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Pt/AlGaN/AlN/GaN Schottky diodes are fabricated and characterized for hydrogen sensing.The Pt Schottky contact and the Ti/Al/Ni/Au ohmic contact are formed by evaporation.Both the forward and reverse currents of the device increase greatly when exposed to hydrogen gas.A shift of 0.3 V at 300K is obtained at a fixed forward current after switching from N2 to 10%H2+N2.The sensor responses under different concentrations from 50ppm H2 to 10%H2+N2 at 373K are investigated.Time dependences of the device forward current at 0.5V forward bias in N2 and air atmosphere at 300 and 373 K are compared.Oxygen in air accelerates the desorption of the hydrogen and the recovery of the sensor.Finally,the decrease of the Schottky barrier height and sensitivity of the sensor are calculated.