engineering

Lead selenide

Lead selenide is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Lead selenide rather than just read about it. In short: Lead selenide (PbSe), or lead(II) selenide, a selenide of lead, is a semiconductor material. It forms cubic crystals of the NaCl structure; it has a direct bandgap of 0.27 eV at room temperature.

Key takeaways

Lead selenide belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Lead selenide to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Lead selenide from memory before moving on to harder problems.

Reference excerpt

Lead selenide (PbSe), or lead(II) selenide, a selenide of lead, is a semiconductor material. It forms cubic crystals of the NaCl 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 detectors for thermal imaging. The mineral clausthalite is a naturally occurring lead selenide. It may be formed by direct reaction between its constituent elements, lead and selenium.

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 infrared detector 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 in multiple applications, from spectrometers 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 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 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 from the valence band 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, lead acetate, potassium iodine 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 an 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 cells.

See also Infrared detector Black-body radiation Hyperspectral imaging Infrared camera Infrared filter Infrared homing Infrared signature Infrared solar cells Infrared spectroscopy Other infrared detector materials: Indium antimonide, Indium arsenide, Lead sulfide, QWIP, QDIP, Mercury cadmium telluride, PbS, Microbolometers, InGaAs

References

Barrow, R. F.; Vago, E. E. (1944). "An emission band-system of PbSe". Proceedings of the Physical Society. 56 (2): 76–78. Bibcode:1944PPS....56...76B. doi:10.1088/0959-5309/56/2/302.

External links National Pollutant Inventory - Lead and Lead Compounds Fact Sheet

Illustrations

Worked examples

Example 1 — a first encounter with Lead selenide

Start with the simplest possible case. Write down what Lead selenide claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Lead selenide before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Lead selenide ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Lead selenide

In research: Lead selenide appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Lead selenide in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Lead selenide is common in secondary-school and first-year university syllabi. It links to neighbouring topics IV-VI semiconductors, Infrared sensor materials, Lead(II) compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Lead selenide outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Lead selenide in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Lead selenide means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Lead selenide out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Lead selenide in simple terms?

Lead selenide (PbSe), or lead(II) selenide, a selenide of lead, is a semiconductor material. It forms cubic crystals of the NaCl structure; it has a direct bandgap of 0.27 eV at room temperature.

Why does Lead selenide matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Lead selenide?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Lead selenide.