Molecular Beam Epitaxial Growth of Al-doped ZnMgO Alloy Films for Modulation-doped ZnO/ZnMgO Heterostructures

Abstract

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 3.8×10 -1 Ω·cm at 1.0×10 18 cm -3 to 8.0×10 -4 Ω·cm at 3.5×10 20 cm -3 . Although Al doping at higher than 10 20 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 Al 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.