Self-organized superlattices along the [001] growth direction in In0.52Al0.48As layers grown on nominally (001) InP substrates by molecular beam epitaxy

Horizontal self-organized superlattice structures consisting of alternating In-rich and Al-rich layers formed naturally during solid-source molecular beam epitaxy (MBE) growth of In0.52Al0.48As on exactly (001) InP substrates, with In and At fluxes unchanged. The growth temperatures were changed from 490 to 510 degrees C, the most commonly used growth temperature for In0.52Al0.48As alloy. No self-organized superlattices (SLs) were observed at the growth temperature 490 degrees C, and self-organized SLs were observed in InAlAs layers at growth temperatures ranging from 498 to 510 degrees C. The results show that the period of the SLs is very highly regular, with the value of similar to 6 nm, and the composition of In or Al varies approximately sinusoidally along the [001] growth direction. The theoretical simulation results confirm that the In composition modulation amplitude is less than 0.02 relative the In composition of the In0.52Al0.48As lattice matched with the InP substrate. The influence of InAs self-organized quantum wires on the spontaneously formed InxAl1-xAs/InyAl1-yAs SLs was also studied and the formation of self-organized InxAl1-xAs/InyAl1-yAs SLs was attributed to the strain-mediated surface segregation process during MBE growth of In0.52Al0.48As alloy. (C) 2005 Published by Elsevier Ltd.

The effect of In content on high-density InxGa1-xAs quantum dots

We have successfully grown self-assembled InxGa1-xAs (x = 0.44, 0.47, 0.50) quantum dots (QDs) with high density (> 10(11)/cm(2)) by MBE. The effect of In content on the high-density QD is investigated by atomic force microscopy (AFM) and photoluminescence (PL) spectra. It is found that sample with In-mole-fraction of 0.5 shows small size fluctuation and high PL intensity. The influence of growth temperature on high-density QD is also investigated in our experiment. (c) 2005 Elsevier B.V. All rights reserved.

Optical properties and exciton localization in GaNas/GaAs

GaNAs/GaAs single quantum wells (SQWs) and dilute GaNAs bulk grown by molecular beam epitaxy(MBE) were studied by photoluminescence (PL), selectively-excited PL, and time-resolved PL. Exciton localization and delocalization were investigated in detail. Under short pulse laser excitation, the delocalization exciton emission was revealed in GaNAs/GaAs SQWs. It exhibits quite different optical properties from N-related localized states. In dilute GaNAs bulk, a transition of alloy band related recombination was observed by measuring the PL dependence on temperature and excitation intensity and time-resolved PL, as well. This alloy-related transition presents intrinsic optical properties. These results are very important for realizing the abnomal features of III-V-N semiconductors.

Photoluminescence study of (GaAs1-xSbx/InyGa1-yAs)/GaAs bilayer quantum well grown by molecular beam epitaxy

Photoluminescence study of (GaAs1-xSbx/InyGa1-yAs)/GaAs bilayer quantum wells (BQWs) grown by molecular beam epitaxy (MBE) were carried out. Temperature and excitation power dependent photoluminescence (PL) study indicated that the band alignment of the BQWs is type - II. The origin of the double-peak luminescence was discussed. Under optimized growth conditions, the PL emission wavelength from the BQWs has been extend up to 1.31 mu m with a single peak at room temperature.

Molecular beam epitaxy growth and photoluminescence study of room temperature 1.31 mu m (InyGa1-yAs/GaAs1-x Sb-x)/ GaAs bilayer quantum wells

Molecular beam epitaxy (MBE) growth of (InyGa1-yAs/GaAs1-xSbx)/GaAs bilayer quantum well (BQW) structures has been investigated. It is evidenced by photo luminescence (PL) that a strong blue shift of the PL peak energy of 47 meV with increasing PL excitation power from 0.63 to 20 mW was observed, indicating type II band alignment of the BQW. The emission wavelength at room temperature from (InyGa1-yAs/GaAs1-xSbx)/GaAs BQW is longer (above 1.2 μ m) than that from InGaAs/GaAs and GaAsSb/GaAs SQW structures (1.1 μ m range), while the emission efficiency from the BQW structures is comparable to that of the SQW. Through optimizing growth conditions, we have obtained room temperature 1.31 μ m wavelength emission from the (InyGa1-yAs/GaAs1-xSbx)/GaAs BQW. Our results have proved experimentally that the GaAs-based bilayer (InyGa1-yAs/GaAs1-xSbx)/GaAs quantum well is a useful structure for the fabrication of near-infrared wavelength optoelectronic devices. © 2005 Elsevier B.V. All rights reserved.

The effect of a combined InAlAs and GaAs strained buffer layer on the structure and optical property of InAs quantum dots

The character of InAs quantum dots (QD) directly deposited on a combined InAlAs-GaAs (XML) strained buffer layer (SBL) has been investigated. This growth technique realizes high-density QD (5.88 x 10(10) cm(-2)) by changing the thickness of GaAs in InAlAs-GaAs SBL. The dependence of the density and the aspect ratio of QD on the GaAs thickness has been discussed in detail. The photoluminescence (PL) measurements demonstrate an obvious redshift with the increase of GaAs thickness. In addition, the deposition of InAs QDs grown on the combined InAlAs-GaAs SBL has an important effect of the QD properties. The ordered QD array can be observed from the sample deposited by atomic layer epitaxy, of which the PL peak shows an obvious redshift in comparison to the molecular beam epitaxy (MBE) QDs when the GaAs thicknesses are equal. (c) 2004 Elsevier B.V. All rights reserved.

Changing planar thin film growth into self-assembled island formation by adjusting experimental conditions

Illustrated in this paper are two examples of altering planar growth into self-assembled island formation by adapting experimental conditions. Partial oxidation, undersaturated solution and high temperature change Frank-Van der Merwe (FM) growth of Al0.3Ga0.7As in liquid phase epitaxy (LPE) into isolated island deposition. Low growth speed, high temperature and in situ annealing in molecular beam epitaxy (MBE) cause the origination of InAs/GaAs quantum dots (QDs) to happen while the film is still below critical thickness in Stranski-Krastanow (SK) mode. Sample morphologies are characterized by scanning electron microscopy (SEM) or atomic force microscopy (AFM). It is suggested that such achievements are of value not only to fundamental researches but also to spheres of device applications as well. (c) 2004 Elsevier B.V. All rights reserved.

Semiconductor nanometer structures and devices

Self-assembled quantum dots and wires were obtained in the InxGa1-xAs/GaAs and InAs/In0.52Al0.48As/lnP systems, respectively, using molecular beam epitaxy (MBE). Uniformity in the distribution, density, and spatial ordering of the nanostructures can be controlled to some extent by adjusting and optimizing the MBE growth parameters. Laser devices and superluminescent diodes were fabricated with InAs/GaAs self-assembled quantum dots as the active region.

Effect of the growth mode on the two- to three-dimensional transition of InAs grown on vicinal GaAs(001) substrates

Some differences were observed between conventional molecular-beam epitaxy (MBE) and mobility enhanced epitaxy (MEE) of InAs on a vicinal GaAs(001) substrate in the variation of the number density N of the InAs islands, with additional InAs coverage (theta - theta(c)) after the critical InAs coverage theta(c) during the two- to three-dimensional (2D-3D) transition. For MBE the variation was consistent with the power law N(theta) (theta similar to theta(c))(alpha); while for MEE, the linear relation N(theta) proportional to (theta - theta(c)) was observed. The difference is discussed in terms of the randomness in the nucleation of the InAs islands.

Optimization of GaInNAs(Sb)/GaAs quantum wells at 1.3-1.55 mu m grown by molecular beam epitaxy

The InGaNAs(Sb)/(GaNAs)/GaAs quantum wells (QWs) emitting at 1.3-1.55 mu m have been grown by molecular beam epitaxy (MBE). The parameters of the radio frequency (RF) such as RF power and flow rate are optimized to reduce the damages from the ions or energetic species. The growth temperature is carefully controlled to prevent the phase segregation and strain relaxation. The effects of Sb on the wavelength and quality are investigated. The GaNAs barrier is used to extend the wavelength and reduce the strain. A 1.5865 mu m InGaNAs(Sb)/GaNAs SQW edge emitting laser lasing at room temperature at continuous wave operation mode is demonstrated. (c) 2006 Elsevier B.V. All rights reserved.

Metamorphic growth of 1.25-1.29 mu m InGaAs quantum well lasers on GaAs by molecular beam epitaxy

We demonstrate 1.25-1.29 mu m metamorphic laser diodes grown on GaAs by molecular beam epitaxy (MBE) using an alloy-graded buffer layer (GBL). Use of Be in the GBL is effective to reduce surface/interface roughness and improves optical quality. The RMS surface roughness of the optimized metamorphic laser is only two atomic monolayers for 1 x 1 mu m(2). Cross-sectional transmission electron microscopy (TEM) images confirm that most dislocations are blocked in the GBL. Ridge waveguide lasers with 4 mu m wide ridge were fabricated and characterized. The average threshold current under the pulsed excitation is in 170-200 mA for a cavity length of 0.9-1.5 mm. This value can be further reduced to about 100 mA by high-reflectivity coating. Lasers can work in an ambient temperature up to at least 50 degrees C. (c) 2006 Elsevier B.V. All rights reserved.

Electro-optic coefficients of Si0.75Ge0.25/Si/Si0.5Ge0.5 asymmetric superlattice measured by polarization-maintaining fiber-optic Mach-Zehnder interferometer

Ten-period 5.5 nm Si0.75Ge0.25/10.3 nm Si/2.5 nm Si0.5Ge0.5 trilayer asymmetric superlattice was prepared on Si (001) substrate by ultrahigh vacuum chemical vapor deposition at 500 degrees C. The stability of Mach-Zehnder interferometer was improved by utilizing polarization-maintaining fibers. According to the electro-optic responses of the superlattice with the light polarization along [110] and [-110], respectively, both electro-optic coefficients gamma(13) and gamma(63) of such asymmetric superlattice were measured. gamma(13) and gamma(63) are 2.4x10(-11) and 1.3x10(-11) cm/V, respectively, with the incident light wavelength at 1.55 mu m. (c) 2006 American Institute of Physics.

A bistable, self-latching inverter by the monolithic integration of resonant tunnelling diode and high electron mobility transistor

This paper reports that the structures of AlGaAs/InGaAs high electron mobility transistor (HEMT) and AlAs/GaAs resonant tunnelling diode (RTD) are epitaxially grown by molecular beam epitaxy ( MBE) in turn on a GaAs substrate. An Al0.24Ga0.76As chair barrier layer, which is grown adjacent to the top AlAs barrier, helps to reduce the valley current of RTD. The peak-to-valley current ratio of fabricated RTD is 4.8 and the transconductance for the 1-mu m gate HEMT is 125mS/mm. A static inverter which consists of two RTDs and a HEMT is designed and fabricated. Unlike a conventional CMOS inverter, the novel inverter exhibits self-latching property.

Electrical properties of undoped In0.53Ga0.47As grown on InP substrates by molecular beam epitaxy

A series of 1-mu m-thick undoped In0.53Ga0.47As with different substrate growth temperature (T-g) or different beam flux pressure (BFP) of As were grown on lattice-matched semi-insulating InP (001) substrates by molecular beam epitaxy (MBE). Van der Pauw Hall measurements were carried out for these In0.53Ga0.47As samples. The residual electron concentration decreased with increasing temperature from 77 to 140 K, but increased with increasing temperature from 140 to 300 K. Rapid thermal annealing (RTA) can reduce the residual electron concentration. The residual electron mobility increased with increasing temperature from 77 to 300 K. All these electrical properties are associated with As antisite defects. (c) 2006 Elsevier B.V. All rights reserved.

Optical characteristics of InAs quantum dots on GaAs matrix by using various InGaAs structures

The effects of various InGaAs layers on the structural and optical properties of InAs self-assembled quantum dots (QDs) grown by molecular-beam epitaxy ( MBE) were investigated. The emission wavelength of 1317 nm was obtained by embedding InAs QDs in InGAs/GgAs quantum well. The temperature-dependent and timed-resolved photoluminescence (TDPL and TRPL) were used to study the dynamic characteristics of carriers. InGaAs cap layer may improve the quality of quantum dots for the strain relaxation around QDs, which results in a stronger PL intensity and an increase of PL peak lifetime up to 170 K. We found that InGaAs buffer layer may reduce the PL peak lifetime of InAs QDs, which is due to the buffer layer accelerating the carrier migration. The results also show that InGaAs cap layer can increase the temperature point when, the thermal reemission and nonradiative recombination contribute significantly to the carrier dynamics.