Annealing behavior of the hydrogen-related defect in LEC indium phosphide

In the quest for semi-insulating undoped InP material, we have investigated the role of hydrogen in reducing free electron concentrations by the process of high temperature annealing. Hydrogen has previously been shown to form the defect V_In-H₄ in InP, and it has been suggested that this defect acts a donor. In order to elucidate the effect of H on the electrical properties of InP, we have performed annealing experiments on both undoped and Fe doped crystals. Samples were annealed at 900°C for 3 days with a phosphorus overpressure of 5 atmospheres. The samples were studied using infrared absorption spectroscopy, which can be used as a direct measure of the concentration of both the Fe impurities and V _In-H₄ defects, and Hall effect. In the undoped samples, annealing results in a reduction of the electron concentration accompanied by an increase in the 77 K mobility. Due to the observed increase in the mobility of the samples, it is apparent that this decrease is not due simply to a change in the concentration of compensating acceptors. In the Fe-doped samples, a decrease in the ratio [Fe²⁺]/[Fe³⁺] is observed after annealing, again indicating a reduction in the number of donors in the sample. In all samples, the changes in the donor concentration upon annealing are accompanied by the complete disappearance of the LVM peak due to V_In-H₄. Taken together, these results confirm the role of hydrogen in the reduction of free carriers during the annealing of bulk InP material