Morphology and Electrical Properties of Pure and Ti-Doped Gas-Sensitive Ga2O3 Film Prepared by Rheotaxial Growth and Thermal Oxidation

An n-type Ga2O3 semiconductor thin film was prepared by rheotaxial growth and thermal oxidation (RGTO) method on SiO2 and Al2O3 substrates. Multilayer growth technique was used to control grain size. The morphology and the electrical properties of the Ga and Ga2O3 films were measured as functions of thickness, temperature, and Ti dopant concentration. Measurements of the sensitivity, the response time, and the recovery time of the Ga2O3 films in response to ethanol and CO were carried out.The results showed that the grain size of Ga film increased with thickness, and a balls-on-ball type morphology was produced as the film exceeded 3000 Å. Ga2O3 nanowires were created when Ga films were oxidized under impure O2 atmosphere. Ga2O3 films had an optimum sensing temperature increasing from 625 °C for a5012 Å film to 675 °C for a 5.6-μm film. The films prepared by multilayer growth technique had smaller grain size, but the sensitivity remained unchanged. The films deposited on SiO2 substrate had a sensitivity higher by 28% than that on Al2O3. Doping of 0.28 at.% Ti enhanced nanowires growth, raised sensitivity by 6%, shortened response time from 40 to 30 s, but prolonged recovery time from 92 to130 s. Formation of nanowires resulted in an increase of sensitivity up to 50%.Doping of 2.18 at.% Ti led to the formation of nanoribbons with a sensitivity lowerby 8% and a recovery time shortened from 130 to 72 s. The RGTO method was shown to produce Ga2O3 gas-sensitive thin film with good reproducibility.