Optical gain of interdiffused InGaAs-As and AlGaAs-GaAs quantum wells

We have analyzed theoretically the effects of interdiffusion on the gain, differential gain, linewidth enhancement factor, and the injection current density of In0.2Ga0.8As-GaAs and Al0.3Ga0.7As-GaAs quantum-well (QW) lasers. We have calculated the electron and hole subband structures including the effects of valence band mixing and strains. The optical gain is then calculated using the density matrix approach. Our results show that the gain spectrum can be blue-shifted without an enormous increase in the injected current density. Imposing an upper limit (416 A·cm-2) on the injection current density for a typical laser structure, we find that the InGaAs-GaAs and AlGaAs-GaAs QW lasers can be blue-shifted by 24 and 54 mn, respectively. Our theoretical results compare well with the tuning ranges of 53 and 66 meV found for AlGaAs-GaAs QWs in some experiments. This indicates that the interdiffusion technique is useful for the tuning of laser operation wavelength for multiwavelength applications.published_or_final_versio

Three-cation intermixed InGaAs/InAlAs quantum well structures and their optical gain properties

Multiple cations intermixed In053Ga047As/In052A104,As quantum well structure with 60 A well width is investigated by using the expanded form of Fick's second law. It was found that a maximum compressive strain of 0.64% is obtained when annealing time reaches 3 hours at 812 °C in the indium sublattice. For a small interdiffusion, i.e. 1 to 1.5 hrs, the subband separation between the lowest heavy and light hole states is at its greatest. This is a major contribution to the band structure and averaged density of states, thus enhancement in optical gain up to 40% is obtained. For a large interdiffusion, i.e. up to 6 hrs., a large blue shift of the peak gain from 0.842 to 1.016eV is observed.published_or_final_versio

Interdiffusion effect on the gain of InGaAs/InP quantum well laser

Lattice-matched In0.53Ga0.47As/InP quantum well (QW) structures are of considerable interest in photonic application since they enabled device operation in the 1.3micrometers to 1.55micrometers wavelength range which is of importance for optical communication systems. The process of interdiffusion modifies the as-grown square QW to a graded QW which alter the subband structure and optical properties of the QW. Thus it provides a useful tool for bandstructure engineering. The interdiffusion process of InGaAs/InP QW provides more degrees of freedom than AlGaAs/GaAs QW system since interdiffusion can occur for group-III, group-V, and groups III plus V together. These are determined by the temperature and chemical environment used during annealing of the QW structure. The effect of interdiffusion on the laser performances of InGaAs/InP QWs is also studied based on these different types of diffusion processes. It is found that the operating wavelength shows both a red shift and a blue shift depending on the types of diffusion process. It is also found that group-III interdiffusion gives the best performance of InGaAs/InP QW laser when comparing to the other tow types of interdiffusion in terms of a smaller threshold carrier density.published_or_final_versio

Electro-absorption and refraction at 1.5 μm in InGaAs/AlGaAssuperlattice growth on GaAs substrate

High indium concentration In0.65Ga0.35As/Al 0.33Ga0.67As superlattices on GaAs substrates are useful for modulators and optical communication applications. This is due to the lowest loss 1.55 μm optimum wavelength for operation of fiber optic systems. The optical parameters such as absorption coefficient and change in refractive index with applied electric field are investigated.published_or_final_versio

Theory of critical layer thickness of noncontant quantum-well width produced by interdiffusion and its optoelectronics consequence

In this paper, the concept of critical layer thickness is applied to the interdiffused quantum well (DFQW) structure. For the as-grown InGaAs/InP lattice matched quantum well, the interdiffusion process will induce in-plane strain into the DFQW forming a lattice mismatched system. The relation between the as-grown well width (Lz) and the diffusion length (Ld) for formation of dislocation is presented.published_or_final_versio

Modeling of optical gain properties of multiple cations InGaAs-InAlAs quantum-well intermixing

Multiple cations intermixing in an In0.53Ga0.47 As-In0.52Al0.48As quantum-well (QW) structure with 60-Å well width is being studied based on the expanded form of Fick's second law. Interdiffusion of the indium sublattice can result in a maximum compressive strain of 0.64% when annealing time reaches 3 h at 812°C. For a small interdiffusion, i.e., 1-1.5 h, the subband separation between the lowest heavy and light hole states is at its greatest. This has a major contribution to the modified band structure and averaged density of states which can result in an enhanced optical gain up to 40%. This initial stage of intermixing provides the best lasing performance. For large interdiffusion, i.e., up to 6 h, a large blue shift of the peak gain from 0.842 eV (λ=1.47 μm) to 1.016 eV (λ=1.22 μm) is obtained, thus giving a high tunability of the lasing wavelength.published_or_final_versio

Analysis of three types of interdiffusion process in InGaAs/InP quantum-well and their devices implications

The optical properties of Ino 53Gao 47AS/I11P single quantum well (QW) (with an as-grown well width of 60Å structures) interdiffused with different cation and anion interdiffusion rates have been theoretically analyzed for applications in optoelectronics. The interdiffusion of InGaAs/InP QW structures is complicated as interdiffusion can occur for either (i) only group-Ill (In,Ga), (ii) group-V (As,P), or (iii) both group-Ill and group-V sublattices. Depending on the resulting composition profiles, the shifts (blue or red) of the transition energies can be tuned to wavelengths between 1.3µm to 1.55µm for device applications. The results show that the control of the rates of cation and anion interdiffusion offers interesting possibilities for designing optoelectronic devices such as modulators and lasers.published_or_final_versio

Optical properties of tensile-strained barrier GaAsP/GaAs intermixed quantum well structure

The tensile-strained barrier GaAsP/GaAs quantum well (QW) structures fabricated on GaAs substrate has a remarkable potential for novel properties of laser structures. In this structure, the GaAs QW layer is embedded with tensile-strained GaAsP barriers grown on GaAs substrates. Recent research has reported that the threshold current densities with tensilestrained barrier QW laser are comparable with GaAsP/A1GaAs tensile-strained well QWs. In the case of tensile-strained barrier GaAsP/GaAs QW, a small amount of light-hole (LH) and heavy-hole (RH) splitting is attainable within a large range of well width and P compositions. By a suitable choice of material and structure parameters, it is possible to cause the coincidence of energy levels of HH and LII resulting in polarization-independent operation devices. In order to shift the HR and LH energy levels, the concept of band-gap engineering is a useful tool to accept the particular devices operation. Basically, intermixing process is one of easy ways to achieve the modification of bandstructure. During the process the asgrown square-QW compositional profile is modified to a graded profile thereby altering the confinement profile and subband structure in the QW. In this paper, the optical properties of intermixed GaAs QW with tensile-strained GaAsP barriers are reported.published_or_final_versio

Bandstructure of Interdiffused InGaN/GaN Quantum Well

Quantum well composition intermixing is a thermal induced interdiffusion of the constituent atoms through the hetero- interface. The intermixed structures created by both impurity induced and impurity-free vacancy promoted processes have recently attracted high attention. In recent years, blue green LED and laser of III-nitride semiconductors have attracted a large amount of interest. This is mainly due to its large bandgap range from 1.89eV to 3.44eV. InGaN/GaN single quantum well structures have been used to achieve high lumens blue and green light emitting diodes. In this paper, we will present the band structure of strained InGaN/GaN single quantum well under the influence of interdiffusion. Band structure is a fundamental aspect in determining the electronic and optical properties of the materials such as optical gain, refractive index, absorption, etc.published_or_final_versio

Interdiffusion-induced polarization-independent optical gain of an InGaAs-InP quantum-well with carrier effects

A theoretical study of the polarization-independent optical gain using group V sublattice interdiffusion in InGaAs-InP quantum wells (QW's) is presented here. The reverse bias and carrier effects on the subband structures, transition energy, and optical gain of the interdiffused QW are discussed. The interdiffused QW structures are optimized in terms of their subband structure, carrier density, structural parameters, and properties of optical gain spectra. The results show that an optimized interdiffused QW structure can produce polarization-independent optical gain over a range of operation wavelengths around 1.5 μm, although the differential gain and linewidth enhancement factor are slightly degraded. The required tensile strain for the polarization-independent optical properties of a lattice-matched QW structure may be generated using interdiffusion. These results suggest that polarization-independent optical devices can be fabricated using interdiffusion in a lattice-matched InGaAsP QW structure.published_or_final_versio