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 x 20 mu m(2) chips, which after placing on the PET substrates were integrated with coplanar strip transmission lines. The devices exhibit low dark currents (<= 2 x 10(-8) A), subpicosecond photoresponse time, and signal amplitudes up to similar to 0.9 V at the bias voltage of <= 80 V and under laser beam excitation power of <= 8 mW at 810-nm wavelength. At the highest bias (similar to 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.