Multiband Effective Mass Research Articles

Comparison of light emission in InGaN/GaN light-emitting diodes with graded, triangular, and parabolic quantum-well structures

The light emission properties of InGaN/GaN quantum well (QW) light-emitting diodes with non-square layers with graded, triangular, and parabolic shapes are investigated using multiband effective mass theory. These results are compared with those of conventional InGaN/GaN QW structures. The spontaneous emission peak of non-square QW structures is shown to be improved compared to a conventional QW structure. In particular, the parabolic QW structures shows a slightly larger emission peak than the graded or triangular QW structure. This can be explained by the fact that a smaller In composition in the well is needed to give a transition wavelength of 440 nm.

Optical Properties of Staggered InGaN/InGaN/GaN Quantum-Well Structures with Ga- and N-Faces

Optical properties of staggered InGaN/InGaN/GaN quantum-well (QW) light-emitting diodes with Ga- and N-faces were investigated using the multiband effective mass theory. The staggered QW structure shows that the carrier density dependence of the transition wavelength is largely reduced compared to the conventional QW structure. On the other hand, the heavy-hole effective mass around the topmost valence band is almost unaffected by the polarity. The N-face staggered InGaN/InGaN/GaN QW structure has a greater spontaneous emission peak than the Ga-face staggered InGaN/InGaN/GaN QW structure because the former has a larger matrix element than the latter. We expect the N-face staggered InGaN/InGaN/GaN QW structure to have improved characteristics compared with the Ga-face staggered InGaN/InGaN/GaN QW structure.

광통신용 GaAs 기반 1.3 μm GaAsSb/InGaAs와 GaAsSb/InGaNAs 양자우물 레이저의 광학적특성 시뮬레이션

Optical gain characteristics of type-II GaAsSb/InGaNAs/GaAs trilayer quantum well structures were studied using multi-band effective mass theory. The results were compared with those of GaAsSb/InGaNAs/GaAs trilayer quantum well structures. In the case of GaAsSb/InGaNAs/GaAs trilayer quantum well structure, the energy difference between the first two subbands in the valence band is smaller than that of GaAsSb/InGaNAs/GaAs trilayer quantum well structure. Also, GaAsSb/InGaNAs/GaAs trilayer quantum well structure shows larger optical gain than GaAsSb/InGaNAs/GaAs trilayer quantum well structure. This means that GaAsSb/InGaNAs/GaAs system is promising as long-wavelength optoelectronic devices for optical communication.

Spontaneous emission rate of green strain‐compensated InGaN/InGaN LEDs using InGaN substrate

AbstractOptical properties of strain‐compensated InGaN/InGaN quantum well (QW) structures using a InGaN substrate are investigated using the multiband effective mass theory. These results are compared with those of conventional InGaN/GaN QW structures using a GaN substrate. The strain‐compensated QW structure shows that a smaller well thickness is needed to obtain the transition wavelength of 530 nm than the InGaN/GaN QW structure. The spontaneous emission peak of a strain‐compensated QW structure is shown to be much larger than that of a conventional QW structure. This is mainly attributed to the fact that the internal field is reduced due to the decrease in the lattice mismatch with a substrate.

Enhancement of light power for strain-compensated hybrid InGaN/InGaN/MgZnO light-emitting diodes

Electronic and optical properties of strain-compensated InGaN/InGaN/MgZnO quantum well (QW) structures using a MgZnO substrate are investigated using the multiband effective mass theory. A strain-compensated InGaN/InGaN/MgZnO QW structure with a larger strain shows larger matrix element than that with a smaller strain. The spontaneous emission peak rapidly increases with increasing compressive strain because the matrix element is enhanced for the strain-compensated QW structure with a larger strain. In addition, we find that the strain-compensated QW structure with the larger Mg composition in the substrate has greater spontaneous emission peak than the strain-compensated QW structure with the smaller Mg composition in the substrate.

Statistical fluctuation of magnetization in Mn-composition modulated Cd1−xMnxTe quantum wires

We have theoretically studied the emission-line width in Mn-composition modulated Cd1−xMnxTe quantum wires by using the multiband effective mass theory and fluctuation-dissipation theorem. The calculated emission-line width exhibits a broadening because of a statistical fluctuation in the magnetization of Mn spins in the exciton magnetic polaron. The line width is sensitive to both the temperature and the magnetic field in the Voigt configuration, which exhibits remarkable anisotropy depending on the external magnetic field direction. The anisotropic behavior is a typical feature of the one-dimensional system resulting from heavy-hole and light-hole mixing.

Optical gain improvement in type-II InGaN/GaNSb/GaN quantum well structures composed of InGaN/and GaNSb layers

Optical gain characteristics of type-II InGaN/GaNSb quantum well (QW) structure are investigated by using the multiband effective mass theory. These results are compared with those of conventional InGaN/GaN QW structures. The transition wavelength rapidly increases with increasing the Sb composition in GaNSb layer while it is less sensitive to the In composition in InGaN layer. Hence, longer wavelength QW structures with a relatively lower In composition can be easily obtained by controlling Sb composition, compared to the conventional type-I InGaN/GaN QW structures. The optical gain and the differential gain (dg/dn) of a type-II QW structure are shown to be much larger than that of a conventional QW structure in an investigated range of carrier densities. This is due to the reduction in the effective well width, in addition to the increase in the optical matrix element.

Optical properties of type-II InGaN/GaAsN/GaN quantum wells

Optical properties of type-II InGaN/GaNAs QW light-emitting diodes are investigated by using the multiband effective mass theory. These results are compared with those of conventional InGaN/GaN QW structures. The type-II InGaN/GaNAs/GaN QW structure shows much larger spontaneous emission and optical gain than that of a conventional QW structure. This can be explained by the fact that, in the case of the type-II QW structure, the effective well width is greatly reduced. A type-II QW structure shows that the peak position at a high carrier density is similar to that (530 nm) at a low carrier density. On the other hand, in the case of a conventional QW structure, the peak position is largely blueshifted at a high carrier density.

FINITE ELEMENT ANALYSIS OF VALENCE BAND STRUCTURE OF SQUARE QUANTUM WELL UNDER THE ELECTRIC FIELD

Valence band structure with spin–orbit (SO) coupling of GaAs/Ga 1-x Al x As square quantum well (SQW) under the electric field by a calculation procedure based on a finite element method (FEM) is investigated using the multiband effective mass theory ([Formula: see text] method). The validity of the method is confirmed with the results of D. Ahn, S. L. Chuang and Y. C. Chang (J. Appl. Phys.64 (1998) 4056), who calculated valence band structure, using axial approximation for Luttinger–Kohn Hamiltonian and finite difference method. Our results demonstrated that SO coupling and electric field have significant effects on the valence band structure.

Investigation of Auger recombination in Ge and Si nanocrystals embedded in SiO 2 matrix

We study theoretically the optical properties of embedded Ge and Si nanocrystals (NCs) in wide band-gap matrix and compared the obtained results for both NCs embedded in SiO 2 matrix. We calculate the ground and excited electron and hole levels in both Ge and Si nanocrystals (quantum dots) in a multiband effective mass approximation. We use the envelope function approximation taking into account the elliptic symmetry of the bottom of the conduction band and the complex structure of the top of the valence band in both Si and Ge (NCs). The Auger recombination (AR) in both nanocrystals is thoroughly investigated. The excited electron (EE), excited hole (EH) and biexciton AR types are considered. The Auger recombination (AR) lifetime in both NCs has been estimated and compared.

Magnetoexciton in semiconductor concentric double rings

We investigate theoretically the magnetoexciton states in semiconductor concentric quantum double rings using the multi-band effective mass theory. We find that a perpendicular magnetic field can lead to oscillations in the exciton energy which appear as kinks in the magneto-photoluminescence (PL) spectra as the magnetic field increases. The spatial distribution of the exciton over the rings depends sensitively on the thicknesses of the inner and outer rings. The tunneling coupling between the inner and outer rings and the heavy-hole and light-hole mixing results in different anticrossing behaviors. Exciton can be converted into a spatially separated type-II exciton by tuning the thickness, the inner and/or outer ring radius and the magnetic field. We show that this type I–type II transition is reflected in the oscillator strength of the PL spectrum which will be the experimental signature that will provide us with information about the spatial distribution of the exciton.

Multiband simulation of quantum transport in nanoscale double-gate MOSFETs

We have investigated quantum electron transport in nanoscale double-gate MOSFETs using the multiband structure model for Si and the non-equilibrium Green function method. To obtain an accurate and realistic Si band structure, the empirical sp 3 s * tight-binding model including nearest and second-nearest neighbor coupling has been adopted. Especially, the dependence of the difference between the drain currents calculated from the present multiband and conventional effective mass models on the silicon layer thickness ( t Si) has been examined. As t Si decreases below 3 nm, the current calculated from the multiband model becomes lower than that based on the effective mass model, and the difference between both currents increases. On the other hand, as t Si increases above 3 nm, the current from multiband structure calculations turns high compared to the current from effective mass calculations.

Anisotropic linear-polarization luminescence in CdTe/CdMnTe quantum wires

We theoretically studied anisotropic linear optical polarization properties in CdTe / Cd 0.75 Mn 0.25 Te quantum wires (QWRs) by using the multi-band effective mass method. In this QWR system, the spatial distribution of the Mn composition influences both the lateral quantum confinement and the sp– d exchange coupling. The calculated expectation value of the hole spin demonstrates that the hole spin is reoriented along the external magnetic field when applying the magnetic field parallel to the QWR. The hole-spin reorientation causes anisotropic behavior in the Zeeman shift and the linearly polarized optical transitions, which sensitively depends on the Mn spatial distribution. Such characteristic features appeared in the QWR have been demonstrated experimentally and compared with the theoretical calculations.

High-efficiency staggered 530 nm InGaN/InGaN/GaN quantum-well light-emitting diodes

Optical properties of staggered 530 nm InGaN/InGaN/GaN quantum-well (QW) light-emitting-diodes are investigated using the multiband effective mass theory. These results are compared with those of conventional 530 nm InGaN/GaN QW structures. A staggered InGaN/InGaN/GaN QW structure is shown to have much larger spontaneous emission than a conventional InGaN/GaN QW structure. This can be explained by the fact that a staggered QW structure has much larger matrix element than a conventional QW structure because a spatial separation between electron and hole wave functions is substantially reduced with the inclusion of a staggered InGaN layer. A staggered QW structure shows that the peak position at a high carrier density (530 nm) is similar to that at a noninjection level.

Spurious Solutions in the Multiband Effective Mass Theory Applied to Low Dimensional Nanostructures

Spurious Solutions in the Multiband Effective Mass Theory Applied to Low Dimensional Nanostructures

Auger recombination in silicon nanocrystals embedded in SiO2 wide band‐gap lattice

AbstractWe calculate the ground and excited electron and hole levels in spherical Si nanocrystals (quantum dots) embedded within SiO2 in a multiband effective mass approximation. The obtained energies of electron and hole are used to estimate the Auger Recombination (AR) lifetime in Si Nanocrystals (NCs). The excited electron, excited hole and biexciton AR types are considered. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electronic and optical properties of 530 nm strain-compensated hybrid InGaN/InGaN/ZnO quantum well light-emitting diodes

Electronic and optical properties of 530 nm strain-compensated hybrid InGaN/InGaN/ZnO quantum well (QW) light-emitting diodes (LEDs) using a ZnO substrate are investigated using the multiband effective mass theory. These results are compared to those of conventional InGaN/GaN QW LEDs using a GaN substrate. A strain-compensated QW structure is found to have much larger spontaneous emission than an InGaN/GaN QW structure. This can be explained by the fact that a strain-compensated QW structure has much larger matrix element than an InGaN/GaN QW structure due to the reduction in the internal field.

Single-particle states in sphericalSi∕SiO2quantum dots

We calculate the ground and excited electron and hole levels in spherical Si quantum dots inside $\mathrm{Si}{\mathrm{O}}_{2}$ in a multiband effective mass approximation. The Luttinger Hamiltonian is used for holes, and the strong anisotropy of the conduction electron effective mass in Si is taken into account. As the boundary conditions for the electron and hole wave functions, we use the continuity of the wave functions and the flux at the boundaries of the quantum dots.

Optical gain of 1.3 µm GaAsSbN/GaAs quantum well lasers

Optical gain of 1.3 µm GaAsSbN/GaAs quantum well (QW) structure is investigated using the multiband effective mass theory. The results are compared with those of 1.3 µm InGaNAs/GaAs and GaAsSb/GaAs QW structures. The optical gain of the GaAsSbN/GaAs QW structure is found to be similar to that of the InGaAsN/GaAs QW structure. In contrast, GaAsSbN/GaAs and InGaNAs/GaAs QW structures show significantly larger optical gain than the GaAsSb/GaAs QW structure. This is mainly attributed to the fact that the former has a larger optical matrix element than the latter. In addition, GaAsSbN/GaAs and InGaNAs/GaAs QW structures have much smaller threshold current density than the GaAsSb/GaAs QW structure. This is because the Auger recombination current density gives dominant contribution to the threshold current density and the former has smaller threshold carrier density than the latter. On the contrary, the threshold current density of the GaAsSbN/GaAs QW structure is shown to be similar to that of the InGaAsN/GaAs QW structure.

Effect of In-segregation on subbands in GaInNAs/GaAs quantum wells emission around 1.3 and 1.55 micron

The effect of In-segregation on optical properties in 7.5-nm GaInNAs/GaAs single quantum well (QW) is studied theoretically. The nominal (In, N) contents in the QW are chosen to be (0.35, 0.015) and (0.39, 0.03) for the emission wavelengths around 1.3 and 1.55 μm, respectively. Muraki’s model is used to model the composition profiles in the QWs. In-plane strain, confinement potential, and subband energy levels of the QW are calculated using multi-band effective mass theory. We show a space-indirect transition between light holes localized in indium deficient region and electrons localized in indium rich region of the quantum well. Our results show that the optical transition energies are approximately constant for the segregation efficiencies smaller than 0.7 in both QWs.