Thermodynamical Consideration for the Preparation of GaAs-Ge Heterojunctions through Closed Tube Process

Abstract

The general transport equations derived in our previous paper are applied to the Ge-GaAs-I2 system. The main reactions in the system are as followed: (a) In the growth of Ge on GaAs substrates, the reaction GaI+GeI2\\rightleftarrowsGe+GaI3 dominates when the iodine concentration is low, while the reaction 2GeI2\\rightleftarrowsGe+GeI4 dominates at high iodine concentration. (b) The deposition of GaAs on Ge substrates is mainly governed by the reaction, 3GaI+½As4\\rightleftarrows2GaAs+GaI3 at low iodine concentration, while at high iodine concentration it is governed by 3GeI2+2GaI3+½As4\\rightleftarrows2GaAs+3GeI4. The transport rates of Ge and GaAs are calculated and compared with that in pure Ge-I2 and GaAs-I2 system. It is found the considerable amount of As will be incorporated into the Ge epitaxial layers grown on the GaAs substrates. These As will therefore convert the grown layer to heavily n-type to about 100 µ in the usual iodine concentration range.