Formation of a two-dimensional electron gas in ZnO/MgZnO single heterostructures and quantum wells

The properties of ZnO/MgZnO heterostructures grown by pulsed-laser deposition on sapphire (112̄0) and ZnO (0001̄) have been compared. Electron accumulation layers have been observed for ZnO/MgZnO heterostructures grown on sapphire by capacitance–voltage (C–V) spectroscopy. The formation of a two-dimensional electron gas (2DEG) in these structures has been confirmed by temperature dependent Hall effect measurements. From C–V measurements the sheet carrier density in a Zn0.8 Mg0.2O/ZnO/Zn0.8 Mg0.2O quantum well (QW) structure with a well width of about 5 nm is calculated to be only about 9.0 × 1010 cm− 2. For the films deposited on sapphire 2D growth is observed in the Burton–Cabrera–Frank mode, as confirmed by atomic force microscopy. Step flow growth mode was achieved for the homoepitaxial thin films. Quantum confinement effects have been confirmed by photoluminescence (PL) measurements. Homoepitaxial QWs are more homogeneous (smaller inhomogeneous recombination broadening) than heteroepitaxial QWs.