DEPENDENCE OF SPACE-CHARGE REGION CONDUCTIVITY OF NONIDEAL HETEROJUNCTION FROM PHOTOEXCITATION CONDITIONS

Investigation of the current transport mechanism in heterojunction, used as optical and x-ray images sensors inevitably takes in the account the light influence on their tunnel-jumping conductivity. Impact of light on nonideal heterojunction essentially influences the parameters of its space charge region (SCR) [1], and hence on tunnel-jumping conductivity of SCR, and heterojunction as a whole. As the sensor generated signal strongly depends on heterojunction conductivity, the question about light influence on SCR and so on conductivity is represented as rather significant. Experimental investigations of light influence on conductivity CdS-Cu 2 S heterojunction are described in [2]. It is established, that with the increase of excitation intensity with white or only short-wave (λ ≈ 520nm) light heterojunction conductivity is essentially increased both on direct and alternating current even in a short-circuited condition, i.e. at constant barrier height. At the same time, photocapacity growth is observed even at light illumination essentially smaller than the solar. Ratio N ph /C d for some elements achieved 10 and more units that testifies the barrier width reduction. Such phenomenon can result in essential growth tunnel-jumping conductivity in SCR . In [3] the current transport in heterojunction without illumination was considered, but it was not taken into account the SCR parameters change under light influence. Therefore, the offered model cannot be applied directly to the sensor work description. We shall consider how it is possible quantitatively to take into account the influence of light on jumping current transport in nonideal heterojunction. For definition SCR heterojunction conductivity it is necessary to set the function Fermi E F (x) level position in each point x [3]. Conductivity G σ (x) of SCR part is calculated from 0 up to x as the solution of the integral equation. However, the solution of this equation is also determined by the form of a potential barrier φ (x). For dark heterojunction φ (x) depends only on submitted bias U and shows the known square-law formula. At heterojunction illumination generated in wide band CdS nonbasic carriers (holes) are captured in SCR on the traps, presented there. We shall assume, that holes are captured by the centers with a