Electronic and mechanical properties of Ge films grown on glass substrates

As germanium is closed lattice matched to GaAs, it a suitable substrate for epitaxial growth. In the quest for inexpensive substrates, thin-film Ge grown on glass is an attractive candidate if suitable grain growth can be achieved. Here we describe Ge films that are deposited by an e-beam evaporator on glass and are approximately 2000 /spl Aring/ thick. The films were annealed at 500/spl deg/C and 600/spl deg/C to improve the quality of the material. The growth was done in three steps with 1000 /spl Aring/ of Ge, 70 /spl Aring/ of Sb, and followed by another 1000 /spl Aring/ of Ge. Sb is an n-type dopant in Ge and is included to enhance grain growth. The best films contained the Sb layer and hole concentrations between 1.4/spl times/10/sup 15/ to 1.6/spl times/10/sup 17/ cm/sup -3/. The largest hole mobility measured was 30.6 cm/sup 2//Vs in the 1.4/spl times/10/sup 15/ p-type sample. The electron lifetime was measured by ultra-high frequency photoconductive decay and the best lifetimes were in the 30- to 40-ns range. Scanning-electron microscope and transmission-electron microscope studies indicated a polycrystalline grain structure with grain size comparable to the film thickness.