Spectral and temporal performance enhancement in a symmetric co-planar Au–Ge/AlGaAs/Au–Ge natural superlattice-based MSM photodetector

A comparative analysis is performed between a symmetric co-planar metal–semiconductor–metal Au–Ge/AlGaAs/Au–Ge photodetector based on naturally ordered superlattice structure in the semiconducting AlGaAs layer and the disordered AlGaAs layer as obtained by annealing the ordered sample at the order–disorder transition temperature. Before the device fabrication, the order to the disorder transition temperature of such periodic structure was determined by observing the X-ray rocking curves at different annealing temperatures and it was found to be 900 °C. The device operability of such structures was found within 400–900 nm of the electromagnetic spectrum. Under + 1 V bias, the peak responsivity, detectivity, and photosensitivity for the ordered sample were calculated to be 159.65 mA W⁻¹, 1.22 × 10¹³ cmHz^1/2 W⁻¹, and 1.29 × 10³ cm² W⁻¹, respectively, and at − 1 V bias, these values were 20.67 mA W⁻¹, 3.1 × 10¹² cmHz^1/2 W⁻¹, and 165.35 cm² W⁻¹, respectively in the presence of illumination of wavelength 750 nm at a fixed optical power. Whereas the device having homogeneous composition showed poor responsivity, detectivity, and photosensitivity of 22.58 mA W⁻¹, 1.13 × 10¹² cmHz^1/2 W⁻¹, and 45.15 cm² W⁻¹, respectively at + 1 V and at − 1 V these values were 10.37 mA W⁻¹, 1.04 × 10¹² cmHz^1/2 W⁻¹, and 41.49 cm² W⁻¹, respectively being peaked at 700 nm. Furthermore, the device with natural superlattice ordering showed superior temporal response with a rise time of 357 μs and decay times of 136 μs and 1.6 ms, respectively. The improvement of the photodetector performance using superlattice structures was explained considering the ordering-induced built-in electric field at the heterointerfaces under proper biasing conditions.