Comparison of the current characteristics of photodiodes formed on CdHgTe films grown by molecular-beam and liquid-phase epitaxy for the 8-12-mu m spectral range

摘要

This paper presents a comparison of the dark currents and differential resistance of photodiodes, obtained using p-type cadmium-mercury telluride (CdHgTe) layers doped with boron ions, grown by molecular-beam epitaxy (MBE) and liquid-phase epitaxy (LPE). The volt-ampere responses for diodes on CdHgTe layers with composition x=0.215, grown by MBE and LPE (x approximate to 0.222) are characterized by various saturation currents (reverse bias -0.25 V) of 1-2 and 5-10 nA, even though the band gap is greater for the latter. In this case, the maximum differential resistance is 4 x 10(9) and 5 x 10(7) Omega for diodes based on MBE and LPE layers, respectively. The experimental data are compared with the calculated values. Numerical modelling showed that, for MBE structures with low biases, the dark current is limited by the diffusion current and by the Shockley-Read-Hall current outside the n-p junction, whereas, in LPE structures, there is a substantial contribution of currents through traps in the depletion region.