Ultrafast low-temperature-grown epitaxial GaAs photodetectors transferred on flexible plastic substrates

We demonstrate low-temperature (LT)-grown GaAs photodetectors transferred on flexible polyethylene terephthalate (PET) plastic substrates. The LT-GaAs layer was patterned into 20×20 μm² chips, which after placing on the PET substrates were integrated with coplanar strip transmission lines. The devices exhibit low dark currents (/spl les/2×10/sup -8/ A), subpicosecond photoresponse time, and signal amplitudes up to /spl sim/0.9 V at the bias voltage of /spl les/80 V and under laser beam excitation power of /spl les/8 mW at 810-nm wavelength. At the highest bias (/spl sim/80 V) level, an increase of the response time (up to 1.3 ps) was observed and attributed to the influence of heating effects due to low thermal conductivity of PET. Our LT-GaAs-on-PET photodetectors withstand hundredfold mechanical bending of the substrate and are intended for applications in hybrid optoelectronic circuits fabricated on noncrystalline substrates, in terahertz imaging, and in biology-related current-excitation tests.