Carrier recombination in InAs/GaAs Quantum Dot and GaInNAs/GaAs Quantum Well LEDs emitting near 1300 nm.
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Carrier recombination in InAs/GaAs Quantum Dot and GaInNAs/GaAs Quantum Well LEDs emitting near 1300 nm. A J Bennett, L Lofgren, P N Stavrinou, C Roberts, R Murray, G Parry. Center for Electronic Materials and Devices, Blackett Laboratory, Imperial College, Prince Consort Road, London SW7 2BZ
J S Roberts EPSRC III-V Semiconductor Central Facility, Dept. of Electronic Engineering, Mappin Street, Sheffield, S1 3JD
Abstract We have studied the emission from LEDs based on GaInNAs Quantum Wells (QWs) and InAs Quantum Dots (QDs) as a function of temperature and current. It is found that the carrier loss in GaInNAs QWs is dominated by non-radiative monomolecular and Auger processes resulting in an external quantum efficiency of only 0.08 % at 10 oC and 1000 A cm-2. In contrast, the InAs QDs have a higher external quantum efficiency, peaking at 0.8 % at 10 oC and 5 A cm-2, but this value rapidly decreases as the excited states of the QDs are filled and Auger-like processes become dominant. These results highlight the issues that must be addressed if these materials are to find commercial application: namely, the areal density of QDs must be increased and the material quality of the GaInNAs QWs must be improved. 1. Introduction GaInNAs Quantum Wells (QWs) and self-assembled InAs Quantum Dots (QDs) are two promising materials for GaAs-based fibre optic communications at 1300 nm. Both offer improved carrier confinement and temperature dependence over InGaAsP/InP QW devices operating at the same wavelength. In addition, monolithic growth of devices containing these materials and high reflectivity AlGaAs/GaAs mirrors is being widely investigated. Thus far, few reports have been made which directly compare the emission properties of InAs QDs and GaInNAs QWs [1, 2]. Presented here are results of an investigation into the processes that dominate carrier recombination in these two materials undertaken by comparing the electroluminescence (EL) from P-I-
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N diodes as a function of temperature and current. This data is analysed using a formalism that has been used by others to investigate other material systems emitting at long wavelength [3,4]. 2. Device and Growth Details The self-assembled InAs QD P-I-N diodes were grown using solid-source molecular beam epitaxy in a V80 MBE machine with the group V element supplied as As4. A single QD layer in the center of the device was formed by the deposition of a 2.6 ML layer of InAs at a substrate temperature of 500 oC. Indium was supplied from a custom-made cell with a circular aperture of ~ 1 mm diameter so as give a stable, low growth rate of 0.01 ML s-1. Such a low growth rate led to room temperature emission of 1260 nm an island density ~ 100 µm-2. More details of the growth process and device structure are given elsewhere [5]. The GaInNAs Quantum Well (QW) device was grown by Metal Organic Chemical Vapour Deposition (MOCVD) by John Roberts at the university of Sheffield’s III-V facility [6]. With the exception of the active region the structure was of nominally the sa
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