Behavior of Electrodeposited Cd and Pb Schottky Junctions on CH[sub 3]-Terminated n-Si(111) Surfaces

Abstract

n-Si/Cd and n-Si/Pb Schottky junctions have been prepared by electrodeposition of Cd or Pb from acidic aqueous solutions onto H-terminated and CH 3-terminated n-type Si͑111͒ surfaces. For both nondegenerately ͑n-͒ and degenerately ͑n +-͒ doped H-Si͑111͒ electrodes, Cd and Pb were readily electroplated and oxidatively stripped, consistent with a small barrier height ͑⌽ b ͒ at the Si/solution and the Si/metal junctions. Electrodeposition of Cd or Pb onto degenerately doped CH 3-terminated n +-Si͑111͒ electrodes occurred at the same potentials as Cd or Pd electrodeposition onto H-terminated n +-Si͑111͒. However, electrodeposition on nondegenerately doped CH 3-terminated n-Si͑111͒ surfaces was significantly shifted to more negative applied potentials ͑by −130 and −347 mV, respectively͒, and the anodic stripping of the electrodeposited metals was severely attenuated, indicating large values of ⌽ b for contacts on nondegenerately doped n-type CH 3-Si͑111͒ surfaces. With either Cd or Pb, current-voltage measurements on the dry, electrodeposited Schottky junctions indicated that much larger values of ⌽ b were obtained on CH 3-terminated n-Si͑111͒ surfaces than on H-terminated n-Si͑111͒ surfaces. Chronoamperometric data indicated that CH 3-Si͑111͒ surfaces possessed an order-of-magnitude lower density of nucleation sites for metal electrodeposition than did H-Si͑111͒ surfaces, attesting to the high degree of structural passivation afforded by the CH 3-Si surface modification.

Molecules on Si: Electronics with Chemistry

“…Having a SiO 2 interlayer between the Si and the molecules prevents penetration of the same metals, because no silicides can be formed. [69,70] Electrochemical deposition of Cd and Pb on methylÀSi(111) was reported to preserve the electrical properties of the monolayer, [68] i.e., which we know now to imply that the junction remained inverted. Atomic layer deposition (ALD) is at present the most promising alternative to non-vacuum deposition methods that are non-invasive, [188] such as Hg, [63,133,154,189] LOFO, [64,87,190] PALO, [191] MoPALO.…”

“…[44,66] Transport across very short alkyl monolayers, directly bound to Si, and characterized by spectroscopy, [33,67] was studied with Hg, [19] Au [2] and other metals as second contact. [68] In other work powerful techniques for characterizing Si MOMS were used and, in part, adapted. [69][70][71][72] Significant contributions have been made to transport modeling for several Si-molecule systems.…”

“…[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). [142] The idea that the Si is inverted in n-SiÀalkyl MOMS is strongly supported by the remarkable reproducibility of current densities between different groups [19,56,65,97] and different contact metals, [20,68] notwithstanding the fact that wet chemistry is used for junction preparation. Inversion explains this reproducibility, because the current density derives directly from the intrinsic properties of the Si and is, thus, insensitive to local variations in C SC as long as the surface remains inverted.…”

Helium atom diffraction measurements of the surface structure and vibrational dynamics of CH3–Si(111) and CD3–Si(111) surfaces

“…3,26,27 Specifically, methyl-terminated Si͑111͒ surfaces offer a particularly robust and durable semiconductor interface for use in devices such as photodiodes and Schottky junctions. 28,29 The two-step halogenation/Grignard methylation method generates surfaces that have nearly complete coverage ͑Ͼ95%͒ and large, atomically flat terraces. 30 Methyl termination electrically and chemically passivates the silicon surface and, in particular, provides resistance against surface oxidation and thermal degradation.…”

Control of the Band-Edge Positions of Crystalline Si(111) by Surface Functionalization with 3,4,5-Trifluorophenylacetylenyl Moieties

“…[32][33][34] Relative to Si(111)-H surfaces, Si(111)-CH 3 surfaces are more stable against oxide formation [35][36][37] and are readily interfaced with metals without the formation of metal silicides. [38][39] However, methyl-termination of Si(111) produces a -0.4 V surface dipole, [38][39][40][41][42] which on p-Si surfaces will lower Φ b at the Si interface and reduce the electric field at the junction that drives the charge separation.…”