In this paper, we describe the growth and characterization of 530-nm-thick superlattices (100 periods) of AlxGa1-xN/AlN (0 ≤ x ≤ 0.1) Stranski-Krastanov quantum dots for application as the active region of electron-beam pumped ultraviolet lamps.Highly dense (>10 11 cm -2 ) quantum dot layers are deposited by molecular beam epitaxy, and we explore the effect of the III/V ratio during the growth process on their optical performance. The study considers structures emitting in the 244-335 nm range at room temperature, with a relative linewidth in the 6-11% range, mainly due to the QD diameter dispersion inherent in self-assembled growth. Under electron pumping, the emission efficiency remains constant for acceleration voltages below 9 kV. The correlation of this threshold with the total thickness of the superlattice and the penetration depth of the electron beam confirms the homogeneity of the nanostructures along the growth axis.Below the threshold, the emission intensity scales linearly with the injected current. The internal quantum efficiency is characterized at low injection, which reveals the material properties in terms of non-radiative processes, and high injection, which emulates carrier 2 injection in operation conditions. In quantum dots synthesized with III/V ratio < 0.75, the internal quantum efficiency remains around 50% from low injection to pumping power densities as high as 200 kW/cm 2 , being the first kind of nanostructures that present such stable behaviour.
In this paper, we describe the design and characterization of 400-nm-long (88 periods) AlxGa1-xN/AlN (0 ≤ x ≤ 0.1) quantum dot superlattices deposited on self-assembled GaN nanowires for application in electron-pumped ultraviolet sources. The optical performance of GaN/AlN superlattices on nanowires is compared with the emission of planar GaN/AlN superlattices with the same periodicity and thickness grown on bulk GaN substrates along the N-polar and metal-polar crystallographic axes. The nanowire samples are less sensitive to nonradiative recombination than planar layers, attaining internal quantum efficiencies (IQE) in excess of 60% at room temperature even under low injection conditions. The IQE remains stable for higher excitation power densities, up to 50 kW/cm 2 . We demonstrate that the nanowire superlattice is long enough to collect the electron-hole pairs generated by an electron beam with an acceleration voltage VA = 5 kV.At such VA, the light emitted from the nanowire ensemble does not show any sign of quenching under constant electron beam excitation (tested for an excitation power density around 8 kW/cm 2 over the scale of minutes). Varying the dot/barrier thickness ratio and the Al content in the dots, the nanowire peak emission can be tuned in the range from 340 to 258 nm.
This paper describes the fabrication of nitrogen-polar AlxGa1-xN/AlN (x = 0, 0.1) quantum dot superlattices integrated along GaN nanowires for application in electron-pumped UV sources. The nanowires are grown using plasma-assisted molecular-beam epitaxy on n-type Si(111) wafers using a low-temperature AlN nucleation layer. Growth conditions are tuned to obtain a high density of non-coalesced nanowires. To improve the uniformity of the height along the substrate, the growth begins with a base long nanowire (~900 nm), with a diameter of 30-50 nm. The AlxGa1-xN/AlN active region is 400 nm long (88 periods of quantum dots), long enough to collect the electron-hole pairs generated by an electron beam with an acceleration voltage £ 5 kV. The spectral response is tuned in the 340 to 258 nm range by varying the dot/barrier This work is supported by the French National Research Agency (ANR) via the UVLASE program (ANR-18-CE24-0014), and by the Auvergne-Rhône-Alpes region (grant PEAPLE). This project has also received funding from the European Research Council under the European Union's H2020 Research and Innovation programme via the e-See project (grant #758385). We also acknowledge technical support from F. Jourdan, Y. Curé and Y. Genuist. We benefited from the access to the technological platform NanoCarac of CEA-Minatech Grenoble in collaboration with the IRIG-LEMMA group.
Electron beam pumping is a promising technique to fabricate compact and efficient light emitters (lamps or lasers) in those spectral ranges where electrical injection is problematic due doping, transport and contacting issues. Interest in this technology has increased in recent years, particularly driven by the demand for ultraviolet sources and the difficulties in developing efficient AlGaN devices to cover the spectral range of 220-350 nm. The use of a highly energetic electron beam enables the semiconductor structure to be pumped without the need for doping or contacting. The active volume is defined by the accelerating voltage, which allows the homogeneous excitation of a large active volume. The efficiency of cathodoluminescent lamps can compete and even outperform LEDs in the deep ultraviolet window, and lasers can deliver high optical power (up to around 100 W). Here, we analyze the advantages and challenges of this technology platform, and discuss its potential applications.
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