The effect of the n(-) layer in a n(+)n(-)p structure made in long-wavelength Hg1-xCdxTe (x = 0.229) epilayers on the zero-bias resistance-area product (R(0)A) is theoretically analysed, acid compared with a n(+)p structure. A step profile is assumed for the concentration in the n(+) and n(-) layers, fabricated by ion implantation and annealing. Various current components (diffusion currents in the n(+), n(-) and p layers, depletion layer and surface generation-recombination (g-r) currents, band-to-band and trap-assisted tunnelling) are taken into account. The effect of the surface recombination velocities, and the concentrations (p-side trap, n(-) layer, and p layer) are discussed in detail. The results of this model clearly indicate the conditions under which a n(+)n(-)p diode can perform better than a n(+)p diode. In broad terms, a n(+)p structure is more suitable for p-type epilayers with lower trap concentrations and higher lifetimes, whereas a n(+)n(-)p structure is advantageous, in terms of increasing R(0)A, for higher trap concentrations and lower lifetimes. Another advantage of the n(+)n(-)p structure is that reduced tunnelling implies that a higher acceptor concentration can be accepted for device fabrication. References: 19
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