Low‐Frequency Photocurrent Oscillations in CdS Crystals with Thermally Induced Negative Differential Conductivity

Abstract

BYIt is the purpose of this note to present experimental results on the generation of low frequency current oscillations of high stability and high amplitude in the region of N-shaped negative differential conductivity of photocurrent (I)-voltagew) characteristics of CdS single crystals under Joule' s heating conditions.The occurrence of nonmonotonic I-U dependences with a region of voltage controlled negative differential conductivity was firstly found by Boer and KUmmel (1, 2) who have given also a qualitative explanation. In a following paper (3) a more quantitative treatment with regard to the close connection between the a(T) dependence (a conductivity, T temperature) and the type of I-U characteristic was given and shown that for high electrical power in crystals with nonmonotonic b(T) curves the I-U characteristics contain regions of N-and S-shaped negative differential conductivity caused by Joule's heating. On the basis of the regions with dI/dU < 0 found theoretically in (3) and experimentally in (4) a 7tphoto-thermistort* (5) was predicted (useful for transformation of light intensity signals in frequency variation by modification of the value of dI/dU in the N-type range etc. ). In the present paper oscillations a r e described which are connected with periodical Joule' s heating and which occur in N-shaped region without periodical change to S-type region (6) and without formation of any current channels (6) o r layer-like field inhomogenei-For the investigations vapour-phase grown plate-shaped CdS crystals with In-Ga alloy contacts (electrode distance -5 mm) were used. The crystals which show pronounced oscillations had the following characteristics: a) the a(T) plot (Fig. 1) 1) Guest from the Faculty of Physics, University of Vilnius.