Rectifying behavior

The history of semiconductor devices can be traced back to tire paper of Braun, published in 1874, describing rectifying behavior of a contact [1], However, for many years semiconductors were considered too difficult a subject and tire science of semiconductors began only during World War IT... 

Both ohmic and rectifying behavior are possible, depending on the sign of Unlike the p—n junction the current in a rectifying Schottky barrier... 

Harnack, O. Pacholski, C. Weller, H. Yasuda, A. Wessels, J. M. 2003. Rectifying behavior of electrically aligned ZnO nanorods. Nano Lett. 3 1097-1101. 

The measurement of properties such as the resistivity or dielectric constant of PS requires some kind of contact with the PS layer. Evaporation of a metal onto the PS film-covered silicon sample produces a metal/PS/Si sandwich, which behaves like an MIS structure with an imperfect insulator. Such sandwich structures usually exhibit a rectifying behavior, which has to be taken into account when determining the resistivity [Si3, Bel4]. This can be circumvented by four-terminal measurements of free-standing PS films, but for such contacts the applied electric field has to be limited to rather small values to avoid undesirable heating effects. An electrolytic contact can also be used to probe PS films, but the interpretation of the results is more complicated, because it is difficult to distinguish between ionic and electronic contributions to the measured conductivity. The electrolyte in the porous matrix may short-circuit the silicon filaments, and wetting of PS in-... 

The fabrication of diodes on silicon substrates was demonstrated using the supramolecular interactions between a 5,10,15,20-tetra(3-fluorophenyl)porphyrin and Ceo fullerene with a rectification ratio of 1,500 (see Fig. 11). The rectifying behavior is explained by theoretical calculations which show that the LUMO orbital is located mainly on the fullerene whereas the HOMO orbital is located on the porphyrin moiety [99]. 

Rectifying behavior was observed in crayfish axons with depolarization at the presynaptic side increasing the junctional conductance [Furshpan and Potter, 1959 Giaume et al., 1987] and in fish [Auerbach and Bennett, 1969]. It has been hypothesised by Bennett et al. [1991] that this rectifying behavior may arise from a heterotypic composition of the channel. 

An early nanopore study focused on an asymmetric Au-molecule-Ti junction based on thiol end-capped biphenyl 81b molecules [45], The asymmetry of the structure led to the observation of a prominent rectifying behavior with larger current when the Ti electrode was negatively biased. Recent work by Bao and coworkers [72] has shown that vapor deposition of Ti on SAMs results in penetration of the monolayer, thus destroying it. Similar observations were made using Au and A1 deposition. However, destruction of the monolayer could in this case be prevented if SAMs of dithiols were used, since the Au or A1 would react with the free thiol end. 

Figure 7.31 demonstrates the very good rectifying behavior of such a Pd Schottky diode on undoped ZnO thin film. The current density ratio determined for bias voltages of +0.6 V and -3V is about 104 as shown in the inset of Fig. 7.31. The ideality factor n is about 1.5. The temperature-dependent current-voltage (IV, see Fig. 7.31) and capacitance-voltage (CV) measurements from 210 to 300 K explain the reason for the slight deviation of the ideality factor from unity and the dependence of the reverse current on the reverse bias. The barrier heights of the diode of Fig. 7.31 jy and

Fig. 7.31. Superior rectifying behavior of a Pd Schottky contact on PLD ZnO film with ohmic ZnO Ai back layer contact, with excellent stability at different temperature. The inset shows the current density-voltage dependence for a larger voltage range at 290 K. Reprinted with permission from [55]...

ZnO LED Au/p(i)-ZnO/n-ZnO single crystal/In structure grown by N2O plasma enhanced PLD, rectifying behavior, bluish-white electroluminescence [102]... 

Zn3P2/ n-ZnO diode PLD of ZnO and Zn3P2 on sapphire(OOOl), laser annealing of the Zn3P2, rectifying behavior [104]... 

Walter Haus Schottky (1886-1976) received his doctorate in physics under Max Planck from the Humboldt University in Berlin in 1912. Although his thesis was on the special theory of relativity, Schottky spent his life s work in the area of semiconductor physics. He alternated between industrial and academic positions in Germany for several years. He was with Siemens AG until 1919 and the University of Wurzburg from 1920 to 1923. From 1923 to 1927, Schottky was professor of theoretical physics at the University of Rostock. He rejoined Siemens in 1927, where he finished out his career. Schottky s inventions include the ribbon microphone, the superheterodyne radio receiver, and the tetrode vacuum tube. In 1929, he published Thermodynamik, a book on the thermodynamics of solids. Schottky and Wagner studied the statistical thermodynamics of point defect formation. The cation/anion vacancy pair in ionic solids is named the Schottky defect. In 1938, he produced a barrier layer theory to explain the rectifying behavior of metal-semiconductor contacts. Metal-semiconductor diodes are now called Schottky barrier diodes. 

Even for inner sphere processes and adsorbed species, owing to the dependence of on barrier height, for an n-type semicondnetor, more positive redox potentials generally yield smaller valnes of 7o, and produce highly rectifying behavior. 

FIGURE 8.15 Typical I-V curve measured from a P3HT/fullerene PV device showing rectifying behavior. The key device parameters, Voc, /so the maximum power voltage (Imp). and current density (/mp), are indicated. 

Alkaline CuCN solutions were used for the first time to electrodeposit homogeneous and adherent Cu films onto silicon. Tire obtained Cu/n-Si(lll) junctions show a nearly perfect rectifying behavior. The Schottky parameters (barrier height 3>b = 630 mV ideality factor n = 1.2) do not change importantly with time. It is also demonstrated that highly adherent Ni films can be plated onto n-Si(lll) from an acidic Watts bath, if copper clusters were elecrodeposited onto the silicon surface first. 

In summary, this study shows the great possibility of generating Cu/n-Si junctions with a nearly perfect rectifying behavior from CuCN solutions. Diode characteristics are comparable to those reported for contacts prepared by physical methods and are not appreciably subject to modification with time. The second promising point is the high adherence of Cu films, which was exploited to electrodeposit adherent Ni films from a modified Watts bath. This two step procedure seems to solve the major difficulty encountered upon growing thick metal layers onto H-Si surfaces from acidic solutions and enables to prepare stable electrical junctions with defined electrical properties. 

---