Nonpolar a-plane p-type GaN and p-n Junction Diodes

Growth and electrical characteristics of Mg-doped p-type nonpolar (112¯0) a-plane GaN films, grown on (11¯02) r-plane sapphire substrates via metalorganic chemical vapor deposition, were investigated as a function of growth rate, the ammonia to trimethylgallium flow ratio (V/III ratio), and the growth temperature. The electrical conductivity of the films exhibited a strong dependence on the growth parameters. Secondary-ion-mass-spectroscopy measurements indicated that more Mg was incorporated at higher growth rate and at lower growth temperatures. The Mg concentration in the films increased linearly with the Mg flow. A maximum hole concentration of 6.8×1017cm−3 was achieved at room temperature for a Mg concentration of 7.6×1019cm−3, corresponding to 0.9% ionization. Further increase in the Mg concentration resulted in increased surface roughness as well as a significant decrease in the hole concentration. p-n junction diodes were fabricated using nonpolar a-plane GaN, and the current-voltage characteristics of these diodes showed a sharp turn-on at ∼3V.