Structural, electrical, and optical properties of transparent gallium oxide thin films grown by plasma-enhanced atomic layer deposition

Abstract

Gallium oxide (Ga2O3) thin films were deposited on silicon (100) and sapphire (001) substrates using the plasma-enhanced atomic layer deposition (PEALD) technique with an alternating supply of reactant source, [(CH3)2GaNH2]3, and oxygen plasma. The thin films were annealed at different temperatures (500, 700, and 900°C, respectively) in a rapid thermal annealing system for 1min. It was found that Ga2O3 thin films deposited by PEALD showed excellent step coverage characteristics. X-ray diffraction measurements showed that the as-deposited thin film was amorphous. However, the thin films annealed at temperatures higher than 700°C showed a (400) orientation of the monoclinic structure. An atomic force microscope was used to investigate the surface morphologies of the thin films. The thin films showed very smooth surfaces; the roughness of the as-deposited thin film was about 4Å. With increasing annealing temperature, the thin film became rougher compared with that annealed at lower temperatures. A double-beam spectrophotometer was used to measure the transmittances of the thin films on the sapphire substrates. The thin films showed a very high transmittance (nearly 100%). The band-gap energies of the thin films were determined by a linear fit of the transmittance spectra and were calculated to be between 5.0 and 5.24eV. The electrical properties of thin films of Pt/film/Si structure were also investigated. It was found that, with increasing annealing temperature, the insulating characteristics of the Ga2O3 thin films were significantly improved. Spectroscopic ellipsometry was used to derive the refractive indices and the thicknesses of the thin films. The refractive indices of the thin films showed normal dispersion behavior. The refractive indices of the thin films annealed at low temperatures were smaller than those annealed at high temperatures.

Wet Thermal Oxidation of GaAs and GaN

“…Transmittances in the range of visible light and UV range exceeding 80% were reported by (Matsuzuki et al, 2006;Orita et al, 2004;Ueda b et al, 1997) and that reaching nearly 100% by (Shan et al, 2005). Enhancement of transmittance could be obtained by increase of oxide layer deposition temperature (Orita et al, 2004;Orita et al, 2000) or appropriate annealing of crystals .…”

“…The breakdown field/voltage depends significantly on technology of fabrication of the material. Values reported for thermally oxidized layers were 0.05-0.1 MV/cm (Readinger et al, 1999), 0.65 MV/cm (Zhou et al, 2008), 1 MV/cm (Lin et al, 2006) and 3.85 MV/cm (Kim et al, 2001) when those for PEALD were 1-1.5 MV/cm (Shan et al, 2005) and e-beam evaporation 3.6 MV/cm (Passlack et al, 1995). …”

“…, 1997) and (b) band gap energy of the as-deposited Ga 2 O 3 and annealed at various temperatures thin films (Shan et al, 2005) Refractive indexes of gallium oxide are generally in the range of 1.8-1.9. Ueda et al have reported in for single crystals values of 1.84 and 1.88 at 980 nm, those for e-beam evaporated layers were 1.841-1.885 at 980 nm (Passlack et al, 1995), for PEALD 1.89 (Shan et al, 2005), and for bulk 1.91 (Passlack et al, 1995 (Battiston et al, 1996;Kim & Kim, 2004) or PLD (Orita et al, 2004). Crystallization of films could be assured by its annealing at high temperature (Battiston et al, 1996;Kim & Kim, 2004;Shan et al, 2005), increase of substrates temperature (Orita et al, 2004) or oxidation at high temperatures.…”

“…The root mean square of layers varies in the range from 5 to 25 Å. Reported values were as follows: 5 Å (Shan et al, 2005), 8-13 Å (Wolter et al, 2000), 10-20 Å (Matsuzaki et al, 2006) and 12-23 Å (Kim & Kim, 2004).…”

“…Value reported in (Zhou et al, 2008) is of about 10.2. Shan et al (Shan et al, 2005) have measured dielectric constant for thin layers deposited on p-Si (100) and sapphire (0001) substrates by PEALD (Plasma Enhanced Atomic Layer Deposition). Substrates temperature during the process was maintained at 200 C.…”