Capacitance-voltage technique

The magnitude of the errors in determining the flat-band potential by capacitance-voltage techniques can be sizable because (a) trace amounts of corrosion products may be adsorbed on the surface, (b) ideal polarizability may not be achieved with regard to electrolyte decomposition processes, (c) surface states arising from chemical interactions between the electrolyte and semiconductor can distort the C-V data, and (d) crystalline inhomogeneity, defects, or bulk substrate effects may be manifested at the solid electrode causing frequency dispersion effects. In the next section, it will be shown that the equivalent parallel conductance technique enables more discriminatory and precise analyses of the interphasial electrical properties. 

This relationship is used in the capacitance-voltage technique for profiling carrier concentrations near diode junctions and is usable for any type of diode in which one side of the junction is much more heavily doped than the other. It can also be used in a transient mode to detect and analyze point defects as they charge and discharge with bias voltage changes. 

Sodium contamination and drift effects have traditionally been measured using static bias-temperature stress on metal-oxide-silicon (MOS) capacitors (7). This technique depends upon the perfection of the oxidized silicon interface to permit its use as a sensitive detector of charges induced in the silicon surface as a result of the density and distribution of mobile ions in the oxide above it. To measure the sodium ion barrier properties of another insulator by an analogous procedure, oxidized silicon samples would be coated with the film in question, a measured amount of sodium contamination would be placed on the surface, and a top electrode would be affixed to attempt to drift the sodium through the film with an applied dc bias voltage. Resulting inward motion of the sodium would be sensed by shifts in the MOS capacitance-voltage characteristic. 

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... 

The analysis of capacitance-voltage data is made difficult by the lack of specific energy information. The DLTS experiment provides this information and consequently is a better technique to obtain the density of states. DLTS distinguishes between deep and shallow states... 

Besides measuring binary or ternary alloy composition, Raman spectroscopy evinces an acute sensitivity to impurity concentrations sometimes well below 1% levels. This makes Raman spectroscopy especially well suited to measuring electrically active dopant concentrations in NWs since techniques such as scanning spreading resistance, capacitance-voltage, or Hall measurements that have been... 

S. Chandra and J. Singh, Capacitance-voltage measurement technique as a tool for in situ characterization of electrochemical etching of silicon, J. Electrochem. Soc. 146, 1206, 1999. 

Kobayashi H., Takeda N., Sugahara H. and Tsubomura H. (1991), SUicon-non-aqueous solution interface studied by capacitance-voltage and conductance-voltage techniques , J. Phys. Chem. 95, 813-818. 

Various techniques are used for these measurements. The most popular are capacitance-voltage (C-V) profiling, spreading resistance and secondary ion mass spectroscopy (SIMS). SIMS is not a strictly electrical characterization technique, but is included here because it is routinely used to measure the dopant atom distribution. The basis for these three techniques are very different and I will briefly describe them. 

The most widely used of these methods in the study of a-Si H have been field-effect, capacitance, and deep level transient spectroscopy (DLTS) measurements. Capacitance measurements actually include quite a number of variations such as capacitance versus applied voltage (C- V), frequency (C- w), or temperature (C-T), and also several kinds of distinct capacitance profiling techniques. The technique referred to as DLTS normally includes both capacitance-transient as well as current-transient measurements and will also be used as a generic term for such recent variations as isothermal capacitance transient spectroscopy (ICTS), constant capacitance methods, and the like. 

Photoluminescence (PL) and EL spectroscopy can be used to determine the presence of traps. Other techniques include current voltage measurements, capacitance voltage measurements, capacitance transient spectroscopy, and admittance spectroscopy. Under favorite conditions, the identification of the nature of the trap is possible. 

The problem of pulse voltage technique can be approached in one of two equivalent ways. The first method involves the transmission line approach which considers the channel as an infinite resistance-capacitance ladder. The current flowing through the channel divides up into these two branches at every point, one that charges up... 

The most important application of SCM is two-dimensional dopant concentration profiling in semiconductors. However, the raw capacitance-voltage data obtained from SCM must be converted by a mathematical model into a dopant concentration. Therefore, development and validation of appropriate models represents a large part of SCM methodology. To validate the various models, other experimental techniques must be employed to measure and verify the dopant profiles independently. SCM data are usually compared to secondary ion mass spectrometry (SIMS) measurements of dopant concentrations. Spreading resistance profiling (SRP) and computer simulations are also employed to check model validity. 

Active electrochemical techniques are not confined to pulse and linear sweep waveforms, which are considered large ampHtude methods. A-C voltammetry, considered a small ampHtude method because an alternating voltage <10 mV is appHed to actively couple through the double-layer capacitance, can also be used (15). An excellent source of additional information concerning active electroanalytical techniques can be found in References 16—18. Reference 18, although directed toward clinical chemistry and medicine, also contains an excellent review of electroanalytical techniques (see also... 

Information on the dielectric properties of a material might also be obtained using noncontact scanning techniques. These can include rf or microwave measurements made with an electrode that is held in the vicinity of the surface. This approach has the advantage that samples remain undamaged by the measurement and thus can be reevaluated or subjected to other studies as needed. However, this approach cannot provide accurate values for the capacitance, in very thin films such that d/e < 4 A. Moreover, the current-voltage measurements are still needed in order... 

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