The conductance method has been used to measure the density of interface states of the ZnS/Hg0.775Cd0.225Te metalhyphen;insulatorhyphen;semiconductor (MIS) system with three different HgCdTe surface treatments. It is found that the density of fast interface states increases from sim;1011eVminus;1thinsp;cmminus;2at the conductionhyphen;band minimum to sim;1013eVminus;1thinsp;cmminus;2near the valencehyphen;band maximum. In addition, the interface states located in the lower part of the band gap communicate with the valence band so efficiently that the effective band gap is reduced. Our observations explain why thephyphen;type MIS photodiode is superior to thenhyphen;type version in terms of breakdown voltage and storage time.
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