Oxygen contamination of low temperature ultrahigh vacuum-deposited Ge films on GaAs

The Fourier transform infrared absorption spectrum for the range of 500–4000 cm−1 wave numbers was measured for several Ge films deposited on GaAs using ultrahigh vacuum e-beam deposition at various substrate temperatures ranging from room temperature (RT) to 500 °C. Spectra indicate oxygen incorporation at low deposition temperatures whether or not the native oxide was removed from the substrate prior to film deposition. Using transmission electron microscopy, we show that Ge films deposited at RT and 100 °C on a (100) GaAs surface that did not have the oxides removed are amorphous while those deposited at 100 °C with the oxide removed are crystalline, but are highly defective. Secondary ion mass spectroscopy (SIMS) measurements show that the amorphous films at RT contain more than two orders of magnitude more oxygen than the films deposited at 100 °C or a single crystal film deposited at 400 °C. Oxygen-18 diffusion studies definitively show that the excess oxygen in the amorphous films percolates in from the atmosphere. SIMS studies further reveal that thermally removing the GaAs substrate surface oxide or depositing an Au film on top of the Ge film has little effect on the incorporation of oxygen.