Influence of alloy composition on carrier transport and solar cell properties of hydrogenated microcrystalline silicon-germanium thin films

Abstract

The authors report on carrier transport properties and spectral sensitivities of hydrogenated microcrystalline silicon-germanium (μc-Si1−xGex:H) alloys fabricated by low-temperature (∼200°C) plasma-enhanced chemical vapor deposition over the wide compositional range. Hall-effect and conductivity measurements reveal a change from weak n-type to strong p-type conduction for x>0.75 and a monotonic decrease in photoconductivity upon Ge incorporation. In a p-i-n diode structure, the Ge incorporation into i layer reduces quantum efficiencies in the short wavelengths, indicating an increased photocarrier recombination at p∕i interface. Nevertheless, under reverse biased condition, a 0.9-μm-thick μc-Si0.6Ge0.4:H absorber yields a large photocurrent of >27mA∕cm2 (air mass 1.5 global) with spectral sensitivities extending into infrared wavelengths, offering a potential advantage over conventional microcrystalline silicon solar cells.