Characteristic of I - V , C - V for a - Ge : Sb / c - GaAs Hetrojunction

Ge:Sb films with thickness (500nm) have been deposited by thermal evaporation technique on glass substrate and c-GaAs wafer at room temperature, under vacuum of 10-5 mbar with rate of deposition equal to 10Ǻ/sec. These films have been annealed at different annealing temperatures (100, 200) 0 C. The structural characteristic of the films prepared on glass and GaAs substrates have been studied by using X-ray diffraction, the tests show that all the films have amorphous structure for all annealing temperatures. The C-V measurement of a-Ge:Sb/c-GaAs heterojunciton at frequency 1 KHz and we found built – in potential (V bi)increase from 0.645 V to 0.84 V with T a increase from RT to 200 0 C. Also from I-V characteristic we found that the quality factor decreases from 2.641 to 2.358 for same annealing temperature, this may be interpreted in term improvement of crystal structure with heat treatment. 1. Introduction Hetrojunction devices of amorphous-crystalline types have been much attention from researcher's studies, because of their potential as wide or narrow band gap in application of thin film transistor, hetrojunction and solar cells a-Si/c-Si, a-Ge/c-Si [1-2].These hetrojunction have widely been studies in Si technology during the last decade since varying properties can be achieved by charging prepared condition as substrate temperature, thickness and annealing temperature [3].Many authors group studies the current-voltage of the junction between c-GaAs/c-Si in field solar cells can proved power for satellites [4]. amorphous thin films possess a large density of dangling bonds, which defect doping attempts because dopant attach themselves to these bonds, but by improvement the prepared condition can illumination these defect and hydrogenation of films to reduce the dangling bond [5]. The purpose of this study is to fabricate the a-Ge:Sb/c-GaAs junction and investigate I-V and C-V characteristic as a function to annealing temperature and built in potential V bi. 2. Experimental Procedure a-Ge:Sb thin film were prepared by thermal evaporation technique in vacuum system supplied by Balzers model(BL510). In order to preparation the hetrojunction, thin film a-Ge:Sb deposited on c-GaAs.