We report on the operation of a monolithically integrated DBR laser electroabsorption modulator fabricated in 1.3 /spl mu/m InAlGaAs strained multiple quantum well structure. The device encompasses three sections of different bandgaps obtained by a two step annealing-sputtering quantum well intermixing process.

As part of an investigation of the optimum growth conditions for the preparation of strained MQW InAlGaAs lasers for operation at 1.3 /spl mu/m, one to six quantum well structures, with up to 1.4% strain, have been grown at temperatures in the range 470 to 585/spl deg/C. Deposition of both digital and bulk alloy layers was carried out in a V80H system, on two- and three inch n-InP substrates, and growth temperatures were monitored using absorption band-edge thermometry. The basic MQW structures consisted of 10 nm lattice matched confinement layers of digital alloy InAlGaAs (/spl sim/1.0 /spl mu/m bandgap), or bulk InAlAs, bounding 6 nm layers of digital alloy In/sub 0.73/Al/sub 0.165/Ga/sub 0.105/As.

Wet oxidation of GaAs/AlGaAs structures is an important technique in the processing of advanced devices such as vertical cavity surface emitting lasers (VCSELs). In one VCSEL application, the low-index and electrically-insulating AlxOy layers have been used to obtain high-reflectivity and broad bandwidth distributed Bragg reflector mirrors (DBRs). A further recent development has shown that combined lateral-vertical oxidation of intracavity AlGaAs layers can be used to tune the resonant wavelength of a semiconductor microcavity. The slow oxidation rate limits the lateral scale of practical wet oxidation to mesas structures of 50-100 mum in width. Therefore post-processing assessment of spectral changes requires micro reflectivity measurement capability with high spatial resolution. In the following, we describe the fabrication and assessment of microcavity structures in the 1.3 mum range. The micro-reflectivity set-up consists of micro scope-objective focussing of broadband light, combined with optics to relay the data to a spectrograph, and a CCD camera for alignment. This simple set-up allows the measurement of calibrated reflectivity for features down to a few 10's of mum in size over a large spectral range (600-1800 nm). We present microreflectivity measurements of wide-bandwidth oxidised DBRs, and most significantly, for the first time to our knowledge, of oxidation control of the resonant wavelength of a microcavity in the 1.3 mum range. (C) 2003 Elsevier B.V. All rights reserved.

We report on the characteristics of quantum well intermixing in GaInNAs/GaAs structures of differing N content. Rapid thermal annealing combined with SiO2 caps deposited on the surface of the samples is used to disorder 1.3 μm GaInNAs/GaAs multiquantum wells which have been preannealed in-situ to the stage of blueshift saturation. The different effects of two capping layer deposition techniques on the interdiffusion of In–Ga have been compared, particular regarding the role of sputtering processes. The dependence of quantum well intermixing-induced photoluminescence blueshift on N concentration has provided extra information on the intrinsic properties of the GaInNAs/GaAs material system. We found that the blueshift decreases as the N concentration increases. This finding not only rules out the possible mechanism of N–As interdiffusion, but also demonstrates the alloy stability of GaInNAs due to the strong bond between In–N.

We report an investigation of selective quantum-well intermixing (QWI) in 1.3-μm GaInNAs/GaAs multi quantum wells by silica-cap-induced disordering processes. After thermal annealing under specific conditions, controlled shifts of band gap at room temperature of over 200 nm have been observed in sputtered SiO 2 -capped samples, while uncapped and SiO 2 -capped samples by plasma-enhanced chemical vapor deposition demonstrated negligible shift. This selective modification of the band gap in GaInNAs quantum wells has been confirmed by detailed photoluminescence and photoluminescence excitation spectroscopy, and by secondary ion mass spectrometry. The controlled tuning of the band gap of GaInNAs/GaAs by QWI is important for a wide range of photonic integrated circuits and advanced device applications.

We report a multi-wavelength passive filter working in the 1.3 μm range, fabricated by a post-growth technique based on the combined lateral–vertical steam oxidation of AlGaAs layers within a microcavity. Wafers are photolithographically patterned and etched through the top to create mesa structures which are oxidized from both edges, and control of resonant wavelength is achieved through mesa width, thickness and compositional control of intracavity layers to be oxidized, and oxidation conditions. Microreflectivity measurements of the processed devices show that in this wavelength range it is possible using this approach to control the resonant wavelength over a range of about 52 nm.

Rapid thermal annealing combined with SiO2 caps deposited on the surface of samples by different techniques is used to selectively disorder 1.3 μm GaInNAs/GaAs multiquantum wells which have been preannealed in situ to the stage of blueshift saturation. After thermal annealing under specific conditions, a shift in band gap of over 170 meV has been obtained in sputtered SiO2-capped samples, while uncapped and plasma enhanced chemical vapor deposited SiO2-capped samples demonstrated a negligible shift. Quantum well intermixing in sputtered SiO2-capped samples originates from enhanced compositional interdiffusion due to the generation of point defects by ion bombardment during the sputtering process. Secondary ion mass spectrometry has confirmed that the enhanced blueshift was caused by the interdiffusion of group III atoms (In and Ga) between the quantum wells and barriers. Detailed photoluminescence and excitation spectroscopy were performed to study the optical properties of both intermixed and nonintermixed samples.

We report on the passive mode locking of InGaAlAs strained quantum well extended cavity lasers emitting at 1.3 /spl mu/m. The passive section is made by quantum well intermixing.

A study of the losses in InGaAs/AlGaInAs multiple-quantum-well ridge waveguides band edge shifted by quantum well intermixing is presented. The intermixing process is based on point defects generated on the sample surface during the deposition of sputtered SiO2 and a subsequent rapid thermal annealing. It is demonstrated that for small wavelength shifts (60-80nm), losses are considerably lower than in samples with maximum band edge shift (150nm). Minimum losses of 6 dB/cm have been measured.