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GaN/AlN Quantum Dots (gan/aln + quantum_dot)
Selected AbstractsNonlinear piezoelectric properties of GaN quantum dots nucleated at the edge of threading dislocationsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007ewski Abstract It was observed experimentally by Rouviere et al. that GaN/AlN Quantum Dots (QDs) nucleate at the edge of threading dislocations (Appl. Phys. Lett. 75, 2632 (1999) [1]). The preferred nucleation of QDs in this way is generally assumed to be due to the influence of the stress/strain field around the dislocation core, which in turn, gives the chemical and geometric conditions for nucleation of the QDs. We solve the finite element problem for QDs situated at the edge of threading dislocations where different lattice parameters, piezoelectric and spontaneous polarisation coefficients are assumed for the QD and its matrix. By solving the elastic and electric equilibrium problems we obtain both the residual stress and electric fields. The computational scheme employed here was obtained by linking two previous finite element algorithms described inreferences (P. D,u,ewski et al., Comput. Mater. Sci. 29, 379 (2004) [2]) and (G. Jurczak et al., phys. stat. sol. (c) 2, 972 (2005) and S.P. ,epkowski et al., Phys. Rev. B 73, 245201 (2005) [3, 4], respectively). This approach allows us to get a deeper physical insight into the mechanics and electrical properties of QDs and ultimately determine the efficiency of light emission from these objects. [source] Si-doped GaN/AlN quantum dot superlattices for optoelectronics at telecommunication wavelengthsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006F. Guillot Abstract We report on the controlled growth of Si doped GaN/AlN quantum dot (QD) superlattices, in order to tailor their intersubband absorption within the 1.3,1.5 µm telecommunication wavelengths. The QD size is tuned by modifying the amount of GaN in the QDs and the growth temperature. Silicon can be incorporated in the QDs to populate the first electronic level, without significant perturbation of the QD morphology. As a proof of the capability of these structures for infrared detection, a quantum-dot intersubband photodetector at 1.38 µm with lateral carrier transport is demonstrated. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Raman study of strain in GaN/AlN quantum dot multilayered structuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005A. Cros Abstract Raman spectroscopy has been used to investigate self-assembled stacks of GaN/AlN quantum dots with increasing number of periods. The E2H phonon modes associated to GaN and AlN are clearly resolved with visible excitation, and their energies allow the simultaneous monitoring of the dot and barrier strain states. The compression of the quantum dots is evidenced by a shift of the E2H phonon mode of circa 29 cm,1 to higher energies with respect to its relaxed value. The strain of the AlN spacer is found to be correlated to that of the dot, with an increase in its tensile component for the samples with fewer periods and a partial relaxation for samples over 50 periods. Additionally, resonant effects of the A1(LO) phonon mode have been investigated by tuning the excitation over a wide range in the ultra-violet region. A discussion of the strain distribution in quantum dots and spacers as a function of the number of periods is performed by means of a theoretical calculation based on the method of inclusions. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of thermal annealing on the structural and optical properties of GaN/AlN quantum dotsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2010M. Peres Abstract The influence of the post-growth thermal annealing on the structural and optical properties of GaN/AlN quantum dots (QDs) is reported. X-ray techniques suggest smooth and high quality interfaces of the stacked multilayer structures for the as-grown and annealed samples without any period thickness change. High-angle annular dark field images by scanning transmission electron microscopy show an intermixing between the GaN QDs and AlN spacers after annealing. The QDs recombination shifts to lower energies (red shift) for big dots and to higher energies (blue shift) for small dots, reflecting two competitive processes taking place during the thermal annealing. [source] Depth profiling of optical and vibrational properties in GaN/AlN quantum dot superlatticesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2009A. Cros Abstract Spatially resolved confocal ,-Raman and ,-photoluminescence experiments were performed to analyze the vibrational and optical properties of GaN/AlN quantum dots as a function of depth. Two approaches have been followed. First, spectra were taken by defocusing the microscope objective at various depths on the sample surface. In a second set of experiments a bevel at an angle of 20° with respect to the surface normal was prepared by mechanical polishing of the surface, and spectra were taken across the bevel. The E2h vibrational modes ascribed to the GaN QDs and the AlN spacer redshift towards the surface, indicating the progressive relaxation of the QDs and a considerable increase of the tensile strain in the AlN spacer. The photoluminescence is found to blueshift and narrow towards the surface. This behaviour is ascribed to the decrease of the QD internal electric field as a consequence of the relaxation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical properties of single non-polar GaN quantum dotsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2006F. Rol Abstract We present a microphotoluminescence study of non polar GaN/AlN quantum dots (QDs) grown along the [110] axis. Despite the high QD density, single exciton lines could be isolated on the high energy side of the spectral distribution of the QD array emission. Linewidths down to 0.5 meV are reported, which is one order of magnitude lower than previously reported linewidths for polar GaN/AlN QDs. This difference is attributed to the drastic reduction of the internal field in non-polar quantum dots. Temperature dependent measurements were performed up to 180 K. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Linear polarized photoluminescence from GaN quantum dots imbedded in AlN matrixPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010K. S. Zhuravlev Abstract We report microphotoluminescence studies of GaN/AlN quantum dots grown along the (0001) crystal axis by molecular-beam epitaxy on sapphire substrates. To obtain quantum dots with different density and size a nominal GaN coverage was varied from 1 to 4 monolayers. The highest density of quantum dots was about 1011 cm -2, so about 103 quantum dots was excited in experiments. We found that the photoluminescence intensity of a sample with the smallest amount of deposited GaN decreases in more than two orders of magnitude under continuous-wave laser exposure during about 30 minutes and then it remains stable. The photoluminescence intensity of the rest samples was time-independent quantity. The emission band of the former sample exhibits a prominent linear polarization along the growth plane. We assume that the quite high degree of polarization can be due anisotropy of strain and/or shape of the quantum dots formed near dislocations which act also as recombination centers causing photoluminescence quenching. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Homogeneous and inhomogeneous linewidth broadening of single polar GaN/AlN quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009F. Demangeot Abstract We report on the dependence on temperature of the homogeneous and inhomogeneous broadening of the fundamental transition of single polar GaN/AlN quantum dots (QDs). Stranski-Krastanov QDs have been grown by molecular beam epitaxy using NH3 as a nitrogen source, with a very low surface density. Low temperature (LT) microphotoluminescence measurements have been performed on 200 nm wide mesas in order to isolate the luminescence of single QDs. The linewidth is found to vary from 590 ,eV at 4 K up to 1350 ,eV at 65 K in a dot of 6 monolayer height. Though the LT linewidth is still dominated by spectral diffusion, the temperature dependent broadening up to 50 K is mainly accounted for by interactions between excitons and acoustic phonons through a coupling coefficient value nearly two orders of magnitude larger than its counterpart in InAs QDs. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Room temperature intraband Raman emission and ultrafast carrier relaxation in GaN/AlN quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009L. Nevou Abstract We report on the intraband emission at room-temperature from GaN/AlN quantum dots grown by plasma-assisted molecular beam epitaxy as well as on the measurements of GaN quantum dot intraband relaxation using femtosecond spectroscopy. The quantum dots exhibit s-pz intraband absorption peaked at 1.55 ,m. The pz -s intraband luminescence at , = 1.48 ,m is observed under optical excitation at , = 1.34 ,m. The population of the pz state arises from Raman scattering by GaN A1 longitudinal optical phonons. Based on the emission spectral shape, we estimate that the homogeneous linewidth of the s-pz intraband transition is less than 4 meV. The carrier lifetime of the pz state (T1) is measured by femtosecond pump-probe spectroscopy. T1 = 165 fs while the thermalization of electrons in the ground state proceeds in 1.5 ps. The saturation intensity of the s-pz intraband absorption is estimated to be in the 15 to 137 MW/cm2 range taking into account the uncertainty on the pump beam waist. These results demonstrate the promising capabilities of GaN/AlN QDs for application to telecom intraband lasers as well as multi-Tbit/s all-optical switching devices. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Raman study of strain in GaN/AlN quantum dot multilayered structuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005A. Cros Abstract Raman spectroscopy has been used to investigate self-assembled stacks of GaN/AlN quantum dots with increasing number of periods. The E2H phonon modes associated to GaN and AlN are clearly resolved with visible excitation, and their energies allow the simultaneous monitoring of the dot and barrier strain states. The compression of the quantum dots is evidenced by a shift of the E2H phonon mode of circa 29 cm,1 to higher energies with respect to its relaxed value. The strain of the AlN spacer is found to be correlated to that of the dot, with an increase in its tensile component for the samples with fewer periods and a partial relaxation for samples over 50 periods. Additionally, resonant effects of the A1(LO) phonon mode have been investigated by tuning the excitation over a wide range in the ultra-violet region. A discussion of the strain distribution in quantum dots and spacers as a function of the number of periods is performed by means of a theoretical calculation based on the method of inclusions. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||