View source for Physics:Thermally stimulated current spectroscopy

{{Short description|Experimental method}}
{{nofootnotes|date=December 2010}}
'''Thermally stimulated current (TSC) [[Physics:Spectroscopy|spectroscopy]]''' (not to be confused with [[Thermally stimulated depolarization current|thermally stimulated depolarization current]]) is an experimental technique which is used to study [[Physics:Energy level|energy level]]s in [[Physics:Semiconductor|semiconductor]]s or [[Physics:Thermal insulation|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 [[Physics:Electric field|electric field]] or a [[Earth:Temperature gradient|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 [[Earth:Temperature gradient|temperature gradient]] is also known as "Thermoelectric Effect Spectroscopy" (TEES) according to 2 scientists (Santic and Desnica) from ex-[[Place:Yugoslavia|Yugoslavia]]; they demonstrated their technique on semi-insulating [[Chemistry:Gallium arsenide|gallium arsenide]] (GaAs). (Note: TSC based on a [[Earth:Temperature gradient|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 [[Physics:Deep-level transient spectroscopy|deep-level transient spectroscopy]] (DLTS), thermally stimulated current (TSC) spectroscopy was a popular technique to study traps in semiconductors. Nowadays, for traps in [[Engineering:Schottky diode|Schottky diode]]s or [[Physics:P-n junction|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 [[Chemistry:Gallium arsenide|gallium arsenide]] (GaAs) substrates. It has also been applied to materials used for [[Physics:Particle detector|particle detector]]s or [[Physics:Semiconductor detector|semiconductor detector]]s used in nuclear research, for example, high-resistivity [[Chemistry:Silicon|silicon]], [[Chemistry:Cadmium telluride|cadmium telluride]] (CdTe), etc. TSC has also been applied to various organic insulators. TSC is useful for [[Physics:Electret|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 [[Place:Singapore|Singapore]]) applied zero-bias thermally stimulated current or zero-temperature-gradient zero-bias thermally stimulated current to ultrathin [[Chemistry:Tantalum pentoxide|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.

TSC technique is used to study dielectric materials and polymers. Different theories was made to describe the response curve for this technique in order to calculate the peak parameters which are, the [[Chemistry:Activation energy|activation energy]] and the relaxation time.

==References==

*von Heinrich Frei and Gerhart Groetzinger, "Liberation of electrical energy during the fusion of electrets" (English translation of the original title in German), Physikalische Zeitschrift, vol. 37, pp.&nbsp;720–724 (October 1936). (Note: This may be the first publication on thermally stimulated current.)
*{{cite journal | last1=Šantić | first1=B. | last2=Desnica | first2=U. V. | title=Thermoelectric effect spectroscopy of deep levels—application to semi‐insulating GaAs | journal=Applied Physics Letters | publisher=AIP Publishing | volume=56 | issue=26 | date=1990-06-25 | issn=0003-6951 | doi=10.1063/1.102860 | pages=2636–2638| bibcode=1990ApPhL..56.2636S }}
*W.S. Lau, "Zero-temperature-gradient zero-bias thermally stimulated current technique to characterize defects in semiconductors or insulators”, US Patent 6,909,273, filed in 2000 and granted in 2005.
*{{cite journal | last1=Lau | first1=W. S. | last2=Wong | first2=K. F. | last3=Han | first3=Taejoon | last4=Sandler | first4=Nathan P. | title=Application of zero-temperature-gradient zero-bias thermally stimulated current spectroscopy to ultrathin high-dielectric-constant insulator film characterization | journal=Applied Physics Letters | publisher=AIP Publishing | volume=88 | issue=17 | date=2006-04-24 | issn=0003-6951 | doi=10.1063/1.2199590 | page=172906| bibcode=2006ApPhL..88q2906L }}
*{{cite journal | last=Lau | first=W. S. | title=Similarity between the first ionized state of the oxygen vacancy double donor in tantalum oxide and the first ionized state of the cadmium vacancy double acceptor in cadmium sulfide | journal=Applied Physics Letters | publisher=AIP Publishing | volume=90 | issue=22 | date=2007-05-28 | issn=0003-6951 | doi=10.1063/1.2744485 | page=222904| bibcode=2007ApPhL..90v2904L }} (Note: This paper explains two-scan thermally stimulated current spectroscopy.)
*{{cite journal | last1=Yousif | first1=M. Y. A. | last2=Johansson | first2=M. | last3=Engström | first3=O. | title=Extremely small hole capture cross sections in HfO<sub>2</sub> / Hf<sub>x</sub>Si<sub>y</sub>O<sub>z</sub> / p-Si structures | journal=Applied Physics Letters | publisher=AIP Publishing | volume=90 | issue=20 | date=2007-05-14 | issn=0003-6951 | doi=10.1063/1.2740188 | page=203506| bibcode=2007ApPhL..90t3506Y }}

[[Category:Semiconductor analysis]]
[[Category:Spectroscopy]]

{{Sourceattribution|Thermally stimulated current spectroscopy}}