The effects of concomitant In and N incorporation on the photoluminescence of GaInNAs

We investigated the effects of concomitant In- and N-incorporation on the photoluminescence (PL) of GaInNAs grown by molecular beam epitaxy. In comparison with the N-free GaInAs epilayer, the PL spectra of the GaInNAs epilayer exhibit an anomalous S-shape temperature dependence of dominant luminescence peak. Through further careful inspection, two PL peaks are clearly discerned and are associated with the interband excitonic recombinations and excitons bound to N-induced isoelectronic impurity states, respectively. By comparing the PL spectra of GaInNAs/ GaAs quantum wells (QWs) with those of In-free GaNAs/GaAs QWs grown under similar conditions, it is found that the concomitant In- and N-incorporation reduces the density of impurities and has an effect to improve the intrinsic optical transition of GaInNAs, but also enhance the N-induced clustering effects. At last, we found that rapid thermal annealing can significantly reduce the density of N-induced impurities. (C) 2002 Elsevier Science B.V. All rights reserved.

Dependence of optical properties on the structure of multi-layer self-organized InAs quantum dots emitting near 1.3 mu m

Self-organized InAs quantum dots (QDs) have been fabricated by molecular beam epitaxy and characterized by photoluminescence (PL). For both single- and multi-layer QDs, PL intensity of the first excited state is larger than that of the ground state at 15 K. Conversely, at room temperature (RT), PL intensity of the first excited state is smaller than that of the ground state. This result is explained by the phonon bottleneck effect. To the ground state, the PL intensities of the multi-layer QDs are larger than that of the single-layer QDs at 15 K, while the intensities are smaller than that of the single-layer QDs at RT. This is due to the defects in the multi-layer QD samples acting as the nonradiative recombination centers. The inter-diffusion of Ga and In atoms in the growth process of multi-layer QDs results in the PL blueshift of the ground state and broadening of the full-width at half-maximum (FWHM), which can be avoided by decreasing the spacers' growth temperature. At the spacers' growth temperature of 520degreesC, we have prepared the 5-layer QDs which emit near 1.3 mum with a FWHM of 31.7 meV at RT, and 27.9 meV at 77 K. (C) 2002 Published by Elsevier Science B.V.

Structural characteristic of cubic GaN nucleation layers on GaAs(001) substrates by MOCVD

The structural characteristic of cubic GaN (C-GaN) nucleation layers on GaAs(0 0 1) substrates by metalorganic chemical vapor deposition was in detail investigated first by X-ray diffraction (XRD) measurements, using a Huber five-circle diffractometer and an intense synchrotron X-ray source. The XRD results indicate that the C-GaN nucleation layers are highly crystallized. Phi scans and pole figures of the (1 1 1) reflections give a convincing proof that the GaN nucleation layers show exactly cubic symmetrical structure. The GaN(1 1 1) reflections at 54.74degrees in chi are a measurable component, however (002) components parallel to the substrate surface are not detected. Possible explanations are suggested. The pole figures of {1 0 (1) over bar 0} reflections from H-GaN inclusions show that the parasitic H-GaN originates from the C-GaN nucleation layers. The coherence lengths along the close-packed [1 1 1] directions estimated from the (1 1 1) peaks are nanometer order of magnitude. (C) 2002 Elsevier Science B.V. All rights reserved.

Effect of InAlAs/InGaAs cap layer on optical properties of self-assembled InAs/GaAs quantum dots

We have investigated the effect of InAlAs/InGaAs cap layer on the optical properties of self-assembled InAs/GaAs quantum dots (QDs). We find that the photoluminescence emission energy, linewidth and the energy separation between the ground and first excited states of InAs QDs depend on the In composition and the thickness of thin InAlAs cap layer. Furthermore, the large energy separation of 103 meV was obtained from InAs/GaAs QDs with emission at 1.35 pm at room temperature. (C) 2002 Elsevier Science B.V. All rights reserved.

A novel line-order of InAs quantum dots on GaAs

A novel line-order of InAs quantum dots (QDs) along the [1, 1, 0] direction on GaAs substrate has been prepared by self-organized growth. After 2.5 monolayer InAs deposition, QDs in the first layer of multi-layer samples started to gather in a line. Owing to the action of strong stress between layers, almost all the dots of the fourth layer gathered in lines. The dots lining up tightly are actually one-dimensional superlattice of QDs, of which the density of electronic states is different from that of isolated QDs or quantum wires. The photoluminescence spectra of our multi-layer QD sample exhibited a feature of very broad band so that it is suitable for the active medium of super luminescent diode. The reason of dots lining up is attributed to the hill-and-valley structure of the buffer, anisotropy and different diffusion rates in the different directions on the buffer and strong stress between QD layers. (C) 2002 Published by Elsevier Science B. V.

Investigation on the origin of crystallographic tilt in lateral epitaxial overgrown GaN using selective etching

The crystallographic tilt of the lateral epitaxial overgrown (LEO) GaN on sapphire Substrate with SiNx mask is investiaated by double crystal X-ray diffraction. Two wing peaks beside the GaN 0002 peak can be observed for the as-grown LEO GaN. During the selective etching of SiNx mask, each wing peak splits into two peaks, one of which disappears as the mask is removed, while the other remains unchanged. This indicates that the crystallographic tilt of the overgrown region is caused not only by the plastic deformation resulted from the bending of threading dislocations, but by the non-uniformity elastic deformation related with the GaN, SiNx interfacial forces. The widths of these two peaks are also studied in this paper. (C) 2002 Elsevier Science B.V. All rights reserved.

Structure and optical properties of self-assembled InAs/GaAs quantum dots with In0.15Ga0.85As underlying layer

A high density of 1.02 x 10(11) cm(-2) of InAs islands with In(0.15)Gao(0.85)As underlying layer has been achieved on GaAs (10 0) substrate by solid source molecular beam epitaxy. Atomic force microscopy and PL spectra show the size evolution of InAs islands. A 1.3 mum photoluminescence (PL) from InAs islands with In(0.15)Gao(0.85)As underlying layer and InGaAs strain-reduced layer has been obtained. Our results provide important information for optimizing the epitaxial structures of 1.3 mum wavelength quantum dots devices. (C) 2002 Elsevier Science B.V. All rights reserved.

Metalorganic chemical vapor deposition of GaNAs alloys using different Ga precursors

The GaNAs alloys have been grown by metalorganic chemical vapor deposition (MOCVD) using dimethylhydrazine (DMHv) as the nitrogen precursor, triethylgallium (TEGa) and trimethylgallium (TMGa) as the gallium precursors, respectively. Both symmetric (004) and asymmetric (1 1 5) high-resolution X-ray diffraction (HRXRD) were used to determine the nitrogen content in GaNAs layers. Secondary ion mass spectrometry (SIMS) was used to obtain the impurity content. T e influence of different Ga precursors on GaNAs quality has been investigated. Phase separation is observed in the < 1 1 5 > direction when using TMGa as the Ga precursor but not observed when using TEGa. This phenomenon should originate from the parasitic reaction between the Ga and N precursors. Furthermore. samples grown with TEGa have better quality and less impurity contamination than those with TMGa. Nitrogen content of 5.742% has been achieved using TEGa and no phase separation observed in the sample. (C) 2002 Elsevier Science B.V. All rights reserved.

Nanodiamond formation by hot-filament chemical vapor deposition on carbon ions bombarded Si

Nanocrystalline diamond films were grown by a two-step process on Si(1 0 0) substrate, which was first pretreated by pure carbon ions bombardment. The bombarded Si substrate was then transformed into a hot-filament chemical vapor deposition (HFCVD) system for further growth. Using the usual CH4/H-3 feed gas ratio for micro crystalline diamond growth, nanodiamond crystallites were obtained. The diamond nucleation density is comparable to that obtained by biasing the substrate. The uniformly distributed lattice damage is proposed to be responsible for the formation of the nanodiamond. (C) 2002 Elsevier Science B.V. All rights reserved.

Nanofabrication of grid-patterned substrate by holographic lithography

The two-dimensional grid patterns on Si(001) in nanometer scale have been fabricated by holographic lithography and reactive ion etching, which can be used as a substrate for positioning Ge islands during self-assembled epitaxy to obtain an ordered Ge quantum dots matrix. By changing the configuration of the holographic lithography and the etching rate and time, we can control the grid period, the shape of the pattern cell, and the orientation of those shapes, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.

Influence of combined InAlAs and InGaAs strain-reducing laser on luminescence properties of InAs/GaAs quantum dots

We have fabricated self-organized InAs/GaAs quantum dots (QDs) capped by 1 nm In0.2Al0.8As and 5 nm In0.2Ga0.8As strain-reducing layer (SRL). The luminescence emission at a long wavelength of 1.33 mum with narrower half width is realized. A wider energy separation between the ground and first excited radiative transitions of up to 102meV was observed at room temperature. Furthermore, the comparative study proves that luminescence properties of InAs/GaAs QDs overgrown with combined InAlAs and InGaAs SRLs are much better than that of one capped with InGaAs or InAlAs SRL. (C) 2002 Elsevier Science B.V. All rights reserved.

(Ga,Mn,As) compounds grown on semi-insulating GaAs with mass-analyzed low energy dual ion beam depositionw

The (Ga,Mn,As) compounds were obtained by the implantation of Mn ions into semi-insulating GaAs substrate with mass-analyzed low energy dual ion beam deposition technique. Auger electron spectroscopy depth profile of a typical sample grown at the substrate temperature of 250degreesC showed that the Mn ions were successfully implanted into GaAs substrate with the implantation depth of 160 nm. X-ray diffraction was employed for the structural analyses of all samples. The experimental results were greatly affected by the substrate temperature. Ga5.2Mn was obtained in the sample grown at the substrate temperature of 250degreesC. Ga5.2Mn, Ga5Mn8 and Mn3Ga were obtained in the sample grown at the substrate temperature of 400degreesC. However, there is no new phase in the sample grown at the substrate temperature of 200degreesC. The sample grown at 400degreesC was annealed at 840degreesC. In this annealed sample Mn3Ga disappeared, Ga5Mn8 tended to disappear,Ga5.2Mn crystallized better and a new phase of Mn2As was generated. (C) 2002 Elsevier Science B,V. All rights reserved.

Study of GaN thin films grown on intermediate-temperature buffer layers by molecular beam epitaxy

A detailed characterisation study of GaN thin films grown by rf-plasma molecular beam epitaxy on intermediate-temperature buffer layers (ITBL) was carried out with Hall, photoluminescence (PL) and deep-level transient Fourier spectroscopy (DLTFS) techniques. The unique feature of our GaN thin films is that the GaN epitaxial layers are grown on top of a double layer that consists of an ITBL, which is grown at 690 degreesC, and a conventional low-temperature buffer layer deposited at 500 degreesC. It is observed that the electron mobility increases steadily with the thickness of the ITBL, which peaks at 377 cm(2)V(-1)S(-1) for an ITBL thickness of 800 nm. The PL also demonstrated systematic improvements with the thickness of the ITBL. The DLTFS results suggest a three-order-of-magnitude reduction in the deep level at E-c-0.40 eV in the device fabricated with the GaN films grown on an ITBL thickness of 1.25 mum in comparison with the control device without an ITBL. Our analyses indicate that the utilization of an ITBL in addition to the conventional low-temperature buffer layer leads to the relaxation of residual strain within the material, resulting in an improvement in the optoelectronic properties of the films. (C) 2002 Elsevier Science BN. All rights reserved.

Carbonization process of Si(100) by ion-beam bombardment

The evolution of carbonization process on Si as a function of ion dose has been carried out by mass-selected ion-beam deposition technique. 3C-SiC layer has been obtained at low ion dose, which has been observed by reflection high energy electron diffraction and X-ray photoelectron spectroscopy (XPS). The chemical states of Si and carbon have also been examined as a function of ion dose by XPS. Carbon enrichment was found regardless of the used ion dose here, which may be due to the high deposition rate. The formation mechanism of SiC has also been discussed based on the subplantation process. The work will also provide further understanding of the ion-bombardment effect. (C) 2001 Published by Elsevier Science B.V.