Enhanced absorption of infrared radiation in semiconductor photodetectors using micro-antenna arrays

This thesis is focused on signal-to-noise (S/N) enhancement of III - V semiconductor photodetectors for use in gas sensing applications within a specific frequency band of interest in the mid infrared (MIR) range. The semiconductor photodetectors can be grown as homostructures, but experiments have shown a clear benefit to using heterostructures and the quantum barriers they incorporate to reduce diode leakage. The proposed method of enhancement is the use of waveguide coupling with different resonating materials of different shapes, known as micro-antennas. The antennas were designed to be responsive to an incoherent light source, such as LEDs. State of the art examples were considered to optimise all aspects of the antenna design (i.e. the length, thickness, pitch and the dielectric constant) to reduce surface scattering and enhance coupling. The experimental demonstration requires consideration of maximisation of energy coupling into the intrinsic regions of Al0.05In0.95Sb (Aluminium Indium Antimonide) semiconductor diodes. The theoretical results were generated as a hybrid model to ensure full calibration and accuracy. Measurements of the semiconductor attenuation coefficient were taken externally and applied to sophisticated Electromagnetic (EM) simulation software. The EM simulations were done using Computer Simulation Technology (CSTTM). It was used to verify the expected results for different antenna sizes and to provide confidence for the outcomes of more elaborate design enhancements, including large scale selective removal of the semiconductor. Selective removal capitalises on energy coupling towards a specific position and depth close to the surface. Further work into investigating far field manipulation effects of antenna design applied to isotropically stimulated LEDs was included. Theoretical and experimental studies are reported that show that the antennas needed to be of an appropriate size to resonate at the appropriate wavelength. The variation with the antenna’s dielectric properties as well as the polarisation angle and trajectory angle of the stimulating source are reported. There are numerous shapes to be considered for various intended applications. The antenna design that has suited our specific purpose has an efficient packaging density, is responsive to a non-collimated stimulation source, is made out of low cost conductive materials, is fabricated in a commercially viable way and provides consistent and stable results