Structural and optical properties of β-Ga2O3 thin films grown by plasma-assisted molecular beam epitaxy

Abstract

Epitaxial beta-gallium oxide (β-Ga2O3) has been deposited on c-plane sapphire by plasma-assisted molecular-beam epitaxy technique using two methods. One method relied on a compound Ga2O3 source with oxygen plasma while the second used elemental Ga source with oxygen plasma. A side-by-side comparison of the growth parameters between these two methods has been demonstrated. With various substrate temperatures, pure phase (2¯01) oriented β-Ga2O3 thin films were obtained using both sources. Reflection high energy electron diffraction patterns displayed a threefold reconstruction during the growth. X-ray photoelectron spectroscopy analysis showed a shift in the binding energy of the Ga 2p peaks consistent with a Ga being in a +3 oxidation state. For transparent oxide like β-Ga2O3, it is important to determine the index of refraction (n) and its functional dependence on the wavelength. The Cauchy dispersion relation was employed to evaluate the refractive index, film thickness, roughness values, and extinction coefficient. The band gap energies of the thin films were calculated to be ∼5.02 eV by extrapolating the linear portion of Tauc-plot analysis and the refractive index is ∼1.89 at the wavelength (λ) of 6328 Å, suggesting high structural quality and packing density of the oxide films.

Epitaxial growth of β-Ga2O3 thin films on Ga2O3 and Al2O3 substrates by using pulsed laser deposition

“…5 To achieve high quality crystalline oxide film through epitaxial growth, two key factors should be considered: one is the technique of growth, and the other is the choice of the substrates. In recent years, various methods of growth have been used for epitaxial growth of Ga 2 O 3 films, for example, metal organic chemical vapor deposition (MOCVD), 6 RF magnetron sputtering, 7 chemical vapor deposition (CVD), 8 atomic layer deposition (ALD), 9 molecular beam epitaxy (MBE) 10,11 and pulsed laser deposition (PLD). [12][13][14] Among them, PLD technique has many advantages for oxide film deposition, such as, easy to use, high deposition rate, low growth temperature, and no limit to the types of target material.…”

Experimental and Theoretical Validation of Ga2O3 Thin Films Deposited by Physical Vapor Deposition

“…1 where we attributed the increase of the Eg for Ga2O3 thin films annealed at 800 °C to the decrease of defect states. Ramana et al [10] and Ghose et al [11] have observed similar trend of decreasing diffraction peaks from β-Ga2O3 at higher temperatures. Ramana et al attributed this trend to the decrease of film thickness due to Ga2O3 film crystallization and densification whilst Ghose et al attributed this trend to the decrease in film thickness, which result from the reduction in sticking coefficient of the Ga2O molecules.…”

Ga2O3 Nanowire Synthesis and Device Applications

“…A wide variety of methods have been used to grow Ga 2 O 3 nanowires. These include thermal oxidation [36], vapor-liquid-solid mechanism [37], pulsed laser deposition [38], sputtering [39], thermal evaporation [40][41][42], molecular beam epitaxy [43], laser ablation [44], arc discharge [45], carbothermal reduction [46], microwave plasma [47], metalorganic chemical vapor deposition [48] and the hydrothermal method [49,50]. Table 3 summarizes the advantages and disadvantages of these methods.…”

“…Molecular beam epitaxy is another option for growing Ga 2 O 3 . It has used to grow Ga 2 O 3 on sapphire using both a Ga 2 O 3 source and an elemental Ga source [43]. The pressure was less than 5 × 10 −10 torr, and oxygen gas was used to protect the substrate from ions.…”