EFFECTIVE BAND-GAP SHRINKAGE IN GAAS

Electrical measurements of the equilibrium np product (n(ie)(2)) in heavily 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-voltage characteristic of a homojunction bipolar transistor to an ideal diode equation modifed to account for transport in thin base transistors. The n(ie)(2) product was then extracted from n(ie)(2) by utilizing diffusivity results obtained with the zero-field time-of-flight technique. Our results show significant effective band-gap shrinkage in heavily doped p-GaAs, and very little effective band-gap shrinkage in heavily 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 effects of degeneracy.