Kinetic studies of the growth of III–V compounds using modulated molecular beam techniques

A knowledge of the interaction kinetics of vapour species of elements of Groups III and V with the surfaces of III–V compounds is of fundamental importance to the understanding of growth from the vapour phase of thin films of these compounds. The use of molecular beams provides a powerful means of obtaining surface kinetic data, and the method has been extensively developed over the past decade, with particular emphasis on beam modulation and ac mass spectrometric detection. In addition, UHV and surface analysis techniques now available enable a detailed assessment of the substrate surface to be made. In this paper the application of such an approach to the study of the interaction kinetics of group III and V elements with surfaces of single crystals of III–V compounds will be reviewed. Starting from a known substrate surface conditions measurements have been made of thermal accommodation coefficients, surface lifetimes, sticking coefficients, desorption energies and reaction orders, mainly in the GaAs-Ga-As₄ and GaAs-Ga-As₂ systems. The important results obtained from this work will be described, and possible kinetic models proposed. By a time of flight measurement of the velocity distribution of species desorbed from the surface it is possible to obtain information on energy exchange processes occurring between incident molecules and surface atoms. The polymetric nature of Group Velements appears to influence the translational energy with which they leave the substrate surface, and possible mechanisms of this effect will be considered.