The Forward Characteristic of the PIN 



Diode 



By D. A. KLEINMAN 



(Manuscript received January 18, 1956) 



A theory is given for the forward current-voltage characteristic of the PIN 

 diffused junction silicon diode. The theory predicts that the device should 

 obey a simple PN diode characteristic until the current density approaches 

 200 amp /cm?. At higher currents an additional potential drop occurs across 

 the middle region proportional to the square root of the current. A moderate 

 ' amount of recomhiriation in the middle region has little effect on the charac- 

 teristic. It is shown that the middle region cannot lead to anomalous char- 

 acteristics at low currents. 

 t 



INTRODUCTION 



In some diode applications it is desirable to have a very low ohmic re- 

 sistance as well as a high reverse breakdown voltage. A device meeting 

 these requirements, in which the resistance is low because of heavily 

 doped P"^ and A^"^ contacts and the breakdown \'oltage is high because 

 of a lightly doped layer between the contacts, has been described by 

 M. B. Prince. The device is shown schematically in Figure la and con- 

 sists of three regions, the P^ contact, the middle P layer, and the A'"'' 

 contact. The device is called a PIN diode because the density P of un- 

 compensated acceptors in the middle region is much less than P"*" or iV"*" 

 and in normal forward operation much less than the injected carrier 

 density.^ 



We shall let the edge of the P^P junction in the middle region be 

 oj = 0, and the edge of the PN^ junction in the middle region be x = w. 

 Thus the region ^ .r ^ w is space charge neutral and bounded at each 

 end by space charge regions whose width is of the order of the Debye 

 length 



1 Prince, M. R., Diffused p-?i .Junction Silicon Rectifiers, B.S.T.,J., page 661 

 of this issue. 



^ A device witli similar geometry has been discussed by R. N. Hall, Proc. 

 I.R.r:., 40, p. 1512, 1952. 



685 



