Standing wave detection by thin transparent n-i-p diodes of amorphous silicon

Interferences of a standing wave created in front of a plane mirror can be detected by thin transparent sensors based on a n-i-p layer sequence with an optical thickness of the i-layer thinner than the wavelength X of the incident light. The detection of the minima and maxima of a standing wave can be used to determine the relative displacement of the plane mirror towards the detector. The optoelectronic properties of thin transparent detectors are studied regarding reflection and transmission, capacitance, and ability to distinguish between the minima and maxima of the standing wave. The developed sensors with a high transmittance consist of thin diodes of amorphous silicon (a-Si:H) and/or silicon carbide (a-SiC:H) with an optical thickness of lambda/2 embedded between two transparent conductive oxide layers with an optical thickness of 3lambda/4. The highest yield and the best device performance are achieved for detectors with an absorber layer of a-SiC:H. (C) 2002 Elsevier Science B.V. All rights reserved.