Evaporated Hall generators of mercury telluride

Abstract

Analysis of the usefulness of mercury telluride thin-films for preparing Hall generators is made in the paper. Hall generators were obtained by evaporation of solid polycrystalline HgTe on a mica substrate. The temperature of the heater was about 280°C, that of the substrate −10°C. The evaporation process was carried out in a vacuum of 10 −5 torr. Films obtained in such a way were heat treated in the atmosphere of mercury vapours and argon to correct the non-stoichiometry of mercury, that arose due to the partial dissociation of the material. Films with thicknesses between 0·1 and 3 μ were prepared. Strong thickness dependence of the following basic properties of thin-films was found: Hall coefficient ( R H ), resistivity (ρ) and mobility of carriers (μ). For a thickness of 0·1 μ the following mean figures for the above parameters were measured: R H = 15 cm 3/ C, ρ = 7·5 × 10 −2 Ω- cm, μ e = 205 cm 2/ V-sec; for a thickness of 3 μ R H = 12·2 cm 3/ C, ρ = 2·9 × 10 −3 Ω- cm, μ e = 4100 cm 2/ V-sec . All films in temperatures higher than 200°K were of intrinsic conductivity. The main advantage of Hall generators made of mercury telluride is their good mechanical properties, mainly elasticity. Owing to the use of a thin mica substrate the Hall generators could be bent with radius of curvature of about 1 cm. The thickness of Hall generators is limited by the thickness of the substrate and therefore the Hall generators with thickness of mica between 30 and 50 μ were made. Films of HgTe thicker than 3 μ are remarkably less elastic and are easily broken during bending. Because of this reason only films thinner than 3 μ were considered in this paper. On the basis of the HgTe films properties the parameters of the Hall-generators as the function of thickness were determined. These were: sensitivity of Hall generator defining the slope of the static characteristic γ' = ( U yH / I x bdB) (V/A kG), sensitivity defining maximal output voltage of Hall generator γ' = ( U yHmax/ B)( μV/G) and the power coefficient defined as p yH = ( P yH / B 2) for the assumption, that the length to width ratio of Hall-generator is ( a/ b) = 2. The obtained results show that the sensitivity γ varies monotonically from a value of 15 V/A kG for c = 0·1 μ to the value of 0·40 V/kG for c = 3 μ, and the sensitivity γ' changes also monotonically from 49 to 38 μV/Gs respectively (for the assumption of the linearity of the static characteristics). On the other hand the power coefficient p yH varying from 4·1 × 10 −14 to 1·96 × 10 −11 W/ G 2 respectively. Temperature characteristics of resistivity and Hall coefficient show minimum values of coefficients: α = (1/ ρ)(d ρ/d T) and β = (1/ R H )(d R H /d T) for the film thickness about 1·3–1·5 μ. Mean values of these coefficients defined for the above mentioned thickness within the temperature range between 0 and 100°C are as follows: α = −0·04%/° C and β = −0·22%/°C. For extreme thicknesses the coefficients α and β reach the mean values of −0·1 to −0·25%/°C and −0·40 to −0·50%/°C respectively.