Leakage currents of large area InP/InGaAs heterostructures
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Leakage currents of large area InP/InGaAs heterostructures Anders Olsson1,2, Abuduwayiti Aierken2, Jani Oksanen1, Harri Lipsanen2, Jukka Tulkki1 1
Department of Biomedical Engineering and Computational Science Department of Micro- and Nanosciences Aalto University Espoo, Finland 2
ABSTRACT Light-emitting diodes (LEDs) based on the conventional III-V compound semiconductors are known to exhibit internal quantum efficiencies (IQE) that are very close to unity. Ideally, the high IQE is expected to enable electroluminescent cooling with a cooling capacity of several Watts per cm2 of emitter area. One key requirement in enabling such cooling is the ability to fabricate high quality large area LEDs. However, detailed information on the performance of relevant large area devices and their yield is extremely scarce. In this report we present data on the yield and related large area scaling of InP/InGaAs LEDs by using current-voltage measurements performed on LED wafers fabricated at five different facilities. The samples were processed to contain square shaped mesas of sizes 0.25 mm2 and 16 mm2 operating as LEDs. While most of the smaller mesas showed relatively good electrical characteristics and low leakage current densities, some of them also exhibited very large leakage currents. In addition, in some cases the large area devices exhibited large, and even almost linearly behaving leakage currents. Such information on the scaling and unidealities of diodes fabricated using established fabrication technologies is crucial for the development of the optical cooling technologies relying on large area devices.
INTRODUCTION Light emitting diodes (LEDs) based on the conventional III-V compound semiconductor double heterojunctions (DHJ) and GaAs/AlGaAs DHJs in particular are known to exhibit internal quantum efficiencies (IQE) that are very close to unity [1]. Ideally the high IQE is expected to enable electroluminescent (EL) cooling [2] as well as thermophotonic (TPX) coolers with a cooling capacity of several Watts per cm2 of emitter area over large temperature differences [3]. While electroluminescent (EL) cooling at these power levels and in the high IQE regime is yet to be demonstrated, the expectations for functional thermophotonic coolers have very recently been reinforced by the demonstrations of EL cooling in GaSb/InGaAsSb LEDs [4,5]. The cooling in these demonstrations took place under very low bias voltages where the IQE is very small, but nevertheless demonstrated electricity-to-light conversion efficiencies exceeding unity by a large margin. In order to demonstrate large power TPX coolers, optimized large area LED structures are needed. InP and InGaAs based material systems rise as natural candidates for realizing the TPX devices, since they represent mature technologies that enable fabricating high quality lattice
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matched DHJ structures. While record-high IQEs have been reported for AlGaAs based devices [1], fabricating thick unstrained LEDs typically requires lifting of the GaAs substrate. On the other han
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