Monolithic Micro Light-Emitting Diode/Metal Oxide Nanowire Gas Sensor with Microwatt-Level Power Consumption.

High-performance, monolithic photoactivated gas sensors based on the integration of gas-sensitive semiconductor metal oxide nanowires on micro light-emitting diodes (μLEDs) are introduced. The μLEDs showed improved irradiance and energy conversion efficiency (i.e., external quantum efficiency, EQE), as the size of LEDs was reduced from 200 × 200 μm2 (irradiance of 46.5 W/cm2 and EQE of 4%) to 30 × 30 μm2 (irradiance of 822.4 W/cm2 and EQE of 9%). Gas-sensitive zinc oxide (ZnO) nanowires were directly synthesized on top of the μLED through a hydrothermal reaction. The direct contact between the sensing component and μLED sensor platform leads to high light coupling efficiency, minimizing power consumption of the sensor. Furthermore, the sensing performance (i.e., sensitivity) at optimal operating power was improved as the LED size was reduced. The smallest fabricated gas sensor (active area = 30 × 30 μm2) showed excellent NO2 sensitivity (ΔR/R0 = 605% to 1 ppm NO2) at the optimal operating power (∼184 μW). In addition, the sensor showed a low limit of detection (∼14.9 ppb) and robustness to high humidity conditions, which demonstrate its potential for practical applications in mobile internet of things (IoT) devices.