768 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 195G 



2.2.1 Potential Probes 774 



2.2.2 Use of the Copper Plating Technique 776 



2.3 Under-Formed and Over-Formed Contacts 781 



3. Properties of Unformed Point Contacts 783 



3.1 Physical Properties of Metal -Semiconductor Contacts 783 



3.2 Experimental Procedures 785 



3.3 Experimental Results 786 



3.3.1 Unformed Transistors on Superoxol-Etched Surfaces 786 ' 



3.3.2 Unformed Transistors on CP4-Etched Surfaces 789 



3.3.3 Diode Characteristics on Electro-Etched Surfaces 789 



3.3.4 Output Characteristic Anomalies 789 



3.3.5 Floating Potential Measurements 790 '■ 



3.3.6 Contamination of Collector Points and Surfaces 792 



3.4 Discussion of Experimental Results 794 



3.4.1 Effects of the Chemical Ti-eatment on the Superoxol-Etched 

 Surfaces 794 



3.4.2 CP4-Etched Surfaces 795 : 



4. Relation of Germanium Surface Properties to Transistor Forming 796 



4.1 Pilot Production Problems 796 



4.2 Experimental Results 797 



4.2.1 Pilot Process Forming Yields 797 



4.2.2 Relation of Unformed Diode Characteristics to Transistor 



"Formability " 801 



4.2.3 Controlled Ambient Experiments 804 



4.2.4 A Statistical Survey Experiment on Transistor Forming 805 



4.2.5 Effect of Contamination Before Etching 806 ' 



4.3 Conclusions 807 < 



5. General Concluding Remarks 808 



5.1 Point-Contact Transistors with High Current Gain 809 



5.2 Current Multiplication in Unformed Transistors 809 ' 



5.3 Surface Properties and Transistor Forming 810 , 



1. INTRODUCTION j 



The point-contact transistor, on the basis of several years use in the I 

 field in Bell System applications, has proved itself to be rugged and de- ■ 

 pendable. For certain military applications, a lasting demand exists for 

 high-speed point-contact transistors. The adaptation of cartridge type 

 units to a hermetically sealed structure has been completed, with further 

 benefits to reliability. To date, the point-contact transistor is one of 

 the few transistors to successfully pass all military specifications for 

 shock, vibration, and high acceleration. Thus, although there are at 

 present limitations to the electrical characteristics that can be built 

 into a point-contact transistor which make it unsuitable for use in some 

 switching circuits, there are many applications in which this type of 

 transistor can give consistent and reliable performance. In fact, applica- 

 tions exist w^herein the specific requirements are uniquely satisfied by 

 the point-contact transistor. 



However, the basic operational principles of this kind of device arc 

 not as well understood as would be desirable for facilitating develop- 

 mental studies for manufacture. Although considerable effort has been 



I 



