OXYGEN CONTAMINATION OF LOW-TEMPERATURE ULTRAHIGH VACUUM-DEPOSITED GEFILMS ON GAAS

The Fourier transform infrared absorption spectrum for the range of 50 0-4000 cm(-1) wave numbers was measured fur several Ge films deposited on GaAs using ultrahigh vacuum e-beam deposition at various substrate temperatures ranging from room temperature (RT) to 500 degrees C. Spe ctra indicate oxygen incorporation at low deposition temperatures whet her or not the native oxide was removed from the substrate prior to Fi lm deposition. Using transmission electron microscopy, we show that Ge films deposited at RT and 100 degrees C on a (100) GaAs surface that did nor have the oxides removed fire amorphous while those deposited a t 100 degrees C with the oxide removed are crystalline, but are highly defective. Secondary ion mass spectroscopy (SIMS) measurements show t hat the amorphous films at RT contain more than two orders of magnitud e more oxygen than the films deposited at 100 degrees C or a single cr ystal film deposited at 400 degrees C. Oxygen-18 diffusion studies def initively show that the excess oxygen in the amorphous films percolate s in from the atmosphere. SIMS studies further reveal that thermally r emoving the GaAs substrate surface oxide or depositing an Ari firm on top of the Ge film has little effect on the incorporation of oxygen. ( C) 1996 American Institute of Physics.