Surface sensitivity of rectification

Abstract

The diffusion coefficient of sulphur into PbS, FeS₂ and other sulphide semiconductors has been studied as a function of temperature by employing the etching and light profile microscope techniques. The penetration of sulphur into an n-type crystal brings about various changes in the electrical parameters of the sample. It is possible to obtain by controlled treatment layers, with the requisite carrier concentration for the study of photovoltaic effect and transistor action. It has been possible to observe in PbS photovoltaic effect and transistor action with current gain equal to 0.83 and voltage gain of about 4. With treatment of natural and artificial n-type crystals, a definite improvement in rectifying characteristics has been observed. The slope α of the semilog plot of such treated samples is nearly 40 V^-1 at room temperature as expected by the theory. The slope α is usually found to depend on ∅ which in turn varies from point to point on the crystal surface and from layer to layer in the treated samples. This point-sensitivity as observed on the surfaces of a number of crystals is attributed to the crystal imperfections which terminate on the surface. Similar results have been observed employing a single crystal of germanium grown by Marconi wireless and co. This crystal surface (111) is seen to be covered with a mosaic structure, the figures being hexagonal in shape. These figures can be interpreted as a row or a lattice of dislocations as pointed out by Burgers. The effect of screw dislocations on the electrical properties has been investigated using SiC crystals. An interesting correlation of the effect of dislocation on the rectifying characteristics has been indicated.