/W at 850 nm. The frequency response of these devices ceases to be determined by device capacitance and is controlled by more complex parasitic package and mounting elements.

Metalorganic chemical vapour deposition of manganese arsenide antimonide for thin film magnetic applications

Thin films of the binary and ternary ferromagnetic materials MnSb and MnAs1-xSbx (0 < x < 0.08) have been grown for the first time by atmospheric pressure metalorganic chemical vapour deposition using the precursors arsine, tricarbonylmethylcyclopentadienyl manganese and trimethylantimony. The growth of the binary MnSb required careful control of the trimethylantimony concentration and growth temperature to prevent the precipitation of free antimony crystals. Growth of the ternary compound MnAS1-xSbx was successful only under conditions of very low arsine flow due to complex interactions between the group V components and preferred incorporation of arsenic into the crystal lattice. Magnetic measurements of the MnAs1-xSbx layers showed the expected decrease in Curie temperature from 313 (x = 0) to 298 K (x = 0.08).

The growth of thin films of the magnetic ternary alloys Fe3Ga2-xAsx by metalorganic chemical vapour deposition

Abstract Thin polycrystalline films of the complex ferromagnetic ternary alloys Fe 3 Ga 2- x As x have been grown for the first time by atmospheric pressure metalorganic chemical vapour deposition. Initial data on the crystal structure and the magnetic properties of the films establish a marked dependency of such properties on the relative amounts of the non-magnetic atoms, gallium and arsenic, incorporated into the crystal lattice; this is entirely consistent with earlier measurements on bulk materials for this series of alloys.