Optical Characterization of InAsSb Based Quantum Structures for Novel Mid-Infrared Light Emitting Diodes

Altayar, Abdullah and Marshall, Andrew (2023) Optical Characterization of InAsSb Based Quantum Structures for Novel Mid-Infrared Light Emitting Diodes. PhD thesis, Lancaster University.

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Abstract

The demand for efficient and cost-effective mid-infrared light-emitting diodes operating in the (3-6 µm) is increasing for various applications such as monitoring the environment and controlling industrial processing. Nevertheless, there is a lack of efficient mid-infrared LEDs operating in this spectral range to facilitate direct low-cost integration into economic systems. In this work possible solutions have been investigated by utilizing different III-V semiconductor materials; compressively strained AlxIn1-xAs/InAs1-ySby (MQWs) and strained-layer superlattices (SLS) of InAs/InAs1-xSbx as active regions incorporated into LEDs structure. The type-I Al0.12In0.88As/InAs0.915Sb0.085 MQWs were grown on GaAs and Si substrates and successfully integrated into the LEDs structure. The structural properties were investigated using high-resolution x-ray diffraction (HRXRD) and atomic force microscopy (AFM); the Si-based MQWs sample exhibited large dislocation density, less intense satellite peaks, and a rougher surface than the GaAs-based MQWs sample. Simulation of AlInAs/InAsSb band structure revealed a prominent band offset, substantial electron-hole overlap, and e-hh1 transition energy in agreement with 4 K PL spectra. The I-V characteristics of GaAs and Si-based LEDs show a comparable resistance of ~ 7Ω indicating the possibility of optimisation of these diodes. Bright electroluminescence spectra from both diodes exhibiting emission of ~ 3.4 µm at room temperature. EL emission spectra were interpreted as recombination between the first confined electron and heavy hole states in the InAsSb QW. The EL temperature dependence analysis suggested that thermally activated electron leakage is currently the major factor limiting room temperature emission intensity in these devices. Even though the Si-based LED exhibits a higher defect density, the output power measured at room temperature is significantly higher than that obtained for the GaAs-based LED when the injected current is higher than 1A, due to the improved thermal conductivity of Si substrate. These results suggest that further reduction of the defect density present in the InAsSb/InAlAs MQWs LED integrated onto Si, could enable the development of next-generation light sources, for cost-effective sensing and monitoring systems. The MBE growth of type-II InAs/ InAs1-xSbx SLS on GaAs substrate was systematically studied to overcome some of the problems associated with type-I band alignment, aiming to reduce the Auger recombination rate, enable operation at high temperature and extend the emission wavelength. Theoretical modelling of the band structure revealed the influence of increasing the antimony alloy fraction in the InAsSb and changing the period thickness, on the optical properties of these SLSs. Two series of PL samples exhibit excellent crystalline quality and bright luminescence up to 220 K. The excitation power-dependent PL spectra at 4 K shows; a blue shift trend in the peak position ~ 7 meV attributed to the bandgap filling effect, and a reduction in the PL intensity by a factor of six as antimony content increased in the InAsSb layers due to reducing wavefunction overlap and increasing non-radiative recombination rate. Temperature-dependence of the PL spectra of the varying antimony and increasing period thickness sample sets show carrier localization behaviour below 80 K associated with the blue shift in the peak position of 10 meV attributed to compositional inhomogeneous or layer thickness fluctuation. Based on the PL study of InAs/ InAs1-xSbx SLS, two prototype diodes containing fifty periods of InAs/ InAs1-xSbx SLS active region were grown by MBE on either a conventional lattice matched GaSb substrate or a cost-effective GaAs substrate and fabricated into LEDs. The principle of these diodes is to enable room temperature operation for purpose of ammonia applications. Mid-infrared electroluminescence was obtained from both LEDs over the 4 – 300 K temperature range, exhibiting an emission above 5.6 μm at room temperature. Simulation results indicate the PL peak is due to the e-hh1 transition at 267 meV, which agrees with the experimental value of 266 meV. A significant thermal quenching of EL spectra is attributed to competition between radiative and non-radiative mechanisms. The GaSb-based LED outperformed the GaAs-based LED showing maximum output power of 175 µW corresponding to an external quantum efficiency of 0.08% at room temperature. Despite this, the integrated intensity of GaAs-based LED was only 1.5 less intense than that on the GaSb substrate. The type-II InAs/ InAs1-xSbx SLS structure shows improvements in the device performance at high temperatures. The integrated EL intensity of SLS LEDs quenches with temperature by a factor of three less than that of MQW LEDs, due to efficiency in suppression of non-radiative loss. Future work is to design a study that directly compares type-I and type-II systems emitting at the same wavelength using III-V materials such as ternary or quaternary semiconductor alloy. There are a lot of complications with designing these materials such as strain which affect how type-I works and inherent quality material.