Indium Phosphide Nanowire Arrays for Gas Sensing Applications

Abstract

Semiconductor chemiresistive gas sensor is one of the most promising technologies for the development of next-generation chemical sensing, with applications ranging from explosive detection and environmental monitoring to industrial safety, healthcare and the Internet of Things (IoTs). Recently, there have been growing efforts in developing room temperature chemiresistive gas sensors with high sensitivity, selectivity, long-term stability, and low power consumption. In this thesis, we develop indium phosphide (InP) nanowire (NW) array based chemiresistive gas sensors and demonstrate that they represent a new and promising platform for achieving high-performance gas sensing for real-world applications.

Firstly, by carefully engineering the NW geometry (i.e., diameter and pitch), we demonstrate a NO2 sensor with superior sensitivity (limit of detection 3.1 ppb) at room temperature, with outstanding selectivity and long-term stability. Kinetic analysis and electrical simulation reveal the array geometry correlated sensing mechanism. To minimize the device power consumption, a novel axial p-i-n homojunction self-powered photovoltaic (PV) NO2 NW sensor was further designed through numerical simulation and optimization. The fabricated InP NW array PV sensor achieved 84% sensing response to 1 ppm NO2 with a record limit of detection down to sub-ppb level even under <5% of 1 sun illumination. With such high atmospheric light fidelity, the sensor was integrated onto a commercial microchip interface for dynamic self-powered monitoring of on-field motor vehicle exhaust.

Not only for oxidizing gas such as NO2, we have also shown that by applying surface-modification, the InP NW array can also be fabricated into highly sensitive sensors to reducing gases such as acetone. This is critical for the development of breath ketone sensors for diabetes monitoring and diagnostics. This acetone sensor was then integrated into a breath testing apparatus, named Ketowhistle, and proven to be highly effective across an ultrabroad range of acetone concentrations from the simulated breath.

Finally, a wearable multipixel InP nanowire array sensor was fabricated on a flexible substrate. A signal decoupling strategy was designed and implemented through careful device fabrication control, surface-functionalisation and different contact metal selection. This approach has led to the demonstration of a multipixel sensor device consisting of four sensing elements with integrated functionality, including NO2 and acetone sensing, as well as simultaneous pulse and body temperature measurements.

The thesis work indicates that III-V compound semiconductor nanowire array presents a promising chemical sensing platform for the development of high performance, miniaturized, low power consumption, multiplexing on-chip sensing system for future large-scale implementation of IoT technology. Show more