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Time resolved photoluminescence study of Si modulation doped GaN/Al 0.07Ga0.93N multiple quantum wells
Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
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2004 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 241, no 5, p. 1124-1133Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2004. Vol. 241, no 5, p. 1124-1133
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-45787DOI: 10.1002/pssb.200301973OAI: oai:DiVA.org:liu-45787DiVA, id: diva2:266683
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2021-09-09
In thesis
1. Optical Characterization of GaN/AIGaN Quantum Well Structures
Open this publication in new window or tab >>Optical Characterization of GaN/AIGaN Quantum Well Structures
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The III-nitride material family is particularly well suited for optoelectronic applications, e.g. as UV light emitters in future lighting solutions that are expected to replace the incandescent and fluorescent lamps in use today. Here a UV primary light emitting diode (LED) excites an efficient phosphor so that the entire LED package produces white light. The LED is expected to be built upon a technology involving multiple quantum wells (MQWs) in the AIGaN/GaN system as the active region. The AIGaN barriers will only have a moderate height, not to block the current flow in the LED, i.e. a low Al composition will be used.

In order to optimize the device design, it is necessary to provide knowledge on the material properties and especially to understand the recombination mechanisms in nitride QWs. A peculiarity of the wurtzite nitrides is the significant macroscopic polarization with both a spontaneous and a piezoelectric component. These polarization charges create internal fields in the QWs that have a fundamental influence on the optical properties, strongly affecting the oscillator strengths of excitons as well as the spectral position of the corresponding photoluminescence (PL) peaks. The radiative recombination processes are strongly modified by these built-inelectric fields in the [0001] direction, which causes a substantial quantum confined stark effect (QCSE).

Screening by doping and/or carrier injection strongly affects the polarization-induced properties. For instance modulation doping can be used to screen the macroscopic polarization field in nitride quantum wells. The screening of the field increases the overlap between confined electron and hole states, enhancing the radiative transition probability across the gap. This can explain the experimental findings of lower laser threshold current, reduced radiative lifetime, and increased emission intensity indoped MQWs.

In this thesis, the influence of Si doping on the exciton localization in modulationdoped GaN/A10.07Ga0.93N multiple-quantum-well (MQW) structures and the radiative recombination mechanisms for the undoped and Si doped samples have been investigated. The thesis is mainly based on experimental investigations by using a combination of photoluminescence (PL), micro photoluminescence (μ-PL) and timeresolved photo-luminescence (TRPL) techniques.

The results of the measurements reveal the hole localization even at highly modulation doped samples. Localization at interfaces leads to spectrally resolve well width fluctuations in the PL spectra for the undoped samples, while these appear to be screened for the case of high n-doping. The hole localization determines the residual PL linewidth in undoped samples, and the recombination kinetics in all samples at low temperatures. At elevated temperatures, the Si doping is found to improve the radiative efficiency.

Place, publisher, year, edition, pages
Linköping: Linköping University, 2004. p. 59
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 866
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-179058 (URN)9173739286 (ISBN)
Public defence
2004-04-16, hörsal Planck, Fysikhuset, Linköpings Universitet, Linköping, 10:15
Opponent
Note

All or some of the partial works included in the dissertation are not registered in DIVA and therefore not linked in this post.

Available from: 2021-09-09 Created: 2021-09-09 Last updated: 2023-02-23Bibliographically approved

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Monemar, BoPaskov, PlamenHoltz, Per-OlofPozina, Galia

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