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

selenide A selenide is a chemical compound containing a selenium with oxidation number of −2. Similar to sulfide, selenides occur both as inorganic compounds and as organic derivatives, which are called organoselenium compound. Inorganic selenides Th ...

lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...

, is a

semiconductor material A semiconductor is a material with electrical conductivity between that of a Electrical conductor, conductor and an Insulator (electricity), insulator. Its conductivity can be modified by adding impurities ("doping (semiconductor), doping") to ...

. It forms

cubic crystal In crystallography, the cubic (or isometric) crystal system is a crystal system where the Crystal structure#Unit cell, unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals. There ...

s of the

NaCl Sodium chloride , commonly known as edible salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. It is transparent or translucent, brittle, hygroscopic, and occurs as the mineral hali ...

structure; it has a

direct bandgap In semiconductors, the band gap of a semiconductor can be of two basic types, a direct band gap or an indirect band gap. The minimal-energy state in the conduction band and the maximal-energy state in the valence band are each characterized by a ...

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 depe ...

s for

thermal imaging Infrared thermography (IRT), thermal video or thermal imaging, is a process where a thermal camera captures and creates an image of an object by using infrared radiation emitted from the object in a process, which are examples of infrared im ...

. The

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

clausthalite Clausthalite is a lead selenide mineral, PbSe. It forms a solid solution series with galena PbS. Occurrence It occurs in low-sulfur hydrothermal deposits with other selenides and in mercury deposits. It is associated with tiemannite, klockmann ...

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

and

selenium Selenium is a chemical element; it has symbol (chemistry), symbol Se and atomic number 34. It has various physical appearances, including a brick-red powder, a vitreous black solid, and a grey metallic-looking form. It seldom occurs in this elem ...

Infrared detection

PbSe was one of the first materials found to be sensitive to the

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

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 devices that detect light or other forms of electromagnetic radiation and convert it into an electrical signal. They are essential in a wide range of applications, from digital imaging and optical ...

in multiple applications, from

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

for gas and

flame A flame () is the visible, gaseous part of a fire. It is caused by a highly exothermic chemical reaction made in a thin zone. When flames are hot enough to have ionized gaseous components of sufficient density, they are then considered plasm ...

detection to infrared

fuze In military munitions, a fuze (sometimes fuse) is the part of the device that initiates its function. In some applications, such as torpedoes, a fuze may be identified by function as the exploder. The relative complexity of even the earliest fu ...

s for artillery ammunition or Passive Infrared Cueing systems (PICs). As a sensitive material to the

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 Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those of ...

– 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 Photoconductivity is an optical and electrical phenomenon in which a material becomes more electrically conductive due to the absorption of electromagnetic radiation such as visible light, ultraviolet light, infrared light, or gamma radiation. W ...

material. Its detection mechanism is based on a change of conductivity of a polycrystalline thin-film of the active material when

photons A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that ...

are incident. These photons are absorbed inside the PbSe micro-crystals causing then the promotion of

electrons The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

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 ...

to the

conduction 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 ...

. 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 Lead telluride is a compound of lead (element), 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 0.3 ...

. 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 chemical formula . 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. S ...

lead acetate Lead () is a chemical element; it has symbol Pb (from 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 cut, lea ...

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 Trioctylphosphine is an organophosphorus compound with the formula P(C8H17)3 sometimes abbreviated TOP. It is usually encountered as a syrup. The compound is colorless. Reactions Trioctylphosphine reacts with oxygen to form trioctylphosphine ox ...

and lead acetate react to produce nanophase lead selenide. Lead selenide nanocrystals embedded into various materials can be used as

quantum dot Quantum dots (QDs) or semiconductor nanocrystals are semiconductor particles a few nanometres in size with optical and electronic properties that differ from those of larger particles via quantum mechanical effects. They are a central topic i ...

s, for example in nanocrystal solar cells.

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