Barrier thickness dependence of the built-in electric field in pseudomorphic ZnO/Zn0.55Mg0.45O multi-quantum wells

The electric polarization of (Zn, Mg)O alloys, known as stable wide-bandgap semiconductors, is an intrinsic property that has a significant impact on the properties and performance of polar ZnO-based optoelectronic devices, such in the case of the quantum-confined Stark effect. Because Wurtzite (WZ)-ZnMgO exhibits a high potential for epitaxial growth with tunable bandgap energy, we fabricated high-quality pseudomorphic ZnMgO thin films on O-polar ZnO substrates and achieved a maximum Mg solubility of 45%. In addition, the high-quality texture and accurate design of ZnO/ZnMgO multi-quantum wells (MQWs) was confirmed. The electric-polarization-induced built-in electric field (Ein) of polar ZnO/ZnMgO MQWs was examined by using a combination of cryogenic photoluminescence measurements and self-consistent Poisson–Schrödinger method. An electric field of 1.9 MV/cm was obtained for a barrier thickness of 13.6 nm. The barrier-thickness-dependent Ein was fitted with an electrostatic model, and a maximum electric field (Einmax) of 2.4 MV/cm was obtained for a 3.4-nm-thick quantum well. This value was perfectly reproduced by using the crystal parameters of the pseudomorphic ZnMgO epilayer. These results are expected to enhance our understanding of WZ-ZnMgO crystallography and provide a method for the systematic design of polar-ZnO-based optoelectronic devices. [Display omitted] •High Mg composition of 45% for pseudomorphic WZ-ZnMgO thin films grown on ZnO substrate by PA-MBE technique.•Confirmation of the high crystalline quality and quantum-confined stark effect in polar ZnO/Zn0.55Mg0.45O MQWs.•Estimation of the built-in electric field (Ein) of 1.90 MV/cm for a quantum well thickness of 3.4 nm in these MQWs.•Extraction of the maximum electric field (Einmax) of 2.40 MV/cm using an electrostatic model.•Einmax was successfully reproduced using the crystal parameters and theoretical spontaneous polarization ofZnMgO epilayers.