Phonon-assisted transport in double-barrier resonant-tunneling structures

The dc current in a biased double-barrier resonant-tunneling structure is calculated using a nonequilibrium Green’s-function formalism. Realistic models involving well, barrier, and interface modes are employed to evaluate the phonon-assisted components of the current. The calculated dc current agrees well with experimental data for a GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As resonant-tunneling structure. The observed phonon-replica peak in the I-V characteristics is attributed to the emission of GaAs-confined modes in the well and AlAs-like symmetric interface modes. The effect of the nonequilibrium well-occupation function is shown to be small. For the ${\mathrm{In}}_{\mathit{x}}$ ${\mathrm{Al}}_{1\mathrm{-}\mathit{x}}$As/${\mathrm{In}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As resonant-tunneling structure, phonon scattering becomes comparable to alloy-well scattering at about 200 K.