Study Of Growth Of ZnO Nanorod Structures And The Optoelectronic Devices

Zinc oxide is a direct, wide bandgap semiconductor material. It has many promising properties for blue/UV optoelectronics, transparent electronics, spintronic devices and sensor applications. For oVer a hundred years, ZnO has been used in its polycrystalline form in a wide range of applications: facial powders, ointments, sunscreens, catalysts, lubricant additiVes, paint pigmentation, piezoelectric transducers, varistors, and as transparent conducting electrodes. ZnO has numerous attractive characteristics for electronics and optoelectronics devices. It has direct bandgap energy of 3.36 eV, which makes it transparent in visible light and operates in the UV to blue wavelengths. The exciton binding energy is～60meV for ZnO, as compared to GaN～25meV; the higher exciton binding energy enhances the luminescence efficiency of light emission. The room temperature electron Hall mobility is～200 cm2 V?1 in single crystal ZnO, though slightly lower than that of GaN, ZnO has higher saturation Velocity. ZnO has been exhibiting better radiation resistance than GaN for possible deVices used in space and nuclear applications. ZnO nanostructures can be grown on inexpensive substrate, such as glass, silicon, at relatively low temperatures. These structures, such as nanowires and nanorods, are ideal for detection applications due to its large surface area to volume ratio. Recent work on ZnO has shown ferromagnetism in ZnO by doping with transition metal, e.g. Mn, with practical Curie temperatures for spintronic devices. One main attractive feature of ZnO is the ability to bandgap tuning via divalent substitution on the cation site to form heterostructures. Bandgap energy of～3.0 eV can be achieved by doping with Cd2+, while Mg2+ increases the bandgap energy to～4.0 eV.Since 1990s, with the wide bandgap semiconductor GaN devices were developed for the blue and white luminescence applications, people were interested in wide band gap semiconductors again.But GaN Luminescence wavelength concentrates in the blue light-emitting wavelength range, and the synthesis temperature is high. Therefore, new advanced wide bandgap semiconductors are pursued. In May 1997, Robert F. Service in the United States published an paper in the world-known magazine'Science',《Will UV Lasers Beat the Blues?》, pointing out that the UV laser can produce UV light to store more information on CD media such as CD-ROM ,but the traditional laser with narrow band gap does not produce UV light. The ZnO band gap is wide enough, so ZnO-based semiconductor materials show a broader application. Compared to GaN, ZnO has higher exciton binding energy, can produce a higher light emission efficiency. In 2001, MH Huang et al. in Science published a monograph, on his view of the hexagonal ZnO nanorods, it can be formed as a cylinder formed from the resonator mirror and realize low-threshold stimulated emission in order to achieve room temperature ultraviolet laser manufacturing. So people are fousing on ZnO nanorods, nanowires Structure.In 2010, Kong H et al.had grown ZnO nanowires on flexible polymer films, producing nano-devices to achieve a flexible prototype Blu-ray.In many available epitaxial growth techniques, MBE and MOCVD have emerged as general purpose tools for heteroepitaxial research and commercial production. Because these two methods afford tremendous ?exibility and the ability to deposit thin layers and complex multilayered structures, Generally, they all have precise control and excellent uniformity. Nowadays, MBE and MOVPE have accounted for virtually all production of compound semiconductor devices. Compared to MOCVD, the drawbacks of MBE are the initial high cost and maintenance requirements of the UHV system and also the limited throughput. MOCVD is a vapor phase epitaxial process that is carried out at atmospheric or reduced pressure using metal organic precursors. Like MBE, MOVPE provides excellent control over the growth of thin layers and multilayered structures, including quantum well devices and superlattices.We used photo-assisted metal organic chemical vapor deposition to grow ZnO nanorod structures by changing the growth conditions, such as incident light intensity, gas flow rate, undoped ZnO nanorods was grown on p-Si (111) substrates, and then using the structure to produce n-ZnO / p-Si light-emitting diodes. When applied positive voltage of 11V to the LED, the electroluminescence wavelength ranges from 370nm-550nm. With ZnO buffer layer, high quality n-ZnO nanorods/p-Si PN structures was grown. Excited by 325nm He-Cd laser with 20mW power and at 3V reverse bias, the ratio of the light current and the dark current is more than 1000. We also utilized the first magnetron sputtering and photo-assisted MOCVD, sputtering GaAs layer on the surface of Silicon, n-ZnO/p-ZnO/p-Si homojunction light-emitting diode was produced. Applying forward voltage of 7.5V to the diode, ultraviolet electroluminescence spectra can be detected significantly.