UC Riverside

ZnO based homojunction light emitting diode, double heterojunction light emitting diode, embedded heterojunction random laser diode and Fabry-Perot nanowire laser devices were fabricated and characterized. A variety of measurements such as X-ray diffraction, photoluminescence, scanning electron microscope and secondary ion mass spectrometry were used to characterize material properties. Current-voltage, capacitance-voltage and electroluminescence measurements were used to characterize device performance.

ZnO p-n junction diode was successfully grown on Si substrate by using Sb and Ga for p-type and n-type dopants respectively. The diode device was fabricated by using standard photolithography process. Due to the improved material quality, dominant ultraviolet light emission from ZnO homojunction diode was firstly observed and the emission properties were studied with increased injection currents. To improve the efficiency, A MgZnO/ZnO double heterojunction structure was realized by molecular beam epitaxy growth on Si substrate. Compared to homojunction structure, the carrier confinement effect in double heterojunction structure gave rise to larger output power at same injection current. With smaller heterojunction well size, ZnO based random laser diode was developed. A thin MgZnO/ZnO/MgZnO well embedded in a ZnO p-n junction was realized by molecular beam epitaxy growth. Random lasing emissions were observed at different injection currents at room temperature. Lasing mechanism was discussed and proved by deep investigation of its nano-structure. Fabry-perot type laser was also developed in our lab, to lower lasing threshold, distributed Bragg reflector was proposed. Vertically aligned ZnO nanowires were firstly successfully grown on distributed Bragg reflectors made of SiO2/SiNx alternative layers. By means of optical excitation, Fabry-Perot type lasing was observed and characterized. Compared to the same length nanowires without distributed Bragg reflectors, better lasing performance was achieved. The discussion of lasing mechanism revealed the function of distributed Bragg reflectors in improving lasing performance.