Mg Doping of N-Polar, In-Rich InAlN

Abstract

Metal organic chemical vapor deposition was used to grow N-polar In_0.63Al_0.37N on sapphire substrates. P-doping was provided by a precursor flow of Cp₂Mg between 0 and 130 nmol/min, reaching a Cp₂Mg/III ratio of 8.3 × 10^-3. The grain structure of 360 nm thick InAlN was spoiled by pits after introducing a flow of CP₂Mg at 30 nmol/min. The surface quality was improved with a flow of 80 nmol/min; however, detrimental deterioration appeared at 130 nmol/min. This correlated with the XRD shape and determined density of dislocations, indicating a phase separation at the highest flow. Degenerated n-type conduction and a free carrier concentration of ~10¹⁹ cm^-3 were determined in all samples, with a minor compensation observed at a CP₂Mg flow of 30 nmol/min. The room temperature (RT) electron mobility of ~40 cm²/Vs of the undoped sample was reduced to ~6 and ~0.3 cm²/Vs with a CP₂Mg flow of 30 and 80 nmol/min, respectively. Scattering at ionized acceptor/donor Mg-related levels is suggested. RT photoluminescence showed a red shift of 0.22 eV from the virgin 1.73 eV peak value with Mg doping. Mobility degradation was found to be the main factor by InAlN resistivity determination, which increased by two orders of magnitude, approaching ~0.5 Ωcm, at the highest Cp₂Mg flow.

Keywords: GaN; InAlN; acceptor doping; electron mobility.