Manipulation Of Schottky Barriers Of ZnO Nanowires And Optoelectronic Properties

One dimensional ZnO nanostructure have received more and more attentions because of their potentialapplications as UV lasers, light-emitting diodes, gas sensors, and UV photodetectors. Photodetectors are themost promising applications of semiconducting NWs. ZnO is a typical n-type wide band gapsemiconductor are regarded as one of the most promising candidates for UV photodetectors. Because of itswide band gap（Eg=3.3eV） with a large exciton binding energy（60meV）, low cost, strong radiationhardness and ease of manufacturing.Although many research group reported that photoelectric transport characteristics of ZnO nanowiresschottky barrier devices has excellent performance in rectifiers and sensors and ZnO nanowire schottky UVdetectors has carried out many meaningful research work, there are still some problems need to be furtherstudied.The transport properties studies of our group based on ZnO and CuO nanowires schottky barriersensors show clearly that barrier is strongly affected by the surface state in early stage. However, due to thespecies diversity and various forms of surface states, the surface states mainly include: forming ionicchemical adsorption of oxygen and deep level defects of oxygen vacancies, which lead to people still can’tto effectively control barrier height of schottky barrier at the moment. In addition, two types of surfacestates （adsorbed oxygen and oxygen vacancies） play a key role in UV detection, as well as the electricaltransport properties and the sensitivity and responding to the recovery time of single ZnO nanowire deviceremains to be further researched.Based on the above problem, different atmosphere, light intensity and thermal annealing treateat werecarried out to study the oxygen adsorption and desorption in specific process and photoelectric transportproperties from rapid thermal annealed ZnO nanowires schottky barrier detector.In Chapter2, high density ZnO nanowires were synthesized by chemical vapor deposition method.The morphology and structure of as grown nanowires（NWs） were characterized by XRD、UV-Visabsorption、SEM and TEM. Then a single ZnO NW was constructed by dielectrophoresis. In Chapter3, we first studied the I-V characteristics of single ZnO nanowire Schottky barrier devicesin oxygen and nitrogen atmosphere which indicated that dynamic process of adsorption and desorbtion ofoxygen on surface of ZnO NW. We found that dark current of ZnO nanowires in the O₂atmospher obviousreduced by about one order of magnitude than that in N₂atmosphere under dark condition; Under UVillumination, the photocurrent in O₂atmosphere rise and decay rate was much faster than in N₂atmosphere,and discussed the corresponding physical mechanism of the photocurrent of ZnO NW schottky barrierphotodecters. Then, I-V characteristic mearsured by using UV source with different nerutral density filters.We found that with the increase of light intensity in the photocurrent increases gradually. By analyzing thefitting resistance with the change of light intensity, we confirmed that light response mainly depend onintrinsic resistance, light can effectively reduce height of single ZnO nanowire surface barrier.In Chapter4, I-V characteristic of single ZnO nanowires schottky device by using the thermalannealing treatment in nitrogen environment showed ohmic contact property. Moreover, photocurrentresponse curve based on single ZnO nanowires device was measured with and without annealing treatmentduring UV light. Dramatically change of photoresponse mainly due to reduced defect state associated withoxygen on the surface of ZnO nanowires.