Photoluminescence in high-quality a-Ge:H

We present quadrature frequency resolved spectroscopy (QFRS) measurements of photoluminescence (PL) in photoconductive and luminescent films of a-Ge:H with a defect density ≈1×1016 cm−3 obtained from electron cyclotron resonance (ECR) plasma chemical vapor deposition (PCVD), together with a study of PL and PL excitation (PLE) spectra. A double-peak lifetime distribution is observed with a short lifetime at ≈1 μs and a long one at ≈0.1 ms as observed in a-Si:H. The dependence of the two lifetimes and their corresponding relative quantum efficiencies on the e–h pair generation rate and temperature is also investigated. The occurrence of double peaks is attributed to the radiative recombination from singlet and triplet exciton states, and the exchange energy between singlet and triplet states is estimated to be ≈3.3 meV in a-Ge:H.