Comprehensive study of the electronic and optical behavior of highly degenerate p-type Mg-doped GaN and AlGaN

摘要

The bulk and 2-dimensional (2D) electrical transport properties of heavily Mg-doped p-type GaN films grown on A1N buffer layers by Metal Modulated Epitaxy are explored. Distinctions are made between three primary p-type conduction mechanisms: traditional valence band conduction, impurity band conduction, and 2D conduction within a 2D hole gas at a hetero-interface. The bulk and 2D contributions to the overall carrier transport are identified and the relative contributions are found to vary strongly with growth conditions. Films grown with Ⅲ/Ⅴ ratio less than 1.5 exhibit high hole concentrations exceeding 2 × 10~(19) cm~(-3) with effective acceptor activation energies of 51 meV. Films with Ⅲ/Ⅴ ratios greater than 1.5 exhibit lower overall hole concentrations and significant contributions from 2D transport at the hetero-interface. Films grown with Ⅲ/Ⅴ ratio of 1.2 and Mg concentrations exceeding 2 × 10~(20) cm~(-3) show no detectable inversion domains or Mg precipitation. Highly Mg-doped p-GaN and p-AlGaN with Al fractions up to 27% similarly exhibit hole concentrations exceeding 2 × 10~(19) cm~(-3). The p-GaN and p-Al_(0.11)Ga_(0.89)N films show broad ultraviolet (UV) photoluminescence peaks, which intercept the valence band, supporting the presence of a Mg acceptor band. Finally, a multi-quantum-well light-emitting diode (LED) and p-i-n diode are grown, both of which demonstrate rectifying behavior with turn-on voltages of 3-3.5 V and series resistances of 6-10 Ω without the need for any post-metallization annealing. The LED exhibits violet-blue luminescence at 425 nm, while the p-i-n diode shows UV luminescence at 381 nm, and both devices still show substantial light emission even when submerged in liquid nitrogen at 77 K.