Paper EM+NC-WeA1
Metal-Molecule-Semiconductor Devices: Accurate Extraction of Device Parameters from Transport Measurements

Wednesday, October 22, 2008, 1:40 pm, Room 210

In recent years there has been considerable interest in integrating molecular components into solid-state electronic devices for high-density memory, nanoelectronic, and sensing applications. Molecular devices directly grafted to semiconductors are of particular interest due to the electrically tunable nature and technological relevance of the substrates. Considerable experimental efforts have been invested in the fabrication and electrical characterization of metal-molecule-semiconductor (MMS) devices. When moderately-doped semiconductors are used in MMS structures, the devices exhibit Schottky diode-like behavior. Typically, current-voltage or capacitance-voltage characteristics of the devices are measured at room temperature and the results are analyzed by using well-known ideal Schottky diode relationships.¹ The Schottky barrier height, Φ _B, is experimentally determined assuming that the electronic and structural properties of the interfaced are not significantly modified by the presence of the molecular layer. Although this approach has been used to offer valuable qualitative insights about effects such as the influence molecular dipole on Φ _B,² it does not consider the detailed structural and electronic properties of the interface. Additional experimental and theoretical tools are needed to capture the interfacial physics introduced by the molecular electronic structure as well as non-idealities which are present at such hybrid interfaces. We present a MMS device model which considers the molecular electronic structure, semiconductor interface states, junction non-uniformity, and other important physical phenomena which are not present in the ideal Schottky diode model. The influence of various effects on current-voltage and capacitance-voltage characteristics are illustrated. Theoretical and experimental evidence is presented to show that temperature dependent transport allows for more accurate extraction of device parameters with fewer assumptions. The improved description MMS devices will shed additional light on the transport mechanisms that dominate these structures as the substrate and molecular properties are varied, leading to improved device design and characterization.

¹ Sze, S. M., Physics of Semiconductor Devices, 2nd ed. Wiley-Interscience, New York, 1981.
² Haick, H.; Ambrico, M.; Ligonzo, T., Tung, R. T.; Cahen, D., J. Am. Chem. Soc. 128 (2006) 6854-6869.