DIFFUSED p-> JUNCTION SILICON RECTIFIERS 663 



drop aiul will pass no current for any applied voltage in the reverse 

 direction. At present no device with this characteristic exists. A typical 

 semiconductor rectifier has a characteristic of the type shown in Fig. 

 1(b). In these devices there is a forward voltage, Vo , that must be de- 

 veloped before appreciable current will flow and a series resistance, 

 Rs, thru which the current will flow. In the reverse biased direction 

 there is a current that will flow due to body and surface leakage and 

 that usually increases with reverse voltage. At some given reverse volt- 

 age, Vb, the device will break down and conduct appreciable currents. 

 To have an efficient rectifier, Vo and Rs should be as small as possible 

 and Vb should be as large as can be made; also, the reverse leakage cur- 

 rents should be kept to a minimum. According to semiconductor theory. 

 To depends mainly upon the energy gap of the semiconductor, in- 

 creasing with increasing energy gap. Rs consists of two parts; body re- 

 sistance of the semiconductor and resistance due to the contacts to the 

 semiconductor. The higher the resistivity of the semiconductor, the 

 higher is the body resistance part of Rs ■ The leakage currents in the 

 reverse direction depend to some extent on the energy gap of the semi- 

 conductor, being smaller with larger energy gap; and Vb depends most 

 strongly on the resistivity of the semiconductor, being larger for higher 

 resistivity material. Another factor that is important in the choice of 

 the semiconductor is the ability of devices fabricated from the semi- 

 conductor to operate at high temperatures; high temperature operation 

 of devices improves with larger energy gap semiconductors. Thus there 

 are two compromises to be made in choosing the material (energy gap) 

 and resistivity of the semiconductor. 



1.3 This paper reports on a special class of rectifiers in which im- 

 proved performance has been obtained. These devices are made by 

 using the diffusion technique with silicon. The diffusion process permits 

 both accurate geometric control and low resistance ohmic contacts, 

 which in turn makes it possible to reduce Rs to very small values inde- 

 pendent of the resistivity of the initial silicon. Therefore, high resis- 

 tivity material can be used to obtain high Vb ■ An explanation of this 

 result is given in Section 3. Silicon permits small reverse currents and 

 high temperature operation. Its only drawback is that Fo ^^ 0.6 volts. 

 Rectifiers made of silicon with the diffusion technique are able to pass 

 j hundreds of amperes per square centimeter continuously in the forward 

 ( direction in areas up to 0.4 square centimeter. One type of device whose 

 i area is 0.06 cm- readily conducts ten amperes with less than one volt 

 forward drop. The forward current voltage characteristic of this family 

 of rectifiers follows an almost exponential characteristic indicating that 



