| 1. |
- Block, Keith I., et al.
(author)
-
Designing a broad-spectrum integrative approach for cancer prevention and treatment
- 2015
-
In: Seminars in Cancer Biology. - : Academic Press. - 1044-579X .- 1096-3650. ; 35, s. S276-S304
-
Research review (peer-reviewed)abstract
- Targeted therapies and the consequent adoption of "personalized" oncology have achieved notable successes in some cancers; however, significant problems remain with this approach. Many targeted therapies are highly toxic, costs are extremely high, and most patients experience relapse after a few disease-free months. Relapses arise from genetic heterogeneity in tumors, which harbor therapy-resistant immortalized cells that have adopted alternate and compensatory pathways (i.e., pathways that are not reliant upon the same mechanisms as those which have been targeted). To address these limitations, an international task force of 180 scientists was assembled to explore the concept of a low-toxicity "broadspectrum" therapeutic approach that could simultaneously target many key pathways and mechanisms. Using cancer hallmark phenotypes and the tumor microenvironment to account for the various aspects of relevant cancer biology, interdisciplinary teams reviewed each hallmark area and nominated a wide range of high-priority targets (74 in total) that could be modified to improve patient outcomes. For these targets, corresponding low-toxicity therapeutic approaches were then suggested, many of which were phytochemicals. Proposed actions on each target and all of the approaches were further reviewed for known effects on other hallmark areas and the tumor microenvironment Potential contrary or procarcinogenic effects were found for 3.9% of the relationships between targets and hallmarks, and mixed evidence of complementary and contrary relationships was found for 7.1%. Approximately 67% of the relationships revealed potentially complementary effects, and the remainder had no known relationship. Among the approaches, 1.1% had contrary, 2.8% had mixed and 62.1% had complementary relationships. These results suggest that a broad-spectrum approach should be feasible from a safety standpoint. This novel approach has potential to be relatively inexpensive, it should help us address stages and types of cancer that lack conventional treatment, and it may reduce relapse risks. A proposed agenda for future research is offered. (C) 2015 The Authors. Published by Elsevier Ltd.
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| 2. |
- Buyanova, Irina A., et al.
(author)
-
Optical properties of GaNAs/GaAs structures
- 2001
-
In: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 82:1-3, s. 143-147
-
Journal article (peer-reviewed)abstract
- We review our recent results on optical characterization of MBE-grown GaNAs/GaAs quantum structures with N content up to 4.5%, by employing photoluminescence (PL), PL excitation, and time-resolved PL spectroscopies. The dominant PL mechanism has been determined as recombination of excitons trapped by potential fluctuations of the band edge, due to composition disorder and strain nonuniformity of the alloy. The estimated value of the localization potential is around 60 meV for the low-temperature grown structures and can be reduced by increasing the growth temperature or using post-growth rapid thermal annealing (RTA). © 2001 Elsevier Science S.A.
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| 3. |
- Buyanova, Irina A., et al.
(author)
-
Strain relaxation in GaNxP1-x alloy : Effect on optical properties
- 2001
-
In: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 308-310, s. 106-109
-
Journal article (peer-reviewed)abstract
- By using scanning electron microscopy and cathodoluminescence (CL), a decrease in radiative efficiency of GaNP alloy with increasing N content is seen due to the formation of structural defects. The defect formation is attributed to relaxation of tensile strain in the GaNP layer, which is lattice mismatched to GaP substrate. Several types of extended defects including dislocations, microcracks and pits are revealed in partly relaxed GaNxP1-x epilayers with x=1.9%, whereas coherently strained layers exhibit high crystalline quality for x up to 4%. According to the CL measurements, all extended defects act as competing, non-radiative channels leading to the observed strong decrease in the radiative efficiency. From CL mapping experiments, non-uniformity of strain distribution around the extended defects is partly responsible for the broadening of the photoluminescence (PL) spectra recorded in the macro-PL experiments. © 2001 Elsevier Science B.V. All rights reserved.
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| 4. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Analysis of band anticrossing in GaNxP1-x alloys
- 2004
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70, s. 085209-
-
Journal article (peer-reviewed)abstract
- Temperature-dependent absorption, photoluminescence excitation, and spectroscopic ellipsometry measurements are employed to accurately determine compositional and temperature dependences of the conduction band (CB) states in GaNP alloys. The CB edge and the higher lying Γc CB minimum (CBM) are shown to exhibit an apparently anticrossing behavior, i.e., the N-induced redshift of the bandgap energy is accompanied by a matching blueshift of the Γc CBM. The obtained data can be phenomenologically described by the band anticrossing model. By considering strong temperature dependence of the energy of the interacting N level, which has largely been overlooked in earlier studies of GaNP, the interacting N level can be attributed to the isolated substitutional NP and the coupling parameter is accurately determined.
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| 5. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Band alignment in the GaNAs/GaAs quantum structures
- 2001
-
Conference paper (peer-reviewed)abstract
- The band alignment in the GaN_xAs_1-x/GaAs quantum well (QW) structures with low N composition is studied by employing time-resolved photoluminescence (PL) spectroscopy, PL polarization measurements and optically-detected cyclotron resonance (ODCR) studies. The type I band line-up is concluded based on the following experimental results. Firstly, radiative lifetime of the near band gap PL emission in the GaNAs/GaAs MQW structures is nearly identical to that for the spatially direct PL transitions in the GaNAs epilayers. Secondly, the observed polarization of the PL emission in GaNAs QWs (preferentially along the growth direction) is more consistent with the type I band line-up in the GaNAs/GaAs QWs. Thirdly, since the ODCR peaks arising from the free electrons and free holes in GaAs disappear under resonant excitation of the GaNAs MQWs, the photo-excited holes are spatially confined within the GaNAs layers under the resonant excitation condition.
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| 6. |
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| 7. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Direct experimental evidence for unusual effects of hydrogen on the electronic and vibrational properties of GaNxP1−x alloys : a proof for a general property of dilute nitrides
- 2004
-
In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 70:24, s. 245215-245219
-
Journal article (peer-reviewed)abstract
- Direct experimental evidence for dramatic effects of hydrogen incorporation on the electronic structure and lattice properties of GaNxP1−x alloys is presented. By employing photoluminescence excitation spectroscopy, postgrowth hydrogenation is shown to reopen the band gap of the GaNP alloys and to efficiently reduce the N-induced coupling between the conduction band states. By Raman spectroscopy, these effects are shown to be accompanied by hydrogen-induced breaking of the Ga-P bond in the alloy, evident from disappearance of the corresponding vibrational mode. According to the performed Raman and x-ray diffraction measurements, the hydrogenation is also found to cause a strong expansion of the GaNP lattice, which changes the sign of strain from tensile in the as-grown GaNP epilayers to compressive in the posthydrogenated structures, due to the formation of complexes between N and H.
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| 8. |
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| 9. |
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| 10. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Effect of growth temperature on photoluminescence of GaNAs/GaAs quantum well structures
- 1999
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 75:24, s. 3781-
-
Journal article (peer-reviewed)abstract
- The effect of growth temperature on the optical properties of GaAs/GaNxAs1-x quantum wells is studied in detail using photoluminescence (PL) spectroscopies. An increase in growth temperature up to 580 °C is shown to improve the optical quality of the structures, while still allowing one to achieve high (>3%) N incorporation. This conclusion is based on: (i) an observed increase in intensity of the GaNAs-related near-band-edge emission; (ii) a reduction in band-edge potential fluctuations, deduced from the analysis of the PL line shape; and (iii) a decrease in concentration of some extended defects detected under resonant excitation of the GaNAs. The thermal quenching of the GaNAs-related PL emission, however, is almost independent of the growth temperature and is attributed to a thermal activation of an efficient nonradiative recombination channel located in the GaNAs layers.
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| 11. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Effects of N incorporation on the electronic structure of GaNP : Origin of the 2.87 eV optical transition
- 2005
-
Conference paper (peer-reviewed)abstract
- Temperature dependent photoluminescence excitation (PLE) spectroscopy is employed to evaluate basic physical properties of the 2.87 eV absorption peak, recently discovered (I. A. Buyanova et al, PRB 69, 201303 (2004)) in the GaNxP1-x alloys. Whereas appearance of this transition is found to be facilitated by incorporation of N and also H atoms, its intensity does not scale with N content. This questions a possible association of this feature with a N-related localized state. Based on the results of temperature dependent measurements, the involved state is concluded to have a non-$\Gamma $ character. Excitation of the known N-related localized states via this state is found to be non-selective, opposed to that between the N-related centers. The observed properties are shown to be hardly consistent with those predicted for the higher lying localized state of the isolated N atom derived from the Γ conduction band minimum (CBM). Alternative explanations for the ``2.87 eV'' state as being due to either a t2 component of the X3c (or L1c CBM or a level arising from a complex of N and H (in some form) are also discussed.
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| 12. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Evidence for type I band alignment in GaNAs/GaAs quantum structures by optical spectroscopies
- 2002
-
In: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier. - 1386-9477 .- 1873-1759. ; 13:2-4, s. 1074-1077
-
Journal article (peer-reviewed)abstract
- Type I band line-up in GaNxAs1−x/GaAs multiple quantum wells (MQW) with xless-than-or-equals, slant3% is concluded based on the following experimental results: (i) a comparable radiative decay time of the GaNAs-related photoluminescence (PL) measured from single GaNAs epilayers and the GaNAs/GaAs MQW structures, (ii) the observed PL polarization, and (iii) the spatial confinement of photoexcited holes within the GaNAs layers under resonant excitation of the GaNAs MQW.
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| 13. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Experimental evidence for N-induced strong coupling of host conduction band states in GaNP : insight into the dominant mechanism for giant band-gap bowing
- 2004
-
In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 69, s. 201303-
-
Journal article (peer-reviewed)abstract
- Direct evidence for N-induced strong coupling of host conduction band (CB) states in GaNxP1-x is provided by photoluminescence excitation. It is manifested as: (1) a drastic change in the ratio of oscillator strengths between the optical transitions involving the CB minimum (CBM) and the high-lying Γ CB state; (2) a strong blueshift of the Γ CB state with increasing x accompanying a redshift of the CBM, (3) pinning of the localized N states and a newly emerging t2 (L or X3) CB state. These findings shed new light on the issue of the dominant mechanism responsible for the giant band-gap bowing of dilute nitrides.
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| 14. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Hydrogen-induced improvements in optical quality of GaNAs alloys
- 2003
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 82:21, s. 3662-3665
-
Journal article (peer-reviewed)abstract
- Strong suppression of potential fluctuations in the band edges of GaNAs alloys due to postgrowth hydrogen treatment, which is accompanied by a reopening of the alloy band gap, is revealed from temperature-dependent photoluminescence (PL) and PL excitation measurements. The effect likely indicates preferential trapping of hydrogen near the lattice sites with the highest nitrogen content. A remarkable improvement in the radiative efficiency of the alloys at room temperature is also demonstrated and is ascribed to efficient hydrogen passivation of competing nonradiative centers.
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| 15. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Mechanism for Light Emission in GaNAs/GaAs Structures Grown by Molecular Beam Epitaxy
- 1999
-
In: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 216:1, s. 125-129
-
Journal article (peer-reviewed)abstract
- A detailed photoluminescence (PL) study reveals that the low-temperature PL emission in GaNAs epilayers and GaAs/GaNxAs1 - x quantum well structures grown by molecular beam epitaxy is governed by recombination of localized excitons. This conclusion is based on the analysis of the PL lineshape, its dependence on the excitation power and measurement temperature, as well as PL transient data. The depth of the localization potential is estimated as about 60 meV, varying slightly among the different structures.
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| 16. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Mechanism for low-temperature photoluminescence in GaNAs/GaAs structures grown by molecular-beam epitaxy
- 1999
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 75:4, s. 501-
-
Journal article (peer-reviewed)abstract
- The mechanism for low-temperature photoluminescence (PL) emissions in GaNAs epilayers and GaAs/GaNxAs1 - x quantum well (QW) structures grown by molecular-beam epitaxy is studied in detail, employing PL, PL excitation, and time-resolved PL spectroscopies. It is shown that even though quantum confinement causes a strong blueshift of the GaNAs PL emission, its major characteristic properties are identical in both QW structures and epilayers. Based on the analysis of the PL line shape, its dependence on the excitation power and measurement temperature, as well as transient data, the PL emission is concluded to be caused by a recombination of excitons trapped by potential fluctuations in GaNAs.
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| 17. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Mechanism for rapid thermal annealing improvements in undoped GaNxAs1-x/GaAs structures grown by molecular beam epitaxy
- 2000
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 77:15, s. 2325-
-
Journal article (peer-reviewed)abstract
- A systematic investigation of the effect of rapid thermal annealing (RTA) on optical properties of undoped GaNAs/GaAs structures is reported. Two effects are suggested to account for the observed dramatic improvement in the quality of the GaNxAs1-x/GaAs quantum structures after RTA: (i) improved composition uniformity of the GaNxAs1-x alloy, deduced from the photoluminescence (PL), PL excitation and time-resolved measurements; and (ii) significant reduction in the concentration of competing nonradiative defects, revealed by the optically detected magnetic resonance studies.
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| 18. |
- Buyanova, Irina, 1960-, et al.
(author)
-
On a possible origin of the 2.87 eV optical transition in GaNP
- 2006
-
In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 18:2, s. 449-457
-
Journal article (peer-reviewed)abstract
- Temperature dependent photoluminescence excitation spectroscopy is employed to evaluate basic physical properties of the 2.87 eV absorption peak, recently discovered for the GaNxP1-x alloys. Whereas the appearance of this transition is found to be facilitated by incorporation of N and also H atoms, its intensity does not scale with the N content in the alloys. This questions the possible association of this feature with an N-related localized state. On the basis of the results of temperature dependent measurements, it is concluded that the state involved has a non-Γ character. Excitation of the known N-related localized states via this state is found to be non-selective, unlike that between the N-related centres. The observed properties are shown to be barely consistent with those predicted for the higher lying localized state of the isolated N atom derived from the Γ conduction band minimum (CBM). Alternative explanations for the '2.87 eV' state as being due to either a t 2 component of the X3c (or L1c) CBM or a level arising from a complex of N and H (in some form) are also discussed. © 2006 IOP Publishing Ltd.
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| 19. |
- Buyanova, Irina, 1960-, et al.
(author)
-
On the Origin of Light Emission in GaNxP1-x
- 2002
-
Conference paper (peer-reviewed)abstract
- Temperature dependent photoluminescence (PL) and absorption measurements are employed to clarify mechanism for light emission in GaNP alloys with low (< 4.1) nitrogen content. The PL emission in GaNP epilayers and GaNP/GaP multiple quantum well structures is shown to be dominated by optical transitions within deep states likely related to N clusters. With increasing N composition these states are shown to become resonant with conduction band of the alloy and thus optically inactive, leading to the apparent red shift of the PL maximum position. On the other hand, band-to-band recombination in the alloy remains predominantly non-radiative presumably due to the presence of a large number of competing recombination channels.
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| 20. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Optical and electronic properties of GaNAs/GaAs structures
- 2000
-
Conference paper (peer-reviewed)abstract
- We review our recent results from studies of electronic properties of GaNAs/GaAs structures with low nitrogen content, by photoluminescence (PL), PL excitation, time-resolved PL spectroscopies as well as optically detected magnetic resonance (ODMR) and cyclotron resonance (ODCR) studies. The issues to be addressed include key material-related properties and fundamental electronic parameters of the GaNAs alloy, relevant to device applications, such as identification of the dominant recombination processes in the alloy, compositional dependence of the electron effective mass and band alignment in the GaNAs/GaAs heterostructures.
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| 21. |
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| 22. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Origin of bandgap bowing in GaNP alloys
- 2004
-
In: IEE Proceedings - Optoelectronics. - : Institution of Engineering and Technology (IET). - 1350-2433 .- 1359-7078.
-
Conference paper (peer-reviewed)abstract
- By employing photoluminescence excitation (PLE) spectroscopy, the authors provide direct evidence for N-induced strong coupling and repelling of host conduction band (CB) states in GaNxP1-x. This strong coupling is manifested as (i) a drastic change in the ratio of oscillator strengths between the optical transition near Eg/rGamma and that near the CB minimum (CBM); (ii) a strong blue shift of the a1(Γ) state with increasing N composition accompanying a red shift of the CBM; (iii) pinning of the energies of the N-related levels; and (iv) the appearance of t2(L) or t2(X3) upon N incorporation of which the energy position is insensitive to N compositions. These findings shed new light on the controversial issue of the dominant mechanism responsible for the giant bandgap bowing of dilute nitrides.
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| 23. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Photoluminescence characterization of GaNAs/GaAs structures grown by molecular beam epitaxy
- 2000
-
In: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 75:2-3, s. 166-169
-
Journal article (peer-reviewed)abstract
- A number of optical spectroscopies, including photoluminescence (PL), PL excitation and cathodoluminescence, are employed for characterization of GaNAs epilayers and GaAs/GaNxAs1-x quantum well structures grown by gas source molecular beam epitaxy at low temperature. The existence of strong potential fluctuations in the band edge of the GaNAs alloy is concluded, even for the samples with high optical quality, from a detailed analysis of the characteristic properties of the GaNAs-related PL emission. Based on the observed similarity in the PL properties between the GaNAs epilayers and the QW structures, the potential fluctuations are suggested to be mainly due to composition disorder and strain nonuniformity of the alloy. ⌐ 2000 Elsevier Science S.A. All rights reserved.
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| 24. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Radiative recombination mechanism in GaNxP1-x alloys
- 2002
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80, s. 1740-
-
Journal article (peer-reviewed)abstract
- Based on the results of temperature-dependent photoluminescence (PL) and absorption measurements, the PL emission in GaNP epilayers and GaNP/GaP multiple quantum well structures with N composition up to 4% is shown to be dominated by optical transitions within deep states likely related to N clusters. With increasing N composition, these states are shown to become resonant with conduction band of the alloy and thus optically inactive, leading to the apparent redshift of the PL maximum position.
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| 25. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Raman Studies of GaNP Alloy
- 2002
-
Conference paper (peer-reviewed)abstract
- Raman scattering (RS) spectroscopy is employed to characterize the effect of nitrogen on structural properties of GaNxP1-x alloy with nitrogen composition up to 3 %. Two-mode behavior of the alloy is clearly shown. The frequency of the GaP-like LO phonons is found to decrease with N composition as -1.13 cm-1 x. This dependence is proposed to be largely due to the biaxial strain in the GaNP epilayers, as a result of lattice mismatch to the GaP substrate. The frequency of the GaN-like phonons is found to be more sensitive to nitrogen content, increasing with the rate of +2.6 cm-1x. The addition of nitrogen is also found to cause a dramatic quenching of the two-phonon Raman scattering and an appearance of the zone edge GaP-like vibrations. These effects are suggested to reflect local distortion in the GaNP lattice induced by nitrogen, as well as possible clustering of N atoms.
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| 26. |
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| 27. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Resonant excitation spectroscopies of GaNAs/GaAs quantum structures
- 2000
-
Conference paper (peer-reviewed)abstract
- We employ resonant optical excitation and Raman spectroscopies to study optical properties of GaNAs-based quantum structures grown by gas source molecular beam epitaxy (GS MBE). Under above band gap non-resonant excitation the PL spectra of GaNAs are shown to be dominated by the commonly observed featureless localised exciton emission. In contrast, when excitation energy is tuned close to the band edge of GaNAs alloy a series of additional narrow lines can be detected in the PL spectra. The peak positions of these lines are at about 10 meV (strongest), and at 20, 32, and 36 below the excitation energy. The dominant 10 meV line can only be excited within very narrow spectral range coinciding with the free exciton emission in GaNAs. Based on performed spectral, temperature dependent, and polarization studies the strongest 10 meV and the weaker 20 meV lines are tentatively attributed to disorder activated Raman scattering which is strongly enhanced close to the mobility edge of the GaNAs. The 32 and 36 meV lines are, on the other hand, caused by Raman scattering involving GaAs-like TO and LO phonons.
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| 28. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Structural properties of a GaNxP1-x alloy : Raman studies
- 2001
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:25, s. 3959-
-
Journal article (peer-reviewed)abstract
- Raman measurements in backscattering configuration are employed to characterize the effect of nitrogen on the structural properties of a GaNxP1-x alloy with x<=3%. The following effects of N incorporation on the vibrational spectra of GaNP are observed. First, frequencies of GaP-like and GaN-like longitudinal optical phonons exhibit strong compositional dependence, due to a combined effect of alloying and biaxial strain. Second, a dramatic quenching of two-phonon Raman scattering and an emergence of zone-edge GaP-like vibrations are observed. These effects are tentatively attributed to a local distortion of the GaNP lattice and/or compositional disorder in the alloy.
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| 29. |
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| 30. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Time-resolved studies of photoluminescence in GaNxP1-x alloys : Evidence for indirect-direct band gap crossover
- 2002
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:1, s. 52-
-
Journal article (peer-reviewed)abstract
- Time resolved photoluminescence spectroscopy is employed to monitor the effect of N incorporation on the band structure of GaNP alloys. Abrupt shortening in radiative lifetime of near-band gap emissions, arising from excitonic radiative recombination within N-related centers, is found to occur at very low N compositions of around 0.5%, i.e., within the same range as the appearance of the direct-band gap-like transitions in the photomodulated transmission spectra of GaNP reported previously. The effect has been attributed to an enhancement in oscillator strength of optical transitions due to band crossover from indirect to direct-band gap of the alloy.
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| 31. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Type I band alignment in the GaNxAs1-x/GaAs quantum wells
- 2001
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:3, s. 333031-333034
-
Journal article (peer-reviewed)abstract
- Three independent experimental techniques, namely, time-resolved photoluminescence (PL) spectroscopy, PL polarization, and optically detected cyclotron resonance, are employed to determine the band alignment of GaNxAS1-x/GaAs quantum structures with a low-N composition. It is concluded that band lineup is type I based on the following experimental results: (i) comparable radiative decay time of the GaNAs-related emission measured from single GaNAs epilayers and from GaNAs/GaAs quantum well (QW) structures, (ii) polarization of the GaNAs-related emission, and (iii) spatial confinement of the photoexcited holes within the GaNAs layers under resonant excitation of the GaNAs QW's.
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| 32. |
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| 33. |
- Chen, Weimin, 1959-, et al.
(author)
-
Nature and Formation of Non-Radiative Defects in GaNAs and InGaAsN
- 2002
-
In: MRS Fall Meeting 2001,2001. - Materials Research Society Symposium - Proceedings, Vol. 692 : MRS. ; , s. 67-72
-
Conference paper (peer-reviewed)abstract
- The optically detected magnetic resonance (ODMR) technique has been employed to examine the nature and formation mechanism of non-radiative defects in GaNAs and InGaAsN. In both alloys, two defects were observed and were shown to be deep-level, non-radiative recombination centers. One of the defects has been identified as a complex involving an AsGa antisite. These two defects gain more importance with increasing N composition up to 3%, presumably due to an increase in their concentration. With a further higher N composition, the defects start to lose importance in carrier recombination that is attributed to an increasingly important role of other new non-radiative channels introduced with a high N composition. On the other hand, effect of In composition up to 3% seems to be only marginal. Both defects were shown to be preferably introduced in the alloys during low-temperature growth by molecular beam epitaxy (MBE), but can be rather efficiently removed by post-growth rapid thermal annealing.
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| 34. |
- Chen, Weimin, 1959-, et al.
(author)
-
Optical and Microwave Double Resonance of III-nitrides
- 1999
-
In: Joint International Meeting the 196th Meeting of The Electrochemical Society ECS and the 1999 Fall Meeting of The Electrochemical Society of Japan ECSJ,1999. ; , s. 764-
-
Conference paper (other academic/artistic)abstract
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| 35. |
- Chen, Weimin, 1959-, et al.
(author)
-
Optical Detection of Cyclotron Resonance (ODCR) in GaNAs/GaAs Quantum Well Structures
- 2000
-
Conference paper (peer-reviewed)abstract
- ODCR has been employed to study effective masses and carrier recombination in GaNAs/GaAs multi-quantum well (MQW) structures, prepared by MBE with the nitrogen composition up to 4.5 above GaAs bandgap excitation consists of the excitonic recombination within the GaNAs MQW, the band edge PL emissions from GaAs and a broad 0.8-eV PL of unknown origin. When monitoring these emissions under the above GaAs excitation, the ODCR spectrum is dominated by the electron and hole CR in GaAs, with effective mass values 0.07m0 and 0.5m_0, respectively. The ODCR mechanism is discussed in terms of hot carrier effects, resulting in a reduced carrier recombination in GaAs and an enhanced carrier trapping in the GaNAs MQW. Under resonant excitation of the GaNAs MQW only a broad ODCR signal can be observed corresponding to an effective mass value 0.1m_0, attributed to the electron CR in the GaNAs MQW, where a higher electron effective mass value and a much lower mobility are expected.
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| 36. |
- Chen, Weimin, et al.
(author)
-
P-N defect in GaNP studied by optically detected magnetic resonance
- 2003
-
In: Proceedings of the 22nd International Conference on Defects in Semiconductors. - : Elsevier BV. ; , s. 399-402
-
Conference paper (peer-reviewed)abstract
- We provide experimental evidence for an intrinsic defect in GaNP from optically detected magnetic resonance (ODMR). This defect is identified as a P-N complex, exhibiting hyperfine structure due to interactions with a nuclear spin I=12 of one P atom and also a nuclear spin I=1 due to one N atom. The introduction of the defect is assisted by the incorporation of N within the studied N composition range of up to 3.1%, under non-equilibrium growth conditions during gas-source molecular beam epitaxy. The corresponding ODMR spectrum was found to be isotropic, suggesting an A1 symmetry of the defect state. The localization of the electron wave function at the P-N defect in GaNP is found to be even stronger than that for the isolated PGa antisite in its parent binary compound GaP. © 2003 Elsevier B.V. All rights reserved.
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| 37. |
- Felici, M, et al.
(author)
-
High Energy Optical Transitions in Ga(PN) : Contribution from Perturbed Valence Band
- 2005
-
In: AIP Conference Proceedings / Volume 772. - : American Institute of Physics (AIP). - 0735402574 ; , s. 265-
-
Conference paper (peer-reviewed)abstract
- The GaP1–xNx conduction band is investigated experimentally (by excitation photoluminescence) andtheoretically (by pseudopotential supercells) for N concentrations up to x=3.5%and photon energies ranging from the optical absorption edge to3.2 eV. With increasing x: (i) a direct-like absorption edgedevelops smoothly and red-shifts rapidly overtaking energy-pinned cluster states; (ii)a broad absorption plateau appears between the X1c and the1c critical points of GaP; (iii) the 1c absorption edgebroadens and gradually disappears. Empirical pseudopotential calculations for GaP1-xNx randomalloy supercells account well for all the PLE results byconsidering N induced changes in the valence band overlooked sofar. ©2005 American Institute of Physics
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| 38. |
- Hai, P. N., et al.
(author)
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Direct determination of electron effective mass in GaNAs/GaAs quantum wells
- 2000
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 77:12, s. 1843-1845
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Journal article (peer-reviewed)abstract
- Electron effective mass (m*e) in GaNxAs1-x/GaAs quantum wells (QWs) is investigated by the optically detected cyclotron resonance technique. The m*e values of 0.12m0 and 0.19m0 are directly determined for the 70-A-thick QWs with N composition of 1.2% and 2.0%, respectively. This sizable increase in the electron effective mass is consistent with the earlier theoretical predictions based on the strong interaction of the lowest conduction band states with the upper lying band states or impurity band induced by the incorporation of N. ⌐ 2000 American Institute of Physics.
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| 39. |
- Hai, P. N., et al.
(author)
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Properties of GaAsN/GaAs quantum wells studied by optical detection of cyclotron resonance
- 2001
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In: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 82:1-3, s. 218-220
-
Journal article (peer-reviewed)abstract
- Effective masses and carrier recombination in GaNAs/GaAs quantum wells (QWs) with nitrogen composition up to 4.5%, have been studied by optical detection of cyclotron resonance (ODCR). When monitoring the PL emissions under the conditions of above-GaAs barrier excitation, the ODCR spectrum is dominated by the electron CR in GaAs with an effective mass value 0.066m0. The ODCR mechanism is discussed in terms of hot carrier effects, resulting in a reduced carrier recombination in GaAs and an enhanced carrier trapping in the GaNAs QW. Under resonant excitation of the GaNAs QWs, only a broad ODCR signal can be observed, corresponding to an effective mass value of 0.12m0 and 0.19m0 when the N composition is about 1.2 and 2%, respectively. This is attributed to the electron CR in the GaNAs QW with a lower electron mobility. This sizeable increase in the electron effective mass is in agreement with earlier theoretical predictions. ⌐ 2001 Elsevier Science B.V.
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| 40. |
- Li, Xin, et al.
(author)
-
Regulation of androgen receptor expression alters AMPK phosphorylation in the endometrium: In Vivo and In Vitro studies in women with polycystic ovary syndrome
- 2015
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In: International Journal of Biological Sciences. - : Ivyspring International Publisher. - 1449-2288. ; 11:12, s. 1376-1389
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Journal article (peer-reviewed)abstract
- © 2015 Ivyspring International Publisher. The failure of reproductive success in polycystic ovary syndrome (PCOS) patients could be in part due to endometrial dysfunction. However, no studies have investigated any causality between androgen, androgen receptor (AR) expression, and adenosine monophosphate activated protein kinase (AMPK) activation in the endometrium under physiological and pathological conditions. In the present study, we show that 1) endometrial AR expression levels fluctuate in non-PCOS and PCOS patients during the menstrual cycle; 2) the menstrual phase-dependent alteration of p-AMPKα expression occurs in non-PCOS patients but not in PCOS patients; 3) AR expression is higher in PCOS patients than non-PCOS patients during hyperplasia while AMPKα activation (indicated by the ratio of p-AMPKα to AMPKα); and 4) co-localization of AR and Ki-67 in epithelial cell nuclei is observed in endometrial hyperplasia. Importantly, using in vitro human tissue culture and an in vivo 5α-dihydrotestosterone-treated rat model, we show that the action of androgen on AMPKα activation is likely mediated through nuclear AR, especially in epithelial cells. Collectively, we present evidence that AR expression and AMPKα activation depend on menstrual cycle phase and the presence of PCOS, and the data suggest that AR-mediated regulation of AMPKα activation might play a role in the development of endometrial hyperplasia.
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| 41. |
- Polimeni, A., et al.
(author)
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Hydrogen related effects in diluted nitrides
- 2003
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In: 22nd Int. Conf. on Defects in Semiconductors,2003. - : Elsevier. ; , s. 371-
-
Conference paper (peer-reviewed)abstract
- Hydrogen irradiation leads to the passivation of the electronic activity of nitrogen in Ga(AsN), thus allowing a fine tuning of the material optical properties. Here, some recent results on the effects that hydrogen irradiation has on the electronic properties of diluted III-N-V alloys are presented. In Ga(AsN), both the increase in the electron effective mass and exciton wave function localization induced by nitrogen are reversed in a fully controllable manner by hydrogen irradiation. In Ga(PN), hydrogen widens the band gap and exposes gradually in the gap nitrogen complex states formerly resonant with the conduction band.
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| 42. |
- Polimeni, A., et al.
(author)
-
Nitrogen passivation induced by atomic hydrogen : The GaP1-yNy case
- 2003
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:20, s. 2013031-2013034
-
Journal article (peer-reviewed)abstract
- We report on the evolution of the optical properties of GaP1-yNy epilayers upon hydrogen irradiation for an extended nitrogen concentration range (y = 0.05% - 1.3%). For y = 0.6%, photoluminescence measurements show that hydrogen leads to an apparent band gap widening and to an ensuing appearance of N cluster states in the forbidden gap of GaP1-yNy, Hydrogen removal from the samples results in a full recovery of the electronic properties of the as-grown material. For lower N concentration (y = 0.05%), hydrogen causes a spectral weight transfer from electronic levels associated with closer N pairs to those associated with more distant N pairs and single N atoms.
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| 43. |
- Rudko, G. Yu., et al.
(author)
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Temperature behavior of the GaNP band gap energy
- 2003
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In: E-MRS 2002 Spring Meeting,2002. - : Elsevier. ; , s. 493-496
-
Conference paper (peer-reviewed)abstract
- We report experimental results from temperature dependence studies of the optical absorption edge of the GaNP alloys with N compositions up to 3.1%. The observed increase in the absorption coefficient with increasing N content, as well as the spectral shape of the absorption edge incline a band crossover to a direct band gap for the alloy, in agreement with previous studies. Temperature variation of the GaNP band gap, however, is found to be rather similar to that in the parental GaP, except for the N composition of ~1% when a slow down in the thermally induced reduction of the band gap energy was observed due to a resonant interaction with the N-related defects. We thus suggest that both contributions from the interaction with the localized states and the increasing Γ character of the conduction band states are important for the alloy formation.
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| 44. |
- Rudko, G. Yu., et al.
(author)
-
Temperature dependence of the GaNxP1-x band gap and effect of band crossover
- 2002
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:21, s. 3984-
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Journal article (peer-reviewed)abstract
- The absorption edge of GaNxP1-x alloys (0.01<=x<=0.03) is shown to exhibit a direct-band gap-like behavior. Thermal variation of the band gap energy Eg, however, is found to be the same or even smaller than that for the indirect band gap of GaP and depends on the N content. The effect is tentatively attributed to the following counteracting contributions to the band edge formation. An interaction with N-related localized states, especially significant in the vicinity of band crossover (e.g., x = 0.013), causes a substantial slow down of the Eg shift with temperature. On the contrary, an increasing contribution of Γc states, which becomes predominant for the higher compositions, leads to the larger thermal variation in Eg.
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| 45. |
- Thinh, N. Q., et al.
(author)
-
Formation of Ga interstitials in (Al,In)yGa1-yNxP1-x alloys and their role in carrier recombination
- 2004
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 85, s. 2827-
-
Journal article (peer-reviewed)abstract
- Formation of complex defects involving a Ga interstitial (Gai) in (Al,In)yGa1-yNxP1-x alloys and their effects on optical quality are studied by photoluminescence (PL) and optically detected magnetic resonance spectroscopies. Introduction of these defects is shown to be largely promoted by incorporation of N. In quaternary alloys, concentrations of the defects are found to critically depend on the group III atoms that replace Ga, i.e., it is largely enhanced by the presence of Al in alloys, but is only marginally affected by In incorporation. The effect is attributed to differences in surface adatom mobilities of the group III atoms involved and their bonding strength with N. The revealed Gai complexes are shown to act as efficient nonradiative recombination centers degrading the PL efficiency. The defects exhibit high thermal stability and can only be partially removed by postgrowth rapid thermal annealing.
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| 46. |
- Thinh, N. Q., et al.
(author)
-
Formation of nonradiative defects in molecular beam epitaxial GaNxAs1-x studied by optically detected magnetic resonance
- 2001
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 79:19, s. 3089-
-
Journal article (peer-reviewed)abstract
- The formation of two nonradiative defects (i.e., an AsGa-related complex and an unknown deep-level defect with g = 2.03) in GaNxAs1-x epilayers and GaAs/GaNxAs1-x multiple-quantum-well structures, grown by molecular beam epitaxy, is studied by the optically detected magnetic resonance technique. It is shown that contributions by these defects in competing carrier recombination strongly vary with the nitrogen composition. An increase in the growth temperature or postgrowth rapid thermal annealing significantly reduces the influence of the nonradiative defects studied, and is accompanied by a remarkable improvement in the optical properties of the structures.
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| 47. |
- Thinh, N. Q., et al.
(author)
-
Grown-in intrinsic defect in GaNAs
- 2001
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In: Proceedings of the 21st International Conference on Defects in Semiconductors.
-
Conference paper (other academic/artistic)
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| 48. |
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| 49. |
- Thinh, N. Q., et al.
(author)
-
Properties of a grown-in intrinsic defect in GaNAs
- 2001
-
In: APS 2001 March Meeting,2001. - Bull. Amer. Phys. Soc. : APS. ; , s. 1185-
-
Conference paper (peer-reviewed)abstract
- Properties of a grown-in intrinsic defect in GaNAs alloys and GaNAs/GaAs quantum well structures with low N composition have been investigated by optically detected magnetic resonance (ODMR). The characteristic hyperfine (HF) structure, arising from S=1/2 and I=3/2, suggests a complex involving the As_Ga antisite as being the most likely candidate for the responsible defect. The strong HF interaction evidences a high localization of the wavefunction of the unpaired electron near the As_Ga antisite, which is found to be rather insensitive to either N composition or quantum confinement. The formation mechanism for the defect has been studied by varying growth temperature or by performing post-growth rapid thermal annealing. It is shown that the defect can be preferably introduced during molecular beam epitaxy (MBE) growth at low temperature under non-equilibrium conditions, similar to the case of its parental compound GaAs grown under similar conditions.
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| 50. |
- Thinh, N.Q., et al.
(author)
-
Properties of Ga-interstitial defects in AlxGa 1-xNyP1-y
- 2005
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 71:12
-
Journal article (peer-reviewed)abstract
- A detailed account of the experimental results from optically detected magnetic resonance (ODMR) studies of grown-in defects in (Al)GaNP alloys, prepared by molecular beam epitaxy, is presented. The experimental procedure and an in-depth analysis by a spin Hamiltonian lead to the identification of two Gai defects (Gai-A and Gai-B). New information on the electronic properties of these defects and the recombination processes leading to the observation of the ODMR signals will be provided. These defects are deep-level defects. In conditions when the defect is directly involved in radiative recombination of the near-infrared photoluminescence band, the energy level of the Gai-B defect was estimated to be deeper than ~1.2 eV from either the conduction or valence band edge. In most cases, however, these defects act as nonradiative recombination centers, reducing the efficiency of light emission from the alloys. They can thus undermine the performance of potential photonic devices. High thermal stability is observed for these defects. ©2005 The American Physical Society.
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