The growth of gallium phosphide layers of high surface quality by liquid phase epitaxy A commercial process for green licht emitting diodes

Abstract

Equipment has been developed for the liquid phase growth of epitaxial layers of gallium phosphide on a commercial scale. A vertical dipping system is used with substrates held in a horizontal plane in a multi-tier configuration giving effectively closed cell growth conditions. Emphasis has been placed on the economical use of the melt and on establishing simple loading and growing procedures. Although the equipment has been used for the growth of metal oxides, gallium arsenide and double epitaxy gallium phosphide, its principal application is in the growth of layers of sulphur-nitrogen doped gallium phosphide for subsequent photoprocessing; in this application surface quality is of prime importance. An analysis of over a thousand layers grown in the equipment has shown that surface quality depends primarily on substrate orientation and preparation technique, the distribution of dislocations in the substrate and nitrogen concentration in the grown layer. The growth cell and crucible geometry enable conditions to be established very simply which are well outside the constitutional supercooling regime with the result that stable growth interfaces and high surface quality can be achieved routinely on commercially available LEC substrates.