Detector Materials alloys

Several close relatives of Pb,. Sn Te have been studied also as photovoltaic detector materials, but they do not have significantly different properties. These variations include Pb, j Sn Se as an alternative alloy system and Pb,, Ge,jTe with small amounts of Ge to give a material with a slightly wider energy gap than PbTe for 3-5 pm detectors. See Appendix C and [4.3]. 

These materials include compounds and alloys formed between elements of groups IV and VI of the periodic table. The properties of the narrow-gap semiconductors of this class which are useful in infrared photon detectors have been reviewed in detail very recently by Harman and Meingailis [4.3], so that we will only summarize here those properties needed in this chapter. The alloy systems Pbi j.Sn Te, Pbi jjSnjj Se and Pb, Ge Te have all been studied as detector materials, but Pbj Sn Te has received the most emphasis. Accordingly, we will review the properties only of Pbj j(Sn Te in this appendix the other materials are analogous. 

Recently, increasing technology development has been devoted to photovoltaic Pb, jjSn,Se and Pb, Sn S alloys while interest in Hg,, Sn Te has been decreasing. Interest in doped Si as infrared detector material remains high. In this update, we shall briefly review the most significant recent results for these materials. No important additions have been made recently to the theory given in Chapter 4. 

Lead(II) sulfide occurs widely as the black opaque mineral galena, which is the principal ore of lead. The bulk material has a band gap of 0.41 eV, and it is used as a Pb " ion-selective sensor and IR detector. PbS may become suitable for optoelectronic applications upon tailoring its band gap by alloying with II-VI compounds like ZnS or CdS. Importantly, PbS allows strong size-quantization effects due to a high dielectric constant and small effective mass of electrons and holes. It is considered that its band gap energy should be easily modulated from the bulk value to a few electron volts, solely by changing the material s dimensionality. 

Electronic and Optoelectronic Applications of Tellurides. Most metal tellurides are semiconductors with a large range of energy gaps and can be used in a variety of electrical and optoelectronic devices. Alloys of the form HgCdTe and PbSnTe have been used as infrared detectors and CdTe has been employed as a gamma, ray detector and is also a promising candidate material for a thin-film solar cell. 

There are many elements and alloys that possess the electrical property known as band gap [5] that are useful for semiconductor devices. Silicon became the lynchpin material for device fabrication. It is currently, and will continue to be, the most important material for integrated circuit fabrication. Alloys of group III and V elements are important for optical devices such as lasers, optical detectors, and specialized high-speed circuits. In this paper, the fabrication of silicon devices will be used to illustrate the role of chemical processing in circuit manufacture. 

EDAX analysis of these materials, as illustrated in Figures 2b and 3b, shew little difference between the samples with the exception of the silicon peak found in the carbon-silicon alloy. It should be noted that EDAX is inherently insensitive to the lower atomic number elements due to the low fluorescent yields of the lighter elements, internal absorption, and low transmission factors for these elements through the beryllium detector window of the instrument. Thus, carbon and oxygen are notably absent from the conventional EDAX spectra. 

---