Forbidden energy gaps in semiconductors

To determine forbidden energy gaps in a semiconductor, one can investigate how its electronic conductivity (a) varies with temperature. Semiconductor theory indicates that the logarithm of the conductivity varies linearly with the inverse temperature. The value of the energy gap, Eg, is given by the slope of the In a Vs. 1/T line. Table 5A.4 contains the values of nine runs performed in duplicate with a germanium intrinsic semiconductor. The data were obtained at the Modern Physics Laboratory of the Physics Department of the Londrina State University, under the supervision of Prof. J. Scarminio. 

The fit of a linear model to the data in the table results in the equation 

The two coefficients are highly significant. The constant term represents the value the electronic conductivity would have if there were no energy difference between the highest value of the valence band and the lowest value of the conduction band of the semiconductor. The residual plot (Fig. 5A.6) shows evidence of lack of fit, suggesting that, at least from a statistical point of view, the model could be improved by the inclusion of a quadratic term. This is confirmed by the ANOVA values. However, we must remark that to simplify the experiment the runs were 

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