InAs self-assembled nanostructures grown on InP(001)

The 6-period stacked layers of self-assembled InAs quasi-quantum wires(qQWRs) and quantum dots(QDs) embedded into InAlAs on InP(001) substrates have been prepared by solid molecular beam epitaxy. The structures are characterized by atomic force microscopy(AFM) and transmission electron microscopy(TEM). From AFM we have observed for the first time that InAs qQWRs and QDs coexist, and we explained this phenomenon from the view of the energy related to the islands. Cross-sectional TEM shows that InAs qQWRs are vertically aligned every other layer along the growth direction [001], which disagrees with conventional vertical self-alignment of InAs QDs on GaAs substrate.

Growth and characterization of strained superlattices delta-GaNxAs1-x/GaAs by molecular beam epitaxy

A series of superlattices delta-GaNxAs1-x/GaAs were grown by a DC plasma-N-2-assisted molecular beam epitaxy. The evolution of the surface reconstruction during the growth has been studied with the use of in situ reflection high-energy electron diffraction. The superlattices have been characterized by high-resolution X-ray diffraction measurements. Distinct satellite peaks indicate that the superlattices are of good quality. The N compositions in strained GaNxAs1-x monolayers are obtained from the dynamical simulations of the measured X-ray diffraction patterns. The periodicity fluctuations of N composition are obtained from a kinematical method dependent on the broadening of the satellite peaks of the X-ray diffraction. (C) 2000 Elsevier Science B.V. All rights reserved.

Effect of arsenic precipitates on Fermi level in GaAs grown by molecular-beam epitaxy at low temperature

A simple model is presented to discuss the effect of As precipitates on the Fermi level in GaAs grown by molecular-beam epitaxy at low temperature (LT-GaAs). This model implements the compensation between point defects and the depletion of arsenic precipitates. The condition that the Fermi level is pinned by As precipitates is attained. The shifts of the Fermi level in LT-GaAs with annealing temperature are explained by our model. Additionally, the role of As precipitates in conventional semi-insulating GaAs is discussed. (C) 2000 American Institute of Physics. [S0021-8979(00)09905-9].

Doping during low-temperature growth of materials for n-p-n Si/SiGe/Si heterojuction bipolar transistor by gas source molecular beam epitaxy

In situ doping for growth of n-p-n Si/SiGe/Si heterojuction bipolar transistor (HBT) structural materials in Si gas source molecular beam epitaxy is investigated. We studied high n-type doping kinetics in Si growth using disilane and phosphine, and p-type doping in SiGe growth using disilane, soild-Ge, and diborane with an emphasis on the effect of Ge on B incorporation. Based on these results, in situ growth of n-p-n Si/SiGe/Si HBT device structure is demonstrated with designed structural and carrier profiles, as verified from characterizations by X-ray diffraction, and spreading resistance profiling analysis. (C) 2000 Elsevier Science B.V. All rights reserved.

Effects of rapid thermal annealing on the optical properties of GaNxAs1-x/GaAs single quantum well structure grown by molecular beam epitaxy

The effect of rapid thermal annealing (RTA) on the optical properties of GaNxAs1-x/GaAs strained single quantum well (SQW) was studied by low-temperature photoluminescence (PL). The GaNxAs1-x/GaAs SQW structures were prepared by dc active nitrogen plasma assisted molecular beam epitaxy. PL measurements on a series of samples with different well widths and nitrogen compositions were used to evaluate the effects of RTA. The annealing temperature and time were varied from 650 to 850 degrees C and 30 s to 15 min, respectively. Remarkable improvements of the optical properties of the samples were observed after RTA under optimum conditions. The interdiffusion constants have been calculated by taking into account error function diffusion and solving the Schrodinger equation. The estimated interdiffusion constants D are 10(-17)-10(-16) cm(2)/s for the earlier annealing conditions. Activation energies of 6-7 eV are obtained by fitting the temperature dependence of the interdiffusion constants. (C) 2000 American Institute of Physics. [S0021-8979(00)10401-3].

Two-dimensional ordering of self-assembled InxGal-xAs quantum dots grown on GaAs(311)B surfaces

Two-dimensional (2D) ordering of self-assembled InxGa1-xAs quantum dots (QDs) fabricated on GaAs(311)B surface by molecular beam epitaxy (MBE) are reported. The QDs are aligned into rows deferring from the direction of the misorientation of the substrate, and strongly dependent on the mole In content x of InxGa1-xAs solid solution. The ordering alignment deteriorates significantly as the In content is increased to above 0.5. The 2D ordering can be described as a centered rectangular unit mesh with the two sides parallel to [01 (1) over bar] and [(2) over bar 33], respectively. Their relative arrangement seems to be determined by a combination of the strongly repulsive elastic interaction between neighbouring islands and the minimization of the strain energy of the whole system. The ordering also helps to improve the size homogeneity of the InGaAs islands. Photoluminescence (PL) result demonstrates that QDs grown on (311)B have the narrowest linewidth and the strongest integrated intensity, compared to those grown on (100) and other high-index planes under the same condition. (C) 1999 Elsevier Science B.V. All rights reserved.

Two-dimensional ordering of self-assembled InxGa1-xAs quantum dots grown on GaAs(311)B surfaces

The two-dimensional (2D) ordering of self-assembled InxGa1-xAs quantum dots (QDs) fabricated on GaAs(3 1 1)B surface by molecular beam epitaxy (MBE) are reported. The QDs are aligned into rows differing from the direction of the misorientation of the substrate, and strongly dependent on the mole In content x of InxGa1-As-x solid solution. The ordering alignment deteriorates significantly as the In content is increased to above 0.5. The 2D ordering can be described as a centered rectangular unit mesh with the two sides parallel to [0 1 (1) over bar] and [(2) over bar 3 3], respectively. Their relative arrangement seems to be determined by a combination of the strongly repulsive elastic interaction between the neighboring islands and the minimization of the strain energy of the whole system. The ordering also helps to improve the size homogeneity of the InGaAs islands. The photoluminescence (PL) result demonstrates that QDs grown on (3 1 1)B have the narrowest linewidth and the strongest integrated intensity, compared to those on (1 0 0) and other high-index planes under the same condition. (C) 1999 Elsevier Science B.V. All rights reserved.

High-density InAs nanowires realized in situ on (100) InP

High-density InAs nanowires embedded in an In0.52Al0.48As matrix are fabricated in situ by molecular beam epitaxy on (100) InP. The average cross section of the nanowires is 4.5 x 10 nm(2). The linear density is as high as 70 wires/mu m. The spatial alignment of the multilayer arrays exhibit strong anticorrelation in the growth direction. Large polarization anisotropic effect is observed in polarized photoluminescence measurements. (C) 1999 American Institute of Physics. [S0003-6951(99)04134-0].

Electrical properties of GaN deposited on nitridated sapphire by molecular beam epitaxy using NH3 cracked on the growing surface

We have found that GaN epilayers grown by NH3-source molecular beam epitaxy (MBE) contain hydrogen. Dependent on the hydrogen concentration, GaN on (0001) sapphire can be either under biaxially compressive strain or under biaxially tensile strain. Furthermore, we notice that background electrons in GaN increase with hydrogen incorporation. X-ray photoelectron spectroscopy (XPS) measurements of the N1s region indicate that hydrogen is bound to nitrogen. So, the microdefect Ga...H-N is an effective nitrogen vacancy in GaN, and it may be a donor partly answering for the background electrons. (C) 1999 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.

High phosphorous doping and morphological evolution during Si growth by gas source molecular beam epitaxy (GSMBE)

Uniform and high phosphorous doping has been demonstrated during Si growth by GSMBE using disilane and phosphine. The p-n diodes, which consist of a n-Si layer and a p-SiGe layer grown on Si substrate, show a normal I-V characteristic. A roughening transition during P-doped Si growth is found. Ex situ SEM results show that thinner film is specular. When the film becomes thicker, there are small pits of different sizes randomly distributed on the flat surface. The average pit size increases, the pit density decreases, and the size distribution is narrower for even thicker film. No extended defects are found at the substrate interface or in the epilayer. Possible causes for the morphological evolution are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.

Enhanced hydrogen desorption from Si sites during low-temperature Si1-xGex growth by disilane and solid-Ge molecular beam epitaxy

A phenomenological model is proposed to explain quantitatively the interesting compositional dependence on the Ge incorporation rate during low-temperature growth of Si1-xGex by disilane and solid-Ge molecular beam epitaxy, based on enhanced hydrogen desorption from Si sites due to the presence of Ge atoms. The hydrogen desorption rate constant for disilane on Si sites is fitted to an exponential function of Ge incorporation rate and a possible physical explanation is discussed. Simulated results are in excellent agreement with experimental data. (C) 1999 American Institute of Physics. [S0021-8979(99)02109-X].

In composition dependence of lateral ordering in InGaAs quantum dots grown on (311)B GaAs substrates

Self-assembled InxGa1-xAs quantum dots (QDs) on (311)A/B GaAs surfaces have been grown by molecular beam epitaxy (MBE). Spontaneously ordering alignment of InxGa1-xAs with lower In content around 0.3 have been observed. The direction of alignment orientation of the QDs formation differs from the direction of misorientation of the (311)B surface, and is strongly dependent upon the In content x. The ordering alignment become significantly deteriorated as the In content is increased to above 0.5 or as the QDs are formed on (100) or (311)A substrates. (C) 1999 Elsevier Science B.V. All rights reserved.

Growth mode and strain relaxation of InAs on InP (111)A grown by molecular beam epitaxy

Growth mode and strain relaxation of molecular-beam-epitaxy grown InAs/InAlAs/InP (111)A system have been investigated using reflection high-energy electron diffraction, transmission electron microscopy, atomic force microscopy, and photoluminescence measurements. In direct contrast to the well-studied InAs/GaAs system, our experimental results show that the InAs grown on InAlAs/InP (111)A follows the Stranski-Krastanov mode. Both self-organized InAs quantum dots and relaxed InAs islands are formed depending on the InAs coverage. Intense luminescence signals from both the InAs quantum dots and wetting layer are observed. The luminescence efficiency of (111)A samples is comparable to that of (001) samples, suggesting the feasibility of fabricating quantum dot optoelectronic devices on InP (111)A surfaces. (C) 1999 American Institute of Physics. [S0003-6951(99)01010-4].

Gas source molecular beam epitaxy and thermal stability of Si1-xGex/Si superlattice materials

Gas source molecular beam epitaxy has been used to grow Si1-xGex alloys and Si1-xGex/Si multi-quantum wells (MQWs) on (100) Si substrates with Si2H6 and GeH4 as sources. Heterostructures and MQWs with mirror-like surface morphology, good crystalline qualify, and abrupt interfaces have been studied by a variety of in situ and ex situ techniques. The structural stability and strain relaxation in Si1-xGex/Si heterostructures have been investigated, and compared to that in the As ion-implanted Si1-xGex epilayers. The results show that the strain relaxation mechanism of the non-implanted Si1-xGex epilayers is different from that of the As ion-implanted Si1-xGex epilayers.