We report the development of high performance low cost SWIR infrared detectors from MBEgrown HgCdTe on 3-inch CdTe-buffered silicon substrates. The experimental findings demonstrate that despite the large lattice mismatch between HgCdTe and Si substrate, the materials and detector performances are sufficiently better than those reported for III-V mixed crystals. High minority carrier lifetime of the order 3 μs at room temperature was measured on the as grown material. Photodetectors fabricated from this material produced low dark current densities on the order of 10-6 A/cm2 and 10-3 A/cm2 at 200K and 300K. Quantum efficiency exceeding 70% at 2.0 μm, without antireflective coating, was measured on single element detectors. Further, 320 X 256, 30 μm pitch FPA’s have been fabricated with this HgCdTe on Si material and dark current operability of ~ 99.5% (mean dark current of 30 pA/Pixel) at 200K has been demonstrated.
A pH adjusted acidic solution of thioacetamide (TAM) was used as a sulfidizing agent to treat long wavelength infrared
(LWIR) superlattice surface for the first time. The results were compared against those for ammonium sulfide [(NH4)2S]
which have been used earlier for the same purpose. X-ray photoelectron spectroscopy (XPS) results revealed that TAM
treatment attains a much pronounced degree of sulfidization on superlattice surface. Electrical measurements on mesa-etched
diodes exhibited maximum zero bias dynamic resistance times area (R0A) value of 590 Ω-cm2, approximately a
four times improvement compared to (NH4)2S treated diodes. XPS studies revealed the reappearance of detrimental
oxides on the TAM treated surface after long term air exposure asserting the need for a suitable capping layer to preserve
the quality of the surface. Atomic layer deposition (ALD) was used to cap the TAM treated surface with zinc sulfide
(ZnS). Precise deposition of few monolayers of ZnS on TAM treated surface was further studied using XPS to
understand the evolution of bond formations at the semiconductor-dielectric interface.