Growth Structure, and Optical Properties of III-Nitride Quantum Dots
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Growth Structure, and Optical Properties of III-Nitride Quantum Dots Hadis Morkoç1, Arup Neogi2, Martin Kuball3 1
Virginia Commonwealth University, Richmond, VA 23284, USA North Texas University, Denton, Texas 76203 3 University of Bristol, Bristol, BS8 1TL UK 2
ABSTRACT Quasi-zero-dimensional (0D) semiconductors have been the subject of considerable interest which is stemmed from their unique physical properties which in turn are conducive to devices such as low threshold lasers and light polarization insensitive detectors, in addition to exciting basic physical phenomena. A laboratory analogue of 0D systems is semiconductor quantum dots (QDs) wherein the electronic states are spatially localized and the energy is fully quantized, loosely similar to an atomic system, making it more stable against thermal perturbations. In addition, the electronic density of states near the band gap is higher than in 3D and 2D systems, leading to a higher probability for optical transitions. Furthermore, the electron localization may dramatically reduce the scattering of electrons by bulk defects and reduce the rate of non-radiative recombination. Semiconductor based and metal based dots have been produced, the former via self-assembly and also by lithographic methods in many II-VI, III-V, and group IV semiconductor. The aim of this paper is focused on III-Nitride based quantum dots covering their production and optical properties, as well as reporting on the GaN quantum dots produced by molecular beam epitaxy utilizing standard, ripening, metal spray followed by nitridation methods. INTRODUCTION Semiconductor nitrides such as aluminum (AlN), gallium nitride (GaN), and indium nitride (InN) are very promising materials for their potential use in optoelectronic devices and high-power/temperature electronic devices, as have been treated in length and reviewed recently (Strite and Morkoç1; Morkoç et al.2; Mohammad et al.3; Mohammad and Morkoç 4; Ambacher5; Morkoç6; Pearton et al.7). These materials and their ternary and quaternary alloys cover an energy bandgap range of 0.7-6.1 eV, suitable for band-to-band light generation with colors ranging from red to ultraviolet (UV) wavelengths. Specially, nitrides are suitable for application such as UV detectors, UV and visible light emitting diodes (LEDs). GaN based LEDs and Laser diodes (LDs) incorporate quantum wells ( QWs). In addition to quantization, the quantum dots have other benefits such as localization which lead to reduced internal quantum yield degradation. Gérard et al.8 pointed out that once the carriers are captured by QDs, they become strongly localized and their migration toward nonradiative recombination centers is made difficult. Furthermore, the increased localization gives rise to increased radiative recombination rates which brings one to the expected low threshold for lasers that have 1
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already been experimentally observed in the InGaAs system. A flurry of interest in lowdimensional GaN and other III-nitride
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