In the present paper a study on the semiconductor properties of a-Ge:Sn and a-Ge:Sn:H films is presented. The films were prepared by the rf sputtering method on substrates held at 180 C. The characterization includes composition, structure, and the transport and optical properties. The role and influence of hydrogen on the properties of the alloy have been established for the first time. The main results of the work follow, a) The addition of Sn narrows the optical band gap of a-Ge. b) The hydrogenated material posseses an activated type dark conductivity. c) No photoconductivity (AM 1 conditions) was detected in any of the alloyed films. d) At high Sn concentrations the metal segregates. e) No Sn-H absorption bands were detected in the infrared transmission spectra of hydrogenated samples (400 – 4000 cm−1 wavenumber range).

The defects that result from light soaking a-Si Ge :H are studied over the alloy range 0<X<0.4. These defects act as recomdinltion centers with a large hole capture cross section. The creation rate for light-induced defects is independent of the Ge content for compositions investigated (x = 0 to 0.4). The transport changes that result from Ge incorporation do not result in the creation of a larger density of these centers; however, the electronic transport properties decrease with increasing Ge content. The possibility that this decrease is due to germanium clusters is explored.

A careful study of the optical constants of a-CSiSn:H films prepared under very similar conditions with varying C or Sn concentration is here presented. Results of an attempt via the use of an effective medium approximation (EMA) theory to identify the contribution of C content to the optical properties are also reported.

Amorphous hydrogenated silicon-tin alloys have been prepared by if sputtering using a target of silicon with stripes of tin placed over the silicon surface in order to attain the appropriate silicon-tin composition. It is shown that for the composition range investigated, 0 ≤ 5 x ≤ 0.51, the addition of Sn moves the conduction band edge, thereby closing the optical band gap. The dependence of Eg on x can not be described by a single linear relationship. Sn also creates dangling bonds which further increase the material disorder. The electrical dc dark conductivity increases less than expected with increasing Sn content based on a simple decrease in band gap. This and the temperature dependence of the dark conductivity suggest a transition from extented state free-carrier conduction to localized state hopping conduction. The bonding between Si and H competes with that of Sn and H. Photoluminescence measurements show the presence of defect state radiative recombination. Calculations of optical band gaps, using the Coherent Potential Approximation with diagonal disorder and the off-diagonal disorder being treated within the virtual crystal approximation, are in excellent agreement with the experimental results.