Hydrogen-related shallow donors in Ge crystals implanted with protons

Electrical properties of germanium crystals, which were subjected to implantation with 300 keV protons (H+) and subsequent anneals, have been studied by means of capacitance-voltage and spreading resistance probe techniques and deep level transient spectroscopy. It was found that heat-treatments of the proton-implanted samples in the temperature range 200-300 °C resulted in the formation of shallow hydrogen-related donors. The maximum concentration of the donors was about 2×1016 cm−3 for a H+ fluence of 1×1015 cm−2. An analysis of changes in the spatial distribution of the H+-related donors upon isothermal and isochronal anneals showed that the donors appeared in the region which is close to the projected depth of implanted protons at the initial stages of heat-treatments in the temperature range of 200-300 °C and spread out of this region upon an increase in annealing time or annealing temperature. The depth of the layer where the donors were formed after a heat-treatment at 250 °C for 9.5 h exceeded the projected length protons by more than one order. Diffusion coefficients of mobile species responsible for the formation of the donors were determined. An analysis of the diffusion coefficients, which were obtained, allowed us to suggest that the H-related donors could be complexes of hydrogen atoms with intrinsic point defects. These complexes were formed in the implantation damage area and diffused as whole units upon annealing. Some indications of the shallow-deep bistability of the donors were found.