UV Responsive Characteristics of n-Channel Schottky Barrier MOSFET with ITO as Source/Drain Contacts

Abstract

Abstract We fabricated a schottky barrier metal oxide semiconductor field effect transistor(SB-MOSFET) by applying indium-tin-oxide(ITO) tothe source/drain on a highly resistive GaN layer grown on a silicon substrate. The MOSFET, with 10
um gate length and 100
um gatewidth, exhibits a threshold gate voltage of 2.7 V, and has a sub-threshold slope of 240 mV/dec taken from the I DS -V GS characteristics at alow drain voltage of 0.05 V. The maximum drain current is 18 mA/mm and the maximum transconductance is 6 mS/mm at V DS =3 V. Weobserved that the spectral photo-response characterization exhibits that the cutoff wavelength was 365 nm, and the UV/visible rejectionratio was about 130 at V DS = 5 V. The MOSFET-type UV detector using ITO, has a high UV photo-responsivity and so is highlyapplicable to the UV image sensors. Keywords : Highly resistive GaN, Schottky Barrier MOSFET, ITO, UV responsivity 1. INTRODUCTION Gallium nitride(GaN) is one of the most promisingmaterials for both opto-electronic devices, such as highsensitive ultraviolet(UV) detector, visible light emissiondiode(LED) and high temperature / high frequency / highpower electronic devices, such as high electron mobilitytransistor(HEMT)[1-3], metal insulator semiconductorfield effect transistor(MISFET)[4, 5].At least until recently, there has not been much interestin enhancement mode transistors, even though there aremany applications for integrated UV image sensors as wellas high power logic integrated circuit applications.Schottky barrier source/drain(S/D) structure MISFET andsilicon implanted S/D MISFET have been presented in [6]and [7], respectively. The schottky barrier S/D is anattractive solution because it excludes the use of the highcost S/D ion implantation process and very hightemperature activation at over 1500 \C[1]. Indium-tin-oxide(ITO), on the other hand, has been widely applied tomany other opto-electronic devices because of its highlyconductive and visible-transparent properties[8].In this study, we investigated both the electrical and theUV responsive characteristics of a fabricated enhancementmode n-channel SB-MOSFET using ITO schottky barrierS/D on a highly resistive GaN layer grown on a siliconsubstrate in the near UV and visible regions for the variousgate/drain bias conditions. The fabricated devices exhibitvery promising behaviors, such as a very high on/offcurrent ratio, high transconductance, and a goodUV/visible rejection ratio.