Hans Dr. Dipl.-Phys. Meixner

Stability of semiconducting gallium oxide thin films

Abstract 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. PO2−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.

Preparation of AlVO4-films for sensor application via a sol-gel/spin-coating technique

Abstract The preparation of thin AlVO4 films on corundum substrates for possible sensor application is described. Thermally stable, crack-free thin films having thicknesses typically below 0.1 μm were obtained by a sol-gel process using alkoxide reagents combined with a spin-coating technique. The films were structurally characterized by XRD, Raman and FTIR spectroscopy and their morphology was analyzed by SEM. XRD showed that the films consisted almost exclusively (> 90%) of AlVO4 after calcination at 923 K.

Impedance spectroscopic and secondary ion mass spectrometric studies of β-Ga2O3/O2 interaction

Abstract In the present work the impedance spectroscopy and secondary ion mass spectrometry (SIMS) were used to study the oxygen/β-Ga2O3 interaction between 578 and 835°C. The overall resistance of the β-Ga2O3 is composed of the bulk resistance and the grain boundary resistance. If oxygen is present, dominantly the characteristics of the space charge region — formed at the grain boundaries — change. The mechanism of the bulk conduction is unchanged between 578 and 835°C, however, the processes determining the grain boundary resistance are different above and below ∼700°C. At low temperatures the formation and adsorption of O2− ions is probable, while at higher temperatures the presence of O− ions is dominant on the grain boundaries.