In-plane anisotropy in m-plane Zn0.8Mg0.2O/ZnO multiple quantum wells
Tsung-Han Yang1*, Hou-Ren Chen1, Chih-Ya Tsai2, Wen-Feng Hsieh1
1Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu, Taiwan
2Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan
* presenting author:Tsung-Han Yang,
In order to avoid the quantum confined Stark effect (QCSE), the nonpolar ZnO/ZnxMg1-xO multiple quantum wells (MQWs) structures are highly require. In this report, we study of 3-pairs ZnO/Zn0.2Mg0.8O MQWs with three different well widths of 5, 11and 16nm, have been fabricated on m-plane (10 ̅10) sapphire substrates by pulsed-laser deposition (PLD). The nonpolar ZnO/Zn0.2Mg0.8O MQWs were grown on the 10% m-MZO buffer by two-step growth, which effectively reduces the extra domain and surface roughness but high basal-plane stacking faults (BSF) density. The photoluminescence (PL) spectra show a blueshift near-band edge (NBE) emission and strong stacking faults, coming from both substrate and heterostructure, optical emissions of MQWs. Comparing three different well width samples, we can observe that the NBE emission in QWs are blue shifted with decreasing well width. In addition, we used various analyses to identify that there have no internal electric in our sample, e.g., for every one of well width MQWs, the results of power-dependent LT-PL show the un-shifted PL peaks with increasing pumping power density that is evidence for no internal in our m-ZnO MQWs. Furthermore, we also can find that NBE emission and exciton binding energy of all samples stay above that of ZnO bulk, which indicated the absence of QCSE. Finally, we discuss the optical anisotropy properties of our m-plane ZnO/Zn0.2Mg0.8O MQWs. We can detect the FXC and FXA emissions, which are separated at high temperature but merged together at low-temperature PL spectra.

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Keywords: pulsed laser deposition, photoluminescence, nonpolar quantum wells, uantum-confined Stark effect, near-band edge emission