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.