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 Å thick. The films were annealed at 500°C and 600°C to improve the quality of the material. The growth was done in three steps with 1000 Å of Ge, 70 Å of Sb, and followed by another 1000 Å 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 1.4×10¹⁵ to 1.6×10¹⁷ cm^-3 . The largest hole mobility measured was 30.6 cm²/Vs in the 1.4×10¹⁵ 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