Abstracts of Bell System Technical Papers* 

 Not Published in This Journal 



The Ejfcct uf InlwmogvncHivs on llie Klcdrical Properties of Diamond. 

 A. J. Ahearn'. Phijs. Rev., 84, pp. 798-802, Nov. 15, 1951. 



To account for the uoii-unifoiiuitios in the electrical properties of diamond, 

 particulaily those ohservetl in t)onil)ardment conduction, the proposal is made 

 that the well-known lattice imi)erfections are not distributed homogeneously 

 in the physical crystal, and that the resulting fluctuations in the height of the 

 energy bands relati\'e to the Fermi level might produce interspersed "pools of 

 mobile charge" separated by barriers within the diamond. These pools and bar- 

 riers should lead to dielectric losses at high frequencies. A single conducting 

 channel, in series with a barrier, could be represented by a series resistance R, 

 and capacity Cs or by the equivalent parallel resistance Rp and capacity Cj, . 



With some, but not all, diamonds measurable dielectric losses at 70 mc/sec 

 were observed. Rp varied from 5 X 10'' ohms, the limit of measurement, to 

 4 X 10^ ohms. Furthermore, the proposed model suggests that, in some cases, 

 these barriers might l)e sufficiently lowered to establish a dc conducting channel 

 all the way through a crystal. With a few of the lossy diamonds precisely this 

 ])henomenon of "high conduction" has been observed, in which a resistance of 

 the order of a megohm is ol)tained with a dc voltage applied. This current 

 appears abruptly in time but it lags behind the application of the voltage. This 

 lag is influenced by irradiation with light or alpha-i)articles or by previous 

 tieatment. 



The jM'oposed i)ools of mobile charge are a sufficient but not necessary de- 

 scription of the dielectric loss observations, but the high conrluction phenom- 

 enon lends further supi:)ort to this idea of conducting cliannels with barriers in 

 lossy diamonds. Such localized conducting channels would introduce inhomog- 

 eneities into an otherwise uniform electric field applied across an insulator. In 

 bombardment conduction, measurements of counting efficiency could be very 

 sensitive to field inhomogeneities. 



Under alpha-particle bombardment a large variation in counting efficiencj' 

 over the surface of typical diamonds is shown. In a group of 20 diamonds, most 

 of those that exhibited definite losses also had high (>25 per cent) counting 

 efficiencies in some region, and the majority of the remainder had low counting 

 efficiencies. These experiments lend further support to the suggestion that in- 



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