Thermally stimulated current
Encyclopedia
Thermally stimulated current (TSC) spectroscopy
is an experimental technique which is used to study energy level
s in semiconductor
s or insulators
(organic or inorganic). Energy levels are first filled either by optical or electrical injection usually at a relatively low temperature, subsequently electrons or holes are emitted by heating to a higher temperature. A curve of emitted current will be recorded and plotted against temperature, resulting in a TSC spectrum. By analyzing TSC spectra, information can be obtained regarding energy levels in semiconductors or insulators.
A driving force is required for emitted carriers to flow when the sample temperature is being increased. This driving force can be an electric field
or a temperature gradient
. Usually, the driving force adopted is an electric field; however, electron traps and hole traps cannot be distinguished. If the driving force adopted is a temperature gradient, electron traps and hole traps can be distinguished by the sign of the current. TSC based on a temperature gradient
is also known as "Thermoelectric Effect Spectroscopy" (TEES) according to 2 scientists (Santic and Desnica) from ex-Yugoslavia
; they demonstrated their technique on semi-insulating gallium arsenide (GaAs). (Note: TSC based on a temperature gradient
was invented before Santic and Desnica and applied to the study of organic plastic materials. However, Santic and Desnica applied TSC based on a temperature gradient to study a technologically important semiconductor material and coined a new name, TEES, for it.)
Historically, Frei and Groetzinger published a paper in German in 1936 with the title "Liberation of electrical energy during the fusion of electrets" (English translation of the original title in German). This may be the first paper on TSC. Before the invention of DLTS (deep level transient spectroscopy), thermally stimulated current (TSC) spectroscopy was a popular technique to study traps in semiconductors. Nowadays, for traps in Schottky diode
s or p-n junction
s, DLTS is the standard method to study traps. However, there is an important shortcoming for DLTS: it cannot be used for an insulating material while TSC can be applied to such a situation. (Note: an insulator can be considered as a very large bandgap semiconductor.) In addition, the standard transient capacitance based DLTS method may not be very good for the study of traps in the i-region of a p-i-n diode while the transient current based DLTS (I-DLTS) may be more useful.
TSC has been used to study traps in semi-insulating gallium arsenide (GaAs) substrates. It has also been applied to materials used for particle detector
s or semiconductor detector
s used in nuclear research, for example, high-resistivity silicon
, cadmium telluride
(CdTe), etc. TSC has also been applied to various organic insulators. TSC is useful for electret
research. More advanced modifications of TSC have been applied to study traps in ultrathin high-k dielectric
thin films. W. S. Lau (Lau Wai Shing
, Republic of Singapore
) applied zero-bias thermally stimulated current or zero-temperature-gradient zero-bias thermally stimulated current to ultrathin tantalum pentoxide samples. For samples with some shallow traps which can be filled at low temperature and some deep traps which can be filled only at high temperature, a two-scan TSC may be useful as suggested by Lau in 2007. TSC has also been applied to hafnium oxide.
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
is an experimental technique which is used to study energy level
Energy level
A quantum mechanical system or particle that is bound -- that is, confined spatially—can only take on certain discrete values of energy. This contrasts with classical particles, which can have any energy. These discrete values are called energy levels...
s in semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
s or insulators
Thermal insulation
Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...
(organic or inorganic). Energy levels are first filled either by optical or electrical injection usually at a relatively low temperature, subsequently electrons or holes are emitted by heating to a higher temperature. A curve of emitted current will be recorded and plotted against temperature, resulting in a TSC spectrum. By analyzing TSC spectra, information can be obtained regarding energy levels in semiconductors or insulators.
A driving force is required for emitted carriers to flow when the sample temperature is being increased. This driving force can be an electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
or a temperature gradient
Temperature gradient
A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location. The temperature gradient is a dimensional quantity expressed in units of degrees per unit length...
. Usually, the driving force adopted is an electric field; however, electron traps and hole traps cannot be distinguished. If the driving force adopted is a temperature gradient, electron traps and hole traps can be distinguished by the sign of the current. TSC based on a temperature gradient
Temperature gradient
A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location. The temperature gradient is a dimensional quantity expressed in units of degrees per unit length...
is also known as "Thermoelectric Effect Spectroscopy" (TEES) according to 2 scientists (Santic and Desnica) from ex-Yugoslavia
Yugoslavia
Yugoslavia refers to three political entities that existed successively on the western part of the Balkans during most of the 20th century....
; they demonstrated their technique on semi-insulating gallium arsenide (GaAs). (Note: TSC based on a temperature gradient
Temperature gradient
A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location. The temperature gradient is a dimensional quantity expressed in units of degrees per unit length...
was invented before Santic and Desnica and applied to the study of organic plastic materials. However, Santic and Desnica applied TSC based on a temperature gradient to study a technologically important semiconductor material and coined a new name, TEES, for it.)
Historically, Frei and Groetzinger published a paper in German in 1936 with the title "Liberation of electrical energy during the fusion of electrets" (English translation of the original title in German). This may be the first paper on TSC. Before the invention of DLTS (deep level transient spectroscopy), thermally stimulated current (TSC) spectroscopy was a popular technique to study traps in semiconductors. Nowadays, for traps in Schottky diode
Schottky diode
The Schottky diode is a semiconductor diode with a low forward voltage drop and a very fast switching action...
s or p-n junction
P-n junction
A p–n junction is formed at the boundary between a P-type and N-type semiconductor created in a single crystal of semiconductor by doping, for example by ion implantation, diffusion of dopants, or by epitaxy .If two separate pieces of material were used, this would...
s, DLTS is the standard method to study traps. However, there is an important shortcoming for DLTS: it cannot be used for an insulating material while TSC can be applied to such a situation. (Note: an insulator can be considered as a very large bandgap semiconductor.) In addition, the standard transient capacitance based DLTS method may not be very good for the study of traps in the i-region of a p-i-n diode while the transient current based DLTS (I-DLTS) may be more useful.
TSC has been used to study traps in semi-insulating gallium arsenide (GaAs) substrates. It has also been applied to materials used for particle detector
Particle detector
In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify high-energy particles, such as those produced by nuclear decay, cosmic radiation, or reactions in a...
s or semiconductor detector
Semiconductor detector
This article is about particle detectors. For information about semiconductor detectors in radio, see Diode#Semiconductor_diodes, rectifier, detector and cat's-whisker detector....
s used in nuclear research, for example, high-resistivity silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
, cadmium telluride
Cadmium telluride
Cadmium telluride is a crystalline compound formed from cadmium and tellurium. It is used as an infrared optical window and a solar cell material. It is usually sandwiched with cadmium sulfide to form a p-n junction photovoltaic solar cell...
(CdTe), etc. TSC has also been applied to various organic insulators. TSC is useful for electret
Electret
Electret is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric fields, and is the electrostatic equivalent of a permanent magnet. Oliver Heaviside coined this term in 1885...
research. More advanced modifications of TSC have been applied to study traps in ultrathin high-k dielectric
High-k Dielectric
The term high-κ dielectric refers to a material with a high dielectric constant κ used in semiconductor manufacturing processes which replaces the silicon dioxide gate dielectric...
thin films. W. S. Lau (Lau Wai Shing
Lau Wai Shing
Wai Shing Lau is also known as Lau Wai Shing. Lau is an electrical engineer and also materials scientist. He worked on both Si-based and III-V based microelectronics.-Biography:...
, Republic of Singapore
Singapore
Singapore , officially the Republic of Singapore, is a Southeast Asian city-state off the southern tip of the Malay Peninsula, north of the equator. An island country made up of 63 islands, it is separated from Malaysia by the Straits of Johor to its north and from Indonesia's Riau Islands by the...
) applied zero-bias thermally stimulated current or zero-temperature-gradient zero-bias thermally stimulated current to ultrathin tantalum pentoxide samples. For samples with some shallow traps which can be filled at low temperature and some deep traps which can be filled only at high temperature, a two-scan TSC may be useful as suggested by Lau in 2007. TSC has also been applied to hafnium oxide.