Optical properties of GaN epilayers and GaN/AlGaN quantum wells grown by molecular beam epitaxy on GaN(0001) single crystal substrate

GaN epilayers and GaN/AlGaN quantum wells (QWs) were grown by molecular bea m epitaxy on GaN(0001) single crystal substrates. Transmission electron mic roscopy (TEM) was used to assess the crystal quality of the homoepitaxial l ayers. A dislocation density of less than 10(5) cm(-2) is deduced from TEM imaging. Low temperature (1.8 K) photoluminescence (PL) of homoepitaxial Ga N reveals PL linewidths as low as 0.3 meV for bound excitons. The PL integr ated intensity variation between 10 and 300 K is compared to that observed on a typical heteroepitaxial GaN/Al2O3 layer. A 2 nm thick GaN/Al0.1Ga0.9N QW has been studied by time-resolved and continuous wave PL. The decay time is close to a purely radiative decay, as expected for a low defect density . Finally, the built-in polarization field measured in a homoepitaxial QW i s shown to be comparable to that measured on heteroepitaxial QWs grown eith er on sapphire or silicon substrates. (C) 2000 American Institute of Physic s. [S0021-8979(00)07513- 7].