Valence band barrier optimization in HgCdTe p-on-n double layer heterostructure: a Silvaco TCAD simulation

HgCdTe is the material of choice for the fabrication of high-performance cryogenic infrared detectors. The p-on-n double layer heterostructure design in HgCdTe device utilizes a high-composition layer to suppress surface leakage, thereby achieving low dark current and high R₀A values. However, valence band barrier introduced by the high-composition layer may adversely affect the quantum efficiency of the detector. In this work, Silvaco TCAD simulations were employed to investigate the influence of material composition and doping concentration on valence band barrier in p-on-n double layer heterostructure. The simulation results revealed that a smaller composition difference and a larger composition gradient between the absorber layer and the high-composition layer lead to a smaller valence band barrier. Moreover, a higher doping concentration in the absorber layer results in a larger valence band barrier, while the doping concentration in the high-composition layer has a relatively minor impact on the valence band barrier. Based on these simulation findings, HgCdTe p-on-n double layer heterostructure materials were grown using the VLPE technique and the composition and doping profiles were characterized using SIMS measurements. The experimental results showed a composition difference of Δx=0.09 and a composition gradient of s=0.02μm^-1 between the absorber and high-composition layers, with an In doping concentration of 1×10¹⁴cm^-3 and an As doping concentration of 3×10¹⁷ cm^-3 . Devices fabricated from these materials exhibited a noise-equivalent temperature difference of 20.1 mK, a dark current of 20.54 pA@ 9.67μm at 77K, which almost the same level with Rule 07 results.