IR-photoconductors

Other hand, the spectral range matched well to the diode laser wavelengths (750-850 nm). Thus phthalocyanines are primarily developed as IR photoconductors for diode laser printers. 

Naphthalocyanines are metallic green powders in the solid state. Due to the extended conjugation, the solution Amax of naphthalocyanines are at 750-850 nm, red-shifted by 100 nm relative to those of phthalocyanines [128]. The thin films of naphthalocyanines also absorb in the same spectral region [129-131]. Although naphthalocyanines have been studied as IR photoconductors [130,131], they are less likely to be developed into any future products because of the higher material cost and the practical success of phthalocyanines. 

The intermetallic compounds with Group 16 (VIA) elements including CdS, CdSe, and CdTe have interesting semiconductor properties for photoconductors, photovoltaic cells, and ir windows. Cadmium sulfide is widely used as a phosphor in television tubes. 

Infrared detectors and sources are of interest for thermal imaging and remote chemical sensing. Photodiodes and photoconductors are used as IR detectors, and injection lasers are used as IR sources. These devices require semiconductors with very small energy gaps to absorb or emit IR photons. 

As shown in Table 25-2, there are two general types of transducers one type responds to photons, the other to heat. All photon detectors are based on the interaction of radiation with a reactive surface either to produce electrons (photoemission) or to promote electrons to energy states in which they can conduct electricity (photoconduction). Only UV, visible, and near-IR radiation possess enough energy to cause photoemission to occur thus, photoemissive detectors are limited to wavelengths shorter than about 2 p.m (2000 nm). Photoconductors can be used in the near-, mid-, and far-IR regions of the spectrum. 

At a difference with thermal detectors, the background noise of photoconducting detectors is frequency-dependent. If it is assumed that the photoconductor is used to detect radiation at a frequency just above its cut-off frequency z/c, the detectors with a cut-off in the near IR display a much smaller background noise than those with a cut-off at lower energies. This is because in the near IR, the black body emissivity contribution at room temperature and below is very small. 

Lead sulfide is a photoconductor with an exceptionally high response in the near IR-region. It has been prepared by atomic layer epitaxy using lead halides, lead acetate or lead bis(/3-diketonate) compounds as the lead source and H2S as the sulfur source [132]. Another route to PbS is atomic layer epitaxy using Pb40(0-r-Bu)f, or polymeric [Pb(0-f-Bu)2] and H2S as precursors [133]. 

Fig. 6.8a and b. The use of CCD registers for TDI. (a) IR active CCD register (monolithic focal plane array with photogeneration in the register), (b) Direct injection with Si parcel in series out CCD register hybrid with IR photodiodes or monolithic with silicon IR extrinsic photoconductors... 

Fig. 6.9. Monolithic IR focal plane using extrinsic photoconductivity in silicon. The CCD material can be grown epitaxially on the IR detector material. A longitudinal detector bias is used with L, being the interelectrode spacing for the photoconductor...

Photoconductor (PC detector) IR radiation changes electric conductivity of semiconductor material... 

Figure 3.9 shows electron concentration profiles, and Fig. 3.10 hole distribution for various reverse bias voltages for the case of an n exclusion photoconductor with gradient junction. The length of the whole structure was 5 pm, material HgCdTe with composition x = 0.205 at a temperature of 295 K. This composition is optimal for an IR wavelength of 7.5 pm. 

OPVs are suitable for various applications in materials science Organic light emitting diodes (OLED), field-effect transistors (FET), semiconductors (doped), photoconductors, solar cells, photovoltaic devices, optical brighteners, laser dyes, nonlinear optics (NLO), optical switching, imaging techniques, photoresists and liquid crystals [la-e, Ij-o, Ir, Iv, 27, 120]. Among these applications, two fields will be selected here, namely NLO and electroluminescence studies. 

---