TE-polarized Optical Gain Research Articles

Comprehensive optimization of electronic and optical properties of polar III-nitride laser

A detailed investigation is performed to obtain optimized optical performance of polar III-nitride single quantum well (SQW) semiconductor lasers by band engineering through symmetric and asymmetric tuning of device parameters. Electronic, optical, and threshold characteristics are calculated to analyze the effects of band engineering on device performance. Here, the InN-In0.25Ga0.75 N SQW structure is chosen as a case study. This work shows a significant improvement in optical properties from higher wavefunction overlap integral obtained from band modification due to the tuning which also provides higher momentum matrix elements, spontaneous emission rate, and optical gain, as well. The maximum TE-polarized optical gain for the symmetric structure is found as around 6291 cm−1 for 6 A well width and 6 A barrier width at 710 nm, while for asymmetric laser structure, a maximum TE-polarized optical gain of around 6225 cm−1 at around 800 nm is observed for 6 A well width with asymmetric barrier width of 6 A and 8 A. The optimization is carried out over 500–1600 nm wavelength range to obtain the optimum structure for maximum optical performance at different wavelengths. A time-efficient genetic algorithm-based optimization is also performed that provides the same optimization results in reduced time.

Temperature effect on structural, morphological and optical properties of 2D-MoS2 layers: An experimental and theoretical study

In this work, we present experimental and theoretical studies of the effect of temperature on the structural, morphological and optical performance of 2D-MoS2 nanosheets. We have used X-ray diffraction, Raman, photoluminescence spectroscopies and electron transmission microscopy to study the structural, morphologic and optical properties of MoS2 synthesized by hydrothermal method. The results indicate that, the structuraland optical properties are significantly temperature-dependent. The number of MoS2-layers has been estimated from the Raman frequencies of the E12g and A1g vibration modes. For the theoretical study we have used k.p and density matrix to calculate the band structure and optical gain for the 2D-MoS2. It is found that the nanosheets exhibit a significant enhancement in the TE-polarized optical gain at room temperature. These results show that 2D-MoS2 layered is promoters for laser device.

Design and analysis of InN − In0.25Ga0.75N single quantum well laser for short distance communication wavelength

A single quantum well semiconductor laser based on wurtzite-nitride is designed and analyzed for short distance communication wavelength (at around 1300 nm). The laser structure has 12 Å well layer of InN, 15 Å barrier layer of In0.25Ga0.75N, and 54 Å separate confinement heterostructure layer of GaN. To calculate the electronic characteristics of the structure, a self-consistent method is used where Hamiltonian with effective mass approximation is solved for conduction band while six-bands Hamiltonian matrix with k · p formalism including the polarization effect, valence-band mixing effect, and strain effect is solved for valence band. The interband optical transition elements, optical gain, differential gain, radiative current density, spontaneous emission rate, and threshold characteristics have been calculated. The wave function overlap integral is found to be 45.93% for TE-polarized structure. Also, the spontaneous emission rate is found to be 6.57 × 1027 s − 1 cm − 3 eV − 1 at 1288.21 nm with the carrier density of 5 × 1019 cm − 3. Furthermore, the radiative current density and the radiative recombination rate are found to be 121.92 A cm − 2 and 6.35 × 1027 s − 1 cm − 3, respectively, while the TE-polarized optical gain of the structure is 3872.1 cm − 1 at 1301.7 nm.

Proposal of InP/AlInGaAs single delta quantum well for fiber-optic communications

In this study, InP/AlGaInAs/delta-InGaAs single quantum well for fiber-optic communications is presented, proposed and compared to the free delta layer even structure. The Al and Ga content and the thickness layers are self-consistently optimized using genetic algorithm. It is found that the optimization of structure confirm an improvement in the electron and hole wave function overlap, which leads to a significant enhancement in TE-polarized optical gain at room temperature. In addition, the transparency carrier density is significantly reduced by the insertion of delta-InGaAs thin layer which can be a necessity for fiber-optic communications.

High-efficiency of AlInGaN/Al(In)GaN-delta AlGaN quantum wells for deep-ultraviolet emission

Band structure and optical gain properties of AlInGaN/AlInGaN-delta-AlGaN quantum wells for deep-ultraviolet light emitting and lasers diodes with wavelength λ ∼229 nm and TE-polarized optical gain peak intensity ∼1.7 times larger than the conventional AlInN-delta-GaN was proposed and investigated in this work. The active region is made up of 20 Å staggered Al0.89In0.03Ga0.08N/Al0.8In 0.01Ga0.19N layers with a 3 Å Al0.46Ga0.54N delta layer. The use of the quaternary AlInGaN well layer permits the independent control of the band gap and the lattice parameter, so that the internal electric field induced by polarizations can be reduced and interband transition energy increases. Therefore, we can predict that the optical performance of the AlInGaN-delta-AlGaN is more convenient for an emission in the deep-ultraviolet than that of the conventional AlInN-delta-GaN-based quantum wells.

Large Optical Gain AlInN-Delta-GaN Quantum Well for Deep Ultraviolet Emitters.

The optical gain and spontaneous emission characteristics of low In-content AlInN-delta-GaN quantum wells (QWs) are analyzed for deep ultraviolet (UV) light emitting diodes (LEDs) and lasers. Our analysis shows a large increase in the dominant transverse electric (TE) polarized spontaneous emission rate and optical gain. The remarkable enhancements in TE-polarized optical gain and spontaneous emission characteristics are attributed to the dominant conduction (C)-heavy hole (HH) transitions achieved by the AlInN-delta-GaN QW structure, which could lead to its potential application as the active region material for high performance deep UV emitters. In addition, our findings show that further optimizations of the delta-GaN layer in the active region are required to realize the high performance AlInN-based LEDs and lasers with the desired emission wavelength. This work illuminates the high potential of the low In-content AlInN-delta-GaN QW structure to achieve large dominant TE-polarized spontaneous emission rates and optical gains for high performance AlN-based UV devices.

Proposal and physics of AlInN-delta-GaN quantum well ultraviolet lasers

The use of AlInN-delta-GaN quantum wells (QWs) active region for ultraviolet (UV) laser with wavelength (λ) ∼ 250–300 nm was proposed and investigated in this work. The design of active region consists of 24 Å staggered Al0.91In0.09N/Al0.82In0.18N layers with a 3 Å lattice-matched GaN delta layer, which enables dominant conduction band (C) to heavy hole (HH) subband transition. In addition, the insertion of the ultra-thin delta GaN layer will strongly localize the electron-hole wave functions toward the center of the QW, which leads to large transverse electric (TE) polarized optical gain. In comparison to the use of a conventional AlGaN QW system, the proposed AlInN-delta-GaN QW structure results in ∼3 times improvement in TE-gain at 255 nm. By tuning the delta-GaN thickness, the TE-polarized optical gain up to 3700 cm−1 can be obtained for λ ∼ 280–300 nm, which is very promising to serve as an alternative active region for high-efficiency UV lasers.

Optical gain characteristics of AlGaN/AlN quantum well structures grown on GaN substrate for ultraviolet TM light source

Optical gain characteristics of ultraviolet AlGaN/AlN quantum well (QW) structures grown on GaN substrate were investigated using the multiband effective-mass theory and non-Markovian model with the many-body effect. The TE-polarized optical gain peak of the QW structure on AlN substrate gradually increases with increasing Al composition and begins to decrease rapidly when the Al composition exceeds 0.6. On the other hand, the QW structure on GaN substrate shows that the TE-polarized optical gain peak continuously decreases with increasing Al composition and the TM-polarized optical gain peak begins to increase at much lower Al composition than that of the QW structure on AlN substrate. As a result, the QW structure on GaN substrate shows that the critical Al composition switching from TE to TM polarization is much smaller than that of the QW structure on AlN substrate. Also, the TM-polarized gain peak of the QW structure on GaN substrate is found to be much larger than that of the QW structure on AlN substrate.

Intersublevel polaron laser with InAs∕GaAs self-assembled quantum dots

We propose a three-level scheme to achieve intersublevel population inversion, optical gain, and intersublevel lasing effect in n-doped InAs∕GaAs self-assembled quantum dots under optical pumping. The proposed Ruby-type laser scheme uses the natural splitting of the s-p polaron intersublevel transitions around 25μm wavelength. The relaxation time engineering, which leads to optical gain in the system, relies (i) on the slow polaron relaxation from the P− state down to the S ground state, governed by the specific strong coupling regime for the electron-phonon Fröhlich interaction and (ii) on the fast nonradiative relaxation of the polaron between the P+ and P− levels through the irreversible emission of acoustic phonons. TE-polarized optical gain up to 330cm−1 is calculated for 80 quantum dot planes in an in-plane monomode waveguide geometry and a laser pump intensity threshold as low as 930W∕cm2, two orders of magnitude smaller than for quantum wells, is predicted.

Structure asymmetry effects in the optical gain of piezostrained InGaN quantum wells

We investigate the effects of structural asymmetry on the electronic and optical properties of indium gallium nitride (InGaN) quantum wells (QW's). Using a pulsed current excitation technique, spectral blue shift as large as 80 meV is observed in a strained 3.0-nm In/sub 0.2/Ga/sub 0.8/N QW as the pulsed current increases from 1 mA to 1 A. Based on a self-consistent calculation, we are able to quantify a gain competition process among the interactions of piezoelectricity, many-body, charge screening, and band filling effects. Such interactions are shown to provide a mechanism for shaping the QW confined potential such that superior carrier confinement and charge screening of the piezoelectric field can be obtained in the asymmetric InGaN QW. At high carrier injection of N/sub inj/>2/spl times/10/sup 19/ cm/sup -3/, a tenfold increase in the TE-polarized optical gain can be achieved by using the asymmetric GaN-InGaN-AlGaN QW instead of the symmetric InGaN-AlGaN QW. Due to the diminishing of piezoelectricity-induced quantum-confined Stark effect, the calculated optical gain spectra of the asymmetric InGaN QW exhibit a spectral blue shift with respect to those of the symmetric InGaN QW.