Dangling-bond states in a SiGe:H,F measured by temperature-dependent mu tau

The authors report a novel technique for measuring the density distribution of the D⁰-/ state in a-Si:H before and after light soaking and in a-SiGe:H,F alloys for solar cells. Electron time-of-flight (TOF) measurements as a function of temperature form the basis of this technique. The deep trapping of electrons controls the mobility-lifetime product ( mu tau )_n, which is evaluated from the integrated TOF current. The dominant deep trap is the D⁰-/ level. The authors determine the density of D⁰-/ states in a:SiGe:H,F that peak at SiE_c-(0.40 to 0.45) eV with maxima in the 10¹⁸ to 10¹⁹-cm^-3 eV^-1 range. In a-Si:H, the peak lies at E_c-0.45 eV; it is observed to grow with increasing light-soaking time.