Non-Destructive Characterization of Semiconductors using Organic Thin Films
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ABSTRACt Rectifying junctions prepared by vacuum deposition of 3A,9,10-perylenrtetracarboxylic dianhydride (PTCDA) and related comproluls ontboth p- and n-type inorganic semiconducting wafers are used for their non-destructive evaluation. By evaporation of metal contact pads onto the crganic layer, we can probe many of the fundanrntal.bulk and surface properties of the semiconductor. The current-vdtage dcaracteristics of these organic-on-inorganic (01) devices on silicon are similar to those Cf abrupt junction diodes due to the higher 01 contact barrier energies, and the absence of edge breakdown in these devices. For example, reverse breakdown voltages are governed by the seniconductor carrier coxrmntration. On many rH-V semicoiductors qualitatively similar results are obtained. For example, high barrier energies have been observed on n-GaAs (0.64 eV) and p-GaAs (0.75 eV), and for the p-type material they are significantly higher than those achieved with conventional Sclhottky devices. Barrier heights are found to be dependent on the surface treatment given to the semiconductor prior to deposition of the crganic film. Bcth current-voltage (I-V) and capadtarre-voltage (C-V) measurements performed on devices over the wafer surface have permitted the generation of maps of the carrier corientrations and epitaxial layer thickiesses. Upon completion Cf such measurerents, the organic layers with their metal contacts are removed with an aqueouls base wash with no damage to the underlying semiconductor. INTRODUCTION Thin films of scrre highly resistive organic molecular solids can be vacuum deposited onto inorganic semiconducting materials such that an energy barrier Cf height >>kT (where kT is the thermal energy at temperature T) is formed between the two materials. With subsequent ohmic metallization on the surface of the organic film in the form of small circular pads, an array Cf individually addressable organic-on-inorganic (01) diodes are thus formed. Because of the highly anisotropic nature of the organic films no current flaws between diodes and each can be measured separately. Standtard capadtance-voltage (C-V) analysis of thrse diodes permits the determination of the free carrier corcentration profiles. When information from many 01 diodes is combined, the spatial variation of doping in 3-dimensions, as well as the uniformity of epitaxial layer thicknesses can be displayed in the form of contour maps. This non-invasive analytical testing procedure does not induce semiconductor damage or surface contamination, and the devices can be removed easily thereby permitting continued sample processing for device fabrication. The full discussion of the theory, application, and the analysis of thrse organic-on-inrrganric semiconductor contact barrier devices has been detailed in a series of papers published over the last few years [1-7]. In this paper we review the methods of preparation of 01 contact barrier devices, discuss the iniorganic semiconductor surface preparation, and present data that dernomtrate the general uti
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