Molecular beam epitaxial growth of Al-doped ZnMgO alloy films for modulation-doped ZnO/ZnMgO heterostructures

In this paper, we describe the characteristics of Al-doped n-type Zn(1-x)Mg(x)O alloy films grown on a-plane sapphire substrates by molecular beam epitaxy, and the application of the films in modulation-doped ZnO/Zn(1-x)Mg(x)O quantum wells (QWs). The results of Hall measurement for the Al-doped Zn(0.8)Mg(0.2)O alloy films revealed an excellent doping efficiency that the resistivity at 300 K decreased from 3.8 x 10(-1) Omega center dot cm at 1.0x 10(18) cm(-3) to 8.0 x 10(-4) Omega center dot cm at 3.5 x 10(20) cm(-3). Although At doping at higher than 1020 cm(-3) resulted in a reduction in intensity and a broadening of the peak width of near-band-edge emission in cathodoluminescence with an increase in absorption-edge energy induced by the Burstein-Moss shift in optical transmittance, highly c-axis-oriented films without rotational domains were obtained in a wide range of doping levels. Such a successful doping was also confirmed for Zn(1-x)Mg(x)O alloy films with a Mg content as high as 0.4. By applying At doping to modulation-doped ZnO/Zn(0.6)Mg(0.4)O QWs, the sheet carrier density of the ZnO well was found to be proportional to the doping level in the Zn(0.6)Mg(0.4)O barrier layer.