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THE BELL SYSTEM TECHXICAL JOURNAL, MARCH 1956 



current is proportional to the equilibrium density of minority carriers 

 (holes). The same conclusion may be drawn from Fig. 4, which shows 

 that the saturation current is higher, the higher the resistivity of the 

 n-type germanium. But the breakdown voltages are variable and usu- 

 ally much lower than one would expect for planar p-n junctions made, 

 for example, by alloying indium into the same n-type germanium. 



Breakdown in bulk junctions is attributed to an avalanche multipli- 

 cation of carriers in high fields.^ The same mechanism may be responsible 

 for breakdown of the germanium-electrolyte barrier; low and variable 

 breakdown voltages may be caused by the pits described below. 



The electrolyte-germanium barrier exhibits a kind of current multi- 

 plication that differs from high-field multiplication in two respects: it 

 occurs at much lower reverse voltages and does not vary much with 

 voltage.^ This effect can be demonstrated very simply by comparison 

 with a metal-germanium barrier, on the assumption that the latter has 

 a current multiplication factor of unity. This assumption is supported 

 by experiments which indicate that current flows almost entirely by 

 hole flow, for good metal-germanium barriers. 



The experimental arrangement is indicated in Fig. 5(a) and (b). The 

 voltage-current curves for an electrolyte barrier and a plated barrier on 

 the same slice of germanium are shown in Fig. 5(c).* The curves for the 



REFERENCE 

 ELECTRODE 



CATHODE 



LIGHT 



Fig. 2 — Arrangement for obtaining voltage current characteristics. 



* In Fig. 5 the dark current for the phited barrier is much hirger than can be 

 exphained on the basis of hole current; it is even higher than the dark current for 

 the electrolyte barrier, which should be at least 1.4 times the hole current. This 

 excess dark current is believed to be leakage at the edges of the plated area and 

 probably does not affect the intrinsic current multiplication of the plated barrier 

 as a whole. 



