Negative differential conductance in cleaved edge overgrown surface superlattices AIP Conf. Proc. 772, 900 (2005); 10.1063/1.1994398Negative high-frequency differential conductivity in semiconductor superlatticesWe analyze the transport properties of a semiconductor superlattice in the presence of a biharmonic electric field. The modification of current-voltage characteristics induced by the biharmonic radiation is obtained. The conditions for absolute negative conductivity and for the spontaneous generation of a significant static electric field are determined. We also show that a simple harmonic field can experience nonlinear amplification even when the differential superlattice dc conductivity is positive, and we determine the corresponding range of parameters.

Characteristics of miniband tunneling and Wannier-Stark levels in semiconductor superlattices are studied as regards their dependence on the symmetry of the unit cells and the type of miniband structure. We modify the k ⋅ p method into a k ⋅ v form and on this basis generalize the Zener formula for the inter-band tunneling in homogeneous semiconductors to the case of inter-miniband tunneling in superlattices, account being taken of the inhomogeneity of the electron effective mass. The corresponding sum rule for the effective masses in such structures is obtained. We develop a unified matrix approach for the calculation of the inter-miniband tunneling and Wannier-Stark levels in the case of an arbitrary number of minibands. We study the electric field dependence of the probability of inter-miniband tunneling for an electron transferred through the Brillouin minizone only once. The peculiarities of the inter-miniband transitions for the case where this transfer is repeated are also examined for various unit cells and miniband structures of the superlattice. In addition, we discuss mechanisms and specific features of the resonant Zener tunneling and its manifestations in electron transport.

In the present work, we show that a usually unstable transparent state of a superlattice can be stabilized by a high-frequency biharmonic field with frequencies that are close, but not multiples of one another (with one of the components having sufficiently low amplitude). Furthermore, an incident biharmonic field having multiple frequencies gives rise to an absolute negative conductivity and consequent spontaneous generation of a static field in superlattices for specific phase relations of the harmonics.

The nonlinear oscillations of field and current in semiconductor superlattices excited by terahertz laser radiation are studied within a self-consistent multifrequency internal field approach. We show that the oscillatory character of the nonlinear susceptibilities and dissipative and parametric instabilities in superlattices leads to multivaluedness and hysteresis of their spectral harmonics as functions of the external field amplitude. The key mechanisms of such spectral behavior are the spontaneous generation of a static field and parametric creation and amplification of the external field harmonics and subharmonics. It is shown that the field inside the superlattice cannot be understood in terms of a single frequency, especially for superlattices having high electron concentration.

The phenomenon of transparency in two-dimensional and three-dimensional superlattices is analyzed on the basis of the Boltzmann equation with a collision term encompassing three distinct scattering mechanisms (elastic, inelastic and electron-electron) in terms of three corresponding distinct relaxation times. On this basis, we show that electron heating in the plane perpendicular to the current direction drastically changes the conditions for the occurrence of self-induced transparency in the superlattice. In particular, it leads to an additional modulation of the current amplitudes excited by an applied biharmonic electric field with harmonic components polarized in orthogonal directions. Furthermore, we show that self-induced transparency and dynamic localization are different phenomena with different physical origins, displaced in time from each other, and, in general, they arise at different electric fields. Typeset using REVT E X 1 1