M.C.Y. Chan

The effects of interdiffusion on the subbands in GaxIn1−xN0.04As0.96/GaAs quantum well for 1.3 and 1.55 μm operation wavelengths

The interdiffusion of GaxIn1−xN0.04As0.96/GaAs single quantum well (QW) structure with well width of 6 nm is studied theoretically. The as-grown Ga concentration in the QW is chosen to be 0.7 and 0.6 for the operation wavelengths of 1.3 and 1.55 μm, respectively. We studied the effects of interdiffusion on the in-plane strain, confinement potential, and subband energy levels of the QW using Fick’s law. The diffusion coefficients of both the well and barrier layers are assumed to be constant. The effects of valence band mixing and strains are included in the calculation of the electron and hole subband structures. We find that the group-III interdiffusion effects can result in blueshifts of 123 and 211 nm in the GaxIn1−xN0.04As0.96/GaAs QW at operation wavelength of 1.3 μm (x=0.7) and 1.55 μm (x=0.6), respectively. Our results show that interdiffusion technique can be used to tune the operating wavelengths of GaInAsN/GaAs lasers for multiwavelength applications such as in the sources of dense wavelength di...

Anodic-oxide-induced interdiffusion in GaAs/AlGaAs quantum wells

Enhancement of interdiffusion in GaAs/AlGaAs quantum wells due to anodic oxides was studied. Photoluminescence, transmission electron microscopy, and quantum well modeling were used to understand the effects of intermixing on the quantum well shape. Residual water in the oxide was found to increase the intermixing, though it was not the prime cause for intermixing. Injection of defects such as group III vacancies or interstitials was considered to be a driving force for the intermixing. Different current densities used in the experimental range to create anodic oxides had little effect on the intermixing.

Anodic-oxide-induced intermixing in GaAs-AlGaAs quantum-well and quantum-wire structures

Anodic oxides of GaAs were shown to enhance the intermixing in GaAs-AlGaAs quantum wells (QW) during rapid thermal processing. Proximity of the anodic oxide to the QW has been shown to influence the photoluminescence (PL) energy shift due to intermixing. Anodic oxide induced intermixing has been used to enhance quantum-wire PL in the structures grown on V-groove patterned GaAs substrates. This has been attributed to enhanced lateral confinement in these structures. Injection of defects such as group-III vacancies or interstitials was considered to be driving force for the intermixing.

Temperature-dependent photoluminescence of GaInP/AlGaInP multiple quantum well laser structure grown by metalorganic chemical vapor deposition with tertiarybutylarsine and tertiarybutylphosphine

A GaInP/AlGaInP multiple quantum well laser structure was grown by low-pressure metalorganic chemical vapor deposition with tertiarybutylarsine and tertiarybutylphosphine. Laser diodes fabricated from this structure lased at room temperature. Photoluminescence (PL) measurements were performed from 10 to 230 K. The PL energy increased with temperature from 10 to 70 K and decreased above 70 K. The former was attributed to thermal activation of trapped carriers due to localization in the quantum wells, while the latter was attributed to temperature-induced band-gap shrinkage. The PL intensity as a function of temperature was fitted by employing two nonradiative recombination mechanisms with good agreement, resulting in two activation energies that correspond to losses of photogenerated carriers to nonradiative centers.

The effect of carrier-induced change on the optical properties of AlGaAs-GaAs intermixed quantum wells

The carrier-induced effects in the change of absorption and refractive index on the AlGaAs-GaAs intermixing modified quantum wells (QWs) have been investigated theoretically. Band-filling, bandgap shrinkage, and free-carrier absorption have been included for various carrier concentrations. The Schrodinger and the Poisson equations have been considered self-consistently. The polarized absorption coefficients are calculated using the Kane k/spl middot/p method for a four band model and followed by the Kramers-Kranig transformation to obtain the refractive index change. The results obtained show a more enhanced bandgap renormalization and change of absorption, but a reduced change in refractive index for the larger intermixing extents. It is important to know the carrier-induced optical parameter changes the intermixed QWs because of their recent interests in photonics.

A tunable blue light emission of InGaN/GaN quantum well through thermal interdiffusion

In recent years, blue light emitting diodes and lasers of III-nitride semiconductors have been of much interest. This is mainly due to its large bandgap ranging from 1.89 eV (wurtzite InN) to 3.42 eV (wurtzite GaN). InGaN/GaN quantum well (QW) structures have been used to achieve high lumens blue LEDs. In this paper, InGaN/GaN QW intermixing structure is theoretically analyzed and is used to optimize and tune the optical emission.

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 (QWs) 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 /spl mu/m, 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.

Quantum well intermixing for the fabrication of InGaAsN/GaAs lasers with pulsed anodic oxidation

Quantum well (QW) intermixing was carried out by post-growth rapid thermal annealing in InGaAsN/GaAs QW laser structures grown by solid-source molecular-beam epitaxy. The intensity and width of the photoluminescence peak showed a dependence on annealing temperature and time, and the maximum intensity and minimum linewidth were obtained after the wafer was annealed at 670 °C for 60 s. The peak luminescence energy blueshifted with increasing annealing time, although it plateaued at an annealing time that corresponded to that yielding the maximum luminescence intensity. The diffusion coefficient for indium was determined from a comparison between experimental data and modeling, but showed that QW intermixing alone was not sufficient to account for the relatively large blueshift after annealing. Defects related to the incorporation of nitrogen in the QW layer were responsible for the low photoluminescence efficiency in the as-grown samples and were annealed out during rapid thermal annealing. During annealing...

Improved thermal stability of AlGaAs/GaAs/AlGaAs single quantum well by growth on Zn-doped GaAs (001)

Abstract The effects of Zn doping in the substrate on the thermal stability of GaAs/Al 0.24 Ga 0.76 As single quantum well are investigated by 900 °C rapid thermal annealing and low-temperature (12 K) photoluminescence measurements. An improvement in thermal stability is demonstrated for structures grown on Zn-doped GaAs in comparison with those grown on semi-insulating and Si-doped GaAs substrates. It is likely that the Zn out-diffusion from the substrate to the quantum well region has lowered the Al–Ga interdiffusion coefficient.

Analysis of photon capturing in light emitting diode with different surfaces

The external efficiency of todays LED is still very small, typically less than 10%, although the internal efficiency can be very high (/spl sim/100%). This is because when light have been generated in the active layer inside the diode, they must be liberated to the outside in order to be of any use. Because the refractive index of semiconductor material is usually quite high (/spl sim/3.5), more than three times as air, therefore the critical angle /spl theta//sub c/ given by Snells law (from semiconductor to air) is very small, typically /spl sim/17/spl deg/. Recently, LEDs having external quantum efficiency as high as 30% has been reported; this was achieved by adding many interesting features including fabricating a coarse texturing on the semiconductor surface with a back reflector, where the escape probability of photons can be increased substantially. However, the mechanism of achieving such a high efficiency due to the textured surface is not yet fully understood. Two programs have been coded to simulate the external efficiency of semiconductor LED-a 3-dimensional LED program without back reflector and a 2-dimensional program with back reflector.