Magnetron Sputter-Deposited β-Ga2O3 Films on c-Sapphire Substrate: Effect of Rapid Thermal Annealing Temperature on Crystalline Quality

Abstract

Gallium oxide (Ga2O3) is a semiconductor with a wide bandgap of ~5.0 eV and large breakdown voltages (>8 MV·cm−1). Among the crystal phases of Ga2O3, the monoclinic β-Ga2O3 is well known to be suitable for many device applications because of its chemical and thermal stability. The crystalline quality of polycrystalline β-Ga2O3 films on c-plane sapphire substrates was studied by rapid thermal annealing (RTA) following magnetron sputtering deposition at room temperature. Polycrystalline β-Ga2O3 films are relatively simple to prepare; however, their crystalline quality needs enhancement. The β-phase was achieved at 900 °C with a crystallite size and d-spacing of 26.02 and 0.2350 nm, respectively, when a mixture of ε- and β-phases was observed at temperatures up to 800 °C. The strain was released in the annealed Ga2O3 films at 900 °C; however, the clear and uniform orientation was not perfect because of the increased oxygen vacancy in the film at that temperature. The improved polycrystalline β-Ga2O3 films with dominant (−402)-oriented crystals were obtained at 900 °C for 45 min under a N2 gas atmosphere.

Enhancing β-Ga2O3-film ultraviolet detectors via RF magnetron sputtering with seed layer insertion on c-plane sapphire substrate

“…Obviously, the presence of the seed layer improved the crystallization quality of the film. As we know, due to lattice mismatch between c-sapphire and Ga 2 O 3 , the sputtering atoms from the Ga 2 O 3 target are easy to suffer from the accumulation rather than migration at the film surface during the deposition process of the seed layer, which results in the amorphous structure of Ga 2 O 3 seed layer [19]. After high temperature annealing, the atoms in Ga 2 O 3 obtain sufficient energy to rearrange and form crystals, which provide smooth surfaces for the secondary deposition of Ga 2 O 3 .…”

“…Due to the low thermal conductivity and high cost of Ga 2 O 3 substrates, heterogenous substrates such as c-plane sapphire, MgO, GaAs, Si and quartz etc, are commonly used for the deposition of Ga 2 O 3 thin films. Among them, the thermal expansion coefficient and crystal structure of c-plane sapphire are similar to β-Ga 2 O 3 and the c-plane sapphire is considered the preferred substrates for depositing gallium oxide thin films [19]. However, the lattice mismatch between Ga 2 O 3 and substrates such as sapphire, silicon, and quartz glass leads to the presence of oxygen vacancies in the deposited Ga 2 O 3 films.…”

Influence of Nitrogen Annealing Treatment on Optical, Microstructural, and Chemical Properties of Ga2O3 Film Grown by Plasma-Enhanced Atomic Layer Deposition

“…The preparation of thin films by magnetron sputtering has the advantages of simple operation and fast growth rate. Therefore, a large number of annealing studies have been performed on Ga 2 O 3 thin films prepared by this method. − Domestic researchers have proved that with the increase of annealing temperature, defects such as oxygen vacancies are inhibited, increasing crystallinity, grain size, and optical bandgap of Ga 2 O 3 films. , …”

Gas-Sensitive Properties of β-Ga2O3 Thin Films Deposited and Annealed at High Temperature

“…RF magnetron sputtering has several advantages over other methods, such as the following: low cost, ease of control, good adhesion, wide variety of materials and high sputtering speed. To improve the crystallinity of the films obtained via this method, it is necessary to anneal at T > 800 • C. When annealing T < 800 • C, amorphous and a mixture of Ga 2 O 3 phases are observed [6,7], another way to obtain crystalline films is by heating the substrate during deposition. This method is poorly widespread and researched.…”