EFFECTIVE BAND-GAP SHRINKAGE IN GAAS

Electrical measurements of the equilibrium np product (n(ie)(2)) in he avily doped n- and p-GaAs were performed. The n(ie)(2)D product (where D is the diffusivity) was measured by fitting the collector current-v oltage characteristic of a homojunction bipolar transistor to an ideal diode equation modifed to account for transport in thin base transist ors. The n(ie)(2) product was then extracted from n(ie)(2) by utilizin g diffusivity results obtained with the zero-field time-of-flight tech nique. Our results show significant effective band-gap shrinkage in he avily doped p-GaAs, and very little effective band-gap shrinkage in he avily doped n-GaAs. At extremely heavy dopings, an effective band-gap widening is observed for both n- and p-GaAs and is attributed to the e ffects of degeneracy.