Effects of polarization field on formation of two-dimensional electron gas in (0 0 0 1) and [formula omitted] plane AlGaN/GaN heterostructures

Abstract

Photoluminescence (PL) and temperature-dependent Hall effect measurements were carried out in (0 0 0 1) and (1 1 2 ̄ 0) AlGaN/GaN heterostructures grown on sapphire substrates by metalorganic chemical vapor deposition. There are strong spontaneous and piezoelectric electric fields (SPF) along the growth orientation of the (0 0 0 1) AlGaN/GaN heterostructures. At the same time there are no corresponding SPF along that of the (1 1 2 0) AlGaN/GaN. A strong PL peak related to the recombination between two-dimensional electron gas (2DEG) and photoexcited holes was observed at 3.258 eV at room temperature in (0 0 0 1) AlGaN/GaN heterointerfaces while no corresponding PL peak was observed in (1 1 2 ̄ 0) . The existence of a 2DEG was observed in (0 0 0 1) AlGaN/GaN multi-layers with a mobility saturated at 6000 cm 2/V s below 80 K, whereas a much lower mobility was measured in (1 1 2 ̄ 0) . These results indicated that the SPF was the main element to cause the high mobility and high sheet-electron-density 2DEG in AlGaN/GaN heterostructures.