IR study of exclusion-accumulation effects enhanced by the geometrical factor

A detailed experimental and theoretical study of exclusion and accumulation at the 1-h contact in cylindrical samples (with a current along the radius ) has been carried out. Two types of the second contact have been used: eit her the same 1-h contact or a recombination type ohmic contact. It has been shown that both the inhomogeneous electric field in a cylinder and the hig h,generation-recombination capability of the second ohmic contact at the la rger radius enhance the exclusion and accumulation effects near the small-r adius contact. This is manifest in lowering the bias voltage needed for a h igh-level depletion or accumulation, the latter becoming competitive with i njection by the excess carrier concentration level. Experimental investigat ions of non-equilibrium charge carrier distribution in these samples have b een implemented by two methods. Along with the well known IR probing techni que in the spectral range of free carrier absorption, the thermovision tech nique, enabling us to visualize the concentration distribution has been use d for the first time. The obtained results are useful for improvement of th e far-infrared source and modulator parameters.