Silicon/Molecule Interfacial Electronic Modifications

Abstract

Electronic structures at the silicon/molecule interface were studied by X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, inverse photoemission spectroscopy, and Kelvin probe techniques. The heterojunctions were fabricated by direct covalent grafting of a series of molecules (-C6H4-X, with X = NMe2, NH2, NO2, and Mo6 oxide cluster) onto the surface of four types of silicon substrates (both n- and p-type with different dopant densities). The electronic structures at the interfaces were thus systematically tuned in accordance with the electron-donating ability, redox capability, and/or dipole moment of the grafted molecules. The work function of each grafted surface is determined by a combination of the surface band bending and electron affinity. The surface band bending is dependent on the charge transfer between the silicon substrate and the grafted molecules, whereas electron affinity is dependent on the dipole moment of the grafted molecules. The contribution of each to the work function can be separated by a combination of the aforementioned analytical techniques. In addition, because of the relatively low molecular coverage on the surface, the contribution from the unreacted H-terminated surface to the work function was considered. The charge-transfer barrier of silicon substrates attached to different molecules exhibits a trend analogous to surface band bending effects, whereas the surface potential step exhibits properties analogous to electron affinity effects. These results provide a foundation for the utilization of organic molecule surface grafting as a means to tune the electronic properties of semiconductors and, consequently, to achieve controllable modulation of electronic characteristics in small semiconductor devices at future technology nodes.

Controlling transistor threshold voltages using molecular dipoles

“…This is borne out quite well by our model. In addition, we demonstrate the accuracy of our model by comparing our computed intermediate ingredients with complementary experimental data obtained on the same set of samples [8]. [4].…”

“…This was accomplished by comparing the projected density of states on the silicon atoms, which is maximized for the HOMO levels of benzene-based molecules [16]. The computed shifts agree [8] very well with experimental data, as seen from the last two columns of Table I, as well as comparisons with ultraviolet photoelectron spectroscopy (UPS)and inverse photoemission spectroscopy (IPES) data combined with Xray photoelectron spectroscopy (XPS) data (Fig.4) The shift shows a monotonic dependence on the dipole moment of the headgroup, which is quite encouraging. Surprisingly, however, there is an additional shift relative to the H-passivated control, which is unexpected (thus, the threshold voltage shifts of the nitro and amino components do not straddle that of the control, but lie on the same side of it).…”

Van Der Waals Heterostructures between Small Organic Molecules and Layered Substrates

“…For example, pentacene possesses a relatively higher mobility in its b-c plane than a-b plane, as shown in Figure 1e [6,7]. Thus, various substrates, metals [8][9][10], native oxide silica [11][12][13][14], and layered materials [6,7,[15][16][17][18], have been chosen for the growth of high quality thin films. In order to optimize the devices performance, it is essential to clarify how the interactions between molecules and substrates affect the growth of organic thin films.…”

Palladium-Catalyzed Coupling Reactions for the Functionalization of Si Surfaces: Superior Stability of Alkenyl Monolayers

“…In addition to chemical and electrical passivation for improved device performance 3,4 , there are emerging applications of Si surfaces modified with more diverse organic species. Grafting polar molecules onto the surface can introduce a net surface dipole, which potentially allows the electronic properties of a material to be modified [5][6][7][8][9] . Electronic tuning of Si surfaces by molecular modification has considerable advantages for nanoscale devices in which high surface area to volume ratios result in surface dominated transport properties 10 .…”