Molecular-beam epitaxy of GaN/AlxGa1−xN multiple quantum wells on R-plane (1012) sapphire substrates

GaN / Al 0.15 Ga 0.85 N multiple quantum wells (MQWs) have been grown by plasma-assisted molecular-beam epitaxy on R-plane (101̄2) sapphire substrates. The orientation relationship was found to be (112̄0) (Al)GaN∥(10 1̄2) Al2O3, resulting in nonpolar GaN/AlGaN heterostructures. Room-temperature photoluminescence studies were performed to compare the optical properties of the MQWs grown on (0001) and (101̄2) Al2O3 substrates. The peak transition energy, as a function of well width for the (112̄0) MQWs, followed the trend for rectangular potential profiles indicating the absence of built-in electrostatic fields. In comparison, the peak transition energies for the (0001) MQWs showed a significant redshift due to the quantum-confined Stark effect, consistent with a built-in field value of 750 kV/cm. In addition, the photoluminescence intensity was 20 to 30 times higher for the (112̄0) MQWs compared to the (0001) MQWs.