THE BELL SYSTEM 



TECHNICAL JOURNAL 



VOLUME XXXV NOVEMBER 1956 number 6 



Copyright 1966, American Telephone and Telegraph Company 



Theory of the Swept Intrinsic Structure 



By. W. T. READ, JR. 



(Manuscript received March 4, 1956) 



The electric field and the hole and electron concentrations are found for 

 reverse biased junctions in which one side is either intrinsic (!) or so weakly 

 doped that the space charge of the carriers cannot he neglected. The analysis 

 takes account of spare charge, drift, diffusion and non linear recombination. 

 A number of figures illustrate the penetration of the electric fii eld into a PIN 

 structure with increasing bias for various lengths of the I region. For the 

 junction between a highly doped and a weakly doped region, the reverse cur- 

 rent increases as the square root of the voltage at high voltages; and the space 

 charge in the weakly doped region approaches a constant value that depends 

 on the fixed charge and the intrinsic carrier concentration. 



The mathematics is greatly simplified by expressing the equations in 

 terms of the electric field and the sum of the hole and electron densities. 



i I. INTRODUCTION 



Applications have been suggested for semiconductor structures having 

 j both extrinsic and intrinsic regions. Examples are the "swept intrinsic" 



structure, in which a region of high resistivity is set up by an electric 

 [ field that sweeps out the mobile carriers, and the analogue transistors, 

 ! where the intrinsic region is analogous to the vacuum in a vacuum tube. 



However, the junction between an intrinsic region and an N or P region 



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