PbSe detector

Lead selenide (PbSe) detectors These are similar in construction and mode of operation to lead sulfide detectors but have an enhanced infrant response to 4500 nm. The relative response curve shown in Figure 5. However, these responses are normalized in sensitivity terms. The PbSe detectors are more than 100 times less sensitive than their PbS counterparts. 

NIR reflectance spectra were collected using a Laser Precision PCM 4000 Fourier transform near-infrared (FT-NIR) spectrometer, equipped with CaF beam splitters and a thermoelectrically cooled PbSe detector. An Axiom difftise/specular reflectance attachment, set at 15" C, was used to collect the reflectance spectrum from each sample coupon. Each sample spectrum was the result of a 5 scan... 

Sources of additional information for PbS and PbSe detectors - including vendor Web sites - are provided in chronological order at the end of this chapter. 

The lead compounds PbS, PbSe, PbTe are narrow-gap semiconductors that have been widely investigated for infrared detectors, diode lasers, and thermo-photovoltaic energy converters. Their photoconductive effect has been utilized in photoelectric cells, e.g., PbS in photographic exposure meters. Integrated photonic devices have been fabricated by their heteroepitaxial growth on Si or III-V semiconductors. 

While most other techniques use a limited amount of detectors (e.g., silica for visible, photomultipliers for UV) and MIR has a small number, NIR uses many types of semiconductors for detectors. The original PbS detectors are still one of the largest used in NIR, however, indium gallium arsenide (InGaAs), indium arsenide (InAs), indium antimonide (InSb), and lead selenide (PbSe) are among the semiconductor combinations used, both cooled and ambient. 

The most important use of CD films for many years was to make PbS and PbSe films for photoconductive detectors [10]. Such detectors, made by CD, are still in use today, although they are facing competition from photovoltaic 111-V detectors. It should be noted that for good photosensitivity, air-annealing of the CD films is carried out, and this annealing treatment is connected with partial oxidation of the PbS and PbSe surfaces. 

The first apparent report in the open literature of CD PbSe for photoconductive detectors was in 1949 [53], The PbSe was deposited from a solution of PbAci and selenourea onto a predeposited (from PbAci and thiourea) layer of PbS. The PbS layer acted as a seed layer, presumably to obtain faster deposition (it was noted that the PbSe deposition was much slower than that of PbS). The photoconductivity of this film exhibited a broad maximum between 3 and 4 p,m, giving a reasonable response out to beyond 4.5 p,m (PbS drops off at 3 iJim). 

Typical materials used in NIR photoconductive detectors are PbS, PbSe, InSb and InAs (lead sulphide, lead selenide, indium antimonide and indium arsenide). 

Fig. 7.15 Detectivities D of some photoconductive and pyroelectric detector materials curve 1, PbS curve 2, InAs curve 3, HgCdTe curve 4, PbSe curve 5, InSb curve 6, L-alanine-doped TGS curve 7, LiTa03 curve 8, PZ curve 9, PVDF. (Curves 1-5 measured at 200 K curves 6-9 measured at 300 K.)...

Quantum detectors are usually made of semiconductor materials or mixtures. Some commonly used quantum detectors are made of lead sulfide (PbS), lead selenide (PbSe), indium antimony (InSb), or mercury cadmium telluride (MCT, HgTe-CdTe). The absorption of infrared radiation in quantum detectors excites electrons... 

Fig. 30. Time resolved spectroscopy. The results are presented in a "three-dimensional" plot intensity versus wave number (1400—2500 cm ) and time, a) time scale from front to rear (0—10 msec. At = 500 /xsec), b) time scale from rear to front (11—1 msec, f = 500 ftsec), c) a section of b) with enlarged time scale (4.1—3.1 msec, At — 50 fisec). The instrument used for this investigation was an Idealab IF-3 Fourier spectrometer with a PbSe (77 K) detector. The data were taken from Ref. 

Although the eommon semieonduetor materials share this basie diamond/zinc blende lattiee strueture, some semieonduetor erystals are based on a hexagonal elose-paeked (hep) lattice. Examples are CdS and CdSe. In this example, all of the Cd atoms are located on one hep lattice whereas the other atom (S or Se) is located on a second hep lattice. In the spirit of the diamond and zinc blende lattices, the complete lattice is constructed by interpenetrating these two hep lattices. The overall crystal structure is called a wurtzite lattice. Type IV-VI semiconductors (PbS, PbSe, PbTe, and SnTe) exhibit a narrow bandgap and have been used for infrared detectors. The lattice structure of these example IV-VI semiconductors is the simple cubic lattice (also called an NaCl lattice). 

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