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Current Status
The band gap energy of InAlGaN system ranges between 1.95 and 6.2 eV at room temperature depending on In and Al composition. Lifetimes exceeding 10000 hr of CW operation of InGaN-AlGaN lasers is reported by Nichia. 40 mW [1] continuos wave operation of MOVPE InGaN-AlGaN laser has been demonstrated.
Attempts to tune emission wave length for GaN-based systems usually is connected with using of InGaN thin layers in the active region of LED or LD. InGaN-GaN LEs are working up to blue optical field. Future increase in wave length leads to rapid degradation of the optical properties due to large differences in lattice constant between GaN and InN resulting in dislocation formation.
Another approach to the control the emission wavelength of the GaN-based HSs is associated with nitrogen related band gap narrowing. In the GaAsN system this narrowing leads to a very strong long wavelength shifts. In comparison InGaN band gap may be varied in 2-3.4 eV range providing a change in the band gap of about 15 meV/%InN. For GaAsN the change in the band gap corresponds to 100-200 meV/%GaAs i.e. approximately one order of magnitude larger than that in the InGaN case. This is a result of extremely pronounced bandgap bowing characteristic to the GaAsN system.
Up to now there are few works devoted to the introduction of As in GaN using MOCVD and MBE methods. These results shows changing of the PL spectrum connected with As presence that may be due to formation of As-related deep centers and due to decreasing of the GaN band gap. Strong increase in PL efficiency and mobility is reported when minor concentration of As is introduced [2]. Up to now, however, there exist no clear experimental results on growth of GaAsN with large GaAs mole fraction and demonstration strong shift of the PL peak in respect to the GaN band gap. This is connected with the large difference in lattice constants between GaN and GaAs (~25%) what results in problems with epitaxial growth: considerable miscibility gap, spinodal decomposition, etc. The largest value of the GaAs content reported in [3] was ~1%.
Besides the modification of the optical properties there are changes of the electrical properties of GaN alloys accompanying incorporation of the As atoms. It was shown increase in carrier mobility in the GaAsN layers [2, 4]. Therefore As-associated growth can be used for improving of the electrical parameters of the contact layers in the GaN-based LDs and LEDs.
The Ioffe Institute team led by Prof. Zh.I. Alferov has a background in semiconductor HS growth and investigations since the first realization of ideal injecting GaAs-AlGaAs heterojunctions [5]. First room temperature operated continuos wave injection lasers were demonstrated here and many pioneering studies in various areas of semiconductor HSs were held at Prof. Zh.I. Alferov’s department [6]. Records of the group include also ultralow threshold current density in QW lasers (40-50 A·cm-2 , 300K [7]), thermodynamic description of growth and phase equlibrium in MBE [8], and numerous activities in III-V and II-VI growth and in optical studies.
More recently, the Ioffe Institute team has a world-recognized success in fabrication of ordered arrays of III-V quantum dots in III-V and II-VI matrixes and in fabrication of injection lasers based on quantum dots. By further development of this approach by using vertically-coupled quantum dots, the group was the first to demonstrate low threshold current density lasing (60 A·cm-2, 300K [9]) via quantum dot ground state. At Ioffe Institute a technology for fabrication of light emitting diodes in GaN and GaN-AlGaN HSs is available. UV LED and photopumped GaN-AlGaN lasers operating at RT are realised [10]. Among international acknoledgenments are talks on various international conferences [9, 11-13].
The Ioffe Institute group has the facilities necessary for conducting the research work in the area of thin film technology and laser development.
MOCVD equipment: “Epiquip VP-50 RP” Reduced Pressure MOCVD growth machine.
Optical characterisation facilities
- PL using He-Cd, N2, Ar+ gas lasers and GaAs LDs as excitation sources. Spectral range available for gratings and detectors is 300 - 5000 nm. Optical reflectance spectroscopy and luminescence excitation spectroscopy, using halogen lamp light dispersed through a monochromator.
- Facilities for electroluminescence and gain measurements
- Galvanomagnetic studies
- Post growth facilities (annealing, laser structure processing), electroluminescence equipment, including the equipment for laser degradation tests.
Other scientific equipment of the Ioffe Institute, which can be used:
- SIMS CAMECA IMS4f,
- transmission electron microscope Philips EM 420,
- complete TEM sample preparation line GATAN,
- electron microscopes CamScan,
- scanning tunnelling microscope.
Development of the theory of quantum dots was started in Institute for Nuclear Problems, Belarus State University in 1996 theoretical research in the field of the electrodynamics of nanostructures. The same name has student research laboratory organized at the INP. Potentiality of the group in the chosen field is based on the previous experience in mathematical methods of diffraction theory [14], laser dynamics, X-rays diffraction and wave packet diffraction by optical gratings, electrodynamics of chiral media and composites.
Since 1996, an investigation of electronic and electromagnetic properties of nanotubes and nanotube-based composites has been carried out as well as of wave diffraction by sculptured thin films. Experience in electrodynamics of nanostructures and composite materials and mathematical diffraction theory and closed cooperation with research teams from A.F.Ioffe Physical-Technical Institute (St.Peterburg), Institute of Solide State Physics (Berlin), Max-Born-Institute for Nonlinear Optics and Short Pulse Spectroscopy (Berlin) made it possible to develop electrodynamics of semiconductor quantum wire and quantum dot arrays. It has been theoretically predicted and experimentally confirmed that arrays of resonantly amplifying quantum wires and quantum dots (QDs) exhibit splitting of the gain band into separate bands for differently polarized field. Experimental results for multiple sheets of ZnCdSe QDs in a ZnSe matrix confirmed the theoretical predictions and signaled the discovery of a new class of "active" composite materials.
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[1].
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S. Nakamura, M .Senoh, S. Nagahama, N. Iwasa, T. Yamada, T. Matsushita, Y. Sugimoto, H. Kiyoku, Appl.Phys.Lett. 70, 2753 (1997)
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[2].
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L.J. Guido, et. al., Appl. Phys. Lett., 72, 2005 (1998).
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[3].
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J. Gotoh, et. al., Japan, Nitride Conference, 1997, p. 202
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[4].
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X. Li, et. al., Appl. Phys. Lett., 72, 1990 (1998).
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[5].
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Zh.I. Alferov, V.M. Andreev, V.I. Korol’kov et. al. Semiconductors, 2, 843 (1969).
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[6].
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Zh.I. Alferov, V.M. Andreev, E.L. Portnoy et. al. Fiz.Tekh.Polupr., 3, 1328 (1969) - Sov.Phys.Semiconductors, 3, 1107 (1970).
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[7].
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Zh.I. Alferov, et. al.,. Pisma Zh. Tehn. Fiz., 14 1803 (1988)
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[8].
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P.S. Kop'ev, N.N. Ledentsov. Semiconductors, 22, 1093 (1988).
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[9].
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N.N. Ledentsov, Proceedings of the 23rd International Conference on the Physics of Semiconductors, Berlin, Germany, July 21-26, 1996, Ed. by M. Scheffler and R. Zimmermann (World Scientific, Singapoure, 1996), v. 1, p. 19.
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[10].
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A.S. Usikov et. al., EW MOVPE VII, Berlin, Germany, 8-11 June, 1997. Workshop Booklet
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[11].
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N.N. Ledentsov, M. Grundmann, N. Kirstaedter, et. al. Proc. 22nd Int. Conf. Phys. Semicond, Vancouver, Canada, August 1994, Ed. D.J. Lockwood, World Scientific, Singapore, Vol. 3, p. 1855.
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[12].
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V.M. Ustinov, et. al., MRS 1997 Fall Meeting, Dec. 1-5, 1997, Boston, MA, USA [Abstrast Book, C5.5, p. 86].
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[13].
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N.N. Ledentsov, et. al. Proc. of the 7th International Conference on Modulated Semiconductor Structures, Madrid, 10-14 July, 1995, Solid State Electronics 40, 785 (1996).
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[14].
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A.S. Ilyinsky, G.Ya. Slepyan., A.Ya. Slepyan, Propagation, scattering and dissipation of electromagnetic waves. London: Peregrinus, 1993.
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