268 INSTRUMENTATION IN SCIENTIFIC RESEARCH [Chap. 5 



electrodes, which cause an ohmic contact at the interfaces. The 

 noise spectrum flattens off at low frequencies. 



Photoconductivity caused by exposure to visible light can be re- 

 duced (quenched) by the radiation from a second, infrared light 

 source. Taft and Hebb 1 have shown that the photoconductive cur- 

 rent caused in a cadmium sulfide crystal by a radiation of about 550 

 m/u can be reduced by additional radiation; the quenching effect is 

 largest for an additional radiation of a wavelength of about 820 to 

 1,380 m/A. An explanation of the effect is given in the same paper. 



The physical properties of the most frequently used photoconduc- 

 tors are summarized in Table 15. It is to be noted that the functional 

 relationships between the parameters for the different photoconduc- 

 tors, as well as their physical properties, may change by orders of 

 magnitude in the presence of impurities or vary with the method of 

 processing. The numerical values found by different authors vary 

 widely, therefore. 



Methods for the preparation of photoconductive layers will be 

 found in the reference column on Table 15. 



(1) V. K. Zworykin and G. E. Ramberg, "Photoelectricity," p. 181, John 

 Wiley & Sons, Inc., New York, 1950; (2) P. K. Weimer and A. D. Cope, RCA 

 Rev., 12, 314 (1951); (3) R. Frerichs, Phys. Rev., 72, 594 (1947); (4) S. M. 

 Thomsen and R. H. Bube, Rev. Set. Instr., 26, 664 (1955); (5) R. H. Bube and 

 S. M. Thomsen, J. Chem. Phys., 23, 15 (1955); (6) F. H. Nicoll and B. Kazan, 

 J. Opt. Soc. Am., 45, 647 (1955); (7) R. W. Smith and A. Rose, Phys. Rev., 

 92(A), 857 (1953); (8) A. Von Hippel et al., J. Chem. Phys., 14, 370 (1946); 



(9) A. Von Hippel and E. S. Rittner, J. Chem. Phys., 14, 370 (1946); 



(10) C. W. Hewlett, Oen. Elec. Rev., 50, 22 (April, 1947); (11) R. J. Cashman, 

 OSRD Rept. 5998, October, 1945; (12) L. Sosnowski, J. Starkiewicz, and 

 O. Simpson, Nature, 159, 818 (June, 1947); (13) B. Wolfe, Rev.Sci. Instr., 27, 

 60 (1956); (14) G. K. Teal, J. R. Fisher, and A. W. Treptow, J. Appl. Phys., 

 17, 879 (1946); (15) J. X. Shive, Bell Lab. Record, 28, 337 (1950); (16) S. Ben- 

 zer, Phys. Rev., 72, 1267 (1947); (17) J. N. Shive, Proc. IRE, 40, 1410 (1952); 

 (18) R. P. Chasmar, in R. G. Breckenridge, B. R. Russell, and E. E. Hahn 

 (eds.), "Photoconductivity Conference," John Wiley & Sons, Inc., New York, 

 1956; also G. W. Mahlman, W. B. Nottingham, and J. C. Slater, in R. G. 

 Breckenridge, B. R. Russell, and E. E. Hahn (eds.), "Photoconductivity Con- 

 ference," John Wiley & Sons, Inc., New York, 1956; (19) R. G. Seed, Ger- 

 manium Photosensitive Devices, Bulletin, Transistor Products, Inc., Waltham, 

 Mass.; (20) Manual, RCA Tube Div., Harrison, N.J.; (21) Pamphlet, "Clairex 

 Crystal Photocell," Clairex Corporation, New York. 



For general references on photoconductivity, see R. G. Breckenridge, B. R. 

 Russell, and E. E. Hahn (eds.), "Photoconductivity Conference (Atlantic City, 

 November, 1954)," John Wiley & Sons, Inc., New York, and Chapman and 

 Hall, Ltd., London, 1956; R. C. Jones, "Performance of Visible and Infrared 



1 E. A. Taft and M. H. Hebb, J. Opt. Soc. Am., 42, 249 (1952). 



