G60 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1956 



e's of pulled Ge crystals by about two orders of magnitude) . The lowest 

 average count that has been observed is 40 pits per cm^ This crystal 

 was found to have the smallest X-Ray rocking-curve widths observed in 

 germanium at Bell Telephone Laboratories — very nearly the the- 

 oretically ideal mdths. The perfection indicated is exceptional — com- 

 parable to that of selected quartz crystals. 



(4) Lifetime of Minority Carriers 



T data are summarized in Fig. 12 in which are plotted averages of the 

 r measurements on the ingot sections against distance from the seed. 

 One sees a systematic rise in t along the length axis of an ingot grown 

 slowly in the after-heater. This is interpreted to indicate that the ingot is 

 being slowly contaminated with chemical recombination centers during 

 its long wait inside the after-heater at high temperatures. If improvement 

 were needed in lifetime, it should be sought first by increasing the chemi- 

 cal cleanliness precautions, which were nonetheless strict in this work. 



SUMMARY 



A zone leveler has been developed to provide growth conditions suit- 

 able for the production of quality germanium single crystals. The crys- 

 tals are nearly uniform and have exceptionally high lattice perfection, jri 

 Similar levelers are in use in production. '' 



The apparatus developed has been used to supply germanium single 

 crystals for experiments and for the pilot production of a variety of point 

 contact, alloy, and diffusion transistors. The machine operating at slow 

 growth rate with an after-heater can produce one 6-inch 250-gm crystal 

 per day. For less critical demands, it can produce several longer crystals 

 per day. 



Evaluation of the product indicates that resistivity variation on a 

 cross-section of the ingot can be ±3 per cent and that along the length 

 axis it can be controlled to ±7 per cent if a continuous charge is used. 

 Furthermore, the crystals contain no grain boundaries or lineage and 

 the scattered etch pit densities average about 1,500 per cm-. Thus, the 

 zone leveling process has proved to be simple, efficient, and capable of 

 more than meeting the present specifications for quality germanium 

 single crystals. 





ACKNOWLEDGMENTS 



i 



The authors arc indebted for the help and cooperation of many people, 

 especially that of L. P. Adda and D. L. Erhart who guided the evaluation 

 of zone leveled material summarized above, and that of F. W. Bergwall 

 through whose patient effort and suggestions the machine worked. 



