Bulk single crystals and physical properties of β-(AlxGa1-x)2O3 (x=0-0.35) grown by the Czochralski method

We have systematically studied the growth, by the Czochralski method, and basic physical properties of a 2 cm and 2 in. diameter bulk beta-(AlxGa1-x)(2)O-3 single crystal with [Al] = 0-35 mol. % in the melt in 5 mol. % steps. The segregation coefficient of Al in the Ga2O3 melt of 1.1-1.2 results in a higher Al content in the crystals than in the melt. The crystals were also co-doped with Si or Mg. [Al] = 30 mol. % in the melt (33-36 mol. % in the crystals) seems to be a limit for obtaining bulk single crystals of high structural quality suitable for homoepitaxy. The crystals were either semiconducting (no intentional co-dopants with [Al] = 0-30 mol. % and Si-doped with [Al] = 15-20 mol. %), degenerately semiconducting (Si-doped with [Al] <= 15 mol. %), or semi-insulating ([Al] >= 25 mol. % and/or Mg-doped). The full width at half maximum of the rocking curve was 30-50 arcsec. The crystals showed a linear but anisotropic decrease in all lattice constants and a linear increase in the optical bandgap (5.6 eV for [Al] = 30 mol. %). The room temperature electron mobility at similar free electron concentrations gradually decreases with [Al], presumably due to enhanced scattering at phonons as the result of a larger lattice distortion. In Si co-doped crystals, the scattering is enhanced by ionized impurities. Measured electron mobilities and bandgaps enabled to estimate the Baliga figure of merit for electronic devices.

Automated summary

We studied the growth and physical properties of β-(AlxGa1-x)(2)O-3 single crystals with different Al contents using the Czochralski method. The Al segregation coefficient in the Ga2O3 melt resulted in higher Al content in the crystals. By co-doping with Si or Mg, we obtained semiconducting, degenerately semiconducting, or semi-insulating crystals. The lattice constants decreased anisotropically, while the optical bandgap increased linearly with Al content.