| Recent years, wide band-gap semiconductor power device has become one of thehottest topics in semiconductor field. AlGaN/GaN Schottky Barrier Diode (SBD) is avery promising power device because of its great advantages and potentialapplications on high power and high voltage devices. Despite of the advancement ofthe heterostructure growth and the fabrication of devices, it is far from mature. In thisarticle two important issues are studied: one is the effects and mechanism of surfacetreatments on the ohmic contacts, and the other is the optimization of Schottkyelectrode and calculation of surface states on the AlGaN surface.Ohmic contact is one of the key factors for fabricating high performanceAlGaN/GaN SBD devices. After surface treatments the specific contact resistivitydramatically decreases. To investigate the mechanism of this improvement, thechemical properties of the AlGaN/GaN surface are characterized by using XPS. Theresults show that surface treatments can not only effectively remove surface oxides,but also form a passivation layer on the surface, which effectively reduces the surfacestate density to lower the electron tunneling barrier height. Both the two factorscontribute to the formation of high quality ohmic contact.Schottky contact is the crucial technology for AlGaN/GaN SBD, which can beaffected by electrode size, metals, semiconductor surface properties, etc.. This articlestudies the rule of forward current and reverse breakdown voltage changing with theelectrode size, and a comparison of two different Schottky contact metals Ni and Pt.Meanwhile, in order to quantitatively study the effect of surface state on theperformance of AlGaN/GaN SBD, a modified equivalent circuit model for surfacestates is discussed. The experiment and theoretical calculation results show thatsurface treatments can effectively optimize the Schottky contact quality by improvingthe Schottky barrier height and thus reduce surface state density. |
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