a Study of Om-Cvd Processes for GALLIUM(1-X)INDIUM(X)ARSENIDE Growth on Gallium-Arsenide Substrates.

This work investigates OM-CVD growth processes of Ga(,l-x)In(,x)As. The motivation for this work has been the eventual application of this material in two-junction, cascaded solar cells. The growths were made using trimethylgallium, triethylindium and arsine and growths have been done on GaAs substrates. An attempt has been made to understand the growth process itself, and a possible mechanism for the growth process is proposed to explain the observations made in many aspects of crystal growth by OM-CVD. Heterogeneous catalysis of AsH(,3) on GaAs is viewed as providing a key step in understanding the growth mechanism. The growth of GaInAs on GaAs is interpreted in terms of an interfacial interaction between the grown layer and the substrate. The growth of InAs is found to be difficult on GaAs due to the large lattice mismatch. As the InAs composition is decreased, a coherent interface appears to be reached below an InAs composition of around 30-40%, where the growth displays single crystal epitaxy. The growth rate of GaInAs on GaAs is found to be more complicated than that for the lattice-matched situation of AlGaAs growth on the same GaAs substrate. Also, introduction of lattice strain appears to make the growth rate smaller than in the strain-free case. Growth of GaInAs on GaAs substrates of different orientations shows that good epitaxial growth with low defect densities can be obtained by some combinations of (100) and (111) faces. It is argued that the excellent epitaxial growth observed on the (511) surface should be on the "B" face by considering predicted growth behaviors on basic planes combined with the crystal growth mechanism of OM-CVD proposed. Background doping concentrations of layers grown by OM-CVD are found to be a strong function of source material purity as concluded by other workers. It is also found that incorporation of group II and group VI dopants decreaes with increasing growth temperature in contrast to group IV impurities, namely, C and Si, which show the opposite trend. Finally, spectral response measurement on GaInAs p-n junctions grown on GaAs exhibits favorable quantum efficiency of up to 40% without any anti-reflective coating. A type of photodetector with an interdigital Al Schottky electrode pattern deposited on lattice-mismatched GaInAs epi-layers grown on semi-insulating GaAs displays very good photodetector responses with rise and fall times of less than 25 and 50 - 100 picoseconds, respectively. The leakage current of the Schottky structure is also very low, on the order of 10-300 nA.