non-Markovian Gain Research Articles

Linewidth enhancement factor of type-II red InGaN/GaNSb/GaN quantum-well lasers

We investigate the linewidth enhancement factor of the type-II red InGaN/GaNSb/GaN quantum-well (QW) laser, employing a non-Markovian gain model with many-body effects included. It is shown that the linewidth enhancement factor of the type-II red InGaN/GaNSb/GaN QW structure is almost independent of the peak-gain coefficient. This behavior is contrasted with that of the conventional type-I InGaN/GaN QW structure, whose linewidth enhancement factor increases as the peak-gain coefficient increases. These results can be explained by the peak-gain dependencies of the differential refractive-index change and the differential gain. Moreover, the type-II red InGaN/GaNSb/GaN QW laser yields much smaller values of the linewidth enhancement factor than the conventional type-I InGaN/GaN QW laser. The type-II red InGaN/GaNSb/GaN QW laser with a relatively small, excitation-independent linewidth enhancement factor is expected to be highly useful for many practical applications.

Linewidth enhancement factor of hybrid green InGaN/MgZnO quantum well structures

Abstract The linewidth enhancement factor of wurtzite (WZ) hybrid green InGaN/MgZnO quantum well (QW) lasers with zero internal field was investigated theoretically by using a non-Markovian gain model with many-body effects. These results are compared with those for WZ conventional InGaN/GaN QW structures. For both QW structures, the linewidth enhancement factor gradually increases with increasing peak-gain coefficient. On the other hand, the InGaN/MgZnO QW structure shows a lower linewidth enhancement factor than a conventional InGaN/GaN QW structure. This can be explained by the fact that the optical matrix elements for the InGaN/MgZnO QW structure are significantly enhanced in comparison with the optical matrix elements for the conventional InGaN/GaN QW structure due to the disappearance of the internal field.

Optimizing Non-Markovian Information Gain Under Physics-Based Communication Constraints

In many exploration scenarios, it is important for robots to efficiently explore new areas and constantly communicate results. Mobile robots inherently couple motion and network topology due to the effects of position on wireless propagation-e.g. distance or obstacles between network nodes. Information gain is a useful measure of exploration. However, finding paths that maximize information gain while preserving communication is challenging due to the non-Markovian nature of information gain, discontinuities in network topology, and zero-reward local optima. We address these challenges through an optimization and sampling-based algorithm. Our algorithm scales to 50% more robots and obtains 2-5 times more information relative to path cost compared to baseline planning approaches.

ZnCdSe/ZnSe quantum-dot semiconductor optical amplifiers

Gain of CdZnSe quantum dot (QD) semiconductor optical amplifiers (SOAs) is studied theoretically using non-Markovian gain model including many-body effects. The calculations are done at three mole fractions. Spontaneous emission and noise figure of the amplifier are studied. The effect of shot noise is included. High gain, polarization independence, and low noise figure are characterize these QD-SOAs. A multi-mode gain appears for Zn0.69Cd0.31Se structure while the structure Zn0.6Cd0.4Se give a low noise.

Effects of AlGaN delta-layer insertion on light emission characteristics of ultraviolet AlGaN/AlN quantum well structures

The light emission characteristics of ultraviolet (UV) AlGaN/AlN quantum well (QW) structures with the AlGaN delta-layer in the active region were investigated using the multiband effective-mass theory and non-Markovian gain model. In a wavelength range of 220–280 nm, AlGaN/AlN QW structures with the ultrathin AlGaN layer are shown to have much larger light emission than conventional AlGaN/AlN QW structures. This can be explained by the fact that the internal field in the well is reduced and the optical matrix element is greatly enhanced with the inclusion of the low-bandgap AlGaN delta-layer. We expect that AlGaN/AlN QW structures with the ultrathin AlGaN layer can be used as a light source with a high efficiency in UV region.

Optical Gain Characteristics in GaAsPN/GaPN Quantum Well Lasers for Silicon Integration

Optical gain characteristics of strain-compensated GaAsPN/GaPN quantum wells (QWs) with the GaPN barrier under 1.0 % tensile strain were investigated using the multiband effective-mass theory and the non-Markovian gain model. The transition energy linearly increases from 1.12 to 1.22 eV when P content ratio changes from 0.1 to 0.4. The theoretical transition energy reasonably agrees with the experiment. The Coulomb enhancement ratio, g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">many</sub> /g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">free</sub> , decreases with increasing compressive strain because the average hole effective mass decreases with increasing strain. As a result, the QW structure with a smaller compressive strain has larger optical gain than that with a larger compressive strain for higher carrier densities. On the other hand, in the case of smaller carrier densities, the QW structure with a larger compressive strain shows larger optical gain than that with a smaller compressive strain because the former has larger optical matrix element producted by Kane's parameter and quasi-Fermi level separation than the latter. The absolute value of the bandgap renormalization increases with increasing carrier density and is about 99 meV at 5×10 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , which is slightly larger than that of GaAs-based or InP-based QW structures.

Many-body effects on optical gain in GaAsPN/GaPN quantum well lasers for silicon integration

Many-body effects on the optical gain in GaAsPN/GaP QW structures were investigated by using the multiband effective-mass theory and the non-Markovian gain model with many-body effects. The free-carrier model shows that the optical gain peak slightly increases with increasing N composition. In addition, the QW structure with a larger As composition shows a larger optical gain than that with a smaller As composition. On the other hand, in the case of the many-body model, the optical gain peak decreases with increasing N composition. Also, the QW structure with a smaller As composition is observed to have a larger optical gain than that with a larger As composition. This can be explained by the fact that the QW structure with a smaller As or N composition shows a larger Coulomb enhancement effect than that with a larger As or N composition. This means that it is important to consider the many-body effect in obtaining guidelines for device design issues.

Large optical gain characteristics of tensile-strained 440-nm InGaN/AlInN quantum well structures

The optical gain characteristics of tensile-strained InGaN/AlInN QW structures are investigated as a function of the In composition in the well by using the non-Markovian gain model with manybody effects. The internal field decreases with increasing In composition in the well and becomes zero at some critical In compositions. The optical gain decreases with increasing In composition when the In composition exceeds 0.08 for the InGaN/Al0.6In0.4N QW structure because the quasi-Fermi level separation decreases with increasing In composition. The optical gain peak of the InGaN/AlInN QW structure with a transition wavelength of 440 nm is shown to be much larger than that of the conventional 440-nm InGaN/GaN QW structure. This can be explained by the fact that the matrix element for the InGaN/AlInN QW structure is much larger than that for the InGaN/GaN QW structure due to a reduction in the internal field.

Optical Emission Characteristics of Pseudopolarization-Matched Green AlInGaN/InGaN Quantum Well Structures

Optical properties of pseudopolarization-matched green AlInGaN/InGaN quantum-well structures with a quaternary AlInGaN well layer were investigated by using non-Markovian gain model with many-body effects. We found that the emission peak can be enhanced by using quaternary AlInGaN well and is sensitive to the In composition in the InGaN barrier. The spontaneous emission coefficient shows a maximum at In composition of 0.22 in the barrier and gradually decreases with increasing In composition. The spontaneous emission coefficient of the AlInGaN/InGaN system with reduced internal field is shown to be increased by 70% compared to that of the conventional InGaN/GaN system. Beff of the AlInGaN/InGaN QW structure is much larger than that of the InGaN/GaN QW structure in the investigated range of the current density.

Light emission enhancement in blue InGaAlN/InGaN quantum well structures

Optical properties of blue AlInGaN/InGaN quantum well (QW) structures with a quaternary AlInGaN well layer were investigated by using the non-Markovian gain model with many-body effects. The band-gap expression of the AlInGaN materials was determined through a comparison with experimental results. We found that the emission peak can be enhanced by using quaternary AlInGaN well and is sensitive on In composition in the InGaN barrier. For example, the spontaneous emission coefficient for Al0.08In0.22Ga0.67 N/InxGa1−xN QW structures shows a maximum at In composition of 0.13 in the barrier and gradually decreases with increasing In composition. This is attributed to the fact that the quasi-Fermi-level separation linearly decreases with increasing In composition in the barrier due to the decrease in the conduction and valence band offsets. The AlInGaN/InGaN system with zero internal field is found to have smaller emission peak than the AlInGaN/InGaN system with nonzero internal field due to smaller band offsets.

Optical gain characteristics in (1 1 0)-oriented CdZnO/MgZnO quantum wells emitting at 360–400 nm

Optical gain characteristics of a-plane CdZnO/MgZnO QW structures with a (1 1 0) crystal orientation were theoretically investigated by using the non-Markovian gain model with many-body effects. These results are compared with those of c-plane quantum-well (QW) structures with a (0 0 0 1) crystal orientation. In the case of the c-plane, the optical gain gradually decreases with increasing Cd composition. This is mainly due to the increase in the piezoelectric and spontaneous polarizations. On the other hand, in the case of the a-plane, the optical gain gradually increases with increasing Cd composition. This can be explained by the fact that the quasi-Fermi-level separation increases with the Cd composition. The a-plane shows much larger optical gain than the c-plane, in particular, for QW structures with a larger Cd composition. This means that the crystal orientation effect is much dominant for the QW structure with a large Cd composition. Also, in the case of a low Cd composition, it is found that the CdZnO/MgZnO QW structure shows much larger optical gain than that of the a-plane InGaN/AlGaN QW structure.

ZnO-MgZnO Quantum-Dot Semiconductor Optical Amplifiers

Abstract: ZnO quantum dot (QD) semiconductor optical amplifier (SOA) is studied theoretically using non-Markovian gain model. SOA performance is then studied by rate equations model. These QD-SOAs have shown to have High gain, low noise figure, and polarization insensitivity. This article appraised patent and patent application related to semiconductor optical amplifier. Keywords: Quantum dot (QD), ZnO, semiconductor optical amplifier (SOA), non-Markovian gain, small-signal gain, rate equations, ground state (GS), excited state (ES), noise figure. 1. INTRODUCTION Zinc oxide (ZnO) has been identified as a promising material for optoelectronics applications ranging from ultra-violet (UV) to red wavelengths due to its large fundamental direct bandgap, high thermal conductivity, high luminous efficiency and mechanical and chemical robustness. ZnO also has an advantage of a large exciton binding energy about 60meV, which assures more efficient excitonic emis-sion at higher temperatures [1, 2]. Various wide-gap semi-conducting materials have been adopted to construct ZnO-related heterostructures. Mg

Properties of laser gain of Li:CdZnO/ZnMgO quantum well

The many-body optical gain in Li:CdZnO/MgZnO quantum well (QW) structures with spontaneous polarization and piezoelectric polarization, and ferroelectric dipole moment is investigated by using the non-Markovian gain model with many-body effects. The CdZnO/MgZnO QW structure with high Cd composition is found to have smaller optical gain because the strain-induced piezoelectric polarization and the spontaneous polarization in the well increase with the inclusion of Cd. The internal field is reduced due to the additional polarization by Li in the CdZnO/MgZnO QW structure. These results show that Li:CdZnO-based QW lasers are promising candidates for optoelectric applications in visible and UV regions.

Internal field engineering in CdZnO/MgZnO quantum well structures

Electronic and optical properties of CdZnO/MgZnO quantum well (QW) structures with the depolarization of an internal field are investigated by using the non-Markovian gain model. The Mg composition is selected to give zero internal field for a given Cd composition. The Mg content to give zero internal field is found to increase with increasing Cd content. The peak gain is improved with increasing Cd composition in a range of Cd&amp;lt;0.07 because a quasi-Fermi-level separation rapidly increases with the Cd composition. However, it begins to decrease when the Cd composition exceeds 0.07.

Optical gain in InGaN∕InGaAlN quantum well structures with zero internal field

Electronic and optical properties of InGaN∕InAlGaN quantum well with zero internal field were investigated by using the non-Markovian gain model with many-body effects. The In composition x in the well to give zero internal field is shown to increase with the In composition y in the barrier. The InGaN∕AlGaInN system has much larger optical gain than the conventional InGaN∕GaN system because the optical matrix element is largely enhanced due to disappearance of the internal field. The peak gain is shown to decrease with increasing In composition for both systems. The decrease in the optical gain for the InGaN∕AlGaInN system is mainly due to the reduction in quasi-Fermi-level separation while that for the InGaN∕GaN system is due to the reduction in the matrix element.

Optical anisotropy in ultraviolet InGaN∕GaN quantum-well light-emitting diodes with a general crystal orientation

The crystal orientation effect on optical anisotropy in ultraviolet InGaN∕GaN quantum-well (QW) light-emitting diodes are investigated using the non-Markovian gain model with many-body effects. The spontaneous emission for the y′ polarization largely increases with a crystal angle because of the reduction in the spontaneous and piezoelectric polarizations. On the other hand, that for the x′ polarization is shown to reach a maximum near θ=24° and begin to decrease when the crystal angle further increases. The absolute value of the anisotropy rapidly increases with a crystal angle and begins to saturate to be about one when a crystal angle exceeds about 50°. This is because, in the case of QW structures with large crystal angles, the states constituting the topmost valence subband near the band edge become predominantly ∣Y′&amp;gt;-like.

Crystal orientation effects on electronic and optical properties of wurtzite ZnO/MgZnO quantum well lasers

Crystal orientation effects on electronic and optical properties of ZnO/MgZnO QW structures are investigated by taking into account the non-Markovian gain model with many-body effects. These results are compared with those for GaN-based QW structures. In a range of small crystal angles, ZnO/MgZnO QW structures have a lower internal field than GaN/AlGaN and InGaN/GaN QW structures. However, ZnO/MgZnO QW structures show a larger internal field than GaN-based QW structures at crystal angles near $${\theta =50^{\circ}}$$ . The WZ ZnO/MgZnO QW structures are shown to have much larger optical gain than the GaN-based QW structures for small crystal angles. This is because WZ ZnO/MgZnO QW structures have larger matrix element and smaller effective masses than InGaN/GaN QW structures near the (0001) crystal orientation. On the other hand, in the case of the (10 $${\bar{1}}$$ 0) crystal orientation, the optical gain of ZnO/MgZnO QW structures becomes smaller than that of InGaN/GaN QW structures due to the increase of the effective mass. In addition, the ZnO/MgZnO QW structures have a maximum in the optical gain near $${\theta =50^{\circ}}$$ , which can be explained by the fact that the average hole effective mass increases although the matrix element at high carrier density is improved with increasing crystal angle.

Electronic and optical properties of 1.3μm GaAsSbN∕GaAs quantum well lasers

The electronic and optical properties of GaAsSbN∕GaAs quantum well (QW) laser are investigated using the multiband effective mass theory and the non-Markovian gain model. The results are compared with those of type II GaAsSb∕GaAs QW laser using a self-consistent method. The GaAsSbN∕GaAs QW structure shows that a relatively low compressive strain is required to obtain 1.3μm wavelength compared to the GaAsSb∕GaAs QW structure. The reduction effect of the compressive strain is shown to be dominant for QW structure with a larger N composition or a thick well width. We know that the GaAsSbN∕GaAs QW structure has significantly larger optical gain than the GaAsSb∕GaAs QW structure. This is because the interband matrix element of the former is much larger than that of the latter. We expect that the GaAsSbN∕GaAs QW structure has the improved lasing characteristic compared to the GaAsSb∕GaAs QW structure.

Optical gain and luminescence of a ZnO-MgZnO quantum well

The optical gain and the luminescence of a ZnO quantum well with MgZnO barriers is studied theoretically. We calculated the non-Markovian optical gain and the luminescence for the strained-layer wurtzite quantum well taking into account the excitonic effects. It is predicted that both optical gain and luminescence are enhanced for the ZnO quantum well when compared with those of the InGaN-AlGaN quantum well structure due to the significant reduction of the piezoelectric effects in the ZnO-MgZnO systems.

Spontaneous and piezoelectric polarization effects in wurtzite ZnO∕MgZnO quantum well lasers

Spontaneous and piezoelectric polarization effects on electronic and optical properties of ZnO∕MgZnO quantum well (QW) structures are investigated by using the non-Markovian gain model with many-body effects. The spontaneous polarization constant for MgO determined from a comparison with the experiment is about −0.070C∕m2, which is larger than the value (−0.050C∕m2) for ZnO. The negligible internal field effect observed in the case of ZnO∕MgZnO QW structures with relatively low Mg composition (x&amp;lt;0.2) and thin well width (Lw&amp;lt;46Å) can be explained by the cancelation of the sum of piezoelectric and spontaneous polarizations between the well and the barrier. The ZnO∕MgZnO QW laser has much larger optical gain than the GaN∕AlGaN QW laser. This is attributed to the fact that the ZnO∕MgZnO QW structure has a larger optical matrix element due to the relatively small internal field, compared to the GaN∕AlGaN QW structure.