Small two-dimensional arrays of mid-wavelength infrared HgCdTe diodes fabricated by reactive ion etching-induced p-to-n-type conversion

Abstract

The reactive ion etching (RIE) technique has been shown to produce high-performance n-on-p junctions by localized-type conversion of p-type mid-wavelength infrared (MWIR) HgCdTe material. This paper presents variable area analysis of n-on-p HgCdTe test diodes and data on two-dimensional (2-D) arrays fabricated by RIE. All devices were fabricated on x = 0.30 to 0.31 liquid-phase epitaxy (LPE) grown p-type (p = ∼1 × 1016 cm−3) HgCdTe wafers obtained from Fermionics Corp. The diameter of the circular test diodes varied from 50 µm to 600 µm. The 8 × 8 arrays comprised of 50 µm × 50 µm devices on a 100-µm pitch, and all devices were passivated with 5000 A of thermally deposited CdTe. At temperatures >145 K, all devices are diffusion limited; at lower temperatures, generation-recombination (G-R) current dominates. At the lowest measurement temperature (77 K), the onset of tunneling can be observed. At 77 K, the value of 1/R0A for large devices shows quadratic dependence on the junction perimeter/area ratio (P/A), indicating the effect of surface leakage current at the junction perimeter, and gives an extracted bulk value for R0A of 2.8 × 107 Ω cm2. The 1/R0A versus P/A at 195 K exhibits the well-known linear dependence that extrapolates to a bulk value for R0A of 17.5 Ω cm2. Measurements at 77 K on the small 8 × 8 test arrays were found to demonstrate very good uniformity with an average R0A = 1.9 × 106 Ω cm2 with 0° field of view and D* = 2.7 × 1011cm Hz1/2/W with 60° field of view looking at 300 K background.