Metal semiconductor capacitance

The sample, a reverse-biased p-n or metal-semiconductor junction, is placed in a capacitance bridge and the quiescent capacitance signal nulled out. The diode is then repetitively pulsed, either to lower reverse bias or into forward bias, and the transient due to the emission of trapped carriers is analyzed. As discussed in the preceding section, for a single deep state with JVT Nd the transient is exponential with an initial amplitude that gives the trap concentration, and a time constant, its emission rate. The capacitance signal is processed by a rate window whose output peaks when the time constant of the input transient matches a preset value. The temperature of the sample is then scanned (usually from 77 to 450°K) and the output of the rate window plotted as a function of the temperature. This produces a trap spectrum that peaks when the emission rate of carriers equals the value determined by the window and is zero otherwise. If there are several traps present, the transient will be a sum of exponentials, each having a time... 

The measurements utilise one-sided pn junction (p+n or pn ) and Schottky diodes, which possess a voltage modulated space charge region near the p/n and metal/semiconductor interface, respectively [8], The common feature of capacitance transient techniques is that the electronic properties of deep levels are determined by monitoring the transient high-frequency differential capacitance response of the diode as the electron occupancy of metastably charged deep levels located within the space charge... 

In bulk heterojunction solar cells, the metal/semiconductor interface is even more complex. Now the metal comes into contact with two semiconductors, one p-type (typically the polymer) and one n-type (typically the fullerene) semiconductor. A classical electrical characterization technique for studying the occurrence of charged states in the bulk or at the interface of a solar cell is admittance spectroscopy. If a solar cell is considered as a capacitor with capacitance C, the complex admittance Y is given by... 

Fig. 7.8.3 Photosensitive structures left, photodiode right, metal-oxide semiconductor capacitance...

Schottky barriers are metal-semiconductor junctions that have the ability to rectify current, because the work fimction of the metal is greater than that of the semiconductor. The junction thus creates a barrier between the semiconductor and the metal that decreases when the junction is forward biased and vice versa. Conduction in Schottky devices is by majority carriers, principally electrons. In conventional p-n devices reverse conduction is predominately via minority carriers. In p- -junction devices, charge is stored in the junction during forward conduction and has to be removed if the jimction is reverse biased before the diode can switch off. The junction capacitance and the capacitive reactance are voltage dependent. 

Electric field and capacitance in the metal-semiconductor interface... 

The principal object of electrochemical interest is given by another type of electrified interface, contacts of an electronic (liquid or solid metal, semiconductor) and an ionic (liquid solution, SEs, membranes, etc) conductor. For numerous contacts of this kind, one can ensure such ionic composition of the latter that there is practically no dc current across the interface within a certain interval of the externally apphed potential. Within this potential interval the system is close to the model of an ideally polarizable interface, the change of the potential is accompanied by the relaxation current across the external circuit and the bulk media that vanishes after a certain period. For sufficiently small potential changes, d , the ratio of the integrated relaxation current, dQ, to dE is independent of the amplitude and it determines the principal electrochemical characteristics of the interface, its differential capacitance per unit surface area, C ... 

To determine the effect of oxidation, a Mott-Schottky plot of the space charge capacitance before and after oxidation was compared. In these plots, which were originally derived for a metal-semiconductor interface (Schottky [ 1939,1942], Mott [1939]) but hold equally well for the metal-electrolyte interface, a linear relationship is predicted between the applied potential and one over the square of the capacitance arising from the space charge layer in the saniconductor. The slope is inversely proportional to the effective donor or acceptor concentration in the semiconductor. For the semiconductor-electrolyte interface (Bard and Faulkner [1980]),... 

The MOSFET can be understood by contrast with other field-effect devices, Kke the junction field-effect transistor (JFET) and the metal-semiconductor field-effect transistor (MESFET) (Hollis and Murphy, 1990). These other transistors modulate the conductance of a majority-carrier path between two ohmic contacts by capacitive control of its cross section. (Majority carriers are those in greatest abundance in... 

Fig. 1.8 Classical schematic drawing illustrating the hydrogen-sensitive Schottky diode-based, capacitance-based, and field-effect transistor-based devices, in which hydrogen atoms adsoibed at the metal-semiconductor or meted oxide interface cause a shift of the electrical characteristics along the voltage axis in devices having catalytic meted (Pd) gates...

Kummer AM, Hierlemann A, Baltes H (2004) Tuning sensitivity and selectivity of complementary metal oxide semiconductor based capacitive chemical microsensors. Anal Chem 76 2470-2477 Kiunmer AM, Burg TP, Hierlemann A (2006) Transient signal analysis using complementary metal oxide semiconductor capacitive chemical microsensors. Anal Chem 78 279-290 Kurzawski P, Hagleitner C, Hierlemann A (2006) Detection and discrimination capabilities of a multitransducer single-chip gas sensor system. Anal Chem 78 6910-6920... 

As outlined above, electron transfer through the passive film can also be cmcial for passivation and thus for the corrosion behaviour of a metal. Therefore, interest has grown in studies of the electronic properties of passive films. Many passive films are of a semiconductive nature [92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102 and 1031 and therefore can be investigated with teclmiques borrowed from semiconductor electrochemistry—most typically photoelectrochemistry and capacitance measurements of the Mott-Schottky type [104]. Generally it is found that many passive films cannot be described as ideal but rather as amorjDhous or highly defective semiconductors which often exlribit doping levels close to degeneracy [105]. 

Electric Breakdown in Anodic Oxide Films Physics and Applications of Semiconductor Electrodes Covered with Metal Clusters Analysis of the Capacitance of the Metal-Solution Interface. Role of the Metal and the Metal-Solvent Coupling Automated Methods of Corrosion Measurement... 

Based on the discussion above, it seems evident that a detailed understanding of kinetic processes occurring at semiconductor electrodes requires the determination of the interfacial energetics. Electrostatic models are available that allow calculation of the spatial distributions of potential and charged species from interfacial capacitance vs. applied potential data (23.24). Like metal electrodes, these models can only be applied at ideal polarizable semiconductor-solution interfaces (25)- In accordance with the behavior of the mercury-solution interface, a set of criteria for ideal interfaces is f. The electrode surface is clean or can be readily renewed within the timescale of... 

Since the metal can be treated as a nearly perfect conductor, C is high compared with C, and cannot influence the value of the measured doublelayer capacitance. The role of the metal in the double layer structure was discussed by Rice, who suggested that the distribution of electrons inside the metal decides the properties of the double-layer. This concept was later used to describe double-layer properties at the semiconductor/electrolyte interface. As shown later, the electron density on the metal side of the interface can be changed under the influence of charged solution species (dipoles, ions). ... 

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