The theoretical considerations and practical aspects of passivating insulator films, in the context of their use on high-performance mercury cadmium 'telluride (MCT) infrared detectors are reviewed. The methods of growth, the interface properties and the applications of' both native and deposited passivant films have been discussed. Native films include anodic, chemical, photochemical, and plasma oxides as well as anodic sulphides and fluoro-oxides. Deposited films include ZnS, photo-CVD-grown S i 4 , CdTe, and SiN,, The properties of all these passivant films on MCT have been summarized.
We report the first model of Zener tunnelling capacitance and its effect on the C-V characteristics of Hg, -,Cd,Te.For narrow band Hg, -,Cd,Te, with x = 0.2, even at moderate doping densities, C-V curves exhibit low-frequency behaviour at measurement frequencies as high as 1 MHz (both for p-type and n-type MCT). The model predicts the reported trends in C-V characteristics as a function of composition, doping density and measurement frequency.
The effect of fixed surface charge density (Q f ) on the performance of HgCdTe (MCT) photoconductive detectors is presented in this study. The figure of merit such as the specific detectivity (D * ) of Hg 0.78 Cd 0.22 Te photoconductive detectors operating at 77 K is calculated with 300 K background and 2π field of view (FOV). The equations leading to the above calculations are developed for the case of a one-dimensional model. Our calculations show that: (i) D * shows maxima with varying Q f ; (ii) improvement in D * due to accumulation is observed for values of Q f up to 5 × 10 10 cm −2 for materials with low as well as high bulk minority carrier lifetimes (τ b ); and (iii) D * is limited by shunt resistance due to passivants having Q f > 5 × 10 10 cm −2 for low-τ b materials. Furthermore, D * is found to degrade by an order of magnitude from its peak value with increase in Q f from 5 × 10 10 cm −2 to 1 × 10 13 cm −2 in a material having τ b = 10 ns, whereas no such degradation in D * is seen for the same range of Q f in a material having τ b ≥ 1 µs. In addition, our calculations predict that the accumulation layer improves D * by a factor of 1.5 for surfaces having an initial surface recombination velocity as high as 10 5 cm s −1 .
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