Vertical Electrical Conductivity of ZnO/GaN Multilayers for Application in Distributed Bragg Reflectors

Abstract

We have demonstrated an electrically conductive ZnO/GaN multilayer structure using hybrid plasma-assisted molecular beam epitaxy. Electrical I-V characteristics were measured through the top three pairs of a six pair ZnO/GaN sample. The total measured resistance was dominated by lateral and contact resistances, setting an upper limit of ∼10 −4 •cm 2 for the vertical specific series resistance of the stack. A strong contribution to the low resistance is the cancellation of spontaneous and piezoelectric polarization that occurs in the in-plane strained ZnO/GaN sample, as shown by electrical simulations. In addition, the simulations show that the actual vertical resistance of the sample could in fact be three orders of magnitude lower and that ZnO/GaN structures with thicknesses fulfilling the Bragg condition should have similar resistance. Our results suggest that ZnO/GaN distributed Bragg reflectors (DBRs) are a promising alternative to pure III-nitride DBRs in GaN-based vertical-cavity surface-emitting lasers.

Enhanced stability of piezoelectric nanogenerator based on GaN/V2O5 core-shell nanowires with capacitive contact

“…However, there is an inherent problem originating from the free carriers of a semiconductorbased PNG: screening of the piezoelectric field and the consequent degradation of the generated PNG output. Theoretical investigations based on the density functional theory show that ZnO has unintentional n-type conductivity due to interfacial charge traps and impurities [8,9]; this conductivity enhances the free-carrier screening effect. Moreover, it is challenging to epitaxially fabricate ZnO pn-homojunction, which is essential for the formation of built-in potential and the suppression of junction current screening.…”