Extraction Photodiodes

The most widely used effect for Auger process suppression in infrared MWIR and LWIR photonic detectors is minority carrier extraction. This is a phenomenon appearing on reversely biased p-n junction, i.e., it is connected with diode-type 

3 Charge Carrier Management (Thermal Noise Engineering) 

Minority carrier extraction can be described as follows (e.g., [360]). Let us consider a schematic presentation of carrier distribution in a p-n junction (Fig. 3.23). 

If we assume that the applied electric fields are low enough, according to the continuity equation the electron spatial distribution will be 

Here L denotes electron diffusion length, much shorter than the width of the quasineutral region in p-type semiconductor. If the p-n junction is reversely biased so that qUIki T 1, the electron concentration becomes 

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The whole concept of extraction photodiodes poses a practical problem, since the requirement exists that the active region thickness must be smaller than the diffusion length. Such a requirement poses design restrictions regarding the absorption path and the total detector active area. One of the approaches utilized to solve the above problem was not to use a single detector but rather a densely packed matrix of separate elements with lateral contacts on a joint substrate and with a joint exclusion junction (Fig. 3.28a) [376]. 

Fig. 3.29 Saturation current density versus operating temperature for various compositions of the active area in a mercury cadmium telluride extraction photodiode limited by radiative processes. The active region width w = 2 pm...

A conclusion is that in homojunction extraction photodiodes whose active area is always extrinsic it is much more convenient to use p-t) e doping, while the performance becomes approximately equal in pseudoextrinsic active regions (extrinsic only after bias is applied). 

Figure 3.39 shows spatial distribution of photoelectric gain within a p jin mercury cadmium extraction photodiode for different bias voltages. The detector parameters are given in the Fig. 3.39. Gain is given for the whole stmcture, including not only the depleted region, but also highly doped parts. An important...

Figure 3.42 shows the dependence of current sensitivity of a homojunction mercury cadmium telluride p Tin extraction photodiode on bias voltage. The signal current was calculated as the dilference between the dark current (obtained by van Roosbroeck-Shockley s model for ag-r term according to (1.85)-(1.86), i.e., without optical generation) and the current of illuminated detector (the optical term (1.80) is added to the g-r term for the dark current. The definition of sensitivity was used (signal current divided by the optical power of monochromatic excitation near the detector cutoff). 

Oscillations in the circuits with negative differential resistance are brought into connection with alternating charging and discharging of very small parasitic capacitances, so that the RC constant is also small and thus the oscillation frequency is high. In the course of their work on extraction photodiodes Elliott et al. [361] avoided... 

The nonequiUbrium depletion and the increase of dynamic resistance in magnetoconcentration detectors is lower than in the case of heterostructure extraction photodiodes, but significantly better than in exclusion-based isotype devices under similar working conditions (lower dark currents and higher operating temperatures). 

The concept of the magnetoconcentration-extraction combination (or, more accurately, magnetoconcentration-extraction-exclusion) is actually similar to the one described in the above section. Basically, one places a nonequilibrium extraction diode into a crossed electric and magnetic field, as shown in Fig. 3.75. This device could potentially offer the best performance of all nonequilibrium detectors, since it further enhances the operation of the extraction photodiode which already furnished superior performance. 

J. Piotrowski, A. Jozwikowska, K. Jozwikowski, R. Ciupa, Numerical analysis of longwavelength extracted photodiodes. Infrared Phys. 34(6), 565-572 (1993)... 

Z. JakSic, Z. Djuric, Extraction Photodiodes with Auger Suppression for All-Weather Free-Space Optical CommunicatioiL Electronics 8(1), 30-32 (2004)... 

A method which uses supercritical fluid/solid phase extraction/supercritical fluid chromatography (SE/SPE/SEC) has been developed for the analysis of trace constituents in complex matrices (67). By using this technique, extraction and clean-up are accomplished in one step using unmodified SC CO2. This step is monitored by a photodiode-array detector which allows fractionation. Eigure 10.14 shows a schematic representation of the SE/SPE/SEC set-up. This system allowed selective retention of the sample matrices while eluting and depositing the analytes of interest in the cryogenic trap. Application to the analysis of pesticides from lipid sample matrices have been reported. In this case, the lipids were completely separated from the pesticides. 

Soxhlet extraction followed by liquid chromatography/photodiode-array detection (LC/PAD) is used for the trace determination of propanil and its major metabolite, 3,4-dichloroaniline, in soil. A 10-g soil sample is extracted with methanol in a Soxhlet system for 8 h. After the extracts have been concentrated to dryness, the residue is dissolved in 500 pL of n-hexane. °... 

Membrane separation coupled on-line to a flow-injection system was employed for the monitoring of propazine and terbutryn in natural water. A microporous hydro-phobic membrane was utilized in which the analytes were extracted from the aqueous medium into an organic solvent that was carried to the flow cell of a photodiode-array spectrophotometer. The LCDs were 4-5 qg so the technique could potentially be used for screening purposes. Samples with positive detection would require further analysis. 

Tarantilis, P. A., G. Tsoupras et al. (1995). Determination of saffron (Crocus sativa L.) components in crude plant extracts using hihg-performance liquid chromatography-UV-visible photodiode array detection-mass spectrometry. J. Chromat. A 699 107-118. 

Herrera MC and Luque de Castro MD. 2005. Ultrasound-assisted extraction of phenolic compounds from strawberries prior to liquid chromatographic separation and photodiode array ultraviolet detection. J Chromatogr A 1100(1) 1 —7. 

Revilla E and Ryan JM. 2000. Analysis of several phenolic compounds with potential antioxidant properties in grape extracts and wines by high-performance liquid chromatography—photodiode array detection without sample preparation. J Chromatogr 881(1-2) 461 169. 

Figure 3.5 Three-dimensional display of the photodiode array absorbance data obtained by HPLC/PDA/MS for a M. truncatula extract. The first dimension is HPLC retention time, second is wavelength, and third is absorbance. The data can be rapidly previewed for specific absorbance regions characteristic of functional groups.

Duverneuil and coworkers (2003) have developed a method for the determination of 11 of the most commonly prescribed non-tricyclic antidepressants and some of their metabolites these include paroxetine, fluoxetine, norfluoxetine, sertraline, citalopram, fluvoxamine mirtazapine, venlafaxine, and 0-des-methylvenlafaxine. The method involves an LLE procedure followed by an HPLC separation with photodiode-array UV detection at three different wavelengths (220, 240, and 290 nm). The total run time was 18 min. The extraction recoveries were calculated to be in the range of 74-109% and the lower limit of detection (LLOD) reported was 2.5-5 ng/ml. A method published by Tournel and associates (2001) also reported the simultaneous determination of several newer antidepressants by RP-HPLC with UV detection. The compounds were isolated from human serum using an LLE process. The LLOQ ranged from 15-50 ng/ml depending on the analyte of interest. The total run time for all compounds eluted was approximately 20 min. 

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