High field domains in low conductivity CdS crystals moving with low velocities to 10 cm/s) from the cathode to the mode (cta layers) were first described by Boer, Hlinsch, and Kiimmel (1). A theoretical study made by BSer and Wilhelm (2) showed that the cta layers under discussion are probably caused by field quenching.Detaiied experimental investigations of the cta layers have shown that in special cases in the "mainff domains moving from the cathode to the anode "subdomainsv1 are observable which move in the opposite direction (3, 4). In this paper high field domains in CdS crystals of low conductivity are reported and discussed which move from the anode to the cathode (atc layers) including as a special case the earlier observed subdomains in the cta layers.Vapour phase grown plate-shaped CdS crystals were Cu doped and contacted with gold (electrode distance 1.5 to 2 mm). The electrooptical method was used as proposed in (5) to make the high field domains visible. The domains could be observed microscopically or detected by a multiplier.The main characteristics of the atc layers and the conditions for the appearance of these layers are the following: a) The atc layers appear above an electric field strength (15 to 20 kV/cm) which is about twice the critical field for appearance of the cta layers. Always several atc layers are observed following each other at nearly the same distance ( LI 0.1 mm). In some crystals 10 to 15 layers move simultaneously. The impression given by atc domains is similar to a moving interference pattern. The boundaries of the atc layers are not as sharp as those of the cta layers. The difference between the maximum and the minimum field strength 1) Guest from the Faculty of physics, University of Sofia.8 physica

A sensitive method for contactless measurements of the electric field strength in CdS (which is applicable for other wide‐gap semiconductors, too) was used to investigate the main parameters of ac high field domains in monocrystalline CdS platelets. The field distribution in the ac domains and the domain velocity were measured in dependence on the intensity of green and infrared (ir) light and on the applied voltage. The occurrence of ac domains under inhomogeneous ir irradiation and double‐injection conditions was observed. The experimental results indicate that holes play an important role in the behaviour of the ac domains.

CdS‐Einkristalle, die in strömender Atmosphäre in Quarzglasrohren nach verschiedenen Verfahrensvarianten gezüchtet worden sind, werden spektralanalytisch in bezug auf Reinheit und durch Ätzen in bezug auf die Konzentration ihrer Baufehler verglichen. Durch Synthese (Cd + H2S, Cd + S2 + H2) hergestellte Kristalle sind im Durchschnitt reiner und an Strukturfehlern mit Dimension >I ärmer als die durch Umsublimation in verschiedenen Trägergasgemischen (N2, N2, + H2, N2 + H2 + H2S, N2 + S2) hergestellten Kristalle. Von den durch Umsublimation gewonnenen Kristallen zeichnen sich die in reinem Stickstoff gezüchteten Kristalle in bezug auf Reinheit und Baufehlerfreiheit aus und ergeben gleiche Werte wie die synthetisierten Kristalle. Die Ergebnisse werden besonders im Hinblick auf den Transport fremder Elemente diskutiert.

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.

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