GaAs/AlGaAs量子阱红外探测器单管及四元线列

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高质量GaAs/AlGaAs二维电子气材料研制及其器件应用

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Electronic structure and optical gain saturation of InAs1-xNx/GaAs quantum dots

The electronic band structures and optical gains of InAs1-xNx/GaAs pyramid quantum dots (QDs) are calculated using the ten-band k . p model and the valence force field method. The optical gains are calculated using the zero-dimensional optical gain formula with taking into consideration of both homogeneous and inhomogeneous broadenings due to the size fluctuation of quantum dots which follows a normal distribution. With the variation of QD sizes and nitrogen composition, it can be shown that the nitrogen composition and the strains can significantly affect the energy levels especially the conduction band which has repulsion interaction with nitrogen resonant state due to the band anticrossing interaction. It facilitates to achieve emission of longer wavelength (1.33 or 1.55 mu m) lasers for optical fiber communication system. For QD with higher nitrogen composition, it has longer emission wavelength and less detrimental effect of higher excited state transition, but nitrogen composition can affect the maximum gain depending on the factors of transition matrix element and the Fermi-Dirac distributions for electrons in the conduction bands and holes in the valence bands respectively. For larger QD, its maximum optical gain is greater at lower carrier density, but it is slowly surpassed by smaller QD as carrier concentration increases. Larger QD can reach its saturation gain faster, but this saturation gain is smaller than that of smaller QD. So the trade-off between longer wavelength, maximum optical, saturation gain, and differential gain must be considered to select the appropriate QD size according to the specific application requirement. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3143025]

ф2”和 ф3”非掺Si-GaAs单晶（片）研究

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Morphology and wetting layer properties of InAs/GaAs nanostructures

In this work, we present the growth of InAs rings by droplet epitaxy. A complete process from the rings formation to their density saturation has been demonstrated: A morphological evolution with the varying of the indium deposition amount has been, clearly observed. Our results indicate that there, is a critical deposition amount (similar to 1.1 ML) for the indium to form InAs dots before droplets form; there is also a critical deposition amount (similar to 1.4 ML) to form InAs ring, but it is caused by the formation of droplets as the deposition amount increases. The density of the rings saturates when the deposition amount exceeds similar to 3.3 ML; because the adsorbed indium atoms block sites for further adsorption and the following supplied In only contributes to the size increase of In droplets. Still, as the In deposition amount increases, we can find coupled quantum rings. Moreover, the wetting layer properties of these structures are studied by reflectance difference spectroscopy, which shows a complicated evolution with the In amount. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Theoretical analysis of modal gain in p-doped 1.3 mu m InAs/GaAs quantum dot lasers

A theoretical study of modal gain in p-doped 1.3 mu m InAs/GaAs quantum dot (QD) lasers is presented. The expression of modal gain is derived, which includes an effective ratio that describes how many QDs contribute to the modal gain. The calculated results indicate that the modal gain with the effective ratio is much smaller than that without the effective ratio. The calculated maximum modal gain is is a good agreement with the experimental data. Furthermore, QDs with lower height or smaller aspect ratio are beneficial in achieving a larger maximum modal gain that leads to lower threshold current density and higher differential modal gain. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Evolution of wetting layers in InAs/GaAs quantum-dot system studied by reflectance difference spectroscopy

The wetting layers (WL) in InAs/GaAs quantum-dot system have been studied by reflectance difference spectroscopy (RDS), in which two structures related to the heavy-hole (HH) and light-hole (LH) transitions in the WL have been observed. The evolution and segregation behaviors of WL during Stranski-Krastanow (SK) growth mode have been studied from the analysis of the WL-related optical transition energies. It has been found that the segregation coefficient of Indium atoms varies linearly with the InAs amount in WL. In addition, the effect of the growth temperature on the critical thickness for InAs island formation has also been studied. The critical thickness defined by the appearance of InAs dots, which is determined by AFM, shows a complex variation with the growth temperature. However, the critical thickness determined by RDS is almost constant in the range of 510-540 degrees C.

LPE法制备的高效GaAs太阳电池

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InAs/GaAs量子点和量子阱的静压光谱研究

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Desorption and Ripening of Low Density InAs Quantum Dots

In this paper, combining low deposition rate with proper growth temperature, we have developed a way to prepare very low-density quantum dots (QDs) suited for the study of single OD properties without resorting to submicron lithography. Experiment results demonstrate that InAs desorption is significant during growing the low density QDs. Ripening of InAs QDs is clearly observed during the post-growth annealing. Photoluminescence spectroscopy reveals that the emission wavelength of low density InAs QDs arrives at 1332.4 nm with a GaAs capping layer.

Terahertz pulse generation with LT-GaAs photoconductive antenna

Low-temperature-grown GaAs (LT-GaAs) of 1-um thickness was grown at 250 degrees C on semi-insulating GaAs (001) substrate using EPI GEN-II solid-source MBE system. The sample was then in situ annealed for 10 min at 600 degrees C under As-rich condition. THz emitters were fabricated on this LTGaAs with three different photoconductive dipole antenna gaps of 1-mm, 3-mm, and 5-mm, respectively. The spectral bandwidth of 2.75 THz was obtaind with time domain spectroscopy. It is found that THz emission efficiency is increased with decreasing antenna gap. Two carrier lifetimes, 0.469 ps and 3.759 ps, were obtained with time-resolved transient reflection-type pump-probe spectroscopy.

Optical and electrical investigation of low dimensional self-assembled InAs quantum dot field effect transistors

Self-assembled InAs QD dot-in-a-well (DWELL) structures were grown on GaAs substrate by MBE system, and heterojunction modulation-doped field effect transistor (MODFET) was fabricated. The optical properties of the samples show that the photoluminescence of InAs/GaAs self-assembled quantum dot (SAQD) is at 1.265 mu m at 300 K. The temperature-dependence of the abnormal redshift of InAs SAQD wavelength with the increasing temperature was observed, which is closely related with the inhomogeneous size distribution of the InAs quantum dot. According to the electrical measurement, high electric field current-voltage characteristic of the MODFET device were obtained. The embedded InAs QD of the samples can be regard as scattering centers to the vicinity of the channel electrons. The transport property of the electrons in GaAs channel will be modulated by the QD due to the Coulomb interaction. It has been proposed that a MODFET embedded with InAs QDs presents a novel type of field effect photon detector.

Corrugated surfaces formed on GaAs (331)a substrates: The template for laterally ordered InGaAs nanowires

Morphology evolution of high-index (331)A surfaces during molecular beam epitaxy (MBE) growth have been investigated in order to uncover their unique physic properties and fabricate spatially ordered low dimensional nanostructures. Atomic Force Microscope (AFM) measurements have shown that the step height and terrace width of GaAs layers increase monotonically with increasing substrate temperature in conventional MBE. However, this situation is reversed in atomic hydrogen-assisted MBE, indicating that step bunching is partly suppressed. We attribute this to the reduced surface migration length of Ga adatoms with atomic hydrogen. By using the step arrays formed on GaAs (331)A surfaces as the templates, we fabricated laterally ordered InGaAs self-aligned nanowires.

Anomalous temperature-dependent bimodal size evolution of InAs quantum dots on vicinal GaAs(100) substrates

Temperature-dependent bimodal size evolution of InAs quantum dots on vicinal GaAs(100) substrates grown by metalorganic chemical vapor deposition (MOCVD) is studied. An abnormal trend of the evolution on temperature is observed. With the increase of the growth temperature, while the density of the large dots decreases continually, that of the small dots first grows larger when temperature was below 520 degrees C, and then there is a sudden decrease at 535 degrees C. Photoluminescence (PL) studies show that QDs on vicinal substrates have a narrower PL line width, a longer emission wavelength and a larger PL intensity.

Molecular-beam epitaxial growth of position controlled InAs islands on cleaved edge of InGaAs/GaAs superlattice

A promising approach for positioning of InAs islands on (110)GaAs is demonstrated. By combining self-assembly of quantum dots with solid source molecular beam epitaxy (MBE) on cleaved edge of InGaAs/GaAs superlattice (SL), linear alignment of InAs islands on the InGaAs strain layers have been fabricated The cleaved edge of InGaAs/GaAs SL acts as strain nanopattern for InAs selective growth. Indium atoms incident on the surface will preferentially migrate to InGaAs regions where favorable bonding sites are available. The strain nanopattern's effect is studied by the different indium fraction and thickness of InxGa1-xAs/GaAs SL. The ordering of the InAs islands is found to depend on the properties of the underlying InGaAs strain layers.