Schottky contact, junction

K. Jdrrendahl and R. F. Davis, Materials Properties and Characterization of SiC V. A. Dmitriev and M. G. Spencer, SiC Fabrication Technology Growth and Doping V. Saxena and A. J. Steckl, Building Blocks for SiC Devices Ohmic Contacts, Schottky Contacts, and p-n Junctions M. S. Shur, SiC Transistors... 

First successful ZnO device demonstrations as for example stable homo-and heteroepitaxial pn-junctions and LED structures, thin film scintillators, and quantum well structures with optical confinement, and oxide-based Bragg reflectors, and high-quality Schottky contacts are based on PLD grown thin films. Several techniques as for example the PLD in UHV conditions (laser MBE), and gradient and combinatorial PLD, and high-pressure PLD for nano-heterostructures show the innovative potential of the advanced growth technique PLD. 

Figure 3. Schematic iiius ations of three important eiements of inorganic semiconductor device structures (a) the Schottky contact, (b) the p-n junction, and (c) the insuiated gate capacitor. E, E and E, are the conduction band, vaience band, and Fermi energies, respectiveiy.

Laser pulse photocurrent transients in solid-state Schottky barrier junctions between dry Ti02 and a platinum contact have been studied by Konenkamp and coworkers [57]. They observe a power law dependence of the collected photocurrent on time,... 

A metal-semiconductor junction will therefore form a barrier for electrons and holes if the Fermi energy of the metal is somewhere between the conduction and valence band edge. Such a contact that is rectifying in nature is called a Schottky contact. 

To consider the photolysis of water based on the inorganic equivalent of the Z-scheme in nature, semiconductor tandem-type structures, such as shown in Fig. 17, can be analyzed. It should be noted that the structure shown in Fig. 17 represents a solid state analogon of two half-cells for the photoelectrolysis of water in a joint scheme. Therefore, compared to solid state devices with two pn junctions, the band bending of the structure shown develops at the respective electrolyte contact or by forming Schottky-type junctions with the electrocatalysts at the surfaces which then... 

Maitrot M, Boudjema B, Andre JJ, Simon J (1986) Molecular material-based junctions formation of a Schottky contact with metallophthalocyanine thin films doped by the cosublimation method. J Appl Phys 60 2396-2400... 

Heterojunctions are any electrical junctions between dissimilar materials. The term is generally used to refer to semiconductor heterojunctions, although technically it applies to Schottky contacts and even to metal-metal junctions such as thermocouples. Here we will use the conventional terminology and consider semiconductor/ semiconductor junctions. 

The optical properties of electrodeposited, polycrystalline CdTe have been found to be similar to those of single-crystal CdTe [257]. In 1982, Fulop et al. [258] reported the development of metal junction solar cells of high efficiency using thin film (4 p,m) n-type CdTe as absorber, electrodeposited from a typical acidic aqueous solution on metallic substrate (Cu, steel, Ni) and annealed in air at 300 °C. The cells were constructed using a Schottky barrier rectifying junction at the front surface (vacuum-deposited Au, Ni) and a (electrodeposited) Cd ohmic contact at the back. Passivation of the top surface (treatment with KOH and hydrazine) was seen to improve the photovoltaic properties of the rectifying junction. The best fabricated cell comprised an efficiency of 8.6% (AMI), open-circuit voltage of 0.723 V, short-circuit current of 18.7 mA cm, and a fill factor of 0.64. 

The term photovoltaic effect is further used to denote non-electrochemical photoprocesses in solid-state metal/semiconductor interfaces (Schottky barrier contacts) and semiconductor/semiconductor pin) junctions. Analogously, the term photogalvanic effect is used more generally to denote any photoexcitation of the d.c. current in a material (e.g. in solid ferroelectrics). Although confusion is not usual, electrochemical reactions initiated by light absorption in electrolyte solutions should be termed electrochemical photogalvanic effect , and reactions at photoexcited semiconductor electodes electrochemical photovoltaic effect . 

The Schottky-Mott theory predicts a current / = (4 7t e m kB2/h3) T2 exp (—e A/kB 7) exp (e n V/kB T)— 1], where e is the electronic charge, m is the effective mass of the carrier, kB is Boltzmann s constant, T is the absolute temperature, n is a filling factor, A is the Schottky barrier height (see Fig. 1), and V is the applied voltage [31]. In Schottky-Mott theory, A should be the difference between the Fermi level of the metal and the conduction band minimum (for an n-type semiconductor-to-metal interface) or the valence band maximum (for a p-type semiconductor-metal interface) [32, 33]. Certain experimentally observed variations of A were for decades ascribed to pinning of states, but can now be attributed to local inhomogeneities of the interface, so the Schottky-Mott theory is secure. The opposite of a Schottky barrier is an ohmic contact, where there is only an added electrical resistance at the junction, typically between two metals. 

Macroscopic n-type materials in contact with metals normally develop a Schottky barrier (depletion layer) at the junction of the two materials, which reduces the kinetics of electron injection from semiconductor conduction band to the metal. However, when nanoparticles are significantly smaller than the depletion layer, there is no significant barrier layer within the semiconductor nanoparticle to obstruct electron transfer [62]. An accumulation layer may in fact be created, with a consequent increase in the electron transfer from the nanoparticle to the metal island [63], It is not clear if and what type of electronic barrier exists between semiconductor nanoparticles and metal islands, as well as the role played by the properties of the metal. A direct correlation between the work function of the metal and the photocatalytic activity for the generation of NH3 from azide ions has been made for metallized Ti02 systems [64]. 

Most electrochemical experiments need an electrical contact of some kind to the silicon substrate. Because of the semiconducting nature of silicon a metallic tip or clip attached to the surface will not produce an ohmic contact but constitutes a Schottky junction. However, for some applications, like the ELYMAT (Section 10.3), where the contact is only operated under forward conditions at low current densities, such a contact is sufficient. For silicon samples with a doping concentration in excess of 1019 cnT3 the contact to a metal becomes ohmic. An ohmic contact to a silicon sample with a doping concentration below 1019 cm-3 can be achieved in different ways ... 

The simplest electronic devices, such as diodes, light-emitting diodes, lasers, and photocells, have a single p-n junction. If we place, say, a p-type doped Si block in contact with n-typed doped Si block, electrons will normally flow from the n to the p regions but not vice versa. Thus, the p-n diode so created can be fitted with ohmic contacts to function as a rectifier of alternating current. Schottky junctions can act in this way to some degree even without deliberate creation of a p-n junction. 

Metals, such as platinum, are usually introduced to improve the electron-hole separation efficiency. In order to analyze the energy structure of the metal-loaded particulate semiconductor, we solved the two-dimensional Poisson-Boltzmann equation.3) When the metal is deposited to the semiconductor by, for example, evaporation, a Schottky barrier is usually formed.45 For the Schottky type contact, the barrier height increases with an increase of the work function of the metal,4 which should decrease the photocatalytic activity. However, higher activity was actually observed for the metal with a higher work function.55 This results from the fact that ohmic contact with deposited metal particles is established in photocatalysts when the deposited semiconductor is treated by heat65 or metal is deposited by the photocatalytic reaction.75 Therefore, in the numerical computation we assumed ohmic contact at the energy level junction of the metal and semiconductor. 

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