Studies on electrical characteristics of organic-inorganic heterostructures

Abstract

Herein, we report the electrical properties of a heterostructure based on n-Si (100) and zinc phthalocyanine (ZnPc) thin films which displays asymmetric current-voltage (I-V) characteristics under the applied voltage sweep. ZnPc thin films were deposited onto clean silicon wafers and quartz substrates through vacuum thermal evaporation technique. Spectroscopic techniques such as UV-visible, PL and FTIR were used in order to investigate the optical properties of the thin films. The α-phase of the as deposited ZnPc film was recognized from the positions and intensity of the peak in the visible region of UV-visible spectroscopy. Optical energy gap of the deposited ZnPc thin film was estimated from the Tauc’s plot and the result is compared with PL spectra. PL spectra show a strong peak located at around ∼ 392 nm, which corresponds to an energy of ∼ 3.13 eV. Microstructural properties of the thin film were studied by the X-ray diffraction which shows preferential orientation along (200) direction and a broad hump appears at around 2θ ∼ 30°. SEM and AFM images display uniform growth of ZnPc thin films, comprising spherical nanoparticles over the substrate surface. The surface RMS roughness of the thin film was estimated from AFM analysis and found to be around ∼ 5.3 nm. The room temperature electrical studies of the fabricated device (Al/n-Si (100)/ ZnPc/ Al) were performed which displays rectifying character in the positive sweep and electrical hysteresis at negative voltage sweep. A suitable energy band diagram is proposed to explain the electrical property of the heterojunction device.