|
With a high bandgap of 4.7 eV, β-Ga2O3 can be made semi-insulating by doping with Fe or Mg and thereby possesses a very high breakdown field necessary for high-powered switches. Somewhat surprisingly, β-Ga2O3 can also be made highly conductive by doping with Si, which leads to great potential for n+ohmic contacts and transparent current spreading layers. In the latter application, the goal is to achieve both high conductivity (high concentration n and mobility μ) and high transparency in the visible and UV regions. Recently we have achieved n = 2 x 1020 cm-3 in β-Ga2O3, using pulsed laser deposition (PLD) with a Ga2O3 target containing 1-wt%-SiO2. Although n is temperature-independent, µ is not, and by fitting µ vs T, we can determine donor ND and acceptor NA concentrations. However, at higher temperatures, µ is strongly affected by longitudinal optical (LO) phonon scattering, which is much more complicated to model in Ga2O3 (9 LO phonons) than in ZnO, GaN, and other binary semiconductors (1 LO phonon). Highly-doped samples have another complication, disorder in the dopant placement. Fortunately, this disorder leads to small quantum corrections delta sigma in the conductivity which are also affected by LO phonons. Indeed, the study of delta sigma vs T and vs magnetic field B at low temperatures is crucial in understanding mobility at 300 K. We demonstrate calculations of ND and NA in PLD-grown β-Ga2O3 under the assumption that the dominant acceptor is the Ga vacancy in various charge states.
|
