Controlling Space Charge of Oxide-Free Si by in Situ Modification of Dipolar Alkyl Monolayers

Abstract

Good passivation of Si, both electrically and chemically, is achieved by monolayers of 1,9-decadiene, directly bound to an oxide-free Si surface. The terminal CC bond of the decadiene serves for further in situ reaction, without harming the surface passivation, to −OH- or −Br-terminated monolayers that have different dipole moments. Such a two-step procedure meets the conflicting requirements of binding mutually repelling dipolar groups to a surface, while chemically blocking all surface reactive sites. We demonstrate a change of 0.15 eV in the Si surface potential, which translates into a 0.4 eV variation in the Schottky barrier height of a Hg junction to those molecularly modified n-Si surfaces. Charge transport across such junctions is controlled both by tunneling across the molecular monolayer and by the Si space charge. For reliable insight into transport details, we resorted to detailed numerical simulations, which reveal that the Si space charge and the molecular tunneling barriers are coupled. As a result, attenuation due to the molecular tunneling is much weaker than in metal/molecule/metal molecular junctions. Simulation shows also that some interface states are present but that they have a negligible effect on Fermi level pinning. These states are efficiently decoupled from the metal (Hg) and interact mostly with the Si.

Fabrication of Reproducible, Integration‐Compatible Hybrid Molecular/Si Electronics

“…[ 38 ] A back contact to the Si was made with an InGa-eutectic. [ 18,47 ] Current-voltage measurements were performed with a Keithley 6430 sub femtoamp source-meter, within a vacuum probe station (LakeShore), equipped with LHe cooling and temperature controller (LakeShore, 336). Current-voltage scans were measured from 0 V to −1 V, to +1 V and back to 0 V in 10 mV steps.…”

“…[ 46 ] However, transport across the SCR is also very sensitive to interface traps. Therefore, while the molecular electrostatic effect can tolerate inhomogeneities in the monolayer, the underlying Si substrate should have a low enough density of residual oxides [ 22,47 ] or dangling bonds, [ 41 ] so that their effects do not dominate the transport. For oxides, we found that even 1% atomic or less can dominate transport.…”

Barrier height distribution and dipolar relaxation in metal-insulator-semiconductor junctions with molecular insulator: Ageing effects

“…32 Note that incorporation of device inhomogeneity is crucial for an accurate modeling of J-V characteristics, otherwise artificially large interface defect densities may be required to account for the large values of the apparent ideality factor. 80 The lateral spatial extension of the low barrier height regions can be estimated from the distribution of c values, derived in the framework of the patch model, which considers that the smaller low barrier height patches are "pinched off." In the limited range of c values, 8-18 Â 10 À4 cm 2/3 V 1/3 , used to describe experimental transport data, the corresponding typical patch radius R P values are expected between 0.2 and 0.5 lm (setting arbitrarily D P % 0.3 eV), which is consistent with the requirements of the dipole approximation, i.e., R P is smaller than the width of the space charge layer W ¼ ð2V bb gÞ 1=2 , with g ¼ ðe S =qN D Þ ¼ 4.4 Â 10 À8 cm 2 V À1 , as long as the band bending V bb ¼ U B À V À V n is larger than 30 mV.…”

Fluorinated alkyne-derived monolayers on oxide-free silicon nanowires via one-step hydrosilylation

“…In this regard, the use of fluorinated alkynes would provide an easily accessible additional tool, namely the stepwise variation of the work function of the underlying Si NWs surface. [32][33][34] In this study, we investigated the formation of five different 1-hexadecyne-derived monolayers with a varying number of fluorine atoms (HCC-(CH 2 ) 6 C 8 H 17-x F x ; x = 0, 1, 3, 9, 17) onto oxidefree hydrogen-terminated Si NWs by a one-step hydrosilylation using 1-alkynes F0 to F17 (Scheme 1). These monolayers were characterized in detail by X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), static contact angle measurements, scanning electron microscopy (SEM) and transmission electron microscopy (TEM …”