2020/07/01 by Hakl, M., Lin, Q. Y., Lepillet, S. +9
#Applied Physics (physics.app-ph) #FOS: Physical sciences #Instrumentation and Detectors (physics.ins-det) #Optics (physics.optics)
paper · doi:10.48550/arxiv.2007.00299
III-V semiconductor mid-infrared photodetectors based on intersubband transitions hold a great potential for ultra-high-speed operation up to several hundreds of GHz. In this work we exploit a ~350nm-thick GaAs/Al0.2Ga0.8As multi-quantum-well heterostructure to demonstrate heterodyne detection at 10um wavelength with a nearly flat frequency response up to 70GHz at room temperature, solely limited by the measurement system bandwidth. This is the broadest RF-bandwidth reported to date for a quantum-well mid-infrared photodetector. Responsivities of 0.15A/W and 1.5A/W are obtained at 300K and 77K respectively. To allow ultrafast operation and illumination at normal incidence, the detector consists of a 50Ohm coplanar waveguide, monolithically integrated with a 2D-array of sub-wavelength antennas, electrically interconnected by suspended wires. With this device architecture we obtain a parasitic capacitance of ~30fF, corresponding to the static capacitance of the antennas, yielding a RC-limited 3dB cutoff frequency >150GHz at 300K, extracted with a small-signal equivalent circuit model. Using this model, we quantitively reproduce the detector frequency response and find intrinsic roll-off time constants as low as 1ps at room temperature.