Lead selenide (PbSe), or lead(II) selenide, a

selenide A selenide is a chemical compound containing a selenium anion with oxidation number of −2 (Se2−), much as sulfur does in a sulfide. The chemistry of the selenides and sulfides is similar. Similar to sulfide, in aqueous solution, the selenide ion ...

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 ...

, is a

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. ...

. It forms cubic crystals of the

NaCl Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g/ ...

structure; it has a direct bandgap of 0.27 eV at room temperature. (Note that incorrectly identifies PbSe and other IV–VI semiconductors as indirect gap materials.) A grey solid, it is used for manufacture of

infrared detector An infrared detector is a detector that reacts to infrared (IR) radiation. The two main types of detectors are thermal and photonic (photodetectors). The thermal effects of the incident IR radiation can be followed through many temperature depen ...

s for thermal imaging. The

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

clausthalite is a naturally occurring lead selenide. It may be formed by direct reaction between its constituent elements,

and

selenium Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...

Infrared detection

PbSe was one of the first materials found to be sensitive to the infrared radiation used for military applications. Early research works on the material as

were carried out during the 1930s and the first useful devices were processed by Germans, Americans and British during and just after World War II. Since then, PbSe has been commonly used as an infrared

photodetector Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. There is a wide variety of photodetectors which may be classified by mechanism of detection, such as photoelectric or photochemical effects, or ...

in multiple applications, from

spectrometers A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the ...

for gas and flame detection to infrared fuzes for artillery ammunition or Passive Infrared Cueing systems (PICs). As a sensitive material to the infrared radiation, PbSe has unique and outstanding characteristics: it can detect IR radiation of wavelengths from 1.5 to 5.2 μm (mid-wave infrared window, abbreviated MWIR – in some special conditions it is possible to extend its response beyond 6 μm), it has a high detectivity at room temperature (uncooled performance), and due to its quantum nature, it also presents a very fast response, which makes this material an excellent candidate as detector of low cost high speed infrared imagers.

Theory of operation

Lead selenide is a photoconductor material. Its detection mechanism is based on a change of conductivity of a polycrystalline thin-film of the active material when photons are incident. These photons are absorbed inside the PbSe micro-crystals causing then the promotion of

electrons The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

from the

valence band In solid-state physics, the valence band and conduction band are the bands closest to the Fermi level, and thus determine the electrical conductivity of the solid. In nonmetals, the valence band is the highest range of electron energies in w ...

to the conduction band. Even though it has been extensively studied, the mechanisms responsible of its high detectivity at room temperature are not well understood. What is widely accepted is that the material and the polycrystalline nature of the active thin film play a key role in both the reduction of the Auger mechanism and the reduction of the dark current associated with the presence of multiple intergrain depletion regions and potential barriers inside the polycrystalline thin films.

Thermoelectric properties

Lead selenide is a thermoelectric material. The material was identified as a potential high temperature thermoelectric with sodium or chlorine doping by Alekseva and co-workers at the A.F. Ioffe Institute in Russia. Subsequent theoretical work at Oak Ridge National Laboratory, USA predicted that its p-type performance could equal or exceed that of the sister compound, lead telluride. Several groups have since reported thermoelectric figures of merit exceeding unity, which is the characteristic of a high performance thermoelectric.

Manufacture of PbSe infrared detectors

Two methods are commonly used to manufacture infrared detectors based on PbSe.

Chemical bath deposition (CBD)

Chemical bath disposition (CBD) is the standard manufacturing method. It was developed in USA during the '60s and is based on the precipitation of the active material on a substrate rinsed in a controlled bath with

selenourea Selenourea is the organoselenium compound with the formula SeC(NH2)2. It is a white solid. This compound features a rare example of a stable, unhindered carbon-selenium double bond. The compound is used in the synthesis of selenium heterocycles ...

lead acetate Lead acetate can refer to: * Lead subacetate (Basic lead acetate), Pb3(OH)4(CH3COO)2 * Lead(IV) acetate Lead(IV) acetate or lead tetraacetate is an organometallic compound with chemical formula . It is a colorless solid that is soluble in nonpo ...

potassium iodine Potassium iodide is a chemical compound, medication, and dietary supplement. It is a medication used for treating hyperthyroidism, in radiation emergencies, and for protecting the thyroid gland when certain types of radiopharmaceuticals are u ...

and other compounds. CBD method has been extensively used during last decades and is still used for processing PbSe infrared detectors. Because of technological limitations associated to this method of processing, nowadays the biggest CBD PbSe detector format commercialized is a linear array of 1x256 elements.

Vapour phase deposition (VPD)

This processing method is based on the deposition of the active material by thermal evaporation, followed by thermal treatments. This method has an intrinsic advantage compared with the CBD method, which is the compatibility with preprocessed substrates, like silicon CMOS-technology wafers, and the possibility of processing complex detectors, such as the focal plane arrays for imagers. In fact, this has been the most important milestone in the last decades concerning the manufacturing of PbSe detectors, as it has opened the technology to the market of uncooled MWIR high-resolution imaging cameras with high frame rates and reduced costs.

PbSe Quantum dots based photodetectors

trioctylphosphine selenide and lead acetate react to produce nanophase lead selenide. Lead selenide nanocrystals embedded into various materials can be used as quantum dots, for example in

nanocrystal solar cell Nanocrystal solar cells are solar cells based on a substrate with a coating of nanocrystals. The nanocrystals are typically based on silicon, CdTe or CIGS and the substrates are generally silicon or various organic conductors. Quantum dot sol ...

Main manufacturers of PbSe IR detectors

* VPD method ** New Infrared Technologies
Company Web Site
* CBD method ** Laser Components
Company Web Site
** Agiltron
Company Web Site
** Cal Sensor
Company/ Web Site
** New England Photoconductor
Company Web Site
** Teledyne Judson Technologies
Company Web Site
** Infrared Materials Inc
Company Web Site

References

External links

National Pollutant Inventory - Lead and Lead Compounds Fact Sheet
{{DEFAULTSORT:Lead Selenide Lead(II) compounds Selenides IV-VI semiconductors Infrared sensor materials Rock salt crystal structure