p‑Si/n‑CrSe2 Heterojunctions Designed as High‑Frequency Capacitors and Photosensors

Abstract

In this work, polycrystalline n-CrSe2 nanosheets with thickness of 100 nm are grown on p-type Si wafers by the thermal deposition technique under vacuum pressure of 10− 5 mbar. Structural and optical investigations showed the preferred growth of the trigonal phase of CrSe2 on Si substrates. Direct allowed transitions within an energy band gap of 2.60 eV were found to be dominant in the films. Silver contacts on the layers allowed construction of hybrid optoelectronic device structure formed from Ag/p-Si Schottky arm and p-Si/n-CrSe2 pn junction. The device runs in such a way that forward biasing of the Schottky arm is accompanied by a reverse biasing of the pn junction. It is observed that the hybrid device structure can perform as a high-frequency capacitor. The capacitance–voltage characteristic curves show that these capacitors can respond to ac signals with frequencies of 100 MHz. They also exhibit bandstop filter characteristics allowing the passing of signals with return loss and voltage standing wave ratios exceeding 10 dB and 1.76, respectively, at 60 MHz. The device under study displayed rectifying and photo-sensing properties with an asymmetry ratio of 60 in the dark and 217 under excitation of visible light. Visible light excitation of these photosensors displayed voltage biasing dependence in their current responsivity, external quantum efficiency and specific detectivity, reaching values of 0.24 A/W, 65.2% and 4.83 × 109 Jones, respectively. The features of the hybrid devices which use CrSe2 nanosheets as active media make them good candidates for use in radio wave and visible light communication technologies.