替代衬底上的碲镉汞长波器件暗电流机理

Dark current mechanism in long-wavelength HgCdTe infrared detectors on alternative substrates

基于暗电流模型,通过变温I-V分析长波器件(截止波长为9~10μm)的暗电流机理和主导机制.实验对比了不同衬底、不同成结方式、不同掺杂异质结构与暗电流成分的相关性.结果表明,对于B+离子注入的平面结汞空位n^+-on-p结构,替代衬底上的碲镉汞(HgCdTe)器件零偏阻抗(R0)在80 K以上与碲锌镉(CdZnTe)基碲镉汞器件结阻抗性能相当.但替代衬底上的HgCdTe因结区内较高的位错,使得从80 K开始缺陷辅助隧穿电流(I_(tat))超过产生复合电流(I_(g-r)),成为暗电流的主要成分.与平面n^+-on-p器件相比,采用原位掺杂组分异质结结构(DLHJ)的p^+-on-n台面器件,因吸收层为n型,少子迁移率较低,能够有效抑制器件的扩散电流.80 K下截止波长9.6μm,中心距30μm,替代衬底上的p^+-on-n台面器件品质参数(R0A)为38Ω·cm2,零偏阻抗较n-on-p结构的CdZnTe基碲镉汞器件高约15倍.但替代衬底上的p+-on-n台面器件仍受体内缺陷影响,在60 K以下较高的Itat成为暗电流主导成分,其R0A相比CdZnTe基n^+-on-p的HgCdTe差了一个数量级.

The dark current characteristics of long-wavelength HgCdTe were analyzed for three types of devices. By I-V measurement under different temperatures, the dominant dark currents of each device were clarified at different temperatures. It is demonstrated that the dark current of B ＋ -implanted n＋ -on- p planar junction on silicon substrate is comparable with that on bulk cadmium zinc telluride （CdZnTe） substrate above 80 K. However, the trap-assisted tunneling current becomes dominant below 80 K due to the high density of dislocations. Compared with n＋ -on-p junctions, the p ＋ -on-n double-layer het- erojunction inhibits the diffusion current effectively, which is good matched with the calculation result with the parameters, derived from I-V curve fitting. This p ＋ -on-n diode has a RoA value of 38 Ω cm2 at 80 K, for the cut-off wavelength of 9.6 μm, while that of the n＋ -on-p diode on bulk CdZnTe is 2. 5 Ω cm2. Below 60 K, the dislocations make the RoA value of the p＋ -on-n diode an order of magni- tude lower than that of the n ＋ -on-p diode on CdZnTe.