Structural and opto-electronic properties of Au/CdTe and Ag/CdTe junctions

Stability of Metal-Semiconductor Structures which are used as Schottky diode or ohmiccontact depends on the stability of its components and interaction between the components.Au and Ag metals are used for Schottky junction or contact material for CdTe thin film baseddevices. Diffusion of Au and Ag metals into CdTe thin film, structural, electrical and opticalproperties of Au and Ag doped CdTe thin films and Au/CdTe, Ag/CdTe structures wereexamined.CdTe thin films were grown by Close Spaced Sublimation (CSS) onto glass substrate and itsstructural properties were examined by the x-ray diffraction method. The films have cubic andhexagonal structured polycrystal properties with grain size 0,1μm. The optical absorptionspectra methods showed that calculated band gap of CdTe is 1,5eV.Contact metal studies shown that GaIn is suitable as an ohmic contact with contact resistivity9,6x106 ohm.cm2 in order to measure electrical properties of CdTe.Au were evaporated onto the CdTe thin film by electron beam evaporation. Thermal diffüsionof Au (350-550oC) into the CdTe thin film were examined by XRF method. Calculeteddiffusion coefficient is 4,4x10-7 cm2/s and diffusion activation energy is 0,54eV. Thestructural effect of diffusion of Au into CdTe film also examined by the x-ray diffractionmethod. Cubic and hexagonal structured grains were investigated in the film. Conductivity-Temperaure, optical absorption spectra and conductivitiy- photon spectra measurementsshowed that Au dope has Ev+0,2 eV acceptor level in the band gap of p type CdTe.Electrical properties of Au/pCdTe structure were studied and ohmic properties of the structurewere shown.Ag were evaporated onto the CdTe thin film by electron beam evaporation. Thermal diffüsionof Ag (350-550oC) into the CdTe thin film were examined by XRF method. Calculeteddiffusion coefficient is 4x10-7 cm2/s and diffusion activation energy is 0,72eV. The structuraleffect of diffusion of Ag into CdTe film also examined by x-ray diffraction method. Cubicand hexagonal structured grains were investigated in the film. XRD measurements on Agdiffused cubic CdTe films showed the existance of Ag2Te phase. Also formation of the Ag2Tephase were observed from the conductivity-temperature measurements. Conductivity-Temperature, optical absorption spectra and conductivitiy- photon spectra measurementsshowed that Ag dope has Ev+0,09 eV acceptor level in the band gap of p type CdTe.Photon induced diffusion of Ag into CdTe thin film were studied at the temperatures between280-420oC. It was shown that photon induced diffusion coefficient is four times higher thanthermal diffusion coefficient at the same temperature interval.Electrical properties of Ag/pCdTe structure were studied and Schottky diode properties wereinvestigated with the barrier height Фb= 0,7-0,8eV, ideality factor β = 1,9-10 and the saturatedcurrent density Js= 3,7x10-8 A/cm2 .Keywords : CdTe, diffusion, Au/CdTe, Ag/CdTe, Ohmic Contact, Schottky JunctionJURY:1. Prof. Dr. Tayyar CAFEROV (Supervisor) Date: 07.07.20062. Prof. Dr. Emel ÇINGI Page: 1143. Prof. Dr. Fatma TEPEHAN4. Prof. Dr. Durul ÖREN5. Prof. Dr. Nurfer GÜNGÖR