A. Di Carlo

Wannier-Stark oscillations in Zener tunneling currents

Abstract We have performed measurements of current-voltage characteristics at low temperatures in p-i-n diodes with a thin intrinsic region containing several (GaAs 5 (AlAs) 2 quantum wells. Under reverse bias, we found an oscillatory structure in the second derivative of the Zener tunneling current. The measurements agree well with theoretical calculations that are based on a transfer matrix approach and a realistic multi-band and multi-channel tight-binding scattering theory. The experiments show that Wannier-Stark oscillations in semiconductors occur in the d.c. current, in the regime of interband tunneling.

Charge Screening of Polarization Fields in Nitride Nanostructures

Spontaneous and piezoelectric polarization play a crucial role in nitride-based nanostructures and devices. The effects of polarization fields can, however, be reduced by free and fix charge screening. Optical transition energy, oscillator strength and recombination times are typical physical parameters that crucially depend on the degree of screening of polarization fields. In the following we will review the topic of polarization field screening and we will show how the screening can influence both static and dynamic properties.

Analysis of Quantum-Transport Phenomena in Mesoscopic Systems: A Monte Carlo Approach

A theoretical investigation of quantum-transport phenomena in mesoscopic systems is presented. In particular, a generalization to open systems of the well-known semiconductor Bloch equations is proposed. Compared to the conventional Bloch theory, the presence of spatial boundary conditions manifests itself through self-energy corrections and additional source terms in the kinetic equations, which are solved by means of a generalized Monte Carlo simulation. The proposed numerical approach is applied to the study of quantum-transport phenomena in double-barrier structures.

Stark-ladder transition in a (GaAs)5/(AlAs)2 Zener tunneling diode

Abstract It has been predicted that resonances between Stark-ladder states and the Zener tunneling current gives rise to oscillatory structure in the derivative of the Zener current. In order to clarify the prediction, we carried out measurements in a p-i-n diode whose intrinsic region consists of a very thin superlattice, and observed oscillatory structure in the second derivative of the current. Electroreflectance (ER) measurements in the same structure were carried out to clarify the relation between the oscillatory structure in the Zener tunneling current and Stark-ladders. The results of the ER measurements are in good agreement with the calculated Zener current.

Organic and inorganic nanostructures: An atomistic point of view

Empirical and density-functional tight-binding approaches as well as pseudopotential approaches are applied to the study of organic and inorganic semiconductor nanostructures. We will show how these microscopic methods relax all limitations of simplified approaches based on envelope function approximations, maintaining, at the same time, the computational cost low. Typical calculations for nanostructured devices are shown for both inorganic and organic materials.

Wannier-Stark Resonances in DC Transport and Electrically Driven Bloch Oscillations

Only recently one has been able to realize the pioneering proposal of Esaki and Tsu from 1970 to utilize Bloch oscillations in superlattices as a source for tunable coherent THz emission.1 This has been achieved by using coherent optical excitations of Bloch wave packets in superlattices and experiments indicate that the emission is superradiant.2–4