High purity LPE InP

Abstract

Typical LPE InP layers have previously been limited to liquid nitrogen mobilities of 25,000 cm2/ V-sec, which implies a total impurity concentration of 9 × 1015/cm3. Of the donor impurities identified in InP, Si is reported to have the highest segregation coefficient, with a value of 30 at typical growth temperatures of 650–700°C (1) . Because of this large segregation coefficient, and the fact that commercially available In has typical Si concentrations in the 0.1 ppm range, it is necessary to take additional purification steps on LPE starting materials to reproducibly obtain epitaxial layers with total impurity concentrations below the previously mentioned limit. This paper will discuss a novel approach to the problem by employing a baking scheme to reduce Si contamination. Thermodynamics of the SiO2 , H2, Si, H2O system will be considered which lead to a detailed schedule of time-temperature cycles for the removal of Si from an In based melt. Experimental data are presented which corroborates our thermodynamic, model, and which reproducibly yields epitaxial layers with 77°K mobilities in the range of 50,000–67,000 cm2/V-sec, and total impurity concentration below 2 × 1015/cm3 . Limiting factors in obtaining higher purity are discussed and suggestions are made for overcoming this problem.