P. A. Alvi

INVESTIGATION OF MATERIAL GAIN OF In0.90Ga0.10As0.59P0.41/InP LASING NANO-HETEROSTRUCTURE

In this paper, we have proposed a step separate confinement heterostructure (SCH) based lasing nano-heterostructure In0.90Ga0.10As0.59P0.41/InP consisting of single quantum well (SQW) and investigated material gain theoretically within TE and TM polarization modes. In addition, the quasi Fermi levels in the conduction and valence bands along with other lasing characteristics like anti-guiding factor, refractive index change with carrier density and differential gain have also been investigated and reported. Moreover, the behavior of quasi Fermi levels in respective bands has also been correlated with the material gain. Strain dependent study on material gain and refractive index change has also been reported. Interestingly, strain has been reported to play a very important role in shifting the lasing wavelength of TE mode to TM mode. The results investigated in the work suggest that the proposed unstrained nano-heterostructure is very suitable as a source for optical fiber based communication systems due to its lasing wavelengths achieved at ~1.35 μm within TM mode, while ~1.40 μm within TE mode.

Qualitative analysis of gain spectra of InGaAlAs/InP lasing nano-heterostructure

This paper deals with the studies of lasing characteristics along with the gain spectra of compressively strained and step SCH based In0.71Ga0.21Al0.08As/InP lasing nano-heterostructure within TE polarization mode, taking into account the variation in well width of the single quantum well of the nano-heterostructure. In addition, the compressive conduction and valence bands dispersion profiles for quantum well of the material composition In0.71Ga0.21Al0.08As at temperature 300 K and strain ~1.12% have been studied using 4 × 4 Luttinger Hamiltonian. For the proposed nano-heterostructure, the quantum well width dependence of differential gain, refractive index change and relaxation oscillation frequency with current density have been studied. Moreover, the G–J characteristics of the nano-heterostructure at different well widths have also been investigated, that provided significant information about threshold current density, threshold gain and transparency current density. The results obtained in the study of nano-heterostructure suggest that the gain and relaxation oscillation frequency both are decreased with increasing quantum well width but the required lasing wavelength is found to shift towards higher values. On behalf of qualitative analysis of the structure, the well width of 6 nm is found more suitable for lasing action at the wavelength of 1.55 μm due to minimum optical attenuation and minimum dispersion within the waveguide. The results achieved are, therefore, very important in the emerging area of nano-optoelectronics.

High pressure effect on optical gain in type-II InGaAs/GaAsSb nano-heterostructure

This paper reports the simulation of optical gain in type-II InGaAs/GaAsSb quantum well based nano-scale heterostructure. In order to simulate the optical gain, the heterostructure has been modeled with the help of six band k.p method. The 6 × 6 diagonalized k.p Hamiltonian has been solved to evaluate the valence sub-bands (i.e. light and heavy hole energies); and then optical matrix elements and optical gain within TE (Transverse Electric) mode has been calculated. The results obtained suggest that peak optical gain of the order of ∼ 9000 /cm in the heterostructure can be achieved at the lasing wavelength ∼ 1.95 µm (SWIR region). The application of high pressure (2 and 5 GPa) on the structure shows that the gain as well as lasing wavelength both approach to higher values. Thus, the structure can be tuned externally by the application of high pressure.

Optical properties of Type-I GaAsP/AlGaAs nano-heterostructure under external uniaxial strain

This paper emphasizes over optical properties of the type-I GaAsP/AlGaAs nano-heterostructures under variable uniaxial external strain. The entire structure is assumed to be grown over the GaAs substrate. In order to calculate the optical gain of the structure, first 4 × 4 Kohn-Luttinger Hamiltonian is solved to determine the sub-band dispersion and corresponding envelope wave functions; and then transition matrix elements calculations is designed to perform calculations of momentum matrix elements and dipole moments of selected transitions taking into account spin concept of the charge carriers. The calculated optical gain corresponding to maximum intensity meets at photonic energy ∼ 1.64 eV and at corresponding wavelength ∼ 756 nm. The maximum gain value corresponds to e1-hh1 transitions. The simulated results are found to match with experimental results.This paper emphasizes over optical properties of the type-I GaAsP/AlGaAs nano-heterostructures under variable uniaxial external strain. The entire structure is assumed to be grown over the GaAs substrate. In order to calculate the optical gain of the structure, first 4 × 4 Kohn-Luttinger Hamiltonian is solved to determine the sub-band dispersion and corresponding envelope wave functions; and then transition matrix elements calculations is designed to perform calculations of momentum matrix elements and dipole moments of selected transitions taking into account spin concept of the charge carriers. The calculated optical gain corresponding to maximum intensity meets at photonic energy ∼ 1.64 eV and at corresponding wavelength ∼ 756 nm. The maximum gain value corresponds to e1-hh1 transitions. The simulated results are found to match with experimental results.

G-J study for GRIN InGaAlAs/InP lasing nano-heterostructures

This paper reports behavior of modal gain with current density for SQW and MQWs based GRIN InGaAlAs/InP lasing nano heterostructures. The calculations have been made in both TE and TM modes. The modal gain obtained for GRIN InGaAlAs/InP lasing nano heterostructures in TE mode is found larger than that in TM mode. Moreover, it has been reported that the modal gain increases as the number of quantum wells in the structure increases in both TE and TM modes. These structures are very useful in the optical fiber communication systems due to minimum optical losses.

Structural, magnetic and surface morphological study of Ni doped SnO2 thin films

Nanocrystalline thin films of Sn1-xNixO2 (x=0% and 10%) were grown by pulse laser deposition technique on LaAlO3(100) substrate and then characterize using various techniques. Single phase nature of the films has been studied using X-ray diffraction, which clearly infer that all films have single phase polycrystalline nature and exclude the presence of any secondary phase. The Surface morphological have been studied using atomic force microscopy (AFM), which revealsthat pure and Ni doped SnO2 films are composed of nano-crystalline grains. The surface roughness measured using AFM micrographs found to increase with Ni doping. DC magnetization measurements performed at room temperature showed that undoped and doped films exhibit the FM ordering at room temperature.Nanocrystalline thin films of Sn1-xNixO2 (x=0% and 10%) were grown by pulse laser deposition technique on LaAlO3(100) substrate and then characterize using various techniques. Single phase nature of the films has been studied using X-ray diffraction, which clearly infer that all films have single phase polycrystalline nature and exclude the presence of any secondary phase. The Surface morphological have been studied using atomic force microscopy (AFM), which revealsthat pure and Ni doped SnO2 films are composed of nano-crystalline grains. The surface roughness measured using AFM micrographs found to increase with Ni doping. DC magnetization measurements performed at room temperature showed that undoped and doped films exhibit the FM ordering at room temperature.

Quantum Well Width Effect on Intraband Optical Absorption in Type-II InAs/AlSb Nano-Scale Heterostructure

In this paper, we have studied theoretically the effect of width variation of quantum well on energy dispersion curves and transverse electric (TE) and transverse magnetic (TM) Intraband optical absorption coefficients in type-II InAs/AlSb nanoscale heterostructure by utilizing eight bands Kohn–Luttinger Hamiltonian. The outcomes of the calculations made in this work suggest that the optical absorption and transition energies can be enhanced by reducing the width of quantum well (active) region of the designed heterostructure. One more observation is that the polarization modes have no effect on the behaviour of change in transition energy with change in well width.

Wavefunctions and optical gain in Al 0.8 Ga 0.2 As/GaAs 0.8 P 0.2 type-I QW-heterostructure under external electric field

Optical transition strength are observed to be affected in Al<inf>0.8</inf>Ga<inf>0.2</inf>As/GaAs<inf>0.8</inf>P<inf>0.2</inf> type-I QW-heterostructure under external electric field. This paper reports optical gain realized in Al<inf>0.8</inf>Ga<inf>0.2</inf>As/GaAs<inf>0.8</inf>P<inf>0.2</inf> type-I QW-heterostructure (varying well width 6nm–22nm). Band alignment, wavefunctions and optical gain of the nano-scale heterostructure under electromagnetic field perturbation is reported. The 6×6 diagonalised k⃗. p⃗ Hamiltonian matrix is evaluated and Luttinger-Kohn model has been applied for the band structure calculations. Optical gain spectrum in the QW-heterostructure under external electric fields of (20, 40 and 60 kV/cm) is calculated. Optical gain (x and z polarizations) of the nano-scale heterostructure under well width and temperature variations is investigated. The optical gain spectrum of the heterostructure is seen to gradually rise with shrinking well width. Also the optical gain curve shows a decrease in gain with rising temperature levels. For a charge carrier injection of 4 × 10¹²/cm² the optical gain is ∼220 under input x polarization [100] and ∼625 under z polarization [001] at 300K. The heterostructure is seen to be operating in the energy range of 1.5 to 1.75 eV (708 to 826 nm). Thus, a wide range wavelength tuning is achievable.

Optical gain in type–II InGaAs/GaAsSb quantum well nano-heterostructure

In this paper, we have simulated optical gain in type-II InGaAs/GaAsSb quantum well based nano-scale heterostructure. In order to simulate the optical gain, the heterostructure has been modeled with the help of six band k.p method. The 6 × 6 diagonalized k.p Hamiltonian has been solved to evaluate the valence sub-bands (i.e. light and heavy hole energies); and then optical matrix elements and optical gain within TE (Transverse Electric) mode has been calculated. The results obtained suggest that peak optical gain in the heterostructure can be achieved at the lasing wavelength ~ 1.95 µm (SWIR region) and at corresponding energy ~ 0.635 eV.

Temperature dependence of material gain of InGaAsP/InP nano-heterostructure

This paper deals with temperature dependent study on material gain of InGaAsP/InP lasing nano-heterostructure with in TE mode. The model is based on simple separate confinement heterostructure (SCH). Material gain for the structure has been simulated for below and above the room temperatures. Different behaviors of the material gain for both ranges of the temperature have been reported in this paper. The results obtained in the simulation of the heterostructures suggest that only the shift in maximum gain takes place that appears at the lasing wavelength ∼ 1.40 μm.