Effect of composition on the optical and electrical parameters of flash evaporated Cu2−yInyTe2 thin films

Abstract

The CuInX2 ( X S , Se, Te) family of chalcopyrites are important compounds due to their potential for opto-electronic devices /1 to 3 / . Of the CuInX ternaries, the tellurides have been scantily investigated as compared to their sulphide and selenide counterparts. Capabilities of these ternary compounds can be enhanced for device fabrication b y varying relative concentrations of CulIn in the Cu In X materials / 4 / , changing the Cu/In ratios is expected to result in modification of optical, electrical, and structural parameters of these compound semiconductors. BY 2 2-Y Y 2 In this note results are reported of optical and electrical investigations carried out on Cu 1.50) films prepared b y the flash evaporation technique / 5 / . The properties have been studied as functions of composition and substrate temperature. Thin films of Cu In Te2 were flash evaporated on optically polished microglass substrates maintained at temperatures between 175 to 275 OC. The source materials for evaporation were prepared by melting appropriately proportioned quantities of Cu, In, and Te (99.999% pure) in silica ampoules sealed under a'vacuum of Pa. The mixtures were heated slowy ( e 20 K/h) and maintained at 420 OC for 1 2 h . Thereafter, the temperature was raised slowly to ~1 0 0 K above the estimated melting point of the ternary alloys. The materials were then homogenised for 24 h at 100 K below the melting point and cooled slowly to 600 O C . After annealing for 72 h at this temperature, the materials were quenched to room temperature. The resulting alloys were powdered for flash evaporation. In Te2 (0.50 5 y 5 2-Y Y 2-Y Y u 0 . 5 0 075 7. 00 725 750 Y-Fig. 1. Variation of band gap with composition in Cu In Te2 films grown a t different substrate temperatures: (Ts = 175(0), 210 ( x ) , 225 ( A ) , 250 t o ) , and 175 O C ( 0 ) ) 2-Y Y New Delhi 110016, India. 13 physica (a)