Room-Temperature, Wide-Band, Quantum Well Infrared Photodetector for Microwave Optical Links at 4.9 μm Wavelength

High-speed, room-temperature, quantum well infrared photodetectors (QWIPs) at λ ∼ 4.9 μm have been realized in a strain compensated In 0.1 Ga 0.9 As/Al 0.4 Ga 0.6 As heterostructure grown on a GaAs substrate. The high-speed properties at room temperature have been optimized by using a specifically designed air-bridge structure, which greatly reduces the time constant of the effective RC circuit, thus, allowing transmission and detection of high-frequency signals. By modulating a high-speed quantum cascade laser (QCL) centered at λ ∼ 4.7 μm, we were able to record a modulation of the photocurrent up to ∼26 GHz, which is limited by our setup. At 300 K and under a bias voltage of −5 V our device shows high responsivity and detectivity of 100 mA/W and 1 × 10 7 Jones, respectively. The developed high-performance QWIPs at this wavelength are highly promising for optical heterodyne measurement, high-speed free space communications in microwave optical links and frequency comb QCLs characterisations.