Inter-Conduction-Band Transitions in the Electroreflectance Spectrum of InSb

Band-population effects in the surface region of semiconductors facilitate identification of parts of their electroreflectance spectrum. Structure exhibiting a red, a blue, or no shift in response to an increase of the surface potential corresponds to transitions starting from, ending at, or bridging the Fermi level. Using this criterion in $n$-type InSb, structure at 3.1 and 3.5 eV, which shows a red-shift, is assigned to transitions from the populated lowest conduction band ${\Gamma }_{6c}$ to the next-higher bands ${\Gamma }_{7c}$ and ${\Gamma }_{8c}$. In addition, these observations, as well as the observation of complementary structure which we assign to valence-to-conduction-band transitions at or near the $\Gamma$ point, give the separation between ${\Gamma }_{8v}$ and ${\Gamma }_{7c}$ as 3.4 eV.