RESUMO
2D transition metal carbides, known as MXenes, are transparent when the samples are thin enough. They are also excellent electrical conductors with metal-like carrier concentrations. Herein, these characteristics are exploited to replace gold (Au) in GaAs photodetectors. By simply spin-coating transparent Ti3 C2 -based MXene electrodes from aqueous suspensions onto GaAs patterned with a photoresist and lifted off with acetone, photodetectors that outperform more standard Au electrodes are fabricated. Both the Au- and MXene-based devices show rectifying contacts with comparable Schottky barrier heights and internal electric fields. The latter, however, exhibit significantly higher responsivities and quantum efficiencies, with similar dark currents, hence showing better dynamic range and detectivity, and similar sub-nanosecond response speeds compared to the Au-based devices. The simple fabrication process is readily integratable into microelectronic, photonic-integrated circuits and silicon photonics processes, with a wide range of applications from optical sensing to light detection and ranging and telecommunications.
RESUMO
Low temperature growth of GaAs (LT-GaAs) near 200 °C results in a recombination lifetime of nearly 1 ps, compared with approximately 1 ns for regular temperature ~600 °C grown GaAs (RT-GaAs), making it suitable for ultra high speed detection applications. However, LT-GaAs detectors usually suffer from low responsivity due to low carrier mobility. Here we report electro-optic sampling time response measurements of a detector that employs an AlGaAs heterojunction, a thin layer of LT-GaAs, a channel of RT-GaAs, and a vertical electric field that together facilitate collection of optically generated electrons while suppressing collection of lower mobility holes. Consequently, these devices have detection efficiency near that of RT-GaAs yet provide pulse widths nearly an order of magnitude faster--~6 ps for a cathode-anode separation of 1.3 µm and ~12 ps for distances more than 3 µm.