p- and n-type cubic GaN epilayers on GaAs

Temperature dependent Hall-effect measurements are performed on cubic GaN layers grown by plasma-assisted molecular-beam epitaxy on (100) GaAs substrates. We find that under N-rich conditions, cubic GaN films are p-type with hole concentrations of approximate to 10(13) cm(-3) and mobilities of about 350 cm(2)/V s at room temperature. The accepters have an activation energy of E(A) = 0.445 +/- 0.015 eV. Ga-rich growth conditions result in n-type conductivity with electron concentrations of about 10(14) cm(-3) and room-temperature mobilities of mu(n) approximate to 100cm(2)/Vs. Since for n-type samples a strong influence of the underlaying semi-insurating GaAs substrate is observed, a two-layer model is used to evaluate the Hair data, yielding a shallow donor with an activation energy of E(D) = 0.16 +/- 0.07 eV and a deeper donor with E(DD) = 0.60 +/- 0.10 eV.