Ideal Schottky diodes on passivated silicon

Abstract

Because of the complicated electronic and metallurgical properties of the metal-semiconductor interface, there is much controversy about the theoretical interpretation of experimental results on Schottky barrier heights. We present a new approach of barrier height measurements on a prototypical clean, abrupt and noninteracting system consisting of mercury contacts to hydrogen-passivated silicon surfaces. The resulting barrier to p-silicon is 0.9 V, totally at variance with all results presented for silicon Schottky barriers fabricated by standard metal deposition techniques. We believe this to be the first report in the limit of noninteracting metal contacts to silicon. PACS numbers: 73.20.-r, 73.30.+y, 73.40.-cThe study of the band lineup between a metal and a semiconductor in intimate contact (Schottky barrier) has led to much controversy concerning the theoretical interpretation of experimental results. Current theoretical models of the band lineup can be divided into two groups. One group of theories proposes that the experimental results are intrinsic to the perfect interface [1]. According to this model the band lineup is determined by the neutrality level at which the Fermi level will normally pin. This opinion currently dominates the physics literature, despite questions as to the universality of the model. The other group of theories postulates an extrinsic effect, typically involving a metallurgical interaction between the metal and the semiconductor, but differing in such details as to the physical origin of this extrinsic effect [2,3]. For example, the two dominant extrinsic models for Schottky barriers both on silicon and on compound semiconductors speculate that the interaction results either in detect formation in the semiconductor material or in an interfacial layer made up of a metallic alloy or mixture of phases. The former model leads to deep levels in the semiconductor, hence changing the band-bending charge distribution within the semiconductor [2], whereas the latter leads to a change in the boundary conditions between the metal and the semiconductor in a simple model of the interface [3].Any experimental attempt to distinguish between intrinsic and extrinsic models of the band lineup must in some fashion modify or eliminate the assumed extrinsic mechanisms. Such mechanisms usually invoke thermally driven or adsorption driven processes. Studies of interface formation at low temperatures have led to the observation of some differences in band alignments [4], but many of these differences are minor and obscured by experimental artifacts such as the photovoltage effects [5] in the photoemission techniques typically used in these studies. Clearly, a different method of investigation is needed on ideal, noninteractive metal-semiconductor interfaces to investigate the band lineup in Schottky barriers.We report here a room-temperature approach which circumvents the possibility of heat of nucleation or adsorption to drive an interaction between the metal and the semiconductor. We achieve this by exp...

Molecules on Si: Electronics with Chemistry

“…Experimentally, though, the junction was found to be ohmic. [19,141] For p-SiÀH/Hg an effective SBH of 0.85 eV is found. [19,141] Binding a methyl group to the Si radically changes the situation and n-SiÀCH 3 /Hg is now strongly inverted with a SBH of 0.8 eV, while the p-SiÀCH 3 /Hg junction is close to ohmic (barrier <0.1 eV).…”

“…[19,141] For p-SiÀH/Hg an effective SBH of 0.85 eV is found. [19,141] Binding a methyl group to the Si radically changes the situation and n-SiÀCH 3 /Hg is now strongly inverted with a SBH of 0.8 eV, while the p-SiÀCH 3 /Hg junction is close to ohmic (barrier <0.1 eV). [19] Similarly, adding a monolayer of benzene was reported to lead to a transition from majority to minority carrier transport for an STM-tip (at direct contact or ''overdrive'') MOMS of W on (2x2)n þ -Si(100).…”

Ambient organic molecular passivation of Si yields near-ideal, Schottky-Mott limited, junctions

“…While metal/p-Si diodes usually exhibit SBHs of less than half the bandgap, a p-Si-H/Hg diode with SBH of 0.9 eV was reported. 49 Such a large barrier height can in principle result from a high density of surface states located below the conduction band of the Si, rather than from ideal Schottky-Mott behavior. Because H-termination is not stable and does not allow further variation of the surface properties, we used here an ultra-thin molecular layer and showed that it can both mitigate the abrupt termination of the Si lattice periodicity and saturate the surface dangling bonds, similar to H-termination, but with much improved stability.…”

Electrowetting at a liquid metal-semiconductor junction

“…Under reverse bias, the capacitance of the junction decreases causing the contact angle of the conducting droplet-indicated by the long dashed line-to decrease as the reverse bias is increased. In order to demonstrate the effect a liquid metal-semiconductor contact, such as Hg-Si, [22][23][24][25][26][27][28] can be used. Indeed, mercury has successfully been used to demonstrate and apply EWOD.…”

“…30 Removal of the oxide prior to Hg deposition produces a Schottky contact. 23,24,26,28 Fig. 3 shows the variation of contact angle-extracted using software 31 -with applied voltage (open circles data) for n-type and p-type silicon.…”