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Birefringence Method for Examining Semiconductors

IP.com Disclosure Number: IPCOM000088731D
Original Publication Date: 1977-Jul-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 21K

Publishing Venue

IBM

Related People

Matthews, JW: AUTHOR [+2]

Abstract

Dislocations in semiconductors can be studied nondestructively by the birefringence method. The technique can be used to observe dislocations with lines inclined at arbitrary angles to the optical axis of a light micoscope. However, for detailed study of the Burgers vector of a dislocation, it is advantageous to orient the sample so that the dislocation line lies along the optical axis of the microscope. Although this sounds like a simple thing to do, it is often difficult in semiconductors. The reason for this is that they tend to have large refractive indices. This greatly restricts the range of directions in a crystal that can be set parallel to the optical axis. This is illustrated in the figure, which shows a semiconducting crystal with parallel polished surfaces.

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Birefringence Method for Examining Semiconductors

Dislocations in semiconductors can be studied nondestructively by the birefringence method. The technique can be used to observe dislocations with lines inclined at arbitrary angles to the optical axis of a light micoscope. However, for detailed study of the Burgers vector of a dislocation, it is advantageous to orient the sample so that the dislocation line lies along the optical axis of the microscope. Although this sounds like a simple thing to do, it is often difficult in semiconductors. The reason for this is that they tend to have large refractive indices. This greatly restricts the range of directions in a crystal that can be set parallel to the optical axis. This is illustrated in the figure, which shows a semiconducting crystal with parallel polished surfaces.

AA' is a ray drawn through a crystal 10. The relationship between i, r and the refractive index n(s) is sin i over sin r = n(s). The dislocations that can be examined "end-on" must have lines which lie inside the (dotted) cone 11 obtained by setting i = 90 degrees or sin i = 1. The cone 11 is thus defined by sin i = 1 over n(s). If n(s) = 3 (which is typical for semiconductors), then r = 19.5 degrees. Thus, a dislocation can be examined "end-on" only if its line is inclined at less than 19.5 degrees to a line 12 normal to the sample surface 13.

One way of increasing the number of dislocations that can be examined "end-on" is to immerse the sample in...