The preparation and characterization of strained-layer superlattices in the GaAs + GaP System

Abstract

The technique of metal organic chemical vapor deposi-tion has been used to prepare strained-layer superlattices in the GaAs + GaP system. The superlattices consist of alternating layers of GaP and GaAs_xP_1−x for x = 0.2 to 1.0, which vary in thickness from 30 to 400 Å. The layers were grown by the decomposition of trlmethylgallium and various mixtures of ASH₃ and PH₃ in H₂ at 800δC. The thickness and uniformity of the layers were determined by optical and transmission electron microscopy and x-ray diffraction. The composition of the layers was determined from x-ray diffraction. A new analysis has been developed to determine the layer strain as well as the composition of thick layers (∼ 300 Å). Transmission electron microscopy has been used to yield direct evidence that strained-layer superlattices can be used to remove the misfit dislocations generated during the epitaxial growth of a GaAs_xP_1-x alloy on a lattice mismatched GaP substrate. These results are in agreement with the previous work of Matthews and Blakeslee. Optical absorption, photocurrent spectroscopy and photoluminescence have been used to deter-mine the band gap energy as well as the energies for other optical transitions. The values are in excellent agreement with the values predicted by tight binding and effective mass calculations.