Calculation of tunneling currents in (Hg,Cd)Te photodiodes using a two-sided junction potential

It has been shown previously that tunneling current can become the dominant dark current and hence the performance-limiting factor in diodes formed in narrow bandgap semiconductors, such as Hg
1_x
Cd
x
Te. In this paper, we calculate the tunneling current using a Kane approximation for the nonparabolic conduction band and a more realistic junction potential than has been used previously. The potential used here is characteristic of a linearly graded n-type region intersecting a uniformly doped p-type region and is a better approximation to the actual potential in a diode formed by ion implantation into a p-type substrate. We show that significant errors sometimes arise when the abrupt junction model is used to calculate tunneling current in these structures. The effect of changes in base carrier concentration and n-side donor gradient is shown for
x
between 0.196 and 0.400, which corresponds to a photodiode spectral cutoff in the important 3- to 14-µm region.