Enhanced formation of oxygen-related thermal donors in Ge crystals exposed to hydrogen plasma

Enhanced thermal donor (TD) formation and oxygen diffusion in silicon exposed to hydrogen plasma are well known and have been widely studied. Similar phenomena are expected to occur in oxygen-rich Ge crystals as well, but they have not been studied in detail yet. In this work the effects of hydrogenation in H+-plasma on the TD formation in Ge are investigated. Both oxygen-rich and oxygen-lean Ge crystals of n- and p-type conductivity were used. The samples were treated in dc H+-plasma in the temperature range 200-350 °C for different durations. The TD depth profiles were obtained by spreading resistance probe measurements on the angle-lapped surfaces of the samples. In oxygen-rich Ge crystals an enhanced formation of TDs has been found to occur upon hydrogenation as well as upon subsequent annealing at 350 °C deeply in the bulk up to depth of about 1 mm. The depth distribution of the TDs formed in enhanced way depends on the hydrogenation procedure as well as on the conditions of the subsequent heat-treatments. A possibility of the deep p-n-junction formation by H+-plasma treatment of the oxygen-rich Ge crystals has been demonstrated. An enhancement factor of the TD formation is estimated and a comparison with similar phenomena in silicon has been carried out.