Investigation of n- and p-type doping of GaN during epitaxial growth in a mass production scale multiwafer-rotating-disk reactor

Abstract

n- and p-doped GaN thin films have been epitaxially grown on c-sapphire substrates by metal-organic chemical-vapor deposition in a production scale multiwafer-rotating-disk reactor. The in situ doping was performed with material having a low background carrier concentration of n∼mid-1016 cm−3. Biscyclopentadienyl magnesium (Cp2Mg) and disilane (Si2H6) were used as the precursors for the p and n dopants, Mg and Si, respectively. The effect of mole flow on material, electrical, and optical properties was studied. We observed that both n- and p-type doped GaN exhibited an excellent surface morphology, even with a high mole flow of doping precursors. After the Mg-doped GaN was annealed in a N2 ambient at ∼700 °C for 30–60 min, the highly resistive GaN was converted into p-type GaN with a low resistance of 0.1–1.0 Ω cm. Transmission electron microscopy showed that the defect density on the annealed Mg-doped GaN is only 4×109 cm−2 which is of the same order as undoped GaN (1.5×109 cm−2). One of the best p-GaN samples has a Hall carrier concentration of 5.2×1018 cm−3 and a hole mobility of 20 cm2/V s, which are the best values reported in the literature to date. The photoluminescence spectra of p-GaN show a strong band edge at 430 nm with a full width at half-maximum of 300 meV at room temperature.