Molecular Beam Epitaxy of GaN/Al sub x Ga sub 1-x N Multiple Quantum Wells on R-Plane (10 12) Sapphire Substrates

GaN/Al sub 0.15 Ga sub 0.85 N multiple quantum wells (MQWs) have been grown by plasma-assisted molecular beam epitaxy on R-plane (10 12) sapphire substrates. The orientation relationship was found to be (11 20) (Al)GaN || (10 12) Al sub 2 O sub 3, resulting in non-polar GaN/AlGaN heterostructures. Room temperature photoluminescence studies were performed to compare the optical properties of the MQWs grown on (0001) and (10 12) Al sub 2 O sub 3 substrates. The peak transition energy as a function of well width for the (11 20) 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 red-shift 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 (11 20) MQWs compared to the (0001) MQWs.