Klaus Schuenemann

A comparison between different numerical methods used to solve Poisson’s and Schroedinger’s equations in semiconductor heterostructures

A comparison between different numerical methods which are used to solve Poisson’s and Schroedinger’s equations in semiconductor heterostructures is presented. Considering Schroedinger’s equation, both the Rayleigh–Ritz method and the finite difference method are examined. The accuracy and the computational speed are investigated as a function of both the mesh size and the number of Rayleigh–Ritz functions and the numerical results are compared with analytical solutions for special cases. To solve Poisson’s equation, direct and iterative methods are implemented and the advantages and limitations of each method are discussed. The previous methods are used to solve Poisson’s and Schroedinger’s equations self‐consistently in typical heterostructures to obtain the wave functions, the carrier distribution, and the subband energies.

Influence of background plasma on electromagnetic properties of "Cold" gyrotron cavity

A simple approximate theory of background plasma influence on the electromagnetic properties of high-power gyrotron cavities is presented. It is shown that a background plasma slightly reduces the operational frequency of gyrotrons, increases the quality factors of operational and neighbouring modes, and modifies the longitudinal field distribution in the gyrotron cavity. The calculated downshift of the operational frequency is compared with long-pulse measurements performed in 140-GHz 1-MW continuous wave gyrotron experiments at Forschungszentrum Karlsruhe

An efficient and accurate self-consistent calculation of electronic states in modulation doped heterostructures

Abstract The energy levels, the carrier concentration, and the conduction band profile in a modulation doped heterostructure are obtained by using an efficient self-consistent calculation of Poissons and Schroedingers equations. Schroedingers equation is solved by using a variational technique to overcome the limitations of previous models which are arising from mesh size and discretization. The method is applied to characterize a modulation doped AlGaAs/GaAs single well and a pseudomorphic AlGaAs/InGaAs/GaAs structure. Advantages and limitations of the new method are finally discussed.

Closed-form calculations of two-dimensional scattering rates in semiconductor heterostructures

Abstract An efficient and accurate method is investigated to characterize the electron transport in a two-dimensional modulation doped heterostructure. Schroedingers equation is solved by using a variational method to obtain the wave functions in closed form. The subband energies, the corresponding wave functions and the carrier concentration are obtained by solving Poissons and Schroedingers equations self-consistently. The closed form of the wave functions is then used to calculate the important two-dimensional scattering rates. In order to illustrate the efficiency and the accuracy of our model, the results are compared with those obtained from the conventional self-consistent finite difference scheme. The present model is proved to be more efficient and less complicated when used in material and device characterization.

Linear theory of electron cyclotron instability of electromagnetic waves in a magnetoactive plasma waveguide

The linear stage of electron cyclotron instability of quasi-TE modes in a waveguide filled with a magnetoactive plasma is studied using a kinetic approach. The dispersion relation of the instability is derived analytically. It is shown that the presence of the plasma can reduce both the linear instability growth rate and the instability region; in this case, the maximum of the growth rate is displaced toward lower frequencies. The results obtained are compared with the available experimental observations. They can be useful for optimizing the operating regimes of high-power continuous-wave gyrotrons.

Influence of Background Plasma on Operation Efficiency of High-Power CW Gyrotrons

A slow wave non-linear single mode stationary theory describing influence of background plasma which occurs in the gyrotron cavity on gyrotron operation has been developed. It is shown that the main effects of a low density background plasma on efficiency are concerned with decreasing the mismatch between operational and cyclotron frequencies and decreasing the beam-wave coupling coefficient. Numerical calculations are performed for the 140 GHz 1 MW CW gyrotron developed in Karlsruhe for fusion applications. Interpretation of some experimental effects which are not yet clearly understood is addressed.

A Rigorous Model of Tunneling and Thermionic Currents in Microwave HFETs

A new model is presented to simultaneously calculate both tunneling and thermionic currents over the heterojunction and over the Schottky barrier (metal-semiconductor contact). The energy band diagram, the subband energies, and the corresponding wave functions are obtained by self-consistent solution of Poissons and Schroedingers equations (SCSPS). The differences between the quasi Fermi levels at the heterojunction and at the metal contact which control the currents are accurately obtained by equating the total current over the heterojunction with the total current over the Schottky barrier. The model is applied to calculate the gate current in typical hetero-FET structures and the obtained results are compared with experimental data.

Noise and Transfer Properties of Harmonically Synchronized Oscillators

A theoretical model of a harmonically synchronized oscillator is developed and verified experimentally. Using this model output power, stability conditions, noise and transfer properties of a harmonic frequency divider are calculated and discussed.

Dispersion properties of a magnetoactive plasma-filled waveguide in the vicinity of the upper hybrid frequency. Part II

The dispersion properties of a magnetoactive plasma-filled waveguide in the vicinity of the upper hybrid frequency ω1 = (ωp2 + ωB2)1/2 (ω1 ≤ ω < ω1 + δ) are studied. In this frequency range, the eigenfrequency spectrum and the structure of the waveguide eigenfields are difficult to analyze, because one of the transverse wavenumbers tends to infinity as the upper hybrid frequency is approached. It is shown that this problem can be solved by transforming the dispersion relation into a form independent of this transverse wavenumber. It is also found that the upper hybrid frequency itself can also be a solution to the dispersion relation. The influence of the properties of the magnetoactive plasma-filled waveguide on such solutions is studied. The structure of the fields for modes with frequencies equal to the upper hybrid frequency and an infinitely large absolute value of one of the transverse wavenumbers is analyzed.

Dual-mode elliptic-function triangular-patch bandpass filters using capacitive-coupling slot technique

A new triangular-patch bandpass filter (BPF) using a pair of V-shape slots is presented in this paper. The pair of the V-shape slots can provide capacitive coupling which produces a dual-mode elliptic-function response. A theoretical analysis of capacitive-coupling characteristics of the dual-mode BPF with different slot dimensions is presented. Also, a set of simple equations is developed to determine the dimensions of the triangular-patch resonator based on the resonant frequency, F0. Finally, measured results are given which demonstrate the validity of the proposed design method.