1220 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1956 



shows a sample with aquadag coating and the hnes marking the p-n 

 junction. Under this, three typical fringe patterns obtained on this sam- 

 ple are presented. As pointed out in the beginning, one can regard the 

 fringe pattern as contour lines for the distance between mirror and sam- 

 ple. The profile along any arbitrary straight line will show the structure 

 of the sample surface. The profiles along the marked x-axes are shown 

 to the right in each case. They were obtained by plotting the points of 

 intersection between the n-th fringe and the x-axis against n. The origi- 

 nal surface and the bevel (in this case 1°) are easily recognized. The 

 dashed line is an extrapolation of the original surface. The vertical line 

 marks the position of the p-n junction. The layer thickness is obtained 

 as the difference in n at this point between the extrapolated original 

 surface and the beveled surface. Note that the beveled surface need not 

 necessarily be flat. 



.iii— i**-ir-*^ 



9 



^S^WSIHpwSS? 



jjpl^*.' 



Fig. 11 ^ — Evaluation of the interference fringe pattern of a steep and high step 

 in a surface. 



