CONDUCTIVITY-MODULATED SILICON RECTIFIER 987 



D = diffusion constant = 3 X 10~ " cm /sec, 



/ = diffusion time = 5.7 X 10 sec, 



Xj = junction depth below surface = 0.003 cm. 



When these numbers are substituted into the equations, at 300° K: 



W = 9.25 X 10"'(0.792 - Vf'^ cm. (4-6) 



For the diodes under consideration : 



r„c = 1.2 X 10"' sec, r^o = 0.4 X 10"' sec. 



When these expressions are substituted into (4-2) , one obtains at 300° C : 



T oo v/ in-7 sinh 19.31 F ,2 /, ^.^ 



/.e = 2.8 X 10 ^Q ..^2 - Vyi^ amp/cm . (4-/) 



In order to fit the experimental data, it is necessary to multiply (4-7) 

 b}^ a factor of 5. This may be due to an overestimation of (r„oTpo)'- There- 

 fore, the eciuation which shall be used in the remainder of tliis section 

 Avill be: 



T 1 t w in-6 si"l^ 19.31 F , 2 (. ON 



he = 1.4 X 10 ^ojQ2 - Vyi^ amp/cm . (4-8) 



A plot of this expression is given in Fig. 6. 



The normal diffusion current for low level diffusion, /dl , is given by 



/dl = h{e'''"' - 1) (4-9) 



where U is given by (2-1). /o for the diodes under discussion is approxi- 

 mately 8 X 10"'^ ampere/cm" at 300° K. ^\Tien the injected minority 

 carrier densit}^ approaches the equilibrium majority carrier density, the 

 form of (4-9) changes. The high injection level diffusion current, /dh , 

 is then given by 



/dh = /DHo(e^"^''" - 1), (4-10) 



where /dho equals qnis/r, and s eciuals the A\'idth of the high resistivity 

 region. For the diodes under discussion, /dho is approximately 2 X 10" 

 amperes/cm at 300° K. A current-voltage plot of these currents at 

 300° K for Vr = 0.50 is given in Fig. 6 together with their sum. It can 

 be observed that the resulting characteristic starts with slope of qV/kT 

 and bends over to a slope of qV/2kT near 0.10 volt. The slope increases 

 again to near qV/kT at 0.35 volts and decreases once more to qV/2kT 

 above 0.40 volts giving a bump to the over-all characteristic. 



