Miniband Transport In Semiconductor Superlattices Research Articles

High-field miniband transport in semiconductor superlattices in a quantizing magnetic field

Miniband transport in semiconductor superlattices in high electric and magnetic fields aligned parallel to the symmetry axis is studied within a quantum-kinetic approach that accounts for intra-collisional field effects of both fields and the heating of the lateral electron motion. Scattering on acoustical and optical phonons as well as impurities is taken into account. Dominating elastic scattering under the condition of strong lifetime broadening and weak screening leads to monotonous current-voltage characteristics. Stark-cyclotron-phonon resonances are strongly enhanced by a magnetic field and are predicted to occur in systems, where the elastic scattering is weak compared with scattering on polar-optical phonons.

High-field miniband transport in semiconductor superlattices under the influence of a transverse magnetic field

The miniband transport in semiconductor superlattices under the influence of high electric and magnetic fields aligned parallel to the superlattice axis is treated within a rigorous quantum-mechanical approach. Intra-collisional field effects due to the electric and magnetic field are taken into account. Pronounced resonances are predicted to occur in the current density due to Landau and Wannier–Stark quantization of the electronic states and due to their scattering on polar-optical phonons. The combined electric and magnetic field effects are treated by a non-equilibrium lateral electron distribution function, which is the solution of a quantum-kinetic equation. The field-dependent coupling between longitudinal and transverse degrees of freedom via the lateral distribution function leads to a non-separable dependence of the current on the electric and magnetic fields. Wannier–Stark current oscillations are strongly enhanced by high magnetic fields. The experimentally detected crossover in the temperature dependence of the current is reproduced. Finally, the influence of an electric field on magneto-phonon resonances is studied.

High-field miniband transport in semiconductor superlattices in parallel electric and magnetic fields

High-field miniband transport in semiconductor superlattices in parallel electric and magnetic fields

Microscopic Theory of High-Field Miniband Transport in Semiconductor Superlattices

A microscopic quantum theory is presented for the high-field miniband transport in semiconductor superlattices. This approach qualitatively reproduces the experimentally detected temperature dependence of the current both in the hopping and band transport regimes. For superlattices with narrow miniband widths the existence of electro-phonon resonance effects is predicted. These resonant-type current anomalies depend strongly on temperature and are more pronounced in a two-dimensional than in a three-dimensional system with a superlattice structure in one direction.

Microscopic theory of high-field miniband transport in semiconductor superlattices

A quantum theory of high-field miniband transport in semiconductor superlattices is developed that is applicable in the electric field range where negative differential conductance appears. The lateral electron distribution function is determined from a quantum kinetic equation, in which intracollisional field effects are included. Scattering on polar optical phonons is taken into account. Unlike the Boltzmann equation approach, our theory reproduces the experimentally detected temperature dependence of the current in both the hopping and band transport regimes. Numerical and analytical results show that at low temperatures the lateral electron distribution function strongly deviates from its equilibrium expression and exhibits sharp edges. For a superlattice with a narrow miniband the existence of electro-phonon resonance effects is predicted. The associated resonant-type current anomalies depend strongly on temperature and are most pronounced at low temperatures.

Miniband transport in semiconductor superlattices in a quantized magnetic field.

Miniband transport of electrons in GaAs-based superlattices under quantized magnetic fields normal to the layers is investigated based on nonparabolic balance equations recently developed. We calculate the drift velocity and electron temperature in both low and high electric fields considering impurity, acoustic, and polar-optic-phonon scatterings. As many as 25 Landau levels are included in the calculation of the frictional accelerations and electron-energy-loss rate. Strong oscillation of linear mobility and drastically different behavior of nonlinear drift velocity versus electric field are exhibited in superlattices with narrow miniband width when polar-optic-phonon scatterings are resonantly enhanced or forbidden due to Landau quantization. The results are in good qualitative agreement with recent experiments.

Electron confinement and oscillatory drift velocity in superlattice miniband transport

Transient drift-velocity response of miniband transport in semiconductor superlattices is analysed using a balance-equation theory. Carrier occupation of transverse subbands and realistic electron-impurity and electron-phonon scatterings are taken into account. We find that thermal excitations of the carrier transverse movement suppress the Bloch oscillation. In a high-electron-density system where carriers are thermalized rapidly in both longitudinal and transverse directions, Bloch-type oscillatory current is unlikely to appear in miniband transport under the influence of a constant electric field.

Effect of elastic scattering on miniband transport in semiconductor superlattices.

Within the quasiclassical Boltzmann-Bloch approach to nonlinear miniband transport in superlattices, elastic scattering is included in a relaxation-time approximation. Elastic scattering makes the problem truly three dimensional and leads in the regime of negative differential conductance to results that are qualitatively different from those of the quasi-one-dimensional models considered previously and compare favorably with recent experiments and balance-equation calculations.

Observation of magnetophonon resonance in the miniband transport in semiconductor superlattices.

We have studied vertical transport of electrons in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As superlattices by applying high magnetic fields normal to the layers. Strong oscillations of magnetophonon resonance are observed in the temperature range between 150 and 300 K, reflecting the singularity of density of states in the superlattice miniband under quantizing magnetic fields. The miniband-width dependence of the resonant spectra is explained by the formation of forbidden gaps between Landau minibands.