Fast-response Symmetric Coplanar Ni/AlGaInP/Ni Visible Photodetector

Abstract A symmetric coplanar metal-semiconductor-metal structure has been successfully fabricated on a quaternary thin film of (AlxGa1-x)yIn1-yP epitaxially grown on (100) semi-insulating GaAs (SI-GaAs) substrate for visible photodetection. The crystallinity and alloy composition of the grown material was investigated with the help of high-resolution x-ray rocking curve and photoluminescence experiment giving the values of y = 0.66 and x = 0.67. The low-temperature photoluminescence study also gave insight into the defect levels in the material. The dark current-voltage curve was fitted by employing a back-to-back connected two-diode model to extract the barrier heights and ideality factor of the nickel contacts which were found to be 0.84 eV, 0.82 eV and 1.014, respectively. The photo-response of the device was studied in the wavelength range of 300−1000 nm which exhibited a peak at 610 nm. The maximum peak responsivity, detectivity and photosensitivity at a fixed applied bias of +15 V appeared to be 1.62 AW−1, 6.34 × 1011 cmHz1/2W-1 and 2.26 × 105 cm2W−1, respectively whereas under −15 V these values were 0.6 AW−1, 2.37 × 1011 cmHz1/2W−1, and 8.72 × 104 cmW−1, respectively in the presence of 610 nm illumination with optical power of 2 μW/cm2. The photodetector showed a rise time of 91 μs and the decay characteristics exhibited two channels of 83 μs and 282 μs, which are quite fast considering the temporal performance of similar kinds of devices. The photocurrent showed sub-linear power dependence with an increasing optical intensity which further refers to the recombination of photogenerated electron-hole pairs through trap and recombination centres within the forbidden gap.