Studies of electron screening effects on the electron mobility in silicon surface inversion layers |
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Authors: | CC Shiue CT Sah |
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Institution: | Department of Physics and Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA |
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Abstract: | Theoretical calculations of the effects of electron screening of the randomly distributed oxide charges on the electron mobility in surface inversion layers at 4.2 K show that screening substantially enhances the mobility even in weakly inverted surface layer. Surface conductances are measured at 4.2 and 77 K on n-channel MOS transistors with 4 × 1011 ions/cm2. Threshold voltages are obtained by matching the inversion layer conductance versus gate voltage data to the theory. The observed mobility magnitude at 4.2 K is about 2000 cm2/V-s which is in excellent agreement with the theory including screening but without adjustable parameters. A conductance tail of several volts wide below the theoretical threshold voltage and a large positive threshold voltage shift are observed at low temperatures which are attributed to an areal inhomogeneous distribution of fast surface states near the silicon conduction band edge. |
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