Electrical Properties of Eyaporated Single-Crystal Thin Films of n-Type PbTe

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Hall coefficient and resistivity measurements were made on n-type PbTe thin films in the temperature range from 77 to 400°K. The evaporants were n-type materials (A: 3×10^<18> and B: >1×10^<19> carriers/cm^8). The deposition rate was about 1μ/min. The film thickness, measured by weighing, ranged from 1.5 to 2.5μ. The films were evaporated in "bridge" shape. and electrical contacts were formed by welding indium. The electrical measurements were carried out with the samples kept in a vacuum system. Fig. 1 shows the temperature dependence of the Hall coefficient. The symbols A and B indicate the kind of the evaporants and the numbers are the substrate temperatures in ℃. The behaviors of the Hall coefficient were the same as those in bulk material. but abnormal temperature dependences of the Hall coefficient were sometimes observed in the films made from the evaporant A at substrate temperatures below 25O℃. Fig. 2 shows the resistivity vs reciprocal ternperature. The values of the resistivity at room temperature were about twice as large as those for bulk crystal. The rates of decreasing in the resistivity with falling temperature were in most cases smaller than those for bulk material. Fig. 3 contains a log-log plot of the Hall mobility data vs reciprocal temperature for typical samples. Our mobility curves are a little convex upward in the entire temperature range investigated: the average slope was 2.2 above 200°K and 1.43 below 200°K. This deviation from the T^<-5/2> temperature dependence of mobility in the lower temperature range may be due to the scattering of carriers by impurities of defects rather than the surface scattering limiting conductivity in very thin films. This seems reasonable, because the ratio of the film thickness to the mean free path in our samples is rather large at 77°K (about 6.7 for A-28). On the basis of the above results, a large amount of impurities which sticks into films from residual gases duringe evaporation are thought to have large influence on the conductivity. For example, at the pressure of 10^<-6> mmHg of oxygen, the maximum oxygen content is calculated to be about 1% in a film deposited at a rate of 1μ/mim at substrate temperature 300℃. Therefore films with higher conductivity may be cbtained by reducing pressures of residual gases.
社団法人日本物理学会の論文
1964-07-05

Electrical Properties of Eyaporated Single-Crystal Thin Films of n-Type PbTe

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