Current generation mechanisms in small band gap HgCdTe p-n junctions fabricated by ion implantation

• Published in: Journal of crystal growth Vol. 86; no. 1-4; pp. 849 - 858
• Main Authors: DeWames, R.E., Williams, G.M., Pasko, J.G., Vanderwyck, A.H.B.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.1988
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/0022-0248(90)90814-2

A detailed study has been made of the current-voltage characteristics of Hd1-xCdxTe ion-implanted p-n junctions with x ⋍ 0.224. It is found that the dark currents, for diodes of high quality, can be represented over a broad range of voltage and temperature by three current components. A diffusion current dominates in the small bias region at temperatures > 50 K. This current component is also observed at sufficiently high forward biases at low temperatures. At temperatures of 30<T<50 K in the small bias region, a current component with a positive temperature coefficient is observed. This component, which we call Type II tunneling, has a logarithmic voltage dependence in forward bias and some of the properties of this current can be accounted for by trap-assisted tunneling models for excess current in Esaki diodes. At sufficiently high reverse bias at elevated temperatures and in the small bias region at T<30 K, the current is generated by internal field emission; this component is called Type I tunneling. The reverse bias current data are analyzed in terms of band-to-band tunneling probability expressions and good agreement is found between experiment and theory. This current has a negative temperature coefficient. Generation-recombination currents are not observed in these diodes; this conclusion is based on the observation that in the forward bias region where diffusion currents are small the observed logarithmic current has a slope which is almost temperature insensitive. In addition, the temperature dependence of the current does not obey an Arrhenius-type expression, as expected for thermally activated processes. The dominant current component limiting the zero bias resistance area (R0A) products at temperatures 30<T<500 K is Type II tunneling and the temperature dependence of this component remains unexplained. The dark currents measured on diodes of different quality in the voltage-temperature region where tunneling is dominant are highly nonuniform. This observation suggests variations in tunneling junction parameters or/and changes in the properties of the defect states contributing to carrier generation. At temperatures below 20 K we observed structures in the forward bias current. These features suggest hump currents associated with discrete defect levels and phonon-assisted tunneling processes.