A broadband width semiconductor optical amplifier is reported using an asymmetric quantum well structure. By applying tensile strain to the quantum wells it is possible to both increase the optical bandwidth while reducing the polarization sensitivity. The effects of the ordering of the asymmetric quantum wells, length of the device and carrier density all affect the performance of the device. Using the asymmetric struture, a 90 nm region of polarization sensitivity less than 1.2 dB within the -3dB band width is achieved.
We report on controlled group V intermixing in a compressively strained In0.76Ga0.24As0.85P0.15/In0.76Ga0.24As0.52P0.48 multi-quantum well laser structure using different encapsulating layers followed by rapid thermal annealing, and the two-section tunable laser made by using this technique. The sample used is a laser structure with emission wavelength at 1.55micrometers . The active region consisting of three In0.76Ga0.24As0.85P0.15 quantum wells with In0.76Ga0.24As0.52P0.48 barriers grown by metal organic chemical vapor deposition. At the same thermal treatment, the blueshift of band gap energy was enhanced most efficiently by capping the sample with an InP layer grown at low temperature and less efficiently by a SiO2 film. While the blueshift was suppressed by a SixNy film with a refractive index of about 2.1. The suppression effect was independent of the SixNy film thickness from 30 nm to 2400 nm. Time of flight secondary ion mass spectra showed that the quantum well intermixing was caused by the interdiffusion of group V atoms between the wells and barriers that have the same group III compositions. A group V interstitial diffusion model was proposed to be responsible for the enhanced intermixing. A 1.55 micrometers two section ridge waveguide laser was fabricated using this technique. The energy transition level of the phase tuning section was tuned to be transparent to the emission wavelength of the active section. A tuning range of about 10 nm can be achieved by simply tuning the bias current for the phase tuning section.
Quantum wells, especially those made of GaAs and InP related compounds, have enabled several unique infrared devices. Two prime examples are quantum well infrared photodetectors (QWIP) and quantum cascade lasers. This paper discusses a few examples of QWIP related devices: (1) QWIPs are well suited for high speed and high frequency applications--work on achieving high absorption efficiency and high operating temperature has been carried out. (2) A variation of conventional QWIP structures can lead to simultaneous visible and infrared detection, and demonstrations using both GaAs and InP based structures have been made. (3) P- type structures may achieve competitive performance and lend to easy fabricating of large focal plane arrays, and good performance has been achieved in resonant-cavity enhanced p- QWIPs.
New methods of implementing quantum well intermixing (QWI) in InP-based materials using defect-enhanced diffusion are presented and compared to the widely reported technique employing dielectric (usuall SiO2) capping with subsequent rapid thermal anneal (RTA) treatments. The new methods discussed use InP layers grown either at low temperature by gas-source molecular beam epitaxy (GSMBE) or using He-plasma-assisted GSMBE where growth surface is subjected to a continuous low energy He-plasma generated in an electron cyclotron resonance (ECR) source. The two new QWI processes, and the SiO2 capping method, are applied to a 1.55(mu) m InGaAsP multiple quantum well laser structure. For application of the QWI process the laser structure growths are interrupted in a manner and location appropriate to carrying out the QWI process and subsequent grating etch for the fabrication of a distributed feedback (DFB) laser. After implementing the QWI and grating etch, growth on the top cladding and contact layers completes the device structure. Finally, the fabrication of a DFB laser with an integrated electro-absorption (EA) modulator is described and the resultant characteristics given.
Bulk layers of GaAsN and InGaAsN and GaAs/InGaAsN/GaAs quantum wells with nitrogen concentration of about 1% have been grown by bas source molecular beam epitaxy with a radio frequency discharge N source. The material has been characterized by X-ray diffraction, secondary ion mass spectrometry, photoluminescence (PL) and Hall effect with the intention of understanding and overcoming the mechanism responsible for the diminished optical quality of the nitride material relative to the material without nitrogen. The PL yield of the InGaAsN quantum wells can be significantly improved by optimized annealing treatment, although the quality is currently still inferior to the nitrogen-free material. Hall effect measurements on the nitride material indicate the presence of states in the bandgap acting as hole traps and electron traps; it is expected that these states act as the non-radiative recombination centres responsible for the reduced optical quality.
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