Colloidal upconversion nanocrystals enable low-temperature-grown GaAs photoconductive switch operating at λ = 1.55 μ m

Abstract Microwave photoconductive switches, allowing an optical control on the magnitude and phase of the microwave signals to be transmitted, are important components for many optoelectronic applications. In recent years, there are significant demands to develop photoconductive switches functional in the short-wave-infrared spectrum window (e.g. λ = 1.3–1.55 μ m) but most state-of-the-art semiconductors for photoconductive switches cannot achieve this goal. In this work, we propose a novel approach, by the use of solution-processed colloidal upconversion nanocrystals deposited directly onto low-temperature-grown gallium arsenide (LT-GaAs), to achieve microwave photoconductive switches functional at λ = 1.55 μ m illumination. Hybrid upconversion Er ³⁺ -doped NaYF ₄ nanocrystal/LT-GaAs photoconductive switch was fabricated. Under a continuous wave λ = 1.55 μ m laser illumination (power density ∼ 12.9 mW μ m ⁻² ), thanks to the upconversion energy transfer from the nanocrystals, a more than 2-fold larger value in decibel was measured for the ON/OFF ratio on the hybrid nanocrystal/LT-GaAs device by comparison to the control device without upconversion nanoparticles. A maximum ON/OFF ratio reaching 20.6 dB was measured on the nanocrystal/LT-GaAs hybrid device at an input signal frequency of 20 MHz.