Soft Contact Deposition onto Molecularly Modified GaAs. Thin Metal Film Flotation: Principles and Electrical Effects

Abstract

We describe and analyze a process to position a ∼ 1 nm thick molecular layer between two solid surfaces without damage to the molecules. The method is used to deposit a metal film in a soft, gentle manner on a semiconductor, yielding functional semiconductor/molecule/metal junctions. It is a combination of the lift‐off procedure, known from, for example, lithography, and the bonding process, known from, for example, wafer bonding. The combined method may find application also outside the area described here. We point out its major difficulties as well as solutions to overcome them. For this we rely on concepts from the physics of liquid and solid surfaces and interfaces. Conditions are found, in terms of choice of solvents, under which the method will be effective. The efficacy of floatation as a soft contacting procedure is demonstrated by the preparation of Au and Al contacts on GaAs single crystal surfaces, modified by a self‐assembled monolayer of small organic molecules. The resulting electrical properties of the contacts depend crucially on how the molecular interface with the contacting metal is formed. This type of wet contacting procedure to make dry devices may be advantageous especially if biomolecules are used.

Molecules on Si: Electronics with Chemistry

“…[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. [20,192] Chemical reactivity across the monolayer explains also why Hg works well with Si or Ag substrate but not with, e.g., Au (amalgamation).…”

Molecular Electronics at Metal/Semiconductor Junctions. Si Inversion by Sub-Nanometer Molecular Films

“…gold Au contacts were used to measure the J-V characteristics 17,18 . The Au contact J-V curve overlaps that obtained with Hg despite the work function difference.…”

Charge transport across metal/molecular (alkyl) monolayer-Si junctions is dominated by the LUMO level

“…Since the emergence of this field, 2,3 it has expanded greatly and now includes several types of device configuration (e.g., two-terminal junctions [4][5][6][7] , three-terminal junctions 8 and electrochemical devices 9 ), where the molecules serve as direct current carriers 10 or indirectly affect the electrical properties of a junction 11,12 .…”