Growth of GaP Layers from Thin Aliquot Melts: Liquid Phase Epitaxy as a Commercial Process

Abstract

The highest electroluminescent device performance in most III – V semiconductor materials was obtained on thin layers grown by liquid phase epitaxy (LPE). LPE has not been developed, however, as a commercial process. From a comparison of the factors affecting layer quality and process economy, it is concluded that a commercial LPE process favors the use of thin melts (possibly discarded after deposition), should provide substrate protection prior to deposition, and should be able to terminate LPE growth. A system has been designed in which a large volume of a saturated melt is sectioned into many small but equal thin melts (aliquot) for each substrate. The key to forming aliquots is wetting the substrate by the large volume of the melt in an apparatus constructed of nonwetted materials. The application of the above concepts to a multislice operation is described. Gallium phosphide LPE layers were grown in a single slice aliquot system from melts of 0.5–12 mm in thickness at cooling rates of 0.6°–6°C/min. Constitutional supercooling had no effect on the surface quality of the grown layers. The layers were degraded, however, if the substrates were thermally etched prior to deposition. High deposition efficiency and excellent thickness control were obtained for layers grown from thin melts. The deposition efficiency for layers grown from thick melts is limited by diffusion controlled mass transport in the melt. The diffusion coefficient of P in Ga has been evaluated at ∼1000°C and no spontaneous nucleation was observed in melts supercooled by less than approximately 15°C.