Carla Denotti

Photoinduced conductivity and nonlinear optical properties of [M(R,R′timdt)2] dithiolenes (M=Ni, Pd, Pt; R,R′timdt=monoreduced imidazolidine-2,4,5-trithione) as materials for optically driven switches and photodetectors

Abstract The unusual NIR-photoconducting properties of [M(Et,Pent-timdt)2] neutral dithiolenes (M=Ni, Pd, Pt; Et,Pent-timdt=monoreduced N-ethyl,N′-pentylimidazolidine-2,4,5-trithione) have been investigated with the aim of developing wavelength-selective air-stable photodetectors. In addition, the ps time-resolved dynamics of the absorption saturation has been studied on the Pd-complex by means of pump–probe experiments.

Organic photodetectors spectrally matched to optical fiber communication windows

The progress in the field of organic photodetectors has recently led to the development of very fast and efficient devices, but their spectral sensitivity is mainly limited to the visible, without covering the regions of the spectrum of greater interest for telecommunications. One of the major issues when dealing with long wavelength organic photodetectors is the usually poor environmental stability of low bandgap organic semiconductors. A possible exception to this scenario is represented by coordination complexes with organic ligands. We employ as photosensitive materials transition metal dithiolene and dioxolene complexes which combine high thermal and photochemical stabilities with high molar extinction coefficients in the near infrared. Taking advantage of the broad tuning of electronic absorption spectra which can be exerted by changing the oxidation state of the complexes, we develop planar metal-semiconductor-metal phostodetectors which are spectrally matched to the optical fiber windows and which can detect light pulses with repetition rates in the range of hundreds of kbit/s. This investigation demonstrates the existence of organic materials of potential telecom interest and that the detection of infrared light pulses is feasible, thus representing a first step toward organic photodetectors for telecommunications.

Organic photodetectors: a possible technology for on-fiber receivers

A new class of photodetectors, whose active material is an organic semiconductor, has been developed. Thanks to the ease of deposition on any dielectric surface, the device may be built directly on the cleaved surface of an optical fiber, therefore realizing an on-fiber-detector (OFD). The photodetector is based on an organic semiconductor belonging to a new general class of neutral dithiolenes deposited onto a quartz substrate with microlithographically defined gold electrodes so to realize a metal-semiconductor-metal surface structure. First experimental results on a photodiode made of (monoreduced imidazolidine-2,4,5-trithione) having peak responsivity at 1014nm, have shown a time response down to 100microseconds, at present limited by the leakage current noise due to the poorly rectifying contacts. Differently from the vast majority of organic semiconductor materials, dithiolenes have shown extremely high chemical and thermal stability. The photoresponse of the dithiolenes in the liquid phase is shown to be wavelength selective with an absorption peak about 150nm wide that can be chemically tailored so to shift from almost 1000nm to 1700nm. Experimental measurements to prove that the absorption property is maintained in the solid state also at wavelengths around 1500nm, thus covering with a photodetector the spectrum of possible telecom applications, are under way.

Hybrid Metal-organic Photodetectors Based on a New Class of Metal-dithiolenes

The paper will describe a new photodetector based on a metal-organic semiconductor material sensitive to the near IR region of the electromagnetic spectrum. The detector has a planar metal-semiconductor-metal structure with the active material deposited from liquid phase over a quartz substrate. Together with the fabrication process and the time response to light pulses, emphasis will be given to the intrinsic wavelength selectivity of the semiconductor material, of about 100nm around its peak sensitivity. The ease of deposition may enable to directly develop optical devices on passive optical component or on electronic substrates.