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Mask-less MOVPE of arrayed n-GaN nanowires on site- and polarity-controlled AlN/Si templates
摘要： We present a novel approach to attain Ga-polar n-GaN nanowires on n-Si(111)/AlN templates, by site- and polarity-controlled metal organic vapor phase epitaxy. A three-stage process is developed to (i) form equally-sized Ga-polar GaN islands, (ii) change the growth direction towards the vertical direction and finally, to (iii) obtain continuous nanowire epitaxy. Homogeneous islands are achieved by minimizing parasitic nucleation and adjusting the adatom diffusion length to the used nanoimprint pattern. The influence of the carrier gas composition on the polarity is studied, achieving pure Ga-polarity by mostly using nitrogen carrier gas. Enhancing the Si/Ga-ratio leads to an amplification of the vertical growth, but also to a reduced number of NWs. 100% growth is attained by a height dependent V/III-ratio adjustment. The results are supported by a qualitative model, explaining how suppression of multi-pod, parasitic and inhomogeneous crystallization can be realized by trading off in situ SiNx passivation and localized GaN growth.
关键词： GaN nanowires,MOVPE,site-controlled,Si templates,polarity-controlled
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Micropillar Lasers with Site-Controlled Quantum Dots as Active Medium
摘要： Cavity-enhanced nano- and microlasers are of high scientific interest as they offer not only a rich spectrum of exciting physics [1], but also have high potential regarding applications in the field of photonic quantum technologies [2]. Advances in the epitaxial growth and the fabrication of semiconductor micro- and nanolasers paved the way to approach the limit where a few quantum dots (QDs) can drive the device to lasing [3]. However, up until now, QD-microlasers have been exclusively based on standard self-assembled QDs which suffer from their random spatial and spectral position relative to the cavity mode. To further push the field of QD microlasers it is highly desirable to apply deterministic fabrication technologies tailor and maximize their optical gain. We report on the realization of high-quality quantum-dot (QD) micropillar lasers based on the buried-stressor growth concept [4]. This advanced growth method allows for the site-controlled (SC) growth of QDs with high optical quality [5]. Importantly, compared to other deterministic methods it is unique in the sense that it enables the localized growth of small ensembles of QDs with a well-defined number of emitters which is determined by strain engineering. The growth of the microlaser structures starts with the lower AlGaAs/GaAs distributed Bragg reflector (DBR) and an AlAs layer. After the processing of large mesas with a diameter of 20-21 μm, the AlAs layer is partially oxidized, so that small AlAs apertures with controlled diameter are left in the center of the mesas. The site-controlled InGaAs QDs are grown in a second epitaxial step and nucleate laterally aligned to the aperture, where the aperture diameter determines the number of localized QDs (s. Fig. 1 (a)). The growth is finalized by the top AlGaAs/GaAs DBR. Finally, micropillar structures with diameters between 3 and 5 μm are fabricated via high-resolution electron-beam lithography and plasma etching (s. inset of Fig. 1 (a)). The resulting micropillars include a controlled number of SCQDs in their field antinode and are characterized by micro-photoluminescence (μPL) measurements at 18 K [4]. They exhibit clear lasing signatures in terms of s-shaped input-output characteristic (Fig. 1 (b)) and pronounced linewidth narrowing. Moreover, the second-order autocorrelation function g(2)(0) approaches unity above lasing threshold as a clear signature of coherent light emission (Fig. 1 (c)). Furthermore, we demonstrate that laser characteristics such as the threshold pump power depend on the number of SCQDs in the active layer (cf. Pillars 1-4 in Fig. 1). Our fabrication technique paves the way for the development of low-threshold high-β microlasers with precisely tailored emission properties that can simply be controlled by the diameter of the integrated oxide aperture.
关键词： Micro-photoluminescence,Site-controlled Quantum Dots,Quantum Dots,Buried-stressor Growth Concept,Micropillar Lasers
更新于2025-09-11 14:15:04