1292 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 



semi-conductor materials available to the designer. The designability 

 of the major small signal transmission parameters of junction devices 

 is illustrated below by a comparison of calculated and measured charac- 

 teristics of both grown and fused junction devices. 



The characteristics calculated are the theoretical short circuit con- 

 ductances and current transmission ratios (alphas), the current trans- 

 mission three db cutoff frequencies, the collector capacitances, the base 

 region spreading resistances, and the low-frequency values of the "h'^ 

 parameters. The latter are computed because of their ease of measure- 

 ment and interpretation and are compared with measured values. 



5.2 n-p-n Drawn Junction Transistor 



The properties assigned to this unit are believed to be reasonable, 

 but a close check on many of them is very difficult. Base region thickness 

 was chosen as a reasonable value for current practice. The physical 

 structure is that of Fig. 2(a), with the bar cross-section a square 20 

 mils on a side. It should be noted that the assumptions made are con- 

 sistent; e.g., the grading of the collector junction is consistent with 

 the collector and base region resistivities. 



The physical parameters of interest are: 

 Vc Collector voltage, 4.5 volts 

 le Emitter current, — 1 ma 

 w Base thickness (not including depletion layers), 3.6 X 10~^ cm or 



1.41 mil 

 Pb Base resistivity, 1 ohm-cm 

 Tb Electron lifetime in base, 10 n sec 

 Pe Emitter resistivity, 0.01 ohm-cm 

 Te Hole lifetime in emitter, 0.45 m sec 

 pc Collector resistivity, 1.7 ohm-cm 

 Tc Hole lifetime in collector, 30 p. sec 



a Concentration gradient in junctions, 3 X 10^^ atoms/cm* 

 A Junction areas, 0.0025 cm^ 



The parameters of this unit are then 



2 1 



ro c^ = ■ . „^o = 0.992 



Pb 



^ ^ 1 = 1- 0.0072 -- 0.993 



2 Dnrb^ 



