Nonlinearities in photoresponse of ultrafast optoelectronic switches are investigated by using a novel correlation technique. Sublinear behavior is found to be typical for low average electrical fields and superlinear for electrical fields higher than the threshold of electron negative-differential-mobility effect. The nonlinearities have been explained in terms of the electrical field redistribution.

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We have directly measured the effect of the bottom shape in the offset spacer on the two-dimensional (2-D) carrier profiles of the sub-50 nm p-metal oxide semiconductor field-effect transistors (MOSFETs). It has been observed that the doping profile of the Sb pocket implanted with a high angle tilt is very sensitive to the bottom shape of the notched offset spacer. It has been confirmed that the Sb pocket deeply implanted leads to the decrease of 2 nm in the average overlap length of the extension region at a depth of 5 nm when the bottom shape is slightly upped at the notched offset spacer. The increased effective channel length is considered to enhance the dependence of the threshold voltage on the body bias voltage. Moreover, it is considered from the measured carrier profiles that the reduction in carrier concentration in the top channel region lowers the threshold voltage.

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