Towards High‐Mobility Heteroepitaxial β‐Ga₂O₃ on Sapphire − Dependence on The Substrate Off‐Axis Angle

Abstract

This paper presents the heteroepitaxial growth of β‐Ga2O3 thin films on off‐axis (0001) c‐sapphire substrates by low pressure chemical vapor deposition (LPCVD). (−201) oriented β‐Ga2O3 thin films are grown using high purity metallic gallium (Ga) and oxygen (O2) as the precursors. N‐type conductivity in silicon doped β‐Ga2O3 thin films is demonstrated. It is found that the film crystalline quality, surface morphology, and electrical conductivity are remarkably sensitive to the off‐axis angles. X‐ray phi‐scan measurements of the β‐Ga2O3 film grown on on‐axis c‐sapphire indicate the presence of six in‐plane rotational domains due to the substrate symmetry. With the increase of off‐axis angle toward <11–20> of sapphire, one of the in‐plane orientations is strongly favored. The use of off‐axis substrate also reduced the X‐ray rocking curve full width at half maximum and increased the intensities of the Raman peaks. The best electrical properties of the β‐Ga2O3 film are exhibited by the film grown on 6° off‐axis c‐sapphire. The room temperature electron Hall mobility was 106.6 cm2 V−1 s−1 with an n‐type carrier concentration of 4.83 × 1017 cm−3. The results from this study demonstrate high electrical quality β‐Ga2O3 thin films grown on off‐axis c‐sapphire substrates, which are promising for high power electronic and short wavelength optoelectronic device applications.

Donors and deep acceptors in β-Ga2O3

“…[30][31][32] The Si doped samples include a bulk CZ sample from Northrop Grumman Synoptics (Sample 3), a bulk EFG sample from Tamura Corporation (Sample 4), and two epitaxial films grown by LPCVD on c-sapphire substrates with 3.5° (Sample 5) and 6° (Sample 6) offcuts. 57 Glow discharge mass spectrometry (GDMS) and secondary ion mass spectrometry (SIMS) analysis of EFG Ga2O3 samples similar to Sample 4 and SIMS analysis of a CZ grown sample similar to Sample 3 confirm that Si is the dominant unintentional donor in the bulk melt-grown Ga2O3 used in this study. Our result is consistent with a previous study which determined that the unintentional Si doping comes from the Ga2O3 powder used as the source material for bulk melt-growth.…”

Investigation of β‐Ga2O3 Film Growth Mechanism on c‐Plane Sapphire Substrate by Ozone Molecular Beam Epitaxy

“…With the growth temperature increase, the (01) diffraction peak slightly shifts by small angles (about 0.03°), which may be subject to the release of stress within the films. The grain size (D) of β‐Ga 2 O 3 films can be extracted from the full width at half maximum (FWHM) of the (02) peaks according to the Scherrer's formula [ 26 ] where λ is the X‐ray wavelength, B is the FWHM of XRD peaks, and θ is the diffraction angle. With increasing the growth temperature, the grain size of β‐Ga 2 O 3 films increases from 33.9 nm (500 °C) to 51.3 nm (700 °C), as shown in Figure 1c.…”

Electrical Properties of Vertical p‐NiO/n‐Ga2O3 and p‐ZnCo2O4/n‐Ga2O3 pn‐Heterodiodes

“…The calculated width is less then the layer thickness of the β ‐Ga 2 O 3 , meaning that there are still free charge carriers. The activation energy of about 26 meV may be attributed to the silicon doping, since it is known that silicon forms a shallow defect in Ga 2 O 3 …”