Electron gas in modulation doped GaN/AlGaN structures

We report low temperature photoluminescence (PL), time resolved PL and electrical transport measurements related to the two-dimensional electron gas (2DEG) in GaN/AlGaN heterostructures and quantum wells grown by MOVPE on sapphire. Electrical measurements of the heterostructure samples show a room temperature mobility of up to 1300 cm2 V−1 s−1 and carrier concentration of 1013 cm−2. The PL spectrum at low temperatures shows a broad emission about 50 meV below the bulk exciton emission, attributed to recombination involving electrons from the lowest subband of the 2DEG at the GaN/AlGaN heterointerface and photoexcited holes in the GaN layer. The data agrees with a self consistent calculation of the energy levels and the electron concentration at the interface. The modulation doped GaN/AlGaN quantum well had an electron concentration of 3.0 × 1012 cm−3 and a mobility of 850 cm2 V−1 s−1 at 300 K. In the low temperature PL spectra we observed three well defined peaks, at 3.53, 3.58 and 3.62 eV, which we attribute to recombination processes in the quantum well (QW).