ANALYSIS OF THE R(0)A PRODUCT IN N(-) HG1-XCDXTE PHOTODIODES()P AND N(+)N()

The effect of the n(-) layer in a n(+)n(-)p structure made in long-wav elength Hg1-xCdxTe (x = 0.229) epilayers on the zero-bias resistance-a rea 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. Va rious current components (diffusion currents in the n(+), n(-) and p l ayers, depletion layer and surface generation-recombination (g-r) curr ents, band-to-band and trap-assisted tunnelling) are taken into accoun t. The effect of the surface recombination velocities, and the concent rations (p-side trap, n(-) layer, and p layer) are discussed in detail . The results of this model clearly indicate the conditions under whic h a n(+)n(-)p diode can perform better than a n(+)p diode. In broad te rms, a n(+)p structure is more suitable for p-type epilayers with lowe r trap concentrations and higher lifetimes, whereas a n(+)n(-)p struct ure is advantageous, in terms of increasing R(0)A, for higher trap con centrations and lower lifetimes. Another advantage of the n(+)n(-)p st ructure is that reduced tunnelling implies that a higher acceptor conc entration can be accepted for device fabrication.