Molecular beam epitaxy growth of a bilayer stacked InAs/GaAs quantum dot structure on a pure GaAs matrix has been systemically investigated.The influence of growth temperature and the InAs deposition of both layers on the optical properties and morphologies of the bilayer quantum dot（BQD） structures is discussed.By optimizing the growth parameters,InAs BQD emission at 1.436μm at room temperature with a narrower FWHM of 27 meV was demonstrated.The density of QDs in the second layer is around 9×109 to 1.4×1010 cm-2. The BQD structure provides a useful way to extend the emission wavelength of GaAs-based material for quantum functional devices.
A theoretical model of the refractive index changes of the TE and TM modes in an electro-absorption modulator (EAM) is deduced. The photon absorption and refractive index changes are analyzed numerically. The influence of pump intensity on the phase difference between the TE and TM modes is studied. The polarization rotation effect is obtained in the EAM, and a novel all-optical fiber loop buffer is designed.
Molecular beam epitaxy growth of GaAs on an offcut Ge (100) substrate has been systemically investigated.A high quality GaAs/Ge interface and GaAs film on Ge have been achieved.High temperature annealing before GaAs deposition is found to be indispensable to avoid anti-phase domains.The quality of the GaAs film is found to strongly depend on the GaAs/Ge interface and the beginning of GaAs deposition.The reason why both high temperature annealing and GaAs growth temperature can affect epitaxial GaAs film quality is discussed.High quality In 0.17 Ga 0.83 As/GaAs strained quantum wells have also been achieved on a Ge substrate.Samples show flat surface morphology and narrow photoluminescence line width compared with the same structure sample grown on a GaAs substrate.These results indicate a large application potential for Ⅲ-Ⅴ compound semiconductor optoelectronic devices on Ge substrates.
Molecular beam epitaxy growth of an InxGa1-xAs/GaAs quantum well（QW） structure（x equals to 0.17 or 0.3） on offcut（100） Ge substrate has been investigated.The samples were characterized by atomic force microscopy,photoluminescence（PL）,and high resolution transmission electron microscopy.High temperature annealing of the Ge substrate is necessary to grow GaAs buffer layer without anti-phase domains.During the subsequent growth of the GaAs buffer layer and an InxGa1-xAs/GaAs QW structure,temperature plays a key role. The mechanism by which temperature influences the material quality is discussed.High quality InxGa1-x As/GaAs QW structure samples on Ge substrate with high PL intensity,narrow PL linewidth and flat surface morphology have been achieved by optimizing growth temperatures.Our results show promising device applications forⅢ-Ⅴcompound semiconductor materials grown on Ge substrates.
The self-assembled growth of InAs/GaAs quantum dots by molecular beam epitaxy is conducted by optimizing several growth parameters,using a one-step interruption method after island formation.The dependence of photoluminescence on areal quantum-dot density is systematically investigated as a function of InAs deposition,growth temperature and arsenic pressure.The results of this investigation along with time-resolved photoluminescence measurements show that the combination of a growth temperature of 490 C,with a deposition rate of 0.02 ML/s,under an arsenic pressure of 1×10 6Torr(1 Torr=1.33322×102Pa),provides the best compromise between high density and the photoluminescence of quantum dot structure,with a radiative lifetime of 780 ps.The applicability of this 5-layer quantum dot structure to high-repetition-rate pulsed lasers is demonstrated with the fabrication and characterization of a monolithic InAs/GaAs quantum-dot passively mode-locked laser operating at nearly 1300 nm.Picosecond pulse generation is achieved from a two-section laser,with a^19.7-GHz repetition rate.
李密锋倪海桥丁颖Bajek DavidKong LiangCataluna Maria Ana牛智川
The growth of GaAs epilayers on silicon substrates with multiple layers of InAs quantum dots(QDs) as dislocation filters by metalorganic chemical vapor deposition(MOCVD) is investigated in detail.The growth conditions of single and multiple layers of QDs used as dislocation filters in GaAs/Si epilayers are optimized.It is found that the insertion of a five-layer InAs QDs into the GaAs buffer layer effectively reduces the dislocation density of GaAs/Si film.Compared with the dislocation density of 5×10~7 cm^(-2) in the GaAs/Si sample without QDs,a density of 2×10~6 cm^(-2) is achieved in the sample with QD dislocation filters.
The GaAs based InGaAs metamorphic structures and their growth by molecular beam epitaxy (MBE) are investigated. The controlling of the source temperature is improved to realize the linearly graded InGaAs metamorphic structure precisely. The threading dislocations are reduced. We also optimize the growth and annealing parameters of the InGaAs quantum well (QW). The 1.3-μm GaAs based metamorphic InGaAs QW is completed. A 1.3-μm GaAs based metamorphic laser is reported.
We propose a novel high-performance digital optical sensor based on the Mach–Zehnder interferential effect and the dual-microring resonators with the waveguide-coupled feedback. The simulation results show that the sensitivity of the sensor can be orders of magnitude higher than that of a conventional sensor, and high quality factor is not critical in it.Moreover, by optimizing the length of the feedback waveguide to be equal to the perimeter of the ring, the measurement range of the proposed sensor is twice as much as that of the conventional sensor in the weak coupling case.
The optimization of a SiO2/TiO2,SiO2/ZnS double layer antireflection coating（ARC）on Ga0.5In0.5P/In0.02Ga0.98As/Ge solar cells for terrestrial application is discussed.The Al0.5In0.5P window layer thickness is also taken into consideration.It is shown that the optimal parameters of double layer ARC vary with the thickness of the window layer.
