Quantum efficiency of detector

SPC techniques are hardly affected by additive noise and multiplicative noise is absent. However, subtractive noise due to the collection efficiency and transmission of optics and the quantum efficiency of the detector do play a role. In addition, at high count rates, the efficiency goes down due to pileup effects. 

EXAMPLE 1.5 The sensitivity of luminescence. Consider a photoluminescence experiment in which the excitation source provides a power of 100 ptW at a wavelength of400 nm. The phosphor sample can absorb light at this wavelength and emit light with a quantum efficiency of r] = O.I. Assuming that kg = 10 fii.e., only one-thousandth of the emitted light reaches the detector) and a minimum detectable intensity of l(f photons per second, determine the minimum optical density that can be detected by luminescence. 

A light beam of 21 mW reaches a photoconduchon detector with a 1 mm thick active area. The absorption coefficient at 965 nm (the incident wavelength) is 23 cm Calcnlate the nnmber of carriers created per unit hme if the quantum efficiency of the process is 0.13. 

Figure 7 shows the absorption efficiency of the BaFBr calculated as a function of the X-ray photon energy. The absorption efficiency is 96% for 17keV X-rays when the phosphor is 150 pm thick. The absorption edge at 37.4 keV is due to barium. The quantum efficiency of integrating detectors, however, can not be determined by the absorption efficiency alone, because the noise level of the system causes the quantum efficiency of these detectors to deteriorate. In Fig. 8, the relative uncertainty... 

The efficiency of detectors can be discussed using a more general term called the detective quantum efficiency (DQE)... 

When a luminescence spectrum is obtained on an instrument such as that used to produce the spectra in Figure 7.23, it will depend on the characteristics of the emission monochromator and the detector. The transmission of the monochromator and the quantum efficiency of the detector are both wavelength dependent and these would yield only an instrumental spectrum. Correction is made by reference to some absolute spectra. Comparison of the absolute and instrumental spectra then yields the correction function which is stored in a computer memory and can be used to multiply automatically new instrumental spectra to obtain the corrected spectra. The calibration must of course be repeated if the monochromator or the detector is changed. 

GaN/AlGaN heterostructures for solar-blind detectors have been grown by both RMBE and PMBE. By tuning the AIGaN bandgap the cut-off wavelength has been varied from 360 to 310 nm in p-i-n photovoltaic devices [72,73], Very competitive data were achieved, regarding the responsivity of 0.15 A/W and external quantum efficiencies of over 50%. 

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