Exciton recombination in spontaneously formed and artificial quantum wells Al_xGa_1‐xN/Al_yGa_1‐yN (x<y∼0.8)

Abstract

We report on photoluminescence (PL) spectroscopy and electron microscopy studies of an AlGaN quantum well (QW) structure grown by molecular beam epitaxy under metal‐rich conditions with substrate rotation. Both techniques reveal unintentional formation within the AlGaN barriers of a quasiperiodic structure of thin Ga‐rich layers, whose period is controlled by both the substrate rotation rate and the AlGaN growth rate. These compositional modulations act as 1‐3 monolayer thick QWs emitting below 250 nm with an internal quantum efficiency (IQE) as high as ∼30% at room temperature under weak excitation. Variational calculations of the QW exciton properties indicate that the observed high IQE can result from strong three‐dimensional localization of the excitons confined in the narrow QWs. (© 2015 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

AlGaN Nanostructures with Extremely High Room-Temperature Internal Quantum Efficiency of Emission Below 300 nm

“…The spectrum is modulated by a periodic structure attributed to light interference in the thick buffer layers. 25 Temperature increase causes a red-shift of the peak, but even at 300 K, most of the line is below 300 nm, in agreement with the target emission wavelength. Remarkably, the temperature-induced decrease in the PL intensity at 300 K does not exceed 20% of the low-temperature value, in agreement with the optimization performed for the sample design and the growth procedure.…”

“…During the growth of the barrier layers, the substrate was rotated sufficiently fast (one rotation per 3 s) to ensure formation of homogeneous alloy without pronounced spontaneous compositional modulation. 25 The QW was formed by the submonolayer digital alloying (SDA) technique 22,26 as a superlattice of 10 9 GaN/Al 0.7 Ga 0.3 N, with growth of GaN layers achieved by briefly shutting off the Al source. Nominal thicknesses of the constituent GaN and Al y Ga 1Ày N layers were selected in such a way that the average QW thickness and composition matched the intended parameter values.…”

Multi-technique physico-chemical characterization of particles generated by a gasoline engine: Towards measuring tailpipe emissions below 23 nm

“…Finally, the sampling for chemical analysis was conducted on the third branch with a NanoMOUDI II cascade impactor (TSI/MSP, model 125R). Being a "Micro-Orifice Uniform-Deposit Impactor", the NanoMoudi works on the well-known principle of inertial impaction (Marple et al, 1991;Marple, 2004). The MOUDI impactors have sharp stage characteristics with steep cut-offs and low inter-stage wall losses.…”

Наноструктуры AlGaN с экстремально высоким внутренним квантовым выходом при 300 K

“…Рост структуры заканчивался формированием слоя AlN толщиной 10 nm. При росте барьерных слоев подложка вращалась с достаточно большой скоростью (один оборот за 3 s), чтобы обеспечить максимально равномерный по подложке рост AlGaN с минимально выраженными спонтанными моду-ляциями состава [9]. Рост КЯ осуществлялся при мень-шей скорости вращения подложки (один оборот за 7 s).…”

“…Проведенные расчеты зонной структуры и экситонных характеристик позволили опре-делить параметры КЯ (ширину и состав), соответству-ющие максимальной энергии локализации носителей за-ряда в КЯ и максимальной энергии связи экситона, тогда как использование метода СДЭ при ПА МПЭ позволило изготовить " дискретные" квантовые ямы с затрудненным транспортом носителей заряда в латеральном направле-нии [9]. Результатом оптимизации явилось изготовление образца, в котором времена жизни фотовозбужденных неравновесных носителей определяются излучательной рекомбинацией во всем диапазоне температур от 5 до 300 K, а внутренний квантовый выход слабо зависит от температуры.…”