One-sided rectifying p–n junction diodes fabricated from n-CdS and p-ZnTe:Te semiconductors

Abstract

The fabrication of a one-sided p–n hetero-junction (HJ) diodes have been successfully carried out using both p-type ZnTe and n-CdS semiconductors. Chemical bath deposition (CBD) and electrodeposition (ED) techniques have been used in the deposition of n-CdS and p-ZnTe layers respectively. Before the fabrication of the one-sided p–n HJ diodes, the electrical properties of glass/FTO/p-ZnTe/Al and glass/FTO/n-CdS/Au rectifying structures were separately studied using capacitance–voltage (C–V) technique so as to determine the doping density of each of the thin films. The results from C–V analyses showed that p-ZnTe is moderately doped with an acceptor density of 3.55 × 1015 cm−3 while n-CdS is heavily doped with a donor density of 9.00 × 1019 cm−3. The heavy doping of n-CdS and moderate doping of p-ZnTe will make the interface between n-CdS and p-ZnTe thin films a one-sided n+p diode. Therefore, to fabricate the CdS/ZnTe hetero-structure, it was ensured that approximately same thickness of CdS and ZnTe thin films being used in the initial experiment to study the electrical properties of glass/FTO/n-CdS/Au and glass/FTO/p-ZnTe/Al were also used in the development of the one-sided n+p junction diodes to obtain more accurate results. The electronic properties of the device structure were studied using both current–voltage (I-V) and C–V measurement techniques. The I–V results show that the one-sided n+p HJ diodes possess good rectifying quality with a series resistance (Rs) of ∼35 Ω and rectification factors exceeding 102.7 under dark condition. The results of the C–V analyses showed that the acceptor density of the one-sided n+p HJ diode is of the order of 1015 cm−3 while the donor density is of the order of 1018 cm−3. The results obtained from this analysis still showed the moderate doping of p-ZnTe and the degenerate nature of n-CdS.