Lead, PbSe

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. 

Aqueous electrolytes proposed in the literature for cathodic electrodeposition of lead selenide are generally composed of dissolved selenous anhydride and a lead salt, such as nitrate or acetate. Polycrystalline PbSe films have been prepared by conventional electrosynthesis from ordinary acidic solutions of this kind on polycrystalline Pt, Au, Ti, and Sn02/glass electrodes. The main problem with these applications was the PbSe dendritic growth. Better controlled deposition has been achieved by using EDTA in order to prevent PbSeOs precipitation, and also acetic acid to prevent lead salt hydrolysis. 

Similar to PbSe, the controlled growth of lead telluride, PbTe, on (111) InP was demonstrated from aqueous, acidic solutions of Pb(II) and Cd(II) nitrate salts and tellurite, at room temperature [13]. The poor epitaxy observed, due to the presence of polycrystalline material, was attributed to the existence of a large lattice mismatch between PbTe and InP (9%) compared to the PbSe/InP system (4.4%). The characterization techniques revealed the absence of planar defects in the PbTe structure, like stacking faults or microtwins, in contrast to II-VI chalcogenides like CdSe. This was related to electronic and structural anomalies. 

The lead precursor in PbSe film deposition was lead acetate complexed with triethanolamine. The growth rate for PbSe was 0.18-0.16nm/cycle. The films were polycrystalline (i.e., cubic) without preferred orientation. The stoichiometry of SILAR-grown PbSe was found to be 1 1 within the limits of the RBS technique. Impurities detected were 5 at.% of oxygen and 8 at.% of hydrogen.103... 

Lead nitrate complexed with EDTA and lead perchlorate and sodium sulphide have been used for PbS ECALE-deposition.158159 The films were cubic and highly (200) oriented, and AFM images showed the same cubic structure.158159 PbSe films were also cubic, and the band gap of a film after 50 deposition cycles was 8000cm-1.160 PbSe/PbTe superlattices, with 4.2-nm and 7.0-nm periods, have been grown by ECALE.161 The (111) reflection in the XRD pattern showed a first-order satellite peak and one second-order peak, indicating the formation of the superlattice. AFM images of the superlattice structure showed a small amount of three-dimensional growth.161... 

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. 

PbSe lead selenide RMSEP root-mean-squared error of... 

Romero, H. E., and M. Drndic. Coulomb Blockade and Hopping Conduction in PbSe Quantum Dots. Available online. URL http //prola. aps.org/abstract/PRL/v95/il5/el56801. Accessed September 24, 2009. The researchers crafted quantum dots made of lead and selenium, and adjusted the packing to turn the solid from a nonconductor into a semiconductor. 

Gobet and Matijevic (17) produced monodisperse submicrometer-size particles of cadmium selenide (CdSe) and lead selenide (PbSe) by reversible release of selenide ions from selenourea in solutions of the corresponding metal salts. The equilibrium between selenourea and selenide ions is written as follows ... 

Fig. 3.2 XRD spectra showing the process of PbSe formation from the reaction of precipitated hydrated lead oxide with Na2SeS03 solution, (a) Starting material (b-e) after 1.5, 3, 4.5, and 6 mn reaction, respectively. (Adapted from Ref. 46.)... 

For low selenosulphate concentrations, only the small crystals were formed, even in thicker films, and this was rationalized by the lower steady-state selenide concentration, which would favor cluster growth over ion-by-ion formation (the product of free lead and selenide ions needs to be larger than the solubility product of PbSe for ion-by-ion deposition to occur). An important difference between the citrate depositions and the NTA or hydroxide ones is that, even in the ion-by-ion citrate deposition, some low concentration of colloidal hydrated oxide was present, due to the relatively low complexing strength of citrate. The pH of the hydroxide baths (> 13) was much higher than that of the citrate or NT A baths (10.8). 

Other complexants have been used for PbSe deposition. Triethanolamine was used in one study [66]. While deposition occurred over a wide range of temperatures, optimum results (in terms of rate of deposition and film thickness) were obtained at a deposition temperature of 75°C. In another study, lead nitrate was dissolved in an excess of hydroxide and excess selenosulphate was also used as an additional complexant [67]. The pH was 10 (adjusted with acetic acid), and depo-... 

A variation of the CD process for PbSe involved deposition of a basic lead carbonate followed by selenization of this film with selenosulphate [64]. White films of what was identified by XRD as 6PbC03-3Pb(0H)2-Pb0 (denoted here as Pb—OH—C) were slowly formed over a few days from selenosulphate-free solutions that contained a colloidal phase and that were open to air (they did not form in closed, degassed solutions). CO2 was necessary for film formation—other than sparse deposits, no film formation occurred of hydrated lead oxide under any conditions attempted in this study. Treatment of these films with selenosulphate solution resulted in complete conversion to PbSe at room temperature after 6 min. The selenization process of this film was followed by XRD, and it was seen to proceed by a breakdown of the large Pb—OH—C crystals to an essentially amorphous phase of PbSe with crystallization of this phase to give finally large (ca. 200 nm) PbSe crystals covered with smaller (15-20 nm) ones as well as some amorphous material. 

Films were deposited from solntions of lead and tin salts (the salts used were not specified) with ammoninm acetate, ethylenediamine, and selenonrea at a pH > 9 (probably at least 11) [34]. To obtain thicker films, deposition was repeated a nnmber of times and the films were annealed therefore it is not known if solid so-Intion formation occnrred in as-deposited films. In annealed films, Pbi -j Snj Se solid solntions with x np to 0.11 were verified by XRD. The spectral response of the photoconductivity of the (annealed—as-deposited films were not photosensitive) films shifted from a peak at ca. 4 p,m (pure PbSe) to ca. 7.5 p,m (11% Sn), supporting solid solution formation of the annealed films. The room-temperature, dark resistance of the (probably annealed, but not certain) films varied from 1 to 300 kO, depending on deposition conditions. 

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