Q. Han

GaAs-based room-temperature continuous-wave 1.59 {mu}m GaInNAsSb single-quantum-well laser diode grown by molecular-beam epitaxy

Starting from the growth of high-quality 1.3μmGaInNAs∕GaAs quantum well (QW), the QW emission wavelength has been extended up to 1.55μm by a combination of lowering growth rate, using GaNAs barriers and incorporating some amount of Sb. The photoluminescence properties of 1.5μm range GaInNAsSb∕GaNAs QWs are quite comparable to the 1.3μm QWs, revealing positive effect of Sb on improving the optical quality of the QWs. A 1.59μm lasing of a GaInNAsSb∕GaNAs single-QW laser diode is obtained under continuous current injection at room temperature. The threshold current density is 2.6kA∕cm2 with as-cleaved facet mirrors.

High-indium-content InxGa1−xAs/GaAs quantum wells with emission wavelengths above 1.25 μm at room temperature

High-indium-content InxGa1-xAs/GaAs single/multi-quantum well (SQW/MQW) structures have been systematically investigated. By optimizing the molecular-beam epitaxy growth conditions, the critical thickness of the strained In0.475Ga0.525As/GaAs QWs is raised to 7 nm, which is much higher than the value given by the Matthews and Blakeslee model. The good crystalline quality of the strained InGaAs/GaAs MQWs is proved by x-ray rocking curves. Photoluminescence measurements show that an emission wavelength of 1.25 mum at room temperatures with narrower full width at half maximum less than 30 meV can be obtained. The strain relaxation mechanism is discussed using the Matthews-Blakeslee model

1.55 {mu}m GaInNAs resonant-cavity-enhanced photodetector grown on GaAs

We report the design, growth, fabrication, and characterization of a GaAs-based resonant-cavity-enhanced (RCE) GaInNAs photodetector operating at 1.55μm. The structure of the device was designed using a transfer-matrix method (TMM). By optimizing the molecular-beam epitaxy growth conditions, six GaInNAs quantum wells were used as the absorption layers. Twenty-five (25)- and 9-pair GaAs∕AlAs-distributed Bragg reflectors were grown as the bottom and top mirrors. At 1.55μm, a quantum efficiency of 33% with a full width at half maximum of 10nm was obtained. The dark current density was 3×10−7A∕cm2 at a bias of 0V and 4.3×10−5A∕cm2 at a reverse bias of 5V. The primary time response measurement shows that the device has a rise time of less than 800ps.

High-performance 1.55 mu m low-temperature-grown GaAs resonant-cavity-enhanced photodetector

A 1.55 mu m low-temperature-grown GaAs (LT-GaAs) photodetector with a resonant-cavityenhanced structure was designed and fabricated. A LT-GaAs layer grown at 200 degrees C was used as the absorption layer. Twenty- and fifteen-pair GaAs/AlAs-distributed Bragg reflectors were grown as the bottom and top mirrors. A responsivity of 7.1 mA/W with a full width at half maximum of 4 nm was obtained at 1.61 mu m. The dark current densities are 1.28x10(-7) A/cm(2) at the bias of 0 V and 3.5x10(-5) A/cm(2) at the reverse bias of 4.0 V. The transient response measurement showed that the photocarrier lifetime in LT-GaAs is 220 fs. (c) 2006 American Institute of Physics.

The effect of low-temperature annealing on ferromagnetic Ga1−xMnxAs thin films studied by photoemission spectroscopy

A systematic photoemission and variable temperature resistivity measurements are carried out on Ga0.946Mn0.054As ferromagnetic semiconductors. It is showed that the Mn 3d valence band and the As 3d core-level spectrum are modified by the annealing treatment. Correlating these modifications with the observed changes in the resistivity and Curie temperatures, we have identified that the low-temperature annealing most likely induces three changes: interstitial Mn out-diffusion, slight increase of the substitution Mn components, and reduction of excess As.

Threading dislocations related persistent photoconductivity effect in hydride vapor phase epitaxy grown GaN epilayers

Deep-level defect-related properties of as-grown and annealed GaN epilayers grown by hydride vapor phase epitaxy (HVPE) are investigated using persistent photoconductivity (PPC) and photoluminescence (PL) measurements. PPC phenomena are seen in these HVPE-GaN epilayers which do not contain the yellow-luminescence (YL) band, suggesting that PPC and YL phenomena are not related. The PPC decay kinetics indicates that the characteristic of the defects which are responsible for the PPC phenomenon would be different from the point defects. The structural qualities of these HVPE-GaN epilayers were characterized by X-ray diffraction. As the densities of threading dislocations decrease, a decrease of photocurrent was clearly observed. The results suggest that the negatively charged threading dislocations are the candidate for PPC effect in our HVPE-GaN epilayers.

Study of the transport properties of annealed (Ga,Mn)As by x-ray absorption spectroscopy

A systematic Mn L-edge x-ray absorption is carried out on carefully prepared Ga0.946Mn0.054As ferromagnetic semiconductors with varying As2∕Ga flux ratio. It is found that the L3 peak of the absorption spectroscopy is enhanced after low temperature (LT) annealing. Furthermore it is shown that a more localized electronic structure nearly like the d5 high-spin state is obtained. It can be attributed to breaking the MnS–MnI pairs during the annealing process. Furthermore the authors present a direct evidence for a slightly increase of the Mn substitutional concentration due to LT annealing.