Different types of buffer layers like InGaN underlayer (UL) and InGaN/GaN superlattices are now well-known to significantly improve the efficiency of c-plane InGaN/GaN based light emitting diodes (LEDs). The present work investigates the role of two different kinds of pregrowth layers (low In-content InGaN UL and GaN UL namely "GaN spacer") on the emission of core-shell m-plane InGaN/GaN single quantum well (QW) grown around Si-doped !̅-GaN microwires obtained by silane-assisted MOVPE. According to photo-and cathodoluminescence measurements performed at room temperature, an improved efficiency of light emission at 435 nm with internal quantum efficiency > 15 % has been achieved by adding a GaN spacer prior to the growth of QW. As revealed by scanning transmission electron microscopy, an ultra-thin residual layer containing Si located at the wire sidewall surfaces favors the formation of highdensity of extended defects nucleated at the first InGaN QW. This contaminated residual incorporation is buried by the growth of GaN spacer and avoids the structural defect formation, therefore explaining the improved optical efficiency. No further improvement is observed by adding the InGaN UL to the structure, which is confirmed by comparable values of the effective carrier lifetime estimated from time-resolved (TR) experiments. Contrary to the case of planar cplane QW where the improved efficiency is attributed to a strong decrease of point defects, the addition of an InGaN UL seem to have no influence in the case of radial m-plane QW.
We report for the first time on the hydride vapor phase epitaxy (HVPE) growth of long (26 μm) InAs nanowires on Si(111) substrate. The thermodynamic and kinetic mechanisms involved during the growth of such long nanowires are identified.
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