Microstructure of Thin Film Photoconductors and its Correlation with Optical and Electronic Properties
- PDF / 2,485,434 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 76 Downloads / 210 Views
70550 Stuttgart, Germany ABSTRACT The objective of this work is to find a material to replace amorphous hydrogenated silicon used as photosensitive part in the "retina" of an "electronic eye". For that reason, ZnS, ZnSe, CdS and CdSe were chosen for investigations. Thin films, prepared by chemical vapour deposition, were characterized by transmission electron microscopy. The observed microstructures were correlated with the optoelectronic properties of these materials. CdSe was found to be the most promising material for our application. Hence, the influence of a dielectric interlayer and the effects of additional annealing treatments were analyzed for CdSe and will be discussed with respect to the optimization of the material. INTRODUCTION Unlike a CCD-camera the "electronic eye" will be based on thin film technique. Optical signal processing and neuronal nets will allow a fast and easy object recognition by massive parallel image processing. The main part of the electronic eye is the "retina", which is supposed to collect light intensities and colors. Similar to the human eye retina, an array of sensors will be constructed, in which each sensor contains a photosensitive resistor (PR) to collect light informations and a thin film transistor (TFT) to read out the information (Fig. 1). Large-area production is feasible, as thin-film technology can handle large-area microelectronics on
substrates larger than the A4 format.
/PR
TFT
PR
11 Substrate El Ta M
Ta2O,
Fig. 1: Section of the retina - sensor array with photoresistor (PR) as light sensitive part and thin film transistors (TFT) for information read-out.
13 U 0
S13N4
a-SI:H Mg, AI
Fig.2: Outline of an amorphous silicon thin film transistor (TFT) combined with photoresistor(PR).
925 Mat. Res. Soc. Symp. Proc. Vol. 452 01997 Materials Research Society
Up to now amorphous hydrogenated silicon (a-Si:H) has been favored for application in the retina. The outline of an amorphous silicon TFT combined with photoresistor is shown in Fig. 2. Such a sensor can be processed in four steps [1]. However, photoconductivity of a-Si:H degrades when exposed to light (Staebler-Wronski effect) [2], which can have disadvantages for technical application. Hence, polycrystalline photosensitive materials are investigated with respect to their feasibility to replace amorphous hydrogenated silicon. Suitable materials have to operate at room temperature and must possess a spectral response in the visible range of the spectrum. Furthermore, long term stabilization has to be guaranteed. The properties of those new materials will determine the efficiency of the camera. EXPERIMENT Thin films of ZnS, ZnSe, CdS and CdSe, about 50 to 120 nm in thickness, were prepared on glass substrates by chemical vapour deposition (CVD). Furthermore, CdSe-films were deposited on glass with an additional dielectric Si0 2 interlayer. The microstructure was characterized with a JEOL 2000 FX transmission electron microscope (TEM). Cross sectional samples were prepared by ion milling. For optoelectroni
Data Loading...
