Electron-Phonon Interactions in InSb Junctions

Both oxide-coated and vacuum-cleaved InSb tunnel junctions have been prepared from single-crystal material with 7 × ${10}^{13}$ carriers/ ${\mathrm{cm}}^3$. Capacitance measurements at 4.2°K show that the barrier height is approximately the same as the energy gap at that temperature. The differential conductance of the junctions as a function of bias voltage shows at least 30 oscillations with a periodicity equal to the LO phonon energy. These oscillations show a striking resemblance to the oscillatory photoconductivity spectra observed in single-crystal InSb and, in fact, a satisfactory model proposed for the tunnel junctions involves a bulk conductance which changes in an oscillatory fashion due to the same mechanism as in the photoconductivity effect. Structure due to both the LA and TA phonons are observed near zero bias owing to inelastic tunneling processes. Further structure, which is particularly prominent in the vacuum-cleaved junctions, is interpreted as the transfer of carriers into the upper $L_1$ band and this gives an energy of 0.39 ± 0.01 eV between the conduction-band minima of $L_1$ and ${\Gamma }_1$ at the center of the zone.