While the design of electron detectors with optimized responsivity for any given energy range requires that attention is paid to a number of parameters (including the semiconductor and dopant type to be used, doping profile, passivating type and thickness etc), the detector’s responsivity is highly dependent on the recombination of produced electron-hole pairs in the detector.

Research has shown that highly localized deep defects on semiconductor surfaces especially at the Si-SiO2 interface, are extremely efficient recombination centres and that these recombination activities can be a dominant mechanism that controls the minority carrier lifetime in silicon. By changing the doping profile, surface recombination velocity and the fixed charge in the silicon/silicon-dioxide interface, the responsivity is monitored. From figure below it is clear that an p+n detector structure is more sensitive to an increased surface recombination velocity compared to an n+p detector structure. The internal Electric field caused by a step dopant profile explains this difference.

Simulation of the effect of surface recombination velocity of minority carriers Sn,p where Qr = 5 x 1011 C/cm2 on the responsivity of the figures.

The fixed oxide charge present in the oxide can change, caused by radiation damage, processing condition etc. In the case of an n+p detector structure an increased fixed charge increase the responsivity as can be seen in the simulated result in figure below. The fixed positive charge gives a contribution to the internal electric field which decrease the time spent on generated carrier close to the silicon/ silicon-dioxide interface.

This work continue with experimental verification of an n+p electron detector and a development of an n+p lateral position sensitive detector for position measurement of low energetic electrons.

 

The influence of fixed oxide charge, Qr or the responsivity from 0,5 keV to 20 keV.