Study On Growth Of Gan By MOCVD And Fabrication F GaN Ultraviolet Detectors

GaN based materials are the ideal candidates for ultraviolet (UV) detectorsbecause of their direct band gap, good thermal and chemical stability and excellentphysics property. Up to now, GaN based UV detectors has become one of the mostinteresting research field of the world since they are solid state, small size, lowenergy consumption and they can be widely used in UV warning, space ultravioletcommunication and fire monitoring. However, the performance of GaN based UVdetectors have been hindered by the high density threading dislocations in GaN dueto lack of GaN substrates. In this paper, we are focus on how to improve theperformance of GaN based detector including the GaN epilayer growth and detectorsfabrication. An idea of "Strain induced in situ laterial growth" has been proposed andinvestigated to reduce defects in GaN epilayer. Besides, the influence of thedisolations on the GaN UV detectors has been investigated and SiO~2nanoparticleshave been deposited on the surface of GaN epilayer to improve the performance ofGaN detectors. Furthermore, asymmetric Schottky barrier height GaNmetal-semiconductor-metal (MSM) detectors have been fabricated and theirperformance has been studied in detail. The main results are as follows:1. Growth of low-defect GaN epilayer by metalorganic phase vapor deposition(MOCVD)To obtain high-quality GaN epilayer, AlN templates are first grown on sapphire substrates by 'two-step' method by using MOCVD. The mechanism ofAlN templates are also clarified by in-situ monitoring system. Then GaN epilayersare growth on the AlN templates resulting in the reduction of disolation density inGaN epilayers because the strain difference between AlN template and GaNepilayer induce epitaxial laterial overgrowth of GaN. The mechanism of the defestsreduction has been investigated in detail.2. Clarified the influence of disolation on the performance of GaN baseddetector and proposed a new way, depositing SiO~2nanoparticles on GaN surface,to improve the performance of GaN based detectors by passivation effect.The influence of dislocations on the performance of GaN MSM detectors hasbeen investigated. The results show that the screw dislocations have a stronginfluence on the dark current of detectors, while edge dislocations have thepredominant effect on their responsivity. The dark current of the detectors increaseswith increasing screw dislocations. However, the responsivity of the detectorsdecreases with increasing edge dislocation density. The reason why theperformance of GaN detectors depend on the dislocations has been studied in detail.Based on above-mentioned study, a new way of depositing SiO~2nanoparticles onGaN surface are suggested, the performance of GaN MSM detectors have beenimproved by depositing SiO~2nanoparticles on a GaN surface. By the passivationeffect of SiO~2nanoparticles, the dark current of GaN detectors reduces more thanone order magnitude, while the responsivity of GaN detectors has also beenenhanced.3. Designed and fabricated asymmetric Schottky barrier height GaN MSMdetectors which have photon response under zero applied bias.Asymmetric Schottky barrier height GaN MSM detectors are fabricated withdifferent Schottky contact metals as the electrodes, such as Ni and Au. The recultsshow that the responsivity of this kind of detector depends on the bias and hasresponsivity at0V applied bias.