Tunnelling interface

FIGURE 1.17. Illustration of the breakdown of the potential barrier at the semiconductor/electrolyte interface, (a) Zener breakdown (b) avalanche breakdown (c) interface tunneling. 

Interface tunneling (shown in Fig. 1.17c), can also generate a large current at a reverse bias for a semiconductor electrode/electrolyte interface when the energetic position of a redox couple is favorable relative to the bands. Interface tunneling has been... 

Large dark current may also be generated by interface tunneling due to the presence of oxidizing species. For example. Fig. 5.30 shows that the dark current on the silicon electrode in NH4F increases with Br2 concentration. According to Gerischer... 

Meek, based on i-V curve and capacitance measurements, proposed that the large current observed on n-Si at an anodic potential in the dark is due to barrier breakdown. The breakdown is not due to a bulk mechanism but rather to interface tunneling from the states at the surface into the conduction band. Also, the breakdown is not uniform but localized causing the formation of the etch pits and tunnels. 

For ra-Si in the dark, the current at anodic potentials is characteristically small due to the reverse bias. The onset potential at which current rises sharply in the dark marks the breakdown of the barrier layer and initiation of interface tunneling on the silicon surface [12]. The breakdown potential, Vj, (shown in Fig. 4), depends on the doping level of the material the lower the doping the higher the breakdown potential [10, 13-15], At the potentials negative of the breakdown potential, the anodic reactions require illumination to generate holes. 

Khoo, I. C., and P. Zhou. 1992. Nonhnear interface tunneling phase shift. Opt. Lett. 17 1325. See also P. Zhou and 1. C. Khoo. 1993. Anti-reflection coating for a nonhnear transmission to total reflection switch Int J. Nonlinear Opt Phys. 2(3). p. 437. 

PTM Photon tunneling microscopy [12] An interface is probed with an evanescent wave produced by internal reflection of the illuminating light Surface structure... 

There has been a general updating of the material in all the chapters the treatment of films at the liquid-air and liquid-solid interfaces has been expanded, particularly in the area of contemporary techniques and that of macromolecular films. The scanning microscopies (tunneling and atomic force) now contribute more prominently. The topic of heterogeneous catalysis has been expanded to include the well-studied case of oxidation of carbon monoxide on metals, and there is now more emphasis on the flexible surface, that is, the restructuring of surfaces when adsorption occurs. New calculational methods are discussed. 

Drake B, Sonnenfeld R, Schneir J and Hansma P K 1987 Scanning tunneling microscopy of process at liquid-solid interfaces Surf. Sc/. 181 92... 

Schneir J, Harary H H, Dagata J A, Hansma P Kand Sonnenfeld R 1989 Scanning tunneling microscopy and fabrication of nanometer scale structure at the liquid-gold interface Scanning Microsc. 3 719... 

Another technique that has proved useful in establishing chemical bonding of coupling agents at interfaces is inelastic electron tunneling spectroscopy (ITES). For example. Van Velzen [16] examined 3-(trimethoxysilyl)propanethiol by this technique. Approximately monolayer quantities of this silane were adsorbed on the barrier oxide of an aluminum-aluminum oxide-metal tunneling junction two metals were investigated, lead and silver. It was concluded that the silane is... 

Section 6.2.1 offers literature data on the electrodeposition of metals and semiconductors from ionic liquids and briefly introduces basic considerations for electrochemical experiments. Section 6.2.2 describes new results from investigations of process at the electrode/ionic liquids interface. This part includes a short introduction to in situ Scanning Tunneling Microscopy. 

The boundary conditions are given by specifying the panicle currents at the boundaries. Holes can be injected into the polymer by thermionic emission and tunneling [32]. Holes in the polymer at the contact interface can also fall bach into the metal, a process usually called interlace recombination. Interface recombination is the time-reversed process of thermionic emission. At thermodynamic equilibrium the rates for these two time-reversed processes are the same by detailed balance. Thus, there are three current components to the hole current at a contact thermionic emission, a backflowing interface recombination current that is the time-reversed process of thermionic emission, and tunneling. Specifically, lake the contact at Jt=0 as the hole injecting contact and consider the hole current density at this contact. 

Parker [55] studied the IN properties of MEH-PPV sandwiched between various low-and high work-function materials. He proposed a model for such photodiodes, where the charge carriers are transported in a rigid band model. Electrons and holes can tunnel into or leave the polymer when the applied field tilts the polymer bands so that the tunnel barriers can be overcome. It must be noted that a rigid band model is only appropriate for very low intrinsic carrier concentrations in MEH-PPV. Capacitance-voltage measurements for these devices indicated an upper limit for the dark carrier concentration of 1014 cm"3. Further measurements of the built in fields of MEH-PPV sandwiched between metal electrodes are in agreement with the results found by Parker. Electro absorption measurements [56, 57] showed that various metals did not introduce interface states in the single-particle gap of the polymer that pins the Schottky contact. Of course this does not imply that the metal and the polymer do not interact [58, 59] but these interactions do not pin the Schottky barrier. 

---