A Very Thin MCT Film in HDVIP Achieves High Absorption

Compared to the traditional flip-chip bonded focal plane array, in high-density vertically integrated photodiode (HDVIP) focal plane technology, the thickness of the mercury cadmium telluride (MCT or Hg_1-xCd_xTe) layer serves as a more critical parameter. This parameter not only influences the efficiency of photon energy absorption but also defines the pn junction area, thereby affecting the magnitude of the dark current. Furthermore, it significantly impacts the manufacturability of via-hole etching and formation processes. This paper investigated the photonic crystal resonances and coherent perfect absorption (CPA) effect of a thin MCT layer in HDVIP by using COMSOL Multiphysics^® 4.3b and optimized the structure of the loop-hole photodiode device. The CPA, which is formed by this structure, achieves high absorption of illumination in a very thin MCT film. It is demonstrated that an absorption rate of infrared radiation of more than 95% with a wavelength during the 8 µm-10 µm range can be achieved in Hg_1-xCd_xTe (x = 0.225) with a thickness of only 1.5 µm-3 µm. The benefit of thinner MCT film is that it decreases the dark current of pn junction and reduces the technical difficulty of etching and metallization of the loop-hole photodiode.