Doping of MBE grown cubic GaN on 3C-SiC (001) by CBr4

We report on carbon doping of cubic GaN by CBr4 using plasma-assisted molecular beam epitaxy on 3C-SiC (00 1) substrates. The samples consist of a 70 nm thick GaN buffer followed by a 550 nm thick GaN:C layer. Carbon doping is realized with a home-made carbon tetrabromide sublimation source. The CBr4 beam equivalent pressure was established by a needle valve and was varied between 2x10(-9) mbar and 6x10(-6) mbar. The growth was controlled by in-situ reflection high energy electron diffraction. The incorporated carbon concentration is obtained from secondary ion mass spectroscopy. Capacitance voltage characteristics were measured using metal-insulator-semiconductor structures. Capacitance voltage measurements on nominally undoped cubic GaN showed n-type conductivity with N-D-N-A=1x10(17) cm(-3). With increasing CBr4 flux the conductivity type changes to p-type and for the highest CBr4 flux N-A-N-D=4.5x10(18) cm(-3) was obtained.