The Study Of The Characteristics Of Ni/Au Schottky Contact On GaN

GaN has wide, direct bandgap, high breakdown field and high electron saturationvelocity. These fundamental electronic properties made GaN an ideal candidate forhigh power microwave devices manufacturing. A high quality Schottky contact is a keyfactor to the device. However Schottky contacts on n-GaN and AlGaN/GaN hetero-structure material are studied very little in our country. So in the dissertation, Schottkycontacts for n-GaN and AlGaN/GaN Heterostructures are studied in detail.The majorachievements are listed.First, based onthe classical theory of the electrical current transport mechanism, the temperature-dependent current-voltage(I-V-T) measurements and thetemperature-dependent capacitance-voltage(C-V-T) measurements, for Schottky diodesfabricated on n-type GaN, the mechanism of the electrical current transport wasdiscussed using thin surface barrier(TSB) model. The experiment results indicated thatthere are different mechanisms in different temperatures and bias. Based on thisassumption we gave a modified I-V characteristic formula and gave excellent fittingresults to the experiment data. The SBHs determined from high-temperature I-V curves,low-temperature C-V curves, and the metal work function agree with each other.Second, the effects of surface oxides and interfacial layer of the GaN andAlGaN/GaN on Schottky contact are studied, combined with pre-metallizationprocessing and annealing process, the excellent performance is obtained on n-GaN.The influence of Ni/Au-n-GaN Schottky barrier height on Si concentration and thedependence of Ni/Au-AlGaN Schottky barrier height on Al mole fraction are studied indetail. The experiment results indicated that the increase of Si concentration will leadto the degradation of Schottky contact, so the best value of Si concentration is1×10¹⁷cm^-3.And as the Al mole fraction increased, the Schottky contact will primarilyincreased, however when Al mole fraction is over 27%, the measured Schottky barrierheight was lower than predicted.Third, inductively coupled plasma-(ICP)-induced traps in n-type GaN have beenstudied from current-voltage (I-V) characteristics and capacitance-voltage (C-V) forSchottky diodes fabricatedon etched surfaces and reference surface. Changes in thesurface morphology of n-type GaN were investigated using atomic forcemicroscopy(AFM) and the metal surface morphology of reference and annealedsamples were investigated using Scanning Electron Microscope(SEM).The result of the experiment indicated that the ICP-induced electron trap may lead to the reductionof Schottky barrier height and increase of the reverse leakage current. Schottkycharacteristics were recovered after annealing at 400℃, and we can get a betterSchottky characteristics after annealing at 600℃.