UC Riverside

Nonvolatile memory devices and random laser devices based on ZnO thin film and nanostructures are studied and discussed in this dissertation. The p-n-p nonvolatile memory was achieved by using Sb-ZnO/ZnO/Sb-ZnO structure in Chapter 2. Secondary ion mass spectrometry result confirmed the formation of the structure. Rectifying current-voltage characteristics between Sb-ZnO and undoped ZnO layers were achieved, proving the p-n junction was formed. The p-type behavior from the p-n-p structure was studied by using the capacitance-voltage measurement and small signal model. The voltage operation led to the charging/discharging of the structure, showing nonvolatile memory effect. Low writing voltage and long retention time were achieved. The n-p-n nonvolatile memory based on Na-doped ZnO nanostructures was also studied in Chapter 3. To achieve n-p-n nonvolatile memory, the Na-doped nanorods were grown on a ZnO seed layer on Si. The p-type conductivity of the Na-doped nanorods was studied by temperature-dependent photoluminescence and nanorod back-gated field effect transistor. Vertically aligned undoped ZnO nanotips, nanotubes and nanorods were synthesized on the top facets of Na-doped ZnO nanorods without catalytic assistance under different growth time in a chemical vapor deposition system. The undoped nanorods, Na-doped nanorods and undoped seed layer form an n-p-n memory structure. The programming and retention characteristics have been demonstrated. Furthermore, the bipolar resistive switching memory using Na-doped ZnO nanowire was also demonstrated in Chapter 4. The mechanism of the self-complianced and self-rectifying effect of the device was studied.

The ZnO based optoelectronics devices are studied in Chapter 5 and 6. An electrically pumped ZnO homojunction random laser diode based on nitrogen doped p-type ZnO nanowires was achieved. The p-type behaviors were studied by output characteristic and transfer characteristic of the nanowire back-gated field effect transistor, as well as low-temperature photoluminescence. The formation of the p-n junction is confirmed by the current-voltage characteristic and electron-beam-induced current. The random lasing behaviors were demonstrated by using both optical pumping and electrical pumping, with a threshold of 300 kW/cm2 and 40 mA, respectively. The angle dependant electroluminescence of the device further proved the random lasing mechanism. To enhance the output power and reduce the threshold current of the random laser, a 10-period SiO2/SiNx distributed Bragg reflector (DBR) was introduced into the device. The formation of the homojunction p-n junction was confirmed by the current-voltage and photocurrent characteristics. The random lasing behaviors were demonstrated by electrical pumping with a low threshold of around 3 mA. The output power was measured to be 220 nW at 16 mA drive current.