Semiconductor Nanowire Assembly And ZnO Nanowire Based Random Lasing

Semiconductor nanowires are typical 1D materials which will play an important role in semiconductor optoelectronics area for their unique physical properties. For example, ZnO owns large exciton binding energy (60 meV) and remarkable optoelectronic properties, which is perfect candidate for low threshold and high performance UV lasers. Large scale alignment and assembly of nanowires is the fundamental of stable device performance. This work focuses on the large scale assembly of discrete nanowires and ZnO nanowire random lasing. A general micropatterning method for functional substrate is developed and large scale ordered nanowire arrays were achieved. ZnO nanowire random lasers based on p-n homojunction and Schottky junction were also realized in this work. Large scale assembly of nanowire arrays is the fundmental of nanowire based device fabrication, and Schottky junction provides alternative device structure for the development of semiconductor random lasing, which are important for nanowire device application.The main results are obtained as follows:(1) A laser induced SAM patterning method is developed in this work and functional substrate with alternative wettability was fabricated. Large scale precisely aligned nanowire arrays were realized. This technique is general and scalable, exhibiting significant application potential in surface engineering and functionalization. Patterned OTS/SiO2 substrate with alternating wettability was fabricated and used as receiver substrate to assemble discrete nanowires from solution. Large scale precisely aligned nanowire arrays were deposited on the hydrophilic areas by the interaction of microfluidic force and shear force, which provides technical fundmental for nanowire based devices.(2) A method of fabricating lateral electrodes on nanowires is developed to improve the injection efficiency in optoelectronic devices. The method uses Aluminum as bottom electrode material, involving with the nanowire transfer and the anodic oxidation process. Structurally matched alumina insulates the electrodes and provides reliable electrical contact. This lateral electrode propels carriers to transport them across nanowires and is crucially beneficial to the injection/extraction in devices.(3) Electrically pumped ZnO p-n homojunction random lasing is demonstrated. Nitrogen-doped ZnO nanowires were grown on ZnO thin film by chemical vapor deposition. The p-n junction behavior was studied by the photocurrent as well as the I-V characteristics. The device was then electrically pumped. The random lasing behavior was detected around 390 nm in the EL spectra and decent output power of 118 nW at 70 mA was also measured from this device. Lasing was generated from the formation of close-loope cavities by strong scattering and ZnO is a perfect candidate for room temperature nanolasers.(4) First electrically pumped random laser based on Schottky juntion is proposed. Undoped n-type ZnO bundle nanowires were grown on ZnO seed thin film layer. Au metal was deposited on the top ends of the nanowires to form metal-semiconductor junction. Good random lasing behavior was detected in the EL spectra and the output power was about 67 nW at 100 mA. Furthermore, Zn plasma is observed near 320 nm and 480 nm at high current of 100 mA. This research indicates that the leakage hole current flowing in Schottky junction is sufficient to help trigger excitonic process in ZnO nanowires, and initiate and maintain excitonic lasing. This study provides an alternative device structure for the development of semiconductor random lasers.