P. Weetman

Theoretical modeling of multiple quantum well lasers with tunneling injection and tunneling transport between quantum wells

Multiple quantum well lasers with tunneling transport of carriers represent a new class of semiconductor lasers. Tunneling can be utilized twofold: as an injection mechanism which drives electrons from a separate confinement heterostructure into active well and also as a mechanism facilitating transport between quantum wells. Since tunneling is normally a very fast process, one can expect that employing the tunneling mechanism for transport of electrons can result in an improvement of modulation bandwidth of multiple quantum well semiconductor lasers. This assertion is justified by an analysis based on the rate equation model (analysis of the tunneling injection) and by determining differential gain (to analyze transport between wells). The analysis, done for 0.98 and 1.55 μm semiconductor lasers, suggests that in tunneling injection lasers it is possible to obtain a substantial increase of intrinsic modulation bandwidth. For the tunneling transport between wells it is shown here within a realistic model ...

The effect of well coupling on effective masses in the InGaAsN material system

The effect of well coupling on effective masses for InGaAsN based heterostructures is numerically analysed. The analysis is based on the 10 × 10 Luttinger–Kohn Hamiltonian which couples valence, conduction and nitrogen bands. Our results show that by adjusting the nitrogen composition and/or the barrier width, effective masses can be effectively modified.

Numerical analysis of the effective masses in InGaAsN quantum-well structures with self-consistent effects

A systematic analysis of the electrostatic effects on the effective masses of holes in InyGa1−yAs1−xNx/GaAs quantum-well structures was performed. A 10-band kp Hamiltonian matrix was used in the calculations and solved self-consistently with the Poisson equation. Numerical results have been presented for a large range of material and structural parameters. Our results show that significant variation in the effective masses is possible by adjusting the relevant parameters and that the effects due to self-consistency are small for most subbands.

Wigner function modeling of quantum well semiconductor lasers using classical electromagnetic field coupling

A model of the quantum well laser is formulated using Wigner functions whose evolution is governed by the quantum Boltzmann equations. This model incorporates the heterostructure potential and electromagnetic interactions using a classical field approximation, scattering processes by simple Boltzmann scattering, and spontaneous emission by quantum Langevin theory. The quantum Boltzmann equations are derived from Heisenberg’s equation of motion and then simplified for practical purposes. Calculations are performed for a simplified test system in the steady state in order to illustrate some numerical techniques as well as results that can be obtained. Results shown are for the electron and hole densities and the self-consistent heterostructure potential with and without electromagnetic coupling, the output power versus energy, and the electron and hole currents versus position for two applied bias potentials.

Characterization of effective masses in InGaAsN quantum well structures by computer simulations

Effective masses of holes in In0.36Ga0.64As1−xNx∕GaAs quantum well structures were determined and analyzed. A ten-band k∙p Hamiltonian matrix was used in the calculations. Systematic numerical results have been presented for a large range of material and structural parameters. Our results show that significant variation in the effective masses is possible by adjusting the relevant parameters.

Modeling a Galfenol based stress sensor capable of sensing up to three axial stresses

A three dimensional rate equation model can be used to calculate the magnetization response in a Galfenol sample under the application of any or all components of stress (axial and shear) [P. Weetman and G. Akhras, J. Appl. Phys. 109, 043902 (2011)]. For a Galfenol based stress sensor, one is essentially interested in the inverse of that calculation: from magnetization measurements, determine which stresses are acting on the system. A conceptual design of a Galfenol based three dimensional dynamical sensor is presented. One assumes the time-varying magnetization and its time derivative in all three directions can be measured for different external magnetic bias fields at different points in time. It is shown that the rate equation model can be used to calculate all the stresses acting on the system from knowledge of the magnetization and the time derivative of magnetization. The necessary calculations are presented and then applied to a sample set of magnetization values, which were generated from a bench...

On the differential gain in coupled quantum wells

We have analyzed the combined self-consistent and well coupling effects on differential gain in quantum wells within the self-consistent solution of the Poisson, Schrodinger, and 4×4 Luttinger–Kohn (LK) equations. The many-body effects of band-gap renormalization, Coulombic scattering interactions, and a non-Markovian distribution are also included. The analysis has been performed for a 1.55 μm InGaAsP/InP lattice-matched system grown in the [001] direction. The analysis shows that self-consistent effects significantly affect the differential gain.

Numerical evaluation of effective masses of quantum-well semiconductor lasers based on nitrides systems with self-consistent effects

We analyzed effective masses for InyGa1-yAs1-xNx/GaAs quantum-well structures within self-consistent approach by solving 10-band k.p Hamiltonian matrix with the Poisson equation. Both single well and double well systems were considered. Numerical results have been presented for a large range of material and structural parameters. Our results show that significant variation in the effective masses is possible by adjusting the relevant parameters and that the effects due to self-consistency are small.

Advanced modeling of quantum well semiconductor lasers based on Wigner function approach

We describe the theory and first results obtained from a newly developed advanced model of semiconductor lasers based on Wigner functions. The approach makes it possible to simultaneously analyze spectral and dynamical properties of the laser. It incorporates classical and heterostructure potentials and classical electromagnetic interactions. Some numerical results are presented.