Heteroepitaxial growth of α-, β-, γ- and κ-Ga2O3 phases by metalorganic vapor phase epitaxy

Abstract

Improved MOVPE (metalorganic vapor phase epitaxy) growth conditions for the different Ga2O3 phases are reported. The influence of the substrate material, the growth conditions and the variation of precursors on the phase formation was investigated. Trimethylgallium (TMG) and N2O were used as common precursors for gallium and oxygen, respectively. In addition, water was supplied for the growth of κ-Ga2O3. The influence of additional triethylboron (TEB) and dimethylhydrazin (DMHy) on the formation of the α-phase is discussed. Growth conditions could be determined, where α-, β-, γ- and κ-Ga2O3 is epitaxially deposited. The κ-phase was epitaxially grown on c-, a- and r-plane Al2O3, (1 1 1) MgO, (1 1 1) MgAl2O4 and on a (0 0 0 1) Al2O3/(0 0 0 1) GaN heterostructure. Successful MOVPE growth of γ-Ga2O3 with defect spinel structure has been achieved on (0 0 0 1) Al2O3, (1 1 1) and (1 0 0) MgAl2O4, (1 0 0) MgO as well as on (0 0 0 1) Al2O3/(0 0 0 1) GaN. Boron addition stabilizes the MOVPE growth of the α-phase on c-, a- and r-plane Al2O3. The various Ga2O3 phases were identified by X-ray diffraction (XRD). The epitaxial relationships between the Ga2O3 phases and the different substrates were determined.Optical transmission spectra measured in the spectral range from 200 to 2000 nm show a well-defined absorption edge at about 4.9 eV for layers of β-, γ- and κ-Ga2O3 and 5.3 eV for layers of α-Ga2O3 grown on c-plane sapphire.