Detection of a space-charge region in an organic photoconductive sensor

In our contribution we will present a transparent photoconductive sensor based on organic materials. The performance of the photoconductive sensor will be demonstrated by electrical and spectral response measurements. The existence of a high-field space charge region near the cathode will be shown by means of local illumination measurements

Lanthanide-assisted deposition of strongly electro-optic PZT thin films on silicon: toward integrated active nanophotonic devices

The electro-optical properties of lead zirconate titanate (PZT) thin films depend strongly on the quality and crystallographic orientation of the thin films. We demonstrate a novel method to grow highly textured PZT thin films on silicon using the chemical solution deposition (CSD) process. We report the use of ultrathin (5–15 nm) lanthanide (La, Pr, Nd, Sm) based intermediate layers for obtaining preferentially (100) oriented PZT thin films. X-ray diffraction measurements indicate preferentially oriented intermediate Ln2O2CO3 layers providing an excellent lattice match with the PZT thin films grown on top. The XRD and scanning electron microscopy measurements reveal that the annealed layers are dense, uniform, crack-free and highly oriented (>99.8%) without apparent defects or secondary phases. The EDX and HRTEM characterization confirm that the template layers act as an efficient diffusion barrier and form a sharp interface between the substrate and the PZT. The electrical measurements indicate a dielectric constant of ∼650, low dielectric loss of ∼0.02, coercive field of 70 kV/cm, remnant polarization of 25 μC/cm2, and large breakdown electric field of 1000 kV/cm. Finally, the effective electro-optic coefficients of the films are estimated with a spectroscopic ellipsometer measurement, considering the electric field induced variations in the phase reflectance ratio. The electro-optic measurements reveal excellent linear effective pockels coefficients of 110 to 240 pm/V, which makes the CSD deposited PZT thin film an ideal candidate for Si-based active integrated nanophotonic devices

Transient and local illumination of an organic photoconductive sensor

In this paper we investigate the performance of a transparent photoconductive sensor based on a double layer of organic materials (m-MTDAB / PTCBI) which are deposited on two interdigitated transparent ITO electrodes. The performance of the sensor is demonstrated with electro-optical measurements: the I(V) curves consist of two linear sections meeting at a knee voltage Vt. Linear regression performed on the I(V) curves below Vt show that the conductance is a power law of the luminance incident on the device. We present a model to describe the behaviour of the sensor below Vt. We present measurements of I(t) for a transient illumination of the sensor. Plotting the inverse of the current as a function of time we find that the transient is consistent with the model for voltages below Vt. For voltages above Vt we find that the sensor behaves like a resistor in series with a space charge (SC) region. We present a local illumination experiment that confirms the existence of a SC region between the electrodes of the photoconductive sensor for V<Vt. The space charge region is located near the cathode of the sensor. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Fabrication and characterization of VCSELs with liquid crystal overlay

We have designed and fabricated a novel liquid crystal (LC) cell developed for optoelectronic devices. A VCSEL laser of 250 µm by 250 µm is placed inside a liquid crystal cell with a gap between the emitting area and the upper glass plate of about 30 µm. This allows to cover the VCSEL with a thin layer of liquid crystal after filling the cell through capillary forces. In this work we present the optimization of the technological processes to fabricate such a device. After mastering the technological aspects, the device can be used to modify the properties of the laser light in terms of polarization, beam shape, wavelength, etc. which may open the way to a wide range of applications. In order to prove that the device works, the properties of the laser beam are investigated, including the optical power, divergence and polarization, all in function of the applied current to the VCSEL and the voltage applied across the liquid crystal layer. The dependence of optical power on the current at different polarization directions is measured in order to obtain the polarization properties of the laser beam (in terms of the Stokes parameters). Before the LC is filled into the cell, I-P curves were acquired. The measurements are then repeated after the LC (E7, Merck) was filled in. It is observed that the dominant polarization direction of the laser beam could be changed by applying different voltages over the LC layer. Stokes parameters were calculated to describe the polarization state in more detail. Our results show that the polarization state is linear polarization when there is no LC in the cell and it changes to elliptical polarization if there is LC in the cell. This technology opens an effective way to fabricate integrated VCSEL chips in optoelectronic devices and different experiments are planned in the future with the fabricated devices

Silicon photonics for on-chip spectrophotometry

Silicon and Silicon Nitride photonics arc on their way to open the route towards integrated on-chip spectropholometers, Cost, miniaturization, miniaturization, hut also performance advantages ace at the origin of their potential We will discuss several integrated on-chip spectropholometers that are on the eve of commercial take up

Silicon photonics for on-chip spectrophotometry

Silicon and Silicon Nitride photonics arc on their way to open the route towards integrated on-chip spectropholometers, Cost, miniaturization, miniaturization, hut also performance advantages ace at the origin of their potential We will discuss several integrated on-chip spectropholometers that are on the eve of commercial take up

A two-dimensional model for an in-plane organic photo-conductive bilayer sensor

In this work we present a two-dimensional (2D) model for an organic thin film photo-conductive sensor containing a planar heterojunction and in-plane electrodes. The model simulates the flow of charge carriers based on the standard one-dimensional semiconductor transport and continuity equations, and combines this with a 2D model for the electric field. This procedure results in a hybrid differential/integral equation formulation. We present and analyse simulation results that resemble very well measured current–voltage characteristics of a real sensor under different illumination levels. We find that for currents below a critical value the sensor behaves like a resistor. Above this critical current the current increases much more slowly due to space charge accumulation close to the cathode. We explain the critical current as the maximum reverse current of the solar cell formed by the heterojunction covering the cathodic electrode