Defence Research Agency

About: Defence Research Agency is a based out in . It is known for research contribution in the topics: Synthetic aperture radar & Radar. The organization has 1211 authors who have published 1109 publications receiving 31542 citations.

Investigation of parameters to obtain reduced Shockley–Read traps and near radiatively limited lifetimes in MOVPE-grown MCT

Abstract: An investigation has been carried out to determine the effect of certain parameters on the minority carrier lifetime of mercury cadmium telluride (MCT) grown by metalorganic vapor phase epitaxy (MOVPE). A model has been used to investigate the relative contributions of the recombination mechanisms, i.e., Auger 1, Auger 7 (A7) radiative and Shockley–Read (S–R) traps. The lifetime was measured from the photoconductive decay induced by a GaAs laser pulse. The parameters investigated were the As doping concentration $$(2 \times 10^{15} - 2 \times 10^{17} {\text{cm}}^{ - {\text{3}}} )$$ for x≈0.32, (ii) variation in x (0.276–0.420) for fixed doping concentration and (iii) the effect of post-growth isothermal annealing in Hg at two temperatures (220 °C and 260 °C). In the majority of cases the measured lifetime showed very good fit to the theoretical combined lifetime and for low doping $$\left( {N_{a - d} \leqslant 8 \times 10^{15} {\text{cm}}^{{\text{ - 3}}} } \right)$$ we achieved radiatively limited lifetimes with low S–R trap densities $$\left( {N_t \leqslant 9 \times 10^{10} {\text{cm}}^{{\text{ - 3}}} } \right)$$ . As the doping was increased, the fitting again was good, but the lifetime started to become A7-limited, which was consistent with the theoretical model. Nt increases as a function of Na−d with an empirical relationship, Nt = 3×10−11 N a−d 1.353 . This implies that if low p-type doping can be achieved, it will be possible to grow material with low Shockley–Read trap densities. However, Nt was independent of composition for the range studied. The annealing temperature (220 °C or 260 °C) did not have an effect on Nt. Devices made in layers grown using the growth and doping conditions established in this work have shown suppressed Auger thermal generation with low Shockley–Read trap densities and have demonstrated near radiatively limited performance.

The effect of the elastic constants on the alignment and electro-optic behaviour of smectic C liquid crystals

Abstract: The static electro-optic behaviour of achiral smectic C samples in the chevron geometry have been modelled using the continuum theory of Leslie et al . [1]. The model assumes that the layer tilt and smectic C director tilt angle are constant, and treats the layers at the chevron interface as an infinitely bound surface. Comparison of the predicted electro-optic behaviour with experimental results gives values for the bend (B 1 ) and splay (B 2 ) c -director elastic constants. However, more detailed optical studies show that surface and chevron interface terms become important at high values of applied electric field.