Characterization of deep centers in AlGaAs/InGaAs/GaAs pseudomorphic HEMT structures grown by molecular beam epitaxy and hydrogen treatment

In AlGaAs/InGaAs/GaAs PM-HEMT structures, the characterization of deep centers, the degradation in electrical and optical properties and their effects on electrical performance of the PM-HEMTs have been investigated by DLTS, SIMS, PL and conventional van der Pauw techniques. The experimental results confirm that the deep level centers correlate strongly with the oxygen content in the AlGaAs layer, the PL response of PM-HEMTs, and the electrical performance of the PM-HEMTs. Hydrogen plasma treatment was used to passivate/annihilate these centers, and the effects of hydrogenation were examined.

Excess arsenic in GaAs grown at low temperatures by molecular beam epitaxy

The structural properties of GaAs grown at low temperatures by molecular beam epitaxy (LTMBE GaAs) were studied. The excess arsenic atoms in LTMBE GaAs exist in the form of arsenic interstitial couples (i,e, two ns atoms share the one host site), and cause an increase in the lattice parameter of LTMBE GaAs. Annealing at above 300 degrees C, the arsenic interstitial couples decomposed, and As precipitates formed, resulting in a decrease in the lattice parameter.

Morphology Evolution of (331)A High-Index Surfaces During Atomic Hydrogen Assisted Molecular Beam Epitaxy (MBE)

Step like morphology of (331)A high-index surfaces during atomic hydrogen assisted molecular beam epitaxy (MBE) growth has been investigated. Atomic Force Microscope (AFM) measurements show that in conventional MBE, the step heights and terrace widths of GaAs layers increase monotonically with increasing substrate temperatures. The terrace widths and step densities increase with increasing the GaAs layer thickness and then saturates. And, in atomic hydrogen assisted MBE, the terrace width reduces and density increases when depositing the same amount of GaAs. It attributes this to the reduced surface migration length of Ga adatoms with atomic hydrogen. Laterally ordered InAs self-aligned nano-wires were grown on GaAs (331)A surfaces and its optical polarization properties were revealed by photoluminescence measurements.

1.3μm InGaAs/InAs/GaAs Self-Assembled Quantum Dot Laser Diode Grown by Molecular Beam Epitaxy

The growth of multi-layer InGaAs/InAs/GaAs self-assembled quantum dots （QDs） by molecular beam epitaxy （MBE） is investigated,and a QD laser diode lasing at 1.33μm in continuous operation mode at room temperature is reported. The full width at half maximum of the band edge emitting peaks of the photoluminescence （PL） spectra at room temperature is less than 35meV for most of the multi-layer QD samples,revealing good,reproducible MBE growth conditions. Moreover,atomic force microscopy images show that the QD surface density can be controlled in the range from 1×10^10 to 7 ×10^10 cm^-2 . The best PL properties are obtained at a QD surface density of about 4×10^10cm^-2. Edge emitting lasers containing 3 and 5 stacked QD layers as the active layer lasing at room temperature in continuous wave operation mode are reported.

Photoluminescence characterization of 1.3 mu m In(Ga)As/GaAs islands grown by molecular beam epitaxy

1.3 mum wavelength In(Ga)As/GaAs nanometer scale islands grown by molecular beam epitaxy (MBE) were characterized by photoluminescence (PL) and atomic force microscopy (AFM) measurements. It is shown that inhomogeneous broadening of optical emission due to fluctuation of the In0.5Ga0.5As islands both in size and in compositions can be effectively suppressed by introducing a AlAs layer and a strain reduction In0.2Ga0.8As layer overgrown on top of the islands, 1.3mum emission wavelength with narrower line-width less than 20meV at room temperature was obtained.

Structural and optical properties of GaAsSb/GaAs heterostructure quantum wells

The structural and optical properties of MBE-grown GaAsSb/GaAs multiple quantum wells (MQWs) as well as strain-compensated GaAsSb/GaAs/GaAsP MQWs are investigated. The results of double crystal X-ray diffraction and reciprocal space mapping show that when strain-compensated layers are introduced, the interface quality of QW structure is remarkably improved, and the MQW structure containing GaAsSb layers with a high Sb composition can be coherently grown. Due to the influence of inserted GaAsP layers on the energy band and carrier distribution of QWs, the optical properties of GaAsSb/GaAs/GaAsP MQWs display a lot of features mainly characteristic of type-I QWs despite the type-II GaAsSb/GaAs interfaces exist in the structure. (C) 2004 Elsevier B.V. All rights reserved.

Growth and structural properties of GaN films on flat and vicinal SiC(0001) substrates

Initial stage GaN growth by molecular-beam epitaxy (MBE) on SiC(0001) substrate is followed by in situ scanning tunneling microscopy. Comparison is made between growth on nominally flat and vicinal substrate surfaces and the results reveal characteristic differences between the two. Ex situ transmission electron microscopy (TEM) and X-ray diffraction (XRD) rocking curve measurements of the films show lower density of defects and better structural quality of the vicinal film. We suggest the improved structural quality of the vicinal film is related to the characteristic difference in its initial stage nucleation and coalescence proccsses than that of the flat film.

Quality improvement of GaInNAs/GaAs quantum wells grown by plasma-assisted molecular beam epitaxy

The optimum growth condition of GaInNAs/GaAs quantum wells (QWs) by plasma-assisted molecular beam epitaxy was investigated. High-resolution X-ray diffraction and photoluminescence (PL) measurements showed that ion damage drastically degraded the quality of GaNAs and GaInNAs QWs and that ion removal magnets can effectively remove the excess ion damage. Remarkable improvement of PL intensity and obvious appearance of pendellosung fringes were observed by removing the N ions produced in the plasma cell. When the growth rate increased from 0.73 to 1.2 ML/s, the optimum growth temperature was raised from 460 degreesC to 480 degreesC and PL peak intensity increased two times. Although the N composition decreased with increasing growth rate, degradation of optical properties of GaInNAs QWs was observed when the growth rate was over 0.92 ML/s. Due to low-temperature growth of GaInNAs QWs, a distinctive reflection high-energy electron diffraction pattern was observed only when the GaAs barrier was grown under lower As-4 pressure. The samples with GaAs barriers grown under lower As-4 pressure (V/III ratio about 24) exhibited seven times increase in PL peak intensity compared with those grown under higher As-4 pressure (V/III ratio about 50). (C) 2001 Elsevier Science B,V. All rights reserved.

Optical properties of self-assembled ternary In(GA/Al)As quantum dots on (100) and (N 1 1)B InP substrates

In this paper, we investigated the self-assembled quantum dots formed on (100) and (N11)B (N = 2, 3, 4, 5) InP substrates by molecular beam epitaxy (MBE). Two kinds of ternary QDs (In0.9Ga0.1As and In0.9Al0.1As QDs) are grown on the above substrates; Transmission electron microscopy (TEM) and photoluminescence (PL) results confirm QDs formation for all samples. The PL spectra reveal obvious differences in integral luminescence, peak position, full-width at half-maximum and peak shape between different oriented surfaces. Highest PL integral intensity is observed from QDs on (411)B surfaces, which shows a potential for improving the optical properties of QDs by using high-index surface. (C) 2000 Elsevier Science B.V. All rights reserved.

Structural and infrared absorption properties of self-organized InGaAs GaAs quantum dots multilayers

Self-organized InGaAs/GaAs quantum dots (QDs) stacked multilayers have been prepared by solid source molecular beam epitaxy. Cross-sectional transmission electron microscopy shows that the InGaAs QDs are nearly perfectly vertically aligned in the growth direction [100]. The filtering effect on the QDs distribution is found to be the dominant mechanism leading to vertical alignment and a highly uniform size distribution. Moreover, we observe a distinct infrared absorption from the sample in the range of 8.6-10.7 mu m. This indicates the potential of QDs multilayer structure for use as infrared photodetector.

Structure and properties of InAs/AlAs quantum dots for broadband emission

The InAs quantum dots (QDs) on an AlAs layer are grown on GaAs substrates by molecular beam epitaxy technique. The properties of materials and optics of such QD structures have been investigated by cross sectional transmission electron microscopy and photoluminescence (PL) techniques. It is discovered that the inhomogeneous strain filed mainly exists below InAs QDs layers in the case of no wetting layer. The full width at half maximums (FWHMs) and intensities of PL emission peaks of InAs QDs are found to be closely related to the thickness of the thin AlAs layers. The InAs QDs on an eight monolayer AlAs layer, with wide FWHMs and large integral intensity of PL emission peaks, are favorable for producing broadband QD superluminescent diodes, external-cavity QD laser with large tuning range.