STABILITY OF SEMICONDUCTING GALLIUM OXIDE THIN-FILMS

In bulk, gallium oxide is a semiconducting oxygen-sensitive material at temperatures of over 500 °C. With the aid of a high frequency sputter process, films could be produced with thicknesses in the micrometre range using a Ga2O3 ceramics target. The stoichiometry and purity of these films could be demonstrated with Rutherford backscattering spectroscopy and X-ray fluorescence. Scanning electron microscopy investigations showed that, at temperatures of over 1100 °C for 50 h, crystallites approximately 200 nm in size are formed. The d.c. conductivity of these films was measured for the first time. At high temperatures, semiconducting properties similar to those of the bulk material were demonstrated. The conductivity of the Ga2O3 films is dependent on the oxygen content of the surrounding atmosphere. The exponent of the σ vs. PO-n curve was n≤ 1 4. Auger spectroscopy was used to show that, at temperatures around 1000 °C, interdiffusion of the Al3+ and the Ga3+ ions takes place on substrates containing aluminium, thus destroying the conductivity of the film. Therefore Al2O3 ceramic substrates which are standard in thick film technology are unsuitable for stable oxygen-sensitive Ga2O3 thin film devices. Alternatives are shown. © 1990.