1008 



THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



It is seen that Ohm's law is followed to several times higher velocities with 

 negligible deviations. The deviations should be a factor of 2 at the field 

 corresponding to 



Vd = 6.04c = 3.26 X W cm/sec. (4.2) 



on the Ohm's law Hne. The deviations are actually much less. 



Another important difference between the data and the theory of Section 

 3 is that the experimental points do not continue on a straight Hne with 

 slope 1/2 but instead tend to flatten out with a roughly constant drift 

 velocity. 



20 30 40 



60 80100 200 400 600 1000 



E IN VOLTS PER CENTIMETER 



2000 4000 



10,000 



Fig. 5 — Comparison of E. J. Ryder's experimental data and the statistical theory of 

 Appendix A7. 



Three theoretical curves are shown. These are based on an approximate 

 treatment that includes the effect of the optical transitions. Due to the ap- 

 proximation, the optical modes are neglected below the points marked 

 Op on the Figure. This approximation also leads to a discontinuity in slope 

 at these points; in a more accurate treatment, this bump would be smoothed 

 out. The optical modes play the least role for the curve at 77°K and for this 

 theory fits experiment within experimental accuracy if a value of 



Vdc « 2.6 X 10« cm/sec. 



(4.3) 



