Minority-carrier properties of microcrystalline germanium

The ambipolar diffusion length and the minority-carrier mobility-lifetime products of microcrystalline hydrogenated germanium thin films, prepared by plasma enhanced chemical vapour deposition, are investigated by using the steady-state photocarrier technique. Different thin film samples were deposited with the dilution of the process gases, germane in hydrogen, GC = [GeH4]/[H2], between 0.2% to 1%. The minority-carrier mobility-lifetime products are almost temperature independent. These results are consistent with a temperature-independent occupation of the negatively charged recombination centres that is determined by the Fermi level. The longest diffusion length was determined for GC = 0.2%, in agreement with earlier complementary results on sensors.