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 will describe Ge films that are deposited by an e-beam; evaporator on glass and are approximately 2000 ..Alpha.. thick. The films were annealed at 500 deg. Cand 600 deg. C to improve the quality of the material. The growth was done in three steps with 1000 ..Alpha.. of Ge, 70 ..Alpha.. of Sb, and followed by an-other 1000 ..Alpha.. angstroms 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 1.4x1015 to 1.6x1017 cm-3 . The largest hole mobility measuredwas 30.6 cm2 /Vs in the 1.4x1015 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.