Metal-n-type Zno Thin Film Contact Characteristics

As one kind of direct wide band-gap semiconductor,Zinc oxide(ZnO) has excellent optical and electrical characteristics,which make it have potential applications in short wavelength lasers,UV photodetectors,transparent conductive films,and so on.In order to fabracte high quality ZnO detectors,one of the primary works is to improve the contacts between metal electrodes and ZnO materials.In this paper,contacts between metals and n-ZnO films were fabricated by the method of pulsed laser deposition(PLD).The ohmic contacts of Al-ZnO and the schottky contacts of Ag-ZnO were systemically studied.1.ZnO thin films were deposited on Al/Si substrates by the pulsed laser deposition(PLD) method.The XRD and SEM images of films had been examined. Highly c-axis oriented ZnO thin films which have uniform compact surface morphology had been fabricated.The size of surface grains is about 30nm.The high quality of ZnO films gives a good condition for fabricating high quality contacts between metals and ZnO.2.The fabricating method of high-quality ohmic electrodes on n-ZnO films with AI material was studied.The metal materials with proper work function were chose as the electrodes can achieve ohmic contacts on n-ZnO films successfully,for example In, Ti,Al,and so on.It was found that the introduction of high doping AZO layer between AI and n-ZnO layers can achieve better ohmic characteristics.Moreover,the crystal quality and conductivity of Al electrodes can be improved efficiently by high temperature annealing while the contact barrier between AI and n-ZnO layers was also reduced.So the excellent contact characteristics were achieved.3.The Schottky barrier ultraviolet detectors with silver Schottky contacts were made on ZnO thin films.Current-voltage characteristics had been measured.The ideality factor is 1.22,while the barrier height is 0.908eV.After annealing at 600℃for 2h,the ideality factor is 1.18 and the barrier height is 0.988eV.Under the illumination of 325nm wavelength UV-light,the photocurrent-to-dark current ratios before and after annealing are 140.4 and 138.4 biased at 5V,respectively.The photocurrents increase more than two orders of magnitude over the dark currents.4.200nm silver films were deposited on ZnO films as electrodes at different temperatures.The structural and electrical properties are analyzed by X-ray diffraction, SEM andⅠ-Ⅴmeasurements.The crystal quality of Ag films was greatly influenced by the growth temperature.TheⅠ-Ⅴcharacteristics at room temperature indicate that the contacts types between Ag and ZnO films are related to the growth temperatures of Ag electrodes.When Ag electrodes were fabricated at 150℃and 200℃,the schottky contacts between Ag and ZnO were obtained,which was attributed to the appearance of p-type inversion layer at the interface between Ag and ZnO films.