| 1. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Analysis of band anticrossing in GaNxP1-x alloys
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70, s. 085209-
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Tidskriftsartikel (refereegranskat)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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| 2. |
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| 3. |
- Buyanova, Irina, 1960-, et al.
(författare)
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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
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 70:24, s. 245215-245219
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Tidskriftsartikel (refereegranskat)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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| 4. |
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| 5. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Effects of N incorporation on the electronic structure of GaNP : Origin of the 2.87 eV optical transition
- 2005
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Konferensbidrag (refereegranskat)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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| 6. |
- Buyanova, Irina, 1960-, et al.
(författare)
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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
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 69, s. 201303-
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Hydrogen-induced improvements in optical quality of GaNAs alloys
- 2003
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 82:21, s. 3662-3665
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Hydrogen passivation of nitrogen in GaNAs and GaNP alloys : How many H atoms are required for each N atom?
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:2, s. 021920-
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Tidskriftsartikel (refereegranskat)abstract
- Secondary ion mass spectrometry and photoluminescence are employed to evaluate the origin and efficiency of hydrogen passivation of nitrogen in GaNAs and GaNP. The hydrogen profiles are found to closely follow the N distributions, providing unambiguous evidence for their preferential binding as the dominant mechanism for neutralization of N-induced modifications in the electronic structure of the materials. Though the exact number of H atoms involved in passivation may depend on the conditions of the H treatment and the host matrixes, it is generally found that more than three H atoms are required to bind to a N atom to achieve full passivation for both alloys. © 2007 American Institute of Physics.
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| 9. |
- Buyanova, Irina, 1960-, et al.
(författare)
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On spin injection in GaMnN/InGaN Light-Emitting Diodes
- 2004
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Ingår i: 3rd International Conference on Physics and Applications of Spin-Related Phenomena in Semiconductors PASPS III,2004.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 10. |
- Buyanova, Irina, 1960-, et al.
(författare)
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On the origin of spin loss in GaMnN/InGaN Light-Emitting Diodes
- 2004
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 84, s. 2599-
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Tidskriftsartikel (refereegranskat)abstract
- Spin polarization of GaMnN/InGaN light-emitting diodes grown by molecular beam epitaxy is analyzed. In spite of the ferromagnetic behavior of the GaMnN spin injector, the diodes are shown to exhibit very low efficiency of spin injection. Based on resonant optical orientation spectroscopy, the spin loss in the structures is shown to be largely due to fast spin relaxation within the InGaN spin detector, which itself destroys any spin polarization generated by optical spin orientation or electrical spin injection.
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| 11. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Optical and electrical characterization of (Ga,Mn)N/InGaN multiquantum well light-emitting diodes
- 2004
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 33:5, s. 467-471
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Tidskriftsartikel (refereegranskat)abstract
- (Ga,Mn)/N/InGaN multiquantum well (MQW) diodes were grown by molecular beam epitaxy (MBE). The current-voltage characteristics of the diodes show the presence of a parasitic junction between the (Ga,Mn)N and the n-GaN in the top contact layer due to the low conductivity of the former layer. Both the (Ga,Mn)N/InGaN diodes and control samples without Mn doping show no or very low (up to 10% at the lowest temperatures) optical (spin) polarization at zero field or 5 T, respectively. The observed polarization is shown to correspond to the intrinsic optical polarization of the InGaN MQW, due to population distribution between spin sublevels at low temperature, as separately studied by resonant optical excitation with a photon energy lower than the bandgap of both the GaN and (Ga,Mn)N. This indicates efficient losses in the studied structures of any spin polarization generated by optical spin orientation or electrical spin injection. The observed vanishing spin injection efficiency of the spin light-emitting diode (LED) is tentatively attributed to spin losses during the energy relaxation process to the ground state of the excitons giving rise to the light emission.
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| 12. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Origin of bandgap bowing in GaNP alloys
- 2004
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Ingår i: IEE Proceedings - Optoelectronics. - : Institution of Engineering and Technology (IET). - 1350-2433 .- 1359-7078.
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Konferensbidrag (refereegranskat)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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| 13. |
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| 14. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Role of nitrogen in photoluminescence up-conversion in GaInNP/GaAs heterostructures
- 2007
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Ingår i: AIP Conference Proceedings / Volume 893. - : American Institute of Physics (AIP). ; , s. 381-382
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Alloying of disordered GaInP with nitrogen is shown to lead to very efficient PLU in GaInNP/GaAs heterostructures grown by gas source molecular beam epitaxy (GS‐MBE). This is attributed to the N‐induced changes in the band alignment at the GaInNP/GaAs heterointerface from the type I for the N‐free structure to the type II in the samples with N compositions exceeding 0.5%. Based on the performed excitation power dependent measurements, a possible mechanism for the energy upconversion is suggested as being due to the two‐step two‐photon absorption. The photon recycling effect is shown to be important for the structures with N=1%, from time‐resolved PL measurements. © 2007 American Institute of Physics
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| 15. |
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| 16. |
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| 17. |
- Izadifard, Morteza, 1965-, et al.
(författare)
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Effects of rapid thermal annealing on optical properties of GaNxP1−x alloys grown by solid source molecular beam epitaxy
- 2005
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 20:5, s. 353-356
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Tidskriftsartikel (refereegranskat)abstract
- Temperature-dependent photoluminescence (PL), PL excitation and time-resolved PL measurements were employed to study the effects of rapid thermal annealing (RTA) on optical properties of GaNxP1−x alloys grown by solid source molecular beam epitaxy. A substantial increase in radiative efficiency of GaNP epilayers, which is especially pronounced for the high-energy PL component, was achieved after RTA and is attributed to annealing out of competing non-radiative centres. The latter is evident from reduced quenching of the PL intensity with increasing measurement temperature, which results in a strong increase (up to 18 times) in the PL intensity at room temperature (RT), as well as from a substantial increase in carrier lifetime at RT deduced from time-resolved PL measurements.
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| 18. |
- Izadifard, Morteza, 1965-, et al.
(författare)
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Effects of rapid thermal annealing on optical quality of GaNP alloys
- 2004
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Ingår i: EMRS-2004 Spring Meeting,2004. - : Institution of Engineering and Technology (IET). ; , s. 335-
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Konferensbidrag (refereegranskat)abstract
- Significant improvements in radiative efficiency of GaNP epilayers grown on GaP substrates by solid-source molecular beam epitaxy (MBE) are achieved by post-growth rapid thermal annealing (RTA). From temperature-dependent CW and time-resolved photoluminescence (PL) spectroscopies combined with PL excitation measurements, the observed improvements are attributed to annealing out of competing nonradiative centres. This conclusion is supported by the following experimental evidence: reduced thermal quenching of the PL intensity resulting in a substantial (up to 18 times) increase at room temperature (RT) after RTA, and simultaneous improvements in carrier lifetime at RT deduced from time-resolved PL measurements.
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| 19. |
- Izadifard, Morteza, 1965-, et al.
(författare)
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Evaluation of optical quality and defect properties of GaNxP1−x alloys lattice matched to Si
- 2004
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 85, s. 6347-
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Tidskriftsartikel (refereegranskat)abstract
- By using a variety of optical characterization techniques, including cathodoluminescence, temperature-dependent cw- and time-resolved photoluminescence (PL), and PL excitation spectroscopies, high optical quality of the GaN0.018P0.982 epilayers lattice matched to Si substrates is demonstrated and is shown to be comparable to that of the “state-of-the-art” GaNP alloys grown on GaP substrates. The growth of GaNP on Si is, however, found to facilitate the formation of several point defects, including complexes involving Ga interstitial atoms (Gai).
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| 20. |
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| 21. |
- Izadifard, Morteza, 1965-, et al.
(författare)
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Role of hydrogen in improving optical quality of GaNAs alloys
- 2003
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Ingår i: 11th Int. Conf. on Narrow Bandgap Semiconductors,2003. - Physica E, Vol 20 : Elsevier. ; , s. 313-316
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Konferensbidrag (refereegranskat)abstract
- Effects of hydrogen irradiation on optical quality of GaNxAs1−x alloys grown by gas source molecular beam epitaxy are studied by photoluminescence (PL) and PL excitation spectroscopies. A strong blue shift of the alloy band gap towards the value of a reference N-free GaAs samples is revealed. Substantial improvements in the optical quality of the structures induced by hydrogen, due to a reduction of band edge potential fluctuations, is also demonstrated. The effect is tentatively attributed to the preferential trapping of hydrogen atoms at the lattice sites with the highest N compositions, which leads to the neutralization of electronic states contributing to the band tail states as well as to the improvement in strain uniformity.
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| 22. |
- Syväjärvi, Mikael, 1968-, et al.
(författare)
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As-grown 4H-SiC epilayers with magnetic properties
- 2004
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Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2003, PRTS 1 AND 2. ; , s. 747-750
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Konferensbidrag (refereegranskat)abstract
- A growth process for diluted magnetic SiC has been explored for as-grown epitaxiallayers by introducing Mn ions. Depending on the growth conditions, either high Mn doping orexcess concentrations with second phases may form in the layers. Under those conditions wherecompound phases appear, there is a magnetic response in the material as demonstrated usingSQUID measurements with a transition temperature of 160K in the as-grown material. There is noresponse in layers for which the second phases have been removed by etching.
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| 23. |
- Syväjärvi, Mikael, 1968-, et al.
(författare)
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Formation of ferromagnetic SiC : Mn phases
- 2005
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Ingår i: Materials Science Forum, Vols. 483-485. ; , s. 241-244
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Konferensbidrag (refereegranskat)abstract
- Ferromagnetic phases in as-grown SiC have been studied. An interpretation about the formation based on details of the phase appearance in the layers from optical microscopy, AFM, and TEM investigations is related to the growth. Some phases were found to have a nucleation at the edge of the phase and detailed TEM investigations show that the phases have an increased grain density at the edge while the main part of the phase is monocrystalline.
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| 24. |
- Thinh, N. Q., et al.
(författare)
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Formation of Ga interstitials in (Al,In)yGa1-yNxP1-x alloys and their role in carrier recombination
- 2004
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 85, s. 2827-
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Tidskriftsartikel (refereegranskat)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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| 25. |
- Vorona, Igor, et al.
(författare)
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Magnetic resonance signatures of grown-in defects in GaInNP alloys grown on a GaAs substrate
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86:22, s. 222110-
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Tidskriftsartikel (refereegranskat)abstract
- Dilute-nitride Ga0.44In0.56NyP1-y alloys with y=0-0.02, grown on a GaAs substrate using gas-source molecular beam epitaxy, are studied by the optically detected magnetic resonance (ODMR) technique. Grown-in paramagnetic defects were found to act as centers of nonradiative recombination. Resolved hyperfine structure for one of the detected ODMR signals suggests involvement of a Ga-interstitial or an As-antisite in the structure of the related defect. © 2005 American Institute of Physics.
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