Gallium arsenide thin films by low-temperature photochemical processes

Abstract

Molecular layer epitaxy (MLE) is a new crystal-growth method which is able to produce thin films of single crystal in the accuracy of atomic order at relatively low temperature. In MLE, adsorption and surface reaction processes are controlled by alternate injection of reactant gases. MLE of GaAs was demonstrated in trimethylgallium–AsH3 (TMG–AsH3) and triethylgallium–AsH3(TEG–AsH3) systems on various faces of GaAs substrate; monomolecular layer growth was realized for (100) face in TMG–AsH3 system. The film thickness, electric properties, and surface morphology were studied as a function of substrate surface crystalline orientations. By using mass spectroscopy, adsorption and surface reaction processes of MLE by TMG–AsH3 systems were studied. The formation and migration of Ga complex adsorbate which was produced from TMG, and the surface reaction of adsorbate with AsH3 were clarified. Influence of photoirradiation on the growing film has been investigated by use of excimer lasers. UV light irradiation improved the surface morphology and, in certain instances, also lowered impurity concentrations of the film. From the results of mass spectroscopic measurements and photoirradiation effects, it is supposed that surface migration species is an adsorbate like Ga (CHn)x, x=0 at the temperature higher than 520 °C and x=1 at the temperature lower than 500 °C, in MLE.