| 1. |
- Arnaudov, B, et al.
(författare)
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Energy position of near-band-edge emission spectra of InN epitaxial layers with different doping levels
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 69:11
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Tidskriftsartikel (refereegranskat)abstract
- We studied the shape and energy position of near-band-edge photoluminescence spectra of InN epitaxial layers with different doping levels. We found that the experimental spectra of InN layers with moderate doping level can be nicely interpreted in the frames of the "free-to-bound" recombination model in degenerate semiconductors. For carrier concentrations above n>5x10(18) cm(-3) the emission spectra can also be modeled satisfactorily, but a contribution due to a pushing up of nonequilibrium holes over the thermal delocalization level in the valence band tails should be considered in the model. The emission spectra of samples with low doping level were instead explained as a recombination from the bottom of the conduction band to a shallow acceptor assuming the same value of the acceptor binding energy estimated from the spectra of highly doped samples. Analyzing the shape and energy position of the free-electron recombination spectra we determined the carrier concentrations responsible for the emissions and found that the fundamental band gap energy of InN is E-g=692+/-2 meV for an effective mass at the conduction-band minimum m(n0)=0.042m(0).
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| 2. |
- Arnaudov, B., et al.
(författare)
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Free-to-bound radiative recombination in highly conducting InN epitaxial layers
- 2004
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Ingår i: Superlattices and Microstructures. - : Elsevier BV. - 0749-6036 .- 1096-3677. ; 36:4-6, s. 563-571
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Tidskriftsartikel (refereegranskat)abstract
- We present a theoretical simulation of near-band-edge emission spectra of highly conducting n-InN assuming the model of 'free-to-bound' radiative recombination (FBRR) of degenerate electrons from the conduction band with nonequilibrium holes located in the valence band tails. We also study experimental photoluminescence (PL) spectra of highly conducting InN epitaxial layers grown by MBE and MOVPE with electron concentrations in the range (7.7 × 1017-6 × 1018) cm-3 and find that the energy positions and shape of the spectra depend on the impurity concentration. By modeling the experimental PL spectra of the InN layers we show that spectra can be nicely interpreted in the framework of the FBRR model with specific peculiarities for different doping levels. Analyzing simultaneously the shape and energy position of the InN emission spectra we determine the fundamental bandgap energy of InN to vary between Eg = 692 meV for effective mass mn0 = 0.042m0 and Eg =710 meV for mn0 = 0.1m0. © 2004 Elsevier Ltd. All rights reserved.
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| 3. |
- Haratizadeh, H., et al.
(författare)
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Time resolved photoluminescence study of Si modulation doped GaN/Al 0.07Ga0.93N multiple quantum wells
- 2004
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 241:5, s. 1124-1133
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Tidskriftsartikel (refereegranskat)abstract
- The effects of the Si doping level on the recombination dynamics and carrier (exciton) localization in modulation doped GaN/Al0.07Ga 0.93N multiple-quantum-well (MQW) structures were studied by means of photoluminescence (PL) and time-resolved PL measurements. All samples with different doping levels show a QW emission which is blue shifted with respect to the 3.48 eV PL peak from the GaN buffer layer. The decay time at the peak position remains nearly constant in the range of 320-420 ps at 2 K for all doping levels. For the undoped and low-doped samples (3 × 1018 cm-3), which have less free electrons in the QWs, a non-exponential PL decay behaviour at 2 K is attributed to localized exciton recombination. The more highly doped samples (5 × 1018 cm-3 to 10 20 cm-3) show almost exponential decay curves at 2 K, suggesting the recombination of free electrons and localized holes. This localization effect appears even at high electron concentrations to cancel the expected lowering of the radiative lifetime with doping at 2 K, such a lowering is clearly observed at elevated temperatures for the highly doped samples, however. The internal polarization-induced fields of the medium and highly-doped samples are partly screened by the electrons originating from the doping in the barriers. Only the PL peak of the undoped and low-doped samples shows a redshift with time delay, related to the photogenerated carriers. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 4. |
- Monemar, Bo, et al.
(författare)
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Optical investigation of AlGaN/GaN quantum wells and superlattices
- 2004
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Ingår i: Physica status solidi. A, Applied research. - : Wiley. - 0031-8965 .- 1521-396X. ; 201:10, s. 2251-2258
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Tidskriftsartikel (refereegranskat)abstract
- We report a detailed optical study of several sets of multiple quantum wells (MQWs) in the AlGaN/GaN system, as well as AlN/GaN superlattice (SL) structures. In this study all materials were grown by MOCVD, as opposed to most previous studies where MBE was employed. In undoped MQWs discrete photoluminescence (PL) peaks related to discrete well width fluctuations by one full c lattice parameter are clearly observed. In doped samples this effect appears to be screened. While the recombination process in undoped samples is excitonic, in MQWs doped with Si above about 5 x 10(18) cm(-3) free electrons (a 2DEG) are dominant, and the PL process is a free electrons-localized hole transition at low temperatures. The hole localization prevails up to very high n-doping, as was previously observed in bulk GaN. The hole localization is demonstrated via several experiments, including results on PL transient decay times and LO phonon coupling. Near surface band bending, due mainly to dopant depletion in doped structures or interaction with surface states in case of higher Al content in barriers, influences the distribution of electron filling among the QWs, making a detailed modeling of the spectral shape somewhat ambiguous. It is found that AlN barriers promote a strong room temperature PL signal from the QWs, as opposed to the case with AlGaN barriers.
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| 5. |
- Monemar, Bo, et al.
(författare)
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Optical properties of InGaN/GaN and AlGaN/GaN multiple quantum well structures
- 2003
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5023, s. 63-67
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We report on low temperature photoluminescence (PL) in In xGa1-xN multiple quantum wells (MQWs) with x in the range 0.1 and highly Si doped barriers of In0.01Ga0.99N. One sample with 3 QWs of width 3.5 nm and barriers of width 10.5 nm had the MQW in the depletion region of the outer surface. Two PL peaks were observed, one QW exciton from the QW closest to the GaN buffer, one lower energy peak related to a 2DEG at the interface to the GaN buffer layer. In a second similar sample 5 QWs of width 3 nm and with 6 nm highly Si doped In0.01Ga 0.99N barriers the MQW was placed in the n-side depletion region of a pn-junction. At low temperatures the PL and electroluminescence (EL) spectra are quite different at no, low, or reverse bias, the PL appearing at higher energy. At high forward bias a spectral component at the EL position appears. This proves a strong influence of the depletion field on the optical spectra. Preliminary results are also reported for n-doped Al0.07Ga 0.93N/GaN structures, with near surface MQWs.
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| 6. |
- Monemar, Bo, et al.
(författare)
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Photoluminescence of InGaN/GaN and AlGaN/GaN multiple quantum well structures : Role of depletion fields and polarization fields
- 2003
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Ingår i: Physica status solidi. A, Applied research. - Weinheim, Germany : Wiley-VCH Verlagsgesellschaft. - 0031-8965 .- 1521-396X. ; 195:3, s. 523-527
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Tidskriftsartikel (refereegranskat)abstract
- We report on low temperature photoluminescence (PL) in InxGa1-xN multiple quantum wells (MQWs) with x in the range 0.1 and highly Si doped barriers of In0.01Ga0.99N. The MQW was placed either in the near surface depletion field or at the n-side depletion field of a pn-junction. At low temperatures the PL and electroluminescence (EL) spectra are quite different at no, low, or reverse bias, the PL appearing at higher energy. At high forward bias a spectral component at the EL position appears in PL. This proves a strong influence of the depletion field on the optical spectra. Preliminary results are also reported for Al0.07Ga0.93N/GaN structures, with near surface MQWs with 5 QWs, both Si-doped and nominally undoped. These structures show clear spectral features related to nonequivalent QWs in a graded depletion field.
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| 7. |
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| 8. |
- Bergman, Peder, et al.
(författare)
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Photoluminescence and electroluminescence characterization of InxGa1-x/InyGa1-yN multiple quantum well light emitting diodes
- 2002
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Ingår i: Materials Science Forum, Vols. 389-393. ; , s. 1493-1496
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Konferensbidrag (refereegranskat)abstract
- We report on a study of radiative recombination in In0.11Ga0.89N/In.0.01Ga0.99N multiple quantum wells (MQWs). The QWs were nominally undoped, while the InGaN barriers were Si doped. The MQW part is situated in the depletion field of a pn-junction structure with electrical contacts, so that both photoluminescence (PL) and electroluminescence (EL) can be studied as a function of bias. The PL and EL spectra are distinctly different, in particular at low temperatures. The spectral properties and related differences in PL decay times reflect different recombination conditions in the MQW region for the individual QWs.
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| 9. |
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| 10. |
- Hai, P. N., et al.
(författare)
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Ga-related defect in as-grown Zn-doped GaN : An optically detected magnetic resonance study
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 62:16, s. R10607-R10609
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Tidskriftsartikel (refereegranskat)abstract
- A detailed study of as-grown Zn-doped GaN employing optically detected magnetic resonance (ODMR) spectroscopy is presented. Besides the well-known ODMR spectra of an effective-mass-like donor and Zn acceptor, a positive ODMR signal of an S=1 / 2 paramagnetic center was observed when monitoring the dominating blue luminescence band peaking at 2.8 eV. The involvement of a single Ga nucleus in the defect center is revealed from the rather well-resolved hyperfine interactions involving the isotopes 71Ga (39.9%) and 69Ga (60.1%), both with nuclear spin I=3 / 2. The C3v symmetry, the hyperfine interaction and the defect formation suggest a Ga-related complex nature of this center.
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| 11. |
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| 12. |
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| 13. |
- Harati Zadeh, Hamid, 1964-, et al.
(författare)
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Photoluminescence study of Si-doped GaN/Al0.07Ga0.93N multiple quantum wells with different dopant position
- 2004
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 84:25, s. 5071-5073
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Tidskriftsartikel (refereegranskat)abstract
- The Si-doped GaN/Al0.07Ga0.93N multiple quantum wells (MQW) were investigated, using photoluminescence (PL) and time-resolved (PL) measurements. The influence of Si doping on the emission energy and recombination dynamics of the MWQs were also investigated, with different dopant position in the wells. It was observed that the redshifted emission of the MQWs was attributed to the self-energy shift of the electron states due to the correlated motion of the electrons exposed to the fluctuating potential of the donor ions. It was also observed that the PL decay time of the sample was ∼760 ps, at low temperature.
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| 14. |
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| 15. |
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| 16. |
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| 17. |
- Kasic, A., et al.
(författare)
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Phonons and free-carrier properties of binary, ternary, and quaternary group-III nitride layers measured by infrared Spectroscopic Ellipsometry
- 2003
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 0:6 SPEC. ISS., s. 1750-1769
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This work reviews recent ellipsometric investigations of the infrared dielectric functions of binary, ternary, and quaternary group-III nitride films. Spectroscopic Ellipsometry in the mid-infrared range is employed for the first time to determine phonon and free-carrier properties of individual group-III nitride heterostructure components, including layers of some ten nanometer thickness. Assuming the effective carrier mass, the free-carrier concentration and mobility parameters can be quantified upon model analysis of the infrared dielectric function. In combination with Hall-effect measurements, the effective carrier masses for wurtzite n- and p-type GaN and n-type InN are obtained. The mode behavior of both the E1(TO) and A1(LO) phonons are determined for ternary compounds. For strain-sensitive phonon modes, the composition and strain dependences of the phonon frequencies are differentiated and quantified. Information on the crystal quality and compositional homogeneity of the films can be extracted from the phonon mode broadening parameters. A comprehensive IR dielectric function database of group-III nitride materials has been established and can be used for the analysis of complex thin-film heterostructures designed for optoelectronic device applications. Information on concentration and mobility of free carriers, thickness, alloy composition, average strain state, and crystal quality of individual sample constituents can be derived. © 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 18. |
- Monemar, Bo, et al.
(författare)
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Influence of depletion fields on photoluminescence of n-doped InGaN/GaN multiple quantum well structures
- 2002
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Ingår i: Physica status solidi. A, Applied research. - 0031-8965 .- 1521-396X. ; 192:1, s. 21-26
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Tidskriftsartikel (refereegranskat)abstract
- We report on a detailed study of low temperature photoluminescence (PL) in InxGa1-xN multiple quantum wells (MQWs) with x in the range 0.1 and highly Si-doped barriers of In0.01Ga0.99N. The entire MQW structure was grown at 800 degreesC. One sample with 3 QWs of width 3.5 nm and barriers of width 10.5 nm had the MQW in the depletion region of the outer surface. Two PL peaks were observed, one QW exciton from the OW closest to the GaN buffer, one lower energy peak related to a 2DEG at the interface to the GaN buffer layer. In a second similar sample, 5 QWs of width 3 nm and with 6 nm highly Si-doped In0.01Ga0.99N barriers the MQW was placed in the n-side depletion region of a pn-junction, i.e. a complete LED structure with semitransparent top metallisation. Two PL peaks are observed also in this case, of similar origin as described above. With forward bias, this structure shows lower-energy PL emission, indicating the gradual activation of the other QWs closer to the pn-junction. At high forward bias the low-energy part of the PL spectrum becomes similar to the electroluminescence (EL) spectrum.
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| 19. |
- Monemar, Bo, 1942-, et al.
(författare)
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Influence of polarization fields and depletion fields on photoluminescence of AlGaN/GaN multiple quantum well structures
- 2003
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 237:1, s. 353-364
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Tidskriftsartikel (refereegranskat)abstract
- We report on a detailed study of low temperature photoluminescence (PL) in Al0.07Ga0.93N/GaN multiple quantum wells (MQWs). The structures were grown on sapphire with the conventional low temperature AlN nucleation layer and thick GaN buffer layer. Several sets of 5 QW MQW samples were studied, one set with Si doping in the barriers up to or above the metallic limit. Nominally undoped MQW samples were also studied. The spectral behaviour of the doped samples was strongly affected by the near surface depletion field, causing overlap of different spectra from non-equivalent QWs. The QWs closest to the surface are presumably inactive in some samples, due to a very high depletion field. For the case of undoped samples, on the other hand, the near surface QWs are active and most prominent in the PL spectra. The structure from discrete well width variations is here resolved in the PL spectra. The results demonstrate that for structures with no additional capping layer both the depletion field and the polarisation fields need to be considered in the interpretation of experimental data. The theoretically estimated fields in this work are consistent with the experimental spectra. The presence of localisation even in the case of metallic samples, as observed by a constant PL decay time independent of doping, is discussed in terms of penetration of the hole wave functions into the AlGaN barriers. This localisation is also manifested in a sizeable LO phonon coupling strength in all samples studied.
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| 20. |
- Monemar, Bo, et al.
(författare)
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Optical characterization of III-nitrides
- 2002
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Konferensbidrag (refereegranskat)abstract
- Recent developments in material properties of GaN and related heterostructure combinations are reviewed, with emphasis on optical data. We discuss recent polarized photoluminescence (PL) data on the free excitons in GaN, obtained from thick HVPE grown layers. The exchange splitting constant is found to be about 0.6 meV, a more accurate value than previous suggestions. The PL signatures of shallow donors and acceptors, i.e. the bound excitons, are discussed and tentatively identified. Intrinsic point defects are discussed in terms of stability and experimental signatures. Quantum well structures in the InGaN/GaN and GaN/AlGaN systems are briefly discussed, with emphasis on localization of carriers and excitons. © 2002 Published by Elsevier Science B.V.
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| 21. |
- Monemar, Bo, et al.
(författare)
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Optical characterization of InGaN/GaN MQW structures without in phase separation
- 2001
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Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 228:1, s. 157-160
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Tidskriftsartikel (refereegranskat)abstract
- Photoluminescence and cathodoluminescence spectroscopies are used to investigate the properties of the band edge emission of InGaN/(In)GaN multiple quantum well (MQW) structures which do not show evidence of phase separation in high resolution electron microscopy. The data still show a clear low energy peak in the spectra. about 0.1 eV below the main exciton peak. Possible interpretations of this second peak are discussed.
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| 22. |
- Monemar, Bo, et al.
(författare)
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Photoluminescence in n-doped In0.1Ga0.9N/In0.01Ga0.99N multiple quantum wells
- 2002
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Ingår i: MRS Internet Journal of Nitride Semiconductor Research. - 1092-5783. ; 7:7, s. 1-
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Tidskriftsartikel (refereegranskat)abstract
- In0.1Ga0.9N/In0.01Ga0.99N multiple quantum wells (MQWs) with heavily Si-doped barriers, grown with Metal Organic Vapor Phase Epitaxy (MOVPE) at about 800(0)C, have been studied in detail with optical spectroscopy. Such structures are shown to be very sensitive to a near surface depletion field, and if no additional layer is grown on top of the MQW structure the optical spectra from the individual QWs are expected to be drastically different. For a sample with 3 near surface QWs and Si-doped barriers, only the QW most distant from the surface is observed in photoluminescence (PL). The strong surface depletion field is suggested to explain these results, so that the QWs closer to the surface cannot hold the photo-excited carriers. A similar effect of the strong depletion field is found in an LED structure where the MQW is positioned at the highly doped n-side of the pn-junction. The internal polarization induced electric field in the QWs is also rather strong, and incompletely screened by carriers transferred from the doped barriers. The observed PL emission for this QW is of localized exciton character, consistent with the temperature dependence of peak position and PL decay time. The excitonic lineshape of 35-40 meV in the QW PL is explained as caused by a combination of random alloy fluctuations and interface roughness, the corresponding localization potentials are also responsible for the localization of the excitons in the low temperature range (
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| 23. |
- Monemar, Bo, et al.
(författare)
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Photoluminescence of excitons in InxGa1-xN/InyGa1-yN multiple quantum wells
- 2002
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Ingår i: Physica status solidi. A, Applied research. - 0031-8965 .- 1521-396X. ; 190:1, s. 161-166
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Tidskriftsartikel (refereegranskat)abstract
- We report on a detailed study of excitons in InxGa1-xN/InyGa1-yN multiple quantum wells (MQWs) with an In composition x in the QWs of about 0.1, and a small In composition y in the barrier of 0.01-0.02. The MOVPE growth procedure was optimized to allow growth without In segregation. The InyGa1-yN barriers had a Si doping of about 5 x 10(18) cm(-3) . The low temperature photoluminescence spectra show two sets of exciton-like spectra with quite different properties. The lower energy emission has a small thermal activation energy (about 5 meV), and thus disappears at elevated temperatures, it is not observed at room temperature. The higher energy exciton state has a decay time of about 5 ns, while the lower energy process is much slower. We have also done preliminary studies on samples where the MQW region is situated in a p-n junction field, with semi-transparent contacts, to study the effects of varying the bias across the MQW structure. The combination of optical data can e interpreted in terms of a substantial potential gradient across the MQW region for both samples. The conclusion is that probably only one QW is emitting at low T (and no bias), and the second lower energy PL peak originates from a shallow notch in the conduction band at the interface between the thick GaN buffer layer and the first Ga(In)N barrier.
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| 24. |
- Paskov, Plamen, 1959-, et al.
(författare)
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Phonon-assisted photoluminescence in InGaN/GaN multiple quantum wells
- 2002
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Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 234:3, s. 755-758
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Tidskriftsartikel (refereegranskat)abstract
- The LO-phonon sidebands of the photoluminescence in InGaN/GaN multiple quantum wells has been investigated in the temperature range from 20 to 300 K. Analysing the intensity distribution among the phonon replicas, the strength of the exciton-phonon interaction has been estimated. The Huang-Rhys factor was found to be ÿ0.3, much larger than in GaN. The enhancement has been attributed to the exciton localization on a length scale smaller than the exciton Bohr radius and to the large internal electric field, which increases the spatial separation of the electron and hole charge densities along the growth axis.
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| 25. |
- Pozina, Galia, et al.
(författare)
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InGaN/GaN multiple quantum wells grown by metalorganic vapor phase epitaxy with mass transport
- 2000
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 77:11, s. 1638-1640
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Tidskriftsartikel (refereegranskat)abstract
- We report on studies of In0.12Ga0.88N/GaN heterostructures with three 35-Angstrom-thick quantum wells (QWs) grown on sapphire substrates by metalorganic vapor phase epitaxy with employment of mass transport. The structure is demonstrated to show good structural and optical properties. The threading dislocation density is less than 10(7) cm(-2) for the mass-transport regions. The photoluminescence (PL) spectrum is dominated by the rather narrow near-band gap emission at 2.97 eV with a linewidth of 40 meV. This emission has a typical PL decay time about 5 ns at 2 K within the PL contour. With increasing excitation intensity, an additional transition with longer decay time (about 200 ns) is enhanced at energy about 2.85 eV. The position of this line depends strongly on the excitation power. We explain the data in terms of a model, where the PL is a result of contribution from at least two nonequivalent QWs, which could be realized due to a potential gradient across the layers. (C) 2000 American Institute of Physics. [S0003- 6951(00)04337-0].
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| 26. |
- Pozina, Galia, et al.
(författare)
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Luminescence of InGaN/GaN multiple quantum wells grown by mass-transport
- 2001
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Ingår i: Materials Science Forum, Vols. 353-356. ; , s. 791-794
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Konferensbidrag (refereegranskat)abstract
- We present an optical study of an In0.12Ga0.88N/GaN structure containing three quantum wells (QW) grown by metalorganic vapor phase epitaxy using mass transport. The mass-transport regions demonstrate a high structural quality with a threading dislocation density less than 10(7) cm(-2). The photoluminescence (PL) spectrum is dominated by a 40 meV - narrow line centered at 2.97 eV at 2 K. This emission has a typical PL decay time about 5 ns at 2 K within the PL contour. An additional line with longer decay time (about 200 ns) is observed at an energy of similar to2.85 eV. The position of this line shifts towards higher energies with increasing excitation power. The data are explained in terms of a model, where the PL originates from two nonequivalent quantum wells, which could be realized due to a potential gradient across the layers.
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| 27. |
- Pozina, Galia, et al.
(författare)
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Multiple peak spectra from InGaN/GaN multiple quantum wells
- 2000
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Ingår i: Physica status solidi. A, Applied research. - 0031-8965 .- 1521-396X. ; 180:1, s. 85-89
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Tidskriftsartikel (refereegranskat)abstract
- Optical properties of In0.12Ga0.88N/GaN multiple quantum well (MQW) structures grown by metalorganic vapor phase epitaxy at 820 degrees C are reported. The transmission electron microscopy measurements show a roughness of the sample surfaces containing small pit like defects of a size 100 to 200 Angstrom with a density far exceeding the dislocation density. The photoluminescence (PL) spectra in this set of samples are dominated by strong multiple peak emissions associated both with the MQW exciton recombination and with strongly localized states of energies much lower than the QW bandgap. We suggest that the low energy PL peaks are due to (i) photocarriers localized in quantum islands closely related to the threading dislocations, and possibly associated with V-defect induced side-wall QWs, (ii) strongly localized excitons in OD quantum dots in the disordered surface region, formed by uncontrolled surface etching processes.
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| 28. |
- Pozina, Galia, et al.
(författare)
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Optical spectroscopy of GaN grown by metalorganic vapor phase epitaxy using indium surfactant
- 2000
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 76:23, s. 3388-3390
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Tidskriftsartikel (refereegranskat)abstract
- The effect of In surfactant during metalorganic vapor phase epitaxial growth on sapphire substructure on the properties of GaN layers is studied using time-resolved photoluminescence. cathodoluminescence. and scanning electron microscopy. The samples are divided into two groups. where hydrogen and nitrogen, respectively, have been used as a carrier gas during growth. It is shown that In-doped samples have a lower dislocation density, a narrower photoluminescence linewidth, and a longer foe exciton lifetime. The influence of indium is stronger for GaN layers grown in nitrogen-rich conditions. The improvements of structural and optical properties are attributed to the effect of In on dislocations. (C) 2000 American Institute of Physics. [S0003-6951(00)02723-6].
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| 29. |
- Pozina, Galia, et al.
(författare)
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Optical study of AlGaN/GaN multiple quantum well structures grown on laterally overgrown GaN templates
- 2002
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Ingår i: Physica status solidi. A, Applied research. - 0031-8965 .- 1521-396X. ; 190:1, s. 107-111
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Tidskriftsartikel (refereegranskat)abstract
- We report on optical studies of Al0.1Ga0.9N/GaN structures with five 30 (A) over circle thick GaN quantum wells (QWs) grown by metal organic vapor phase epitaxy using the lateral overgrowth technique. Overgrown regions demonstrate better structural and optical properties. The low temperature photoluminescence (PL) is dominated by the multiple quantum well (MQW) emission at 3.53 eV with the linewidth of similar to50 meV. The PL decay time for this line was measured to be similar to600 ps. Comparison with an AlGaN/GaN MQW light-emitting diode (LED) structure is done. The LED structure was grown with a p-type doped AlGaN top layer and a p-GaN contact layer. The PL spectrum of the LED structure shows besides the donor-acceptor pair recombination from the top layer an additional 60 meV wide line at 3.64 eV. The presence of two MQW peaks may be related to the potential gradient present across the MOW structure.
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| 30. |
- Pozina, Galia, et al.
(författare)
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Origin of multiple peak photoluminescence in InGaN/GaN multiple quantum wells
- 2000
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Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 88:5, s. 2677-2681
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Tidskriftsartikel (refereegranskat)abstract
- Optical spectroscopy has been performed for a set of In0.12Ga0.88N/GaN multiple quantum wells (MQW) grown by metalorganic vapor phase epitaxy at 820 degrees C. Time-resolved, temperature- and power-dependent photoluminescence as well as spatially-resolved cathodoluminescence measurements have been applied to elucidate the nature of the recombination mechanisms responsible for the radiative transitions in the samples. The photoluminescence spectra in this set of samples are dominated by strong multiple peak emissions associating with both confined levels of the MQW system (the higher energy band) and with strongly localized states of energies much lower than the QW band gap. We suggest that the photoluminescence originate from (i) the MQW exciton recombination, (ii) excitons localized in the quasidot regions with indium concentrations higher than in the alloy due to segregation processes, and (iii) from localized states in zero-dimensional quantum islands created by surface defects such as pits and V defects. Buried side-wall quantum wells caused by V defects might also influence the photoluminescence spectra. (C) 2000 American Institute of Physics. [S0021-8979(00)00117-1].
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| 31. |
- Pozina, Galia, et al.
(författare)
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Photoluminescence of InGaN/GaN multiple quantum wells grown by mass transport
- 2001
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 230:3-4, s. 473-476
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Tidskriftsartikel (refereegranskat)abstract
- We report on studies of an In0.12Ga0.88N/GaN structure with three 35 Å thick quantum wells (QWs) grown by metalorganic vapor phase epitaxy with employment of mass transport. The mass-transport regions demonstrate a threading dislocation density less than 107 cm-2. The photoluminescence (PL) spectrum is dominated by a 40 meV-narrow line centered at 2.97 eV at 2 K. This emission has a typical PL decay time of about 5 ns at 2 K within the PL contour. An additional line with longer decay time (about 200 ns) is observed at an energy about 2.85 eV. The position of this line shifts towards higher energies with increasing excitation power. The data are consistent with a model, where the PL originates from at least two nonequivalent QWs, which could be realized due to a potential gradient across the layers. © 2001 Elsevier Science B.V. All rights reserved.
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| 32. |
- Pozina, Galia, et al.
(författare)
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Time-resolved optical properties of GaN grown by metalorganic vapor phase epitaxy with indium surfactant
- 2001
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Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 82:1-3, s. 137-139
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Tidskriftsartikel (refereegranskat)abstract
- The effects of isoelectronic indium doping on optical properties of GaN layers grown by metalorganic vapor-phase epitaxy have been studied. Two sets of samples have been grown with hydrogen and with nitrogen as carrier gas. It has been shown from scanning electron microscopy, cathodoluminescence and time-resolved photoluminescence that In-doped samples have a lower dislocation density, a narrower photoluminescence line width and a longer free exciton lifetime. The improvements of structural and optical properties are attributed to the effect of In on dislocations. © 2001 Elsevier Science B.V.
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| 33. |
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| 34. |
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| 35. |
- Valcheva, E., et al.
(författare)
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Growth-induced defects in AlN/GaN superlattices with different periods
- 2003
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Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526.
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Konferensbidrag (refereegranskat)abstract
- MOCVD-grown AlN/GaN superlattices (SL) with different thickness of the well and barrier are investigated by transmission electron microscopy in low-magnification and high-resolution modes. Growth-induced defects are observed in some places causing different degree of disturbances of the regularity of the SLs. The SL grown with a thickness of the AlN barrier higher than the critical thickness hc for coherent growth reveals 2D growth of AlN platelets that give rise to cusps or irregularities at the interfaces. The SL with thickness of the GaN and AlN layers lower than hc is coherently grown. There is some evidence of dot-like structures formation in separate areas due to the large strain field present. © 2003 Elsevier B.V. All rights reserved.
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| 36. |
- Wagner, Matthias, 1969-, et al.
(författare)
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Magneto-optical studies of the 0.88-eV photoluminescence emission in electron-irradiated GaN
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 62:24, s. 16572-16577
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Tidskriftsartikel (refereegranskat)abstract
- Properties of the 0.88-eV photoluminescence (PL) in electron-irradiated wurtzite GaN have been investigated in detail by a combination of various magneto-optical techniques, including Zeeman measurements of PL, optically detected magnetic resonance (ODMR), and level anticrossing (LAC). ODMR observed by monitoring the PL emission is demonstrated to originate from a spin triplet. The symmetry of the corresponding defect is shown to be rhombic with its principal axes pointing into the high-symmetry directions Z=[0001], Y=[11¯00], and X=[112¯0]. From the Zeeman measurements the emission is shown to arise from an optical transition between a singlet excited state and the singlet ground state, providing convincing evidence for indirect detection of the spin triplet ODMR. LAC investigations of the same PL emission reveal two LAC lines, among which one is related to the spin triplet detected in ODMR.
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