D. Fekete

Characterization of strained quantum wells by high‐resolution x‐ray diffraction

The GaAs/GaInAs/GaAs quantum‐well structures grown by metalorganic chemical vapor deposition were studied using high‐resolution x‐ray diffractometry and photoluminescence techniques. Diffraction profiles were fitted to experimental rocking curves by a simulation procedure, based on the direct summation of scattered waves. The analytical expressions obtained shed light on various relevant parameters and, together with a specific growth procedure, permitted determination of the thickness and composition of strained quantum wells. By following fine interference effects in the x‐ray diffraction spectra quantum wells as thin as 1.4 nm could be characterized. In order to check the validity of the procedure, the obtained quantum‐well parameters were used to calculate the peak positions in luminescence spectra and good agreement with experimental data was found.

n‐type delta‐doped quantum well lasers with extremely low transparency current density

It is demonstrated that placing an n‐type Te δ doping aside a single strained quantum well (QW) is an efficient way to control the initial carrier concentration in the QW and thus to lower transparency current density, Jtr, while preserving low internal losses. This is in contrast with uniform doping of the active area. Jtr of 11.3 A/cm 2 and threshold current density of 54.4 A/cm2, which are both the lowest values reported to date for strained InxGa1−xAs/GaAs semiconductor lasers, were obtained. A somewhat higher injection efficiency is obtained when the energy levels are adjusted so that the electrons tunnel from the delta well directly into the QW.

Phonon study of strained InGaAs layers

Relaxation of strain in InxGa1−xAs layers on GaAs is studied by Raman spectroscopy for layers below and above the critical thickness. We show that the enormous strain of the perfect epitaxial layer is released stepwise with the thickness. It is suggested that dislocations formed at the layer surface impose the growth of the next sublayer of partially released strain, preserving the former grown sublayer of higher strain.

Improved hole confinement in GaInAsN-GaAsSbN thin double-layer quantum-well structure for telecom-wavelength lasers

In this work we demonstrated increased hole confinement in a bilayer quantum well that consists of two thin layers of GaInAsN/GaAsSbN confined by GaAs barriers. Comparison between the temperature dependence of photoluminescence intensity of the bilayer and GaInAsN quantum wells indicated that electrons rather than holes are the less confined carriers in the bilayer structure. This structure enables independent control of the band gap energy, band offsets and reduces the temperature sensitivity of laser performance. The calculations showed that a bilayer based short-period superlattice would provide a high optical gain at 1.3–1.55 μm due to increased electron-hole wave functions overlap.

X-ray diffraction in quantum-well structures

Abstract An extended kinematical approach is applied to the simulation of X-ray diffraction spectra from triple-layered quantum-well structures. A problem caused by a thick substrate is solved by using the exponentially decaying amplitude of the incident beam due to both extinction and absorption effects. The interface roughness is taken into account by statistical averaging of the scattering amplitudes. The analytic expressions obtained well describe the experimental rocking curves and are used to derive the parameters of GaAs/GaInAs/GaAs quantum wells a few nm thick grown on the (1 1 1)-oriented GaAs substrates.

Utilizing the interface adsorption of nitrogen for the growth of high-quality GaInAsN/GaAs quantum wells by metal organic chemical vapor deposition for near infrared applications

We have investigated the composition and optical properties of GaInAsN/GaAs single quantum wells grown using metal organic chemical vapor epitaxy at 500 °C. Using time-of-flight secondary ion mass spectrometry and photoluminescence spectroscopy, we have shown the presence of a 1–2 nm thick nitrogen-rich interfacial layer at the first interface grown. The inhomogeneous asymmetric distribution of nitrogen atoms along the growth direction is attributed to the dominance of surface kinetics, nonlinear dependence of N incorporation on In content, and the strain gradient effect on the effective diffusion of N. We have utilized this finding to grow high quality quantum wells.

Dilute nitride InGaAsN/GaAs V-groove quantum wires emitting at 1.3 μm wavelength at room temperature

Site-controlled InGaAsN quantum wires (QWRs) emitting at 1.3 μm at room temperature were grown on V-grooved GaAs substrates by modulated-flux metallorganic vapor phase epitaxy. The nonplanar substrate template is shown to enhance the nitrogen uptake, evidenced by a redshift in photoluminescence wavelength twice larger for the QWRs than for the adjacent quantum well regions. The mechanism of this increase in nitrogen incorporation efficiency, achieved without degradation in optical properties, is explained by the extended gradient of In content at the step-rich QWR interfaces.

Strained InGaAs-GaAs single-quantum-well lasers coupled to n-type /spl delta/-doping-improved static and dynamic performance

A new concept for improving the performance of quantum-well (QW) lasers is reported. The enhancement, both in static and dynamic characteristics, was accomplished by the use of Te n-type /spl delta/-doping, coupled to a single strained InGaAs-GaAs QW. The internal parameters were investigated, and their enhancement origin is revealed. It is shown to be mainly a consequence of the higher carrier population in the QW and due to the strong coupling between the QW and the /spl delta/-doping well.

n-type delta-doped strained quantum well lasers for improved temperature-dependent performance

It is demonstrated that the incorporation of Te n-type δ doping close to a single-strained InGaAs/GaAs quantum well improves the temperature stability of the laser, as indicated by the higher characteristic temperature and by the reduced sensitivity of the threshold current to temperature variations. This improvement results from the strong coupling between the quantum well and the δ-doping well.

A pulsed high-power quantum well laser using an asymmetric waveguide

A , strained InGaAs quantum well laser, reaching a record high power of 31 W at 50 A in 230 ns pulsed operation, is reported. The new structure is based on a wide asymmetric multimode optical waveguide that reduces the optical power density on the lasers mirrors, to produce a higher maximum output power. Modal discrimination is obtained by proper positioning of the quantum well.