van de Tg Theo Roer

Accurate modelling of the accumulation region of a double barrier resonant tunnelling diode

Abstract We have developed a computer program which calculates the electron concentration, potential profile and sub-band energies in the accumulation region of a double barrier resonant tunnelling diode. The calculations employ a local density approximation to calculate the 3D electron density and an expansion in orthogonal functions for the 2D wave functions. The total potential is separated into two parts: one part originating from 2D electrons and the other part due to 3D electrons and doping effects. The numerical profile of the latter part is modelled by a simple analytical function in a satisfactory way even for non-uniform doping profiles. Also, the potential caused by 2D electrons may be written in an appropriate functional form. With the help of both potential models, we are able to build an electron Hamiltonian in which the effects of 2D and 3D electrons, as well as the doping, are taken into account. In this way, the wave functions of the 2D electrons may be obtained semi-analytically by diagonalizing the Hamiltonian and solving Poissons equation to a restricted degree of self-consistency. Tunnelling of electrons through the barrier is taken into account. The routine is combined with an analysis of the tunnelling process and a model for the depletion region to give an accurate description of the current-voltage characteristics of double barrier resonant tunnelling diodes.

Hot electron injection laser: vertically integrated transistor-laser structure for high-speed, low-chirp direct modulation

The first hot electron injection laser (HEL), a vertically integrated transistor-laser structure, is designed to investigate carrier-heating effects on the optical gain and wavelength chirp. Simulations show the potential of carrier-heating assisted gain-switching to directly modulate the optical field intensity at frequencies up to 100 GHz and to decrease the wavelength chirp. Lasing has been observed for the first time now at 70 K, with a threshold current density of about 1.7 kA/cm/sup 2/, from the current AlGaAs-GaAs HEL with InGaAs bulk active layer.

Regenerative pulsations in semiconductor etalon due to competition between carrier generation and heating effects on band filling

Competition between carrier concentration and effective temperature effects on the dielectric function of a degenerate semiconductor in a spectral range near its fundamental absorption edge is suggested as a mechanism for regenerative pulsations in a stationary pumped optical etalon. The origin of self-pulsations is similar to that in a bistable etalon with competing concentration and thermal optical nonlinearities, but, due to its purely electronic nature, the proposed mechanism provides a way for a much higher repetition frequency, probably in the GHz range. The model of the phenomenon and modeling examples are all related to a Fabry–Perot resonator filled with the bulk n+-In0.53Ga0.47As as an active medium.