Abstract

There are many physical mechanisms which give rise to N-type current-voltage characteristic (CVC) in semiconductors. Of special interest is the possibility of obtaining N-type CVC for photocurrent of semiconductor photosensitive element due to the reduction in the absorbed light power (P) when the applied voltage (V) is increased. On the basis of such electrooptical elements it was possible to fabricate devices (SEED) for optical radiation control. The principle of obtaining N-type CVC in the SEED can be explained in the following way. In any photoelectric devices photocurrent is defined by the concentration of carriers n created by light. This concentration is proportional to product: n~∝P, where ∝ - is absorption coefficient of the SEED material. N-type CVC may take place if any of the values ∝ or P decrease when V grows. In-crease of V (i.e. electric field E inside the SEED) can alter the refraction index or/and the absorption coefficient of the SEED material. The change in the refraction index may produce essential change in concentration n if the SEED is made like a Fabry-Perot resonator (FPR). In this case continuous increase or decrease of the refaction index with E causes continuous change in the optical length of the FPR and, consequently, oscillations of P inside the SEED. The reduction of P in this case gives rise to N-type CVC [1-3]. For the photon energy ħω close to the energy gap E_g of the semiconductor the increasing of E results in the increase of ∝ , if ħω<E_g, and may result in decrease of ∝ , if ħω slightly exceeds E_g. The growth of ∝ with E in the active layer of the resonator SEED can result in the reduction of n , i.e. N-type CVC. This may occur because in the resonance region the increase in ∝ results in a drastic drop in the P inside the FPR, so that in the product this reduction overcompensates the rise of the ∝ [2,3]. On the other hand, reduction of ∝ with E in the narrow gap i-type layer of the SEED made on the basis of the double P - i - N heterostructure enables us to obtain N-type CVC in a simple and elegant way [3-5]. In the latter case the SEED has no resonator and nonmonochromatic radiation can be used.

© 1988 Optical Society of America