Probing energy barriers and quantum confined states of buried semiconductor heterostructures with ballistic carrier injection: An experimental study

A three-terminal spectroscopy that probes both subsurface energy barriers and interband optical transitions in a semiconductor heterostructure is demonstrated. A metal-base transistor with a unipolar $p$-type semiconductor collector embedding $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dots (QDs) is studied. Using minority- or majority-carrier injection, ballistic electron emission spectroscopy and its related hot-carrier scattering spectroscopy measure barrier heights of a buried ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ layer in conduction band and valence band, respectively; the band gap of ${\mathrm{Al}}_{0.4}{\mathrm{Ga}}_{0.6}\mathrm{As}$ is therefore determined as $2.037\ifmmode\pm\else\textpm\fi{}0.009\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ at $9\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Under forward collector bias, interband electroluminescence is induced by the injection of minority carriers with sub-band-gap kinetic energies. Three emission peaks from InAs QDs, InAs wetting layer, and GaAs are observed in concert with minority-carrier injection.