Integration of ZnO microcrystals with tailored dimensions forming light emitting diodes and UV photovoltaic cells

This article reports a new integration approach to produce arrays of ZnO microcrystals for optoelectronic and photovoltaic applications. Demonstrated applications are n-ZnO/p-GaN heterojunction LEDs and photovoltaic cells. The integration process uses an oxygen plasma treatment in combination with a photoresist pattern on magnesium doped GaN substrates to define a narrow sub-100 nm width nucleation region. Nucleation is followed by lateral epitaxial overgrowth producing single crystal disks of ZnO with desired size over 2 in. wafers. The process provides control over the dimensions (< 1% STD) and the location (0.7% STD pitch variation) of the ZnO crystals. The quality of the patterned ZnO is high; the commonly observed defect related emission in the electroluminescence spectra is completely suppressed, and a single near-band-edge UV peak is observed.