Optical and interferometric studies of growth phenomena on carborundum crystals

Abstract

The theory of the growth of a perfect crystal is outlined and a brief description is given of the development of this theory, taking into account the presence of imperfections, especially dislocations, in the crystal. The molecular 'growth spirals' and other features predicted by this theory put forward by Burton, Cabrera and Prank require improved experimental techniques for their study, which are described. The experimental study of the growth features divides itself into two parts: (1) Microscopic studies. (2) Interferometric studies. The different growth features observed on the faces of silicon-carbide (Si-C) crystals are illustrated and explained. The observed 'growth spirals' can be divided into three types: (1) Elementary spirals with step heights equal to the size of the X-ray unit cell. (2) Spirals originating from dislocations of multiple strength, the step heights being a multiple of the X-ray unit cell. (3) Interlaced spirals in which the step heights are a fraction of the unit cell. The microscopic studies illustrate the information about the shape of the spirals, the behaviour and interaction of growth fronts with one another, originating from different sources, the growth pattern for a number of screw dislocations emerging on the crystal face fault surfaces, and their statiscal properties such as density of dis-locations etc. From these studies the type of information obtainable about the conditions of growth is the size of the critical nucleus and the supersaturation. The interferometric techniques utilized for the measurement of step heights are discussed. A study of the measured step heights leads to an understanding of the interesting property of 'polytypism' as observed in silicon-carbide crystals which occur in different types as shown by X-ray diffraction data. The 'growth spirals' demonstrate the X-ray predictions and confirm them.