Electrical passivation by hydrogen of substitutional cobalt in monocrystalline germanium

Co has been implanted at 90 keV in n- and p-type germanium wafers and in-diffused using a 5 min thermal anneal at 500∘C. Deep level transient spectroscopy reveals three levels which are considered to be due to substitutional Co impurities. To passivate the electrical levels of substitutional Co, samples were hydrogenated using a DC-plasma for 4 h at 200∘C. For both the n- and p-type material the Co levels have disappeared up to at least 5μm beyond the surface. Directly after the plasma treatment different levels due to irradiation damage have been observed, one of which was assigned to the di-vacancy. The irradiation damage related defects disappeared due to a rapid thermal anneal of 1 min at 400∘C. Two electron traps E230 and E270 which were only present in Co-implanted samples after a hydrogenation have been tentatively assigned to cobalt related defect levels.