Alloy states in dilute GaAs1-xNx alloys (x < 1%)

A set of GaAs1-xNx samples with small nitrogen composition (x<1%) were investigated by continuous-wave photoluminescence (PL), pulse-wave excitation PL, and time-resolved PL. In the PL spectra, an extra transition located at the higher-energy side of the commonly reported N-related emissions was observed. By measuring the PL dependence on temperature and excitation power, the PL peak was identified as a transition of alloy band edge-related recombination in GaAsN. The PL dynamics further confirms its intrinsic nature as being associated with the band edge rather than N-related bound states. (C) 2003 American Institute of Physics.

Photoluminescence from ZnS1-xTex alloys under hydrostatic pressure

ZnS1-xTex (0.02less than or equal toxless than or equal to0.3) alloys are studied by photoluminescence under hydrostatic pressure at room temperature. Only a wide emission band is observed for each sample. Its peak energy is much lower than the corresponding band gap of alloys. These bands are ascribed to the radiative annihilation of excitons bound at Te-n(ngreater than or equal to2) isoelectronic centers. The pressure coefficients of the emission bands are smaller than those of alloy band gaps from 48% to 7%. The difference of the pressure coefficient of the emission band and the band gap increases when the binding energy of Te-n centers decreases. It seems contrary to our expectation and needs further analysis. The integrated intensities of emission bands decrease with increasing pressure due to the decreasing of the absorption coefficient associated with the Te-n centers under pressure. According to this model the Stokes shifts between the emission and absorption bands of the Te-n centers are calculated, which decrease with the increasing Te composition in alloys.

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.

Zero-field spin splitting in In0.52Al0.48As/InxGa1-xAs metamorphic high-electron-mobility-transistor structures on GaAs substrates using Shubnikov-de Haas measurements

Shubnikov-de Haas measurements were carried out for In0.52Al0.48As/InxGa1-xAs metamorphic high-electron-mobility-transistor structures grown on GaAs substrates with different indium contents and/or different Si delta-doping concentrations. Zero-field (B-->0) spin splitting was found in samples with stronger conduction band bending in the InGaAs well. It was shown that the dominant spin splitting mechanism is attributed to the contribution by the Rashba term. We found that zero-field spin splitting not only occurs in the ground electron subband, but also in the first excited electron subband for a sample with Si delta-doping concentration of 6x10(12) cm(-2). We propose that this In0.52Al0.48As/InxGa1-xAs metamorphic high-electron-mobility-transistor structure grown on GaAs may be a promising candidate spin-polarized field-effect transistors. (C) 2002 American Institute of Physics.

InxGa1-xAs/AlyGa1-yAs/AlzGa1-zAs asymmetric step quantum-well middle wavelength infrared detectors

InxGa1-xAs/AlyGa1-yAs/AlzGa1-zAs asymmetric step quantum-well middle wavelength (3-5 mum) infrared detectors are fabricated. The components display photovoltaic-type photocurrent response as well as the bias-controlled modulation of the peak wavelength of the main response, which is ascribed to the Stark shifts of the intersubband transitions from the local ground states to the extended first excited states in the quantum wells, at the 3-5.3 mum infrared atmospheric transmission window. The blackbody detectivity (D-bb*) of the detectors reaches to about 1.0x10(10) cm Hz(1/2)/W at 77 K under bias of +/-7 V. By expanding the electron wave function in terms of normalized plane wave basis within the framework of the effective-mass envelope-function theory, the linear Stark effects of the intersubband transitions between the ground and first excited states in the asymmetric step well are calculated. The obtained results agree well with the corresponding experimental measurements. (C) 2001 American Institute of Physics.

Thermal redistribution of localized excitons and its effect on the luminescence band in InGaN ternary alloys

Temperature-dependent photoluminescence measurements have been carried out in zinc-blende InGaN epilayers grown on GaAs substrates by metalorganic vapor-phase epitaxy. An anomalous temperature dependence of the peak position of the luminescence band was observed. Considering thermal activation and the transfer of excitons localized at different potential minima, we employed a model to explain the observed behavior. A good agreement between the theory and the experiment is achieved. At high temperatures, the model can be approximated to the band-tail-state emission model proposed by Eliseev et al. [Appl. Phys. Lett. 71, 569 (1997)]. (C) 2001 American Institute of Physics.

Random telegraph noise in the photoluminescence of individual GaxIn1-xAs quantum dots in GaAs

We have investigated random telegraph noise in the photoluminescence from InGaAs quantum dots in GaAs. Dots switching among two and three levels have been measured. The experiments show that the switching InGaAs dots behave very similarly to switching InP dots in GaInP. but differently from the more commonly investigated colloidal dots. The switching is attributed to defects, and we show that the switching can be used as a monitor of the defect.

The effects of pre-irradiation on the formation of Si1-xCx alloys

Carbon ions were implanted into crystal Si to a concentration of (0.6-1.5)at% at room temperature. Some samples were pre-irradiated with S-29(i)+ ions, while others were not pre-irradiated. Then the two kinds of samples were implanted with C-12(+) ions simultaneously, and Si1-xCx alloys were grown by solid phase epitaxy with high-temperature annealing. The effects of preirradiation on the formation of Si1-xCx alloys were studied. If the dose of implanted C ion was less than that for amorphizing Si crystals, the implanted C atoms would like to combine with defects produced during implantation, and then it was difficult for Si1-xCx alloys to form after annealine, at 950 degreesC. Pre-irradiation was advantageous for Si1-xCx alloy formation. With the increase of C ion dose, the damage produced by C ions increased. Pre-irradiation was unfavorable for Si1-xCx, alloy formation. If the implanted C concentration was higher than that for solid phase epitaxy solution, only part of the implanted C atoms form Si1-xCx alloys and the effects of pre-irradiation could be neglected. As the annealing temperature was increased to 1050 degreesC, Si1-xCx alloys in both pre-irradiated and unpreirradiated samples of low C concentration remained, whereas most part of Si1-xCx alloys in samples with high C concentration vanished.

Modification of emission wavelength of self-assembled In(Ga)As/GaAs quantum dots covered by InxGa1-xAs(0 <= x <= 0.3) layer

Red shifts of emission wavelength of self-organized In(Cla)As/GaAs quantum dots (QDs) covered by 3 nm thick InxGa1-xAs layer with three different In mole fractions (x = 0.1, 0.2 and 0.3, respectively) have been observed. Transmission electron microscopy images demonstrate that the stress along growth direction in the InAs dots was reduced due to introducing the InxGa1-xAs (x = 0.1, 0.2 and 0.3) covering layer instead of GaAs layer. Atomic force microscopy pictures show a smoother surface of InAs islands covered by an In0.2Ga0.8As layer. It is explained by the calculations that the redshifts of the photoluminescence (PL) spectra from the QDs covered by the InxGa1-xAs (x greater than or equal to 0.1) layers were mainly due to the reducing of the strain other than the InAs/GaAs intermixing in the InAs QDs. The temperature dependent PL spectra further confirm that the InGaAs covering layer can effectively suppress the temperature sensitivity of PL emissions. 1.3 mum emission wavelength with a very narrow linewidth of 19.2 mcV at room temperature has been obtained successfully from In,In0.5Ga0.5As/GaAs self-assembled QDs covered by a 3-nm In0.2Ga0.2As strain reducing layer. (C) 2001 Elsevier Science B.V. All rights reserved.

Properties and turning of intraband optical absorption in InxGa1-xAs/GaAs self-assembled quantum dot superlattice

We investigated properties of intraband absorption in In-x Ga1-xAs quantum dots (QDs) superlattice. Energy levels in conduction band in QDs were calculated for a cone-shaped quantum dot associated with coupling between QDs in the framework of the effective-mass envelope-function theory. Theoretical results demonstrated that energy levels in conduction band were greatly affected by the vertical coupling between quantum dots, which can be used to modify transition wavelength by adjusting the space layer thickness. Intraband transition is really sensitive to normal incidence and the absorption peak intensity is dependent on the polarization. A satisfying agreement is found between theoretical and experimental values. This result opens up prospects for the fabrication of QDs infrared detectors, which work at atmospheric windows.

Effect of InxGa1-xAs (0 <= x <= 0.4) capping layer on self-assembled 1.3 mu m wavelength InAs/GaAs quantum islands

We report the effect of InchiGa1-chiAs (0 less than or equal to chi less than or equal to0.4) capping layer on photoluminescence (PL) properties of 1.3 mum wavelength self-assembled InAs quantum islands, which are formed via depositing 3.5 monolayers (ML) InAs on GaAs (1 0 0) substrate by molecular beam epitaxy (MBE). Compared with the InchiGa1-chiAs capping layer containing a larger In mole fraction chi greater than or equal to0.2 and the GaAs capping layer (chi = 0), the InAs islands covered by the In0.1Ga0.9As layer show PL with lower emission energy, narrower full-width at half-maximum (FWHM), and quite stronger intensity. The PL peak energy and FWHM become more temperature dependent with the increase of In content in the InchiGa1-chiAs capping layer (chi greater than or equal to0.2), while the InAs islands covered by the In0.1Ga0.9As layer is much less temperature sensitive. In addition, the InAs islands covered by the In0.1Ga0.9As capping layer show room temperature PL wavelength at about 1.3 mum. (C) 2001 Published by Elsevier Science B.V.

Structural anisotropy and optical properties of InxGa1-xAs quantum dots on GaAs(001)

InAs and InxGa1-xAs (x = 0.2 and 0.5) self-organized quantum dots (QDs) were fabricated on GaAs(0 0 1) by molecular beam epitaxy (MBE) and characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), acid photoluminescence polarization spectrum (PLP). Both structural and optical properties of InxGa1-xAs QD layer are apparently different from those of InAs QD layer. AFM shows that InxGa1-xAs QDs tend to be aligned along the [1 (1) over bar 0] direction, while InAs QDs are distributed randomly. TEM demonstrates that there is strain modulation along [1 1 0] in the InxGa1-xAs QD layers. PLP shows that In0.5Ga0.5As islands present optical anisotropy along [1 1 0] and [1 (1) over bar 0] due to structural and strain field anisotropy for the islands. (C) 2001 Elsevier Science B.V. All rights reserved.

The formation and stability of Si1-xCx alloys in Si implanted with carbon

Si1-xCx alloys of carbon (C) concentration between 0.6%-1.0% were grown in Si by ion implantation and high temperature annealing. The formation of Si1-xCx alloys under different ion doses and their stability during annealing were studied. If the implanted dose was less than that for amorphizing Si crystals, the implanted C atoms would like to combine with defects produced during implantation and it was difficult to form Si1-xCx alloys after being annealed at 850 degreesC. With the increment of implanted C ion doses, the lattice damage increased and it was easier to form Si1-xCx alloys. But the lattice strain would become saturate and only part of implanted carbon atoms would occupy the substitutional positions to form Si1-xCx alloys as the implanted carbon dose increased to a certain degree. Once Si1-xCx alloys were formed, they were stable at 950 degreesC, but part of their strain would release as the annealing temperature increased to 1 000 degreesC. Stability of the alloys became worse with the increment of carbon concentration in the alloys.

The formation and characteristics of Si1-xCx alloys in Si crystals by means of implantation of cions with different doses

Carbon ions with concentration of (0.6-1.5)% were implanted into silicon crystals at room temperature and Si1-xCx alloys were grown by solid phase epitaxy with high temperature annealing. The formation and characteristics of Si1-xCx alloys under different implanted carbon doses were studied. If the implanted carbon atom concentration was less than 0.6%, carbon atoms would tend to combine with the defects produced during implantation and it was difficult for Si1-xCx alloys to form during annealing at 850-950 degreesC. With the increase of implanted C concentration, almost all implanted carbon atoms would occupy substitution positions to form Si1-xCx alloys, but only part of implanted carbon atoms would occupy the substitution position to form Si1-xCx alloys as the implanted dose increased to 1.5 %. Most Si1-xCx alloy phases would vanish as the annealing temperature was increased higher.

Study of self-assembled InAs quantum dot structure covered by InxGa1-xAs(0 <= x <= 0.3) capping layer

InAs self-assembled quantum dots(QDs) covered by 3-nm-thick InxGa1-xAs(0 less than or equal tox less than or equal to0.3) capping layer have been grown on GaAs(100) substrate. Transmission electron microscopy shows that InGaAs layer reduces the strain in the InAs islands,and atomic force microscopy evidences the deposition of InGaAs on the top of InAs islands when x = 0.3.The significant redshift of the photoluminescence (PL) peak energy and the reduction of PL linewidth of InAs quantum dots covered by InGaAs are observed. In addition,InGaAs overgrowth layer suppresses the temperature sensitivity of PL peak energy. Based on our analysis, the strain-reduction and the size distribution of the InAs QDs are the main cause of the redshift and temperature insensitivity of the PL respectively.