Lead tin telluride, also referred to as PbSnTe or Pb_1−xSn_xTe, is a ternary alloy of

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

tin Tin is a chemical element with the symbol Sn (from la, stannum) and atomic number 50. Tin is a silvery-coloured metal. Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent, t ...

and

tellurium Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally fou ...

, generally made by alloying either tin into

lead telluride Lead telluride is a compound of lead and tellurium (PbTe). It crystallizes in the NaCl crystal structure with Pb atoms occupying the cation and Te forming the anionic lattice. It is a narrow gap semiconductor with a band gap of 0.32 eV. It occurs ...

or lead into

tin telluride Tin telluride is a compound of tin and tellurium (SnTe); is a IV-VI narrow band gap semiconductor and has direct band gap of 0.18 eV. It is often alloyed with lead to make lead tin telluride, which is used as an infrared detector material. Tin ...

. It is a IV-VI narrow band gap

semiconductor material A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

. The

band gap In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in ...

of Pb_1−xSn_xTe is tuned by varying the composition(x) in the material. SnTe can be alloyed with Pb (or PbTe with Sn) in order to tune the band gap from 0.29 eV (PbTe) to 0.18 eV (SnTe). It is important to note that unlike II-VI

chalcogenides : 220px, Cadmium sulfide, a prototypical metal chalcogenide, is used as a yellow pigment. A chalcogenide is a chemical compound consisting of at least one chalcogen anion and at least one more electropositive element. Although all group 16 elements ...

, e.g. cadmium, mercury and zinc chalcogenides, the band gap in Pb_1−xSn_xTe does not changes linearly between the two extremes. In contrast, as the composition (x) is increased, the band gap decreases, approaches zero in the concentration regime (0.32–0.65 corresponding to temperature 4-300 K, respectively) and further increases towards bulk band gap of SnTe. Therefore, the lead tin telluride alloys have narrower band gaps than their end point counterparts making lead tin telluride an ideal candidate for mid

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

, 3–14 μm opto-electronic application.

Properties

Lead tin telluride is

p-type semiconductor An extrinsic semiconductor is one that has been '' doped''; during manufacture of the semiconductor crystal a trace element or chemical called a doping agent has been incorporated chemically into the crystal, for the purpose of giving it different ...

at 300 K. The hole concentration increases as the tin content is increased resulting in an increase in

electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allow ...

. For composition range x = 0 to 0.1, electrical conductivity decreases with increase in temperature up to 500 K and increases beyond 500 K. For composition range, x ≥ 0.25, electrical conductivity decreases with increases in temperature. The

Seebeck coefficient The Seebeck coefficient (also known as thermopower, thermoelectric power, and thermoelectric sensitivity) of a material is a measure of the magnitude of an induced thermoelectric voltage in response to a temperature difference across that material ...

of Pb_1−xSn_xTe decreases with increases in Sn content at 300 K. For composition x > 0.25,

thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...

of Pb_1−xSn_xTe increases with increase in Sn content. Thermal conductivity values decreases with increase in temperature over the entire composition range, x > 0. For Pb_1−xSn_xTe, the optimum temperature corresponding to maximum thermoelectric power factor increases with increase in composition x. The pseudo binary alloy of Lead tin telluride acts as a thermoelectric material over 400–700 K temperature range. Lead tin telluride has a positive

temperature coefficient A temperature coefficient describes the relative change of a physical property that is associated with a given change in temperature. For a property ''R'' that changes when the temperature changes by ''dT'', the temperature coefficient α is def ...

i.e. for a given composition x, band gap increases with temperature. Therefore, temperature stability has to be maintained while working with lead tin telluride based

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...

. However, the advantage is that the operating

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

of the laser can simply be tuned by varying the operating temperature. The optical

absorption coefficient The linear attenuation coefficient, attenuation coefficient, or narrow-beam attenuation coefficient characterizes how easily a volume of material can be penetrated by a beam of light, sound, particles, or other energy or matter. A coefficient valu ...

of lead tin telluride is typically ~750 cm⁻¹ as compared to ~50 cm⁻¹ for the extrinsic semiconductors such as doped silicon. The higher optical coefficient value not only ensures higher sensitivity but also reduces the spacing required between individual detector elements to prevent optical cross talk making

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

technology easily accessible.

Application

Due to tunable narrow band gap and relatively higher operating temperature of lead tin telluride as compared to mercury cadmium telluride, it has been a material of choice for commercial applications in IR sources,

band-pass filter A band-pass filter or bandpass filter (BPF) is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range. Description In electronics and signal processing, a filter is usually a two-por ...

s and IR detectors. It has found applications as photovoltaic devices for sensing radiation in 8-14 μm window. Single Crystal Pb_1−xSn_xTe diode lasers have been employed for detection of gaseous pollutants like sulfur dioxide. Lead tin tellurides have been used in thermoelectric devices.Hockings, Eric F and Mularz, Walter L (1961) "Lead telluride-tin telluride thermoelectric compositions and devices"

References

{{Reflist, colwidth=30em Tellurides Lead alloys Tin alloys IV-VI semiconductors