Bandgap narrowing in silicon bipolar transistors

Martinelli [1] recently reported on measurements of theI-Vcharacteristics of silicon bipolar transistors as a function of temperature. His conclusion was that there was no evidence of bandgap narrowing in the transistors. Our experiments [2] on n-p-n transistors indicate that the bandgap does narrow for impurity concentrations aboveN = 10¹⁷cm-3. The reason for this discrepancy follows from Martinelli's assumption that the temperature dependence of the minority carrier mobility in the p-type base is given by T-2.6, independently of the impurity concentration, which is not justified by our measurements.