Phonon-Assisted Tunneling in Silicon and Germanium Esaki Junctions

Phonon cooperation in indirect tunneling transitions in narrow $p-n$ junctions causes structure in the current voltage characteristics at low temperatures. These effects have been studied in silicon and germanium Esaki junctions using special equipment which plots continuously on an $X-Y$ recorder the bias dependence of the current $I$, conductance $G=\left(\frac{\mathrm{dI}}{\mathrm{dV}}\right)$, and $\left(\frac{d^{2}I}{d{V}^2}\right)G^{-2\mathrm{}}$. Twelve phonon and phonon-combination energies have been definitely revealed on the Si junctions and seven in the Ge junctions. Assignments of these energies are given; those for the Si junctions are mostly combinations of the transverse acoustic or optic phonons with intervalley scattering phonons and optic phonons of zero wave number. In the silicon junctions, in addition to the phonon-induced structure, over certain ranges of forward bias there are prominent oscillations in the second derivative curves. The origin of these oscillations is not satisfactorily understood though they have been tentatively ascribed to the Stark splitting of the energy bands in the high electric field of the junction.