The effects of degenerate Fermi statistics on electron injection currents for p+‐GaAs grown by molecular beam epitaxy are presented. To achieve Be dopant concentrations of greater than 8×1019 cm−3, the substrate temperature during growth was reduced to approximately 450 °C from the usual 600 °C. In this heavily doped material, we measure unexpectedly large electron injectioncurrents which are interpreted in terms of an effective narrowing of the band gap. At extremely heavy doping densities, the Fermi level pushes into the valence band and degenerate Fermi statistics must be taken into account. For doping concentrations greater than 1×1020 cm−3, effects due to degenerate Fermi statistics oppose the band‐gap shrinkage effects; consequently, a reduction in the electron injection currents is observed. The result is a substantial reduction in gain for AlGaAs/GaAs heterostructure bipolar transistors when the base is doped above 1020 cm−3.


Copyright (1991) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters > Volume 58, Issue 15 and may be found at http//dx.doi.org/10.1063/1.105152. The following article has been submitted to/accepted by Applied Physics Letters. Copyright (1991) E. S. Harmon, M. R. Melloch, M. S. Lundstrom, and M. L. Lovejoy. This article is distributed under a Creative Commons Attribution 3.0 Unported License.

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Applied Physics Letters : Volume 58, Issue 15



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