PHOTOCONDUCTIVITY SPECTROSCOPY (CPM) ON A-GE-H AT LOW-TEMPERATURES

The constant photoconductivity measurement technique (CPM) is applied to high quality hydrogenated amorphous germanium (a-Ge:H) samples at t emperatures between 300 and 130K. Considering the temperature dependen ce of the Urbach energy E(o) an upper limit of 30meV is found for the contribution of the structural disorder to E(o) in a-Ge:H. From CPM me asurements at temperatures below 170K the defect density can be succes sfully determined. A comparison of CPM and PDS results reveals a stron g influence of surface defects on the total defect density of high qua lity a-Ge:H.