Avalanche diodes

Mosconi, D., Stoppa, D., Pancheri, L., Gonzo, L. and Simoni, A. (2006). CMOS single-photon avalanche diode array for time-resolved fluorescence detection. IEEE ESSCIRC. 564-67. 

Niclass, C., Gersbach, M., Henderson, R., Grant, L. and Charbon, E. (2007). A single photon avalanche diode implemented in 130-nm CMOS technology. IEEE J. Sel. Top. Quant. Electron 13, 863-9. 

A photodetector with a suitable spectral response for the detection of the fluorescence emission. As mentioned above, the fluorescence of most Cr3+-activated materials consists of either the red R-lines or a broadband infrared emission with the peak wavelengths ranging from -750 to 1000 nm, or both emissions. Thus, the widely available, compact and inexpensive silicon PIN photodiodes are the most suitable photodetectors for these applications. In some particular circumstances, where high speed and high sensitivity of detection are required, a silicon-based avalanche diode could be the best alternative to the PIN photodiode, at small price premium ... 

S. Cova, A. Longoni and G. Ripamonti, Active-quenching and gating circuits for single-photon avalanche diodes (SPADS), IEEE Trans. Nucl. Sci. NS-29, 599-601 (1982). 

S. Cova, A. Lacaita, M. Ghioni, G. Ripamonti and T. A. Louis, 20ps timing resolution with single-photon avalanche diodes, Rev. Sci. Instrum. 60, 1104-1110(1989). 

T. A. Louis, G. Ripamonti and A. Lacaita, Photoluminescence lifetime microscope spectrometer based on time-correlated single-photon counting with an avalanche diode detector, Rev. Sci Instrum. 61, 11-22(1990). 

Light scattering measurements were made with an ALV DLS/SLS 5022F goniometer equipped with optical fiber coupling and an avalanche diode, with a 22 mW HeNe laser working at 632.8 nm and an ALV 5000E multi-tau correlator. 

Avalanche diodes exhibit a sharp turn at the knee, but zener diodes go through this transition more gradually. This implies that the avalanche diode is a better suppressor for transients than zener diodes. 

Photomultipliers, charge coupled devices (CCDs) and avalanche diode detectors are able to detect single photons over the visible to near-IR range with efficiencies approaching unity. The arrival of photons at a detector is not correlated, due to the quantum nature of electromagnetic radiation. Measurements of intensity as the averaged sum of photon events has a well-defined stochastic variance associated with a Poisson distribution. This variance scales as the square root of the number of photons. 

The application of modem epitaxial techniques (see Chapter 8) has led to a rapid improvement in the material quality of SiC and made practical SiC devices a reality. The applications of SiC include high-temperature, high-power devices, microwave devices (both avalanche diodes and field effect transistors), and optoelectronic devices, such as photodiodes and light-emitting diodes which emit throughout the visible spectrum into the ultraviolet. 

S. Cova, M. Ghioni, A. Lotito, I. Rech, F. Zappa, Evolution and prospects for single-photon avalanche diodes and quenching circuits, J. Mod. Opt. 15, 1267-1288 (2004)... 

L-Q. Li, L.M. Davis, Single photon avalanche diode for single molecule detection, Rev. Sci. Insfrum. 64, 1524-1529 (1993)... 

T. Louis, G.H. Schatz, P. Klein-Bolting, A.R. Holzwarth, G. Ripamonti, S. Cova, Performance comparison of a single-photon avalanche diode with a microchannel-plate photomultiplier in time-correlated single-photon counting, Rev. Sci. Instram. 59, 1148-1152 (1988)... 

Rech, I., Cova, S., Restelli, A., Ghioni, M., Chiari, M., and Cretich, M., Microchips and single-photon avalanche diodes for DNA separation with high sensitivity. Electrophoresis, 27, 3797-3804, 2006. 

The high contrast of the spectrometer is achieved either by triple passing each FP or the whole tandem setup. It results theoretically in an elevation of the apparatus function of each interferometer to the cube, which strongly enhances the contrast defined as the ratio of the maximum transmission over its minimum value. In order to achieve this high contrast, the tandem sits in a highly collimated beam between spatial filters, which also allows the stray light at the entrance to be diminished and the bandwidth at the exit pinhole in front of a photomultiplier or an avalanche diode to be selected (Fig. 2). 

Cova,S.,LoildOpi.A..andAn(heont. A-.1981,Tbw rfa Mcoeccond fcsolution widi stelk-pboton avalanche diodes. Rev. ScL butnan. 52-.408-412. 

Niclass C, Rochas A, Besse PA, Popovic R, Charbon E (2006) A 4 ps integration time imager based on CMOS single photon avalanche diode technology. Sensors Actuators A 130-131 273-281... 

In the practical applications, the concentration of luminescent species is usually very low and consequently a photomultiplier is commonly used as a detector. If the emission can be efficiently focused into a small entrance, an avalanche diode can also be used. A reasonably fast detector is anyway needed also in the frequency-domain method due to the phase error induced by the detector. StiU the requirements are not as strict as in the case of prompt organic fluorophores. In the case of the most commonly used lanthanides, the upper limit of modulation is around 100 kHz, but still the reasonably error-free phase detection requires ca. 1 MHz bandwidth from the detector and accompanying current-to-voltage preamplifier. 

The theoretical detection limit is plotted for three band-widths, 1 kHz, 1 MHz, and 1 GHz. Also shown are the corresponding pulsewidths, 0.5 ms, 0.5 /zs, and 0.5 ns. This ultimate performance is essentially only obtainable with the vacuum photomultiplier and then only within a factor of 4 (25% quantum efficiency) at wavelengths of 0.5 /xm and shorter. Avalanche photodiodes can also approach the theoretical limit at high bandwidths, as discussed in Section V.B.3. Although the avalanche diode in the Geiger mode can count individual photoevents, it is not operable in a continuous or analog signal mode. 

Fig.4.90a-d. Avalanche diode (a) schematic illustration of avalanche formation (n, are heavily doped layers) (b) amplification factor M V) as a function of the bias voltage V for a Si-avalanche diode (c) spatial variation of band edges and bandgap without external field and (d) within an external electric field... 

Such modern avalanche diodes may be regarded as the solid-state analog to photomultipliers (Sect. 4.5.4). Their advantages are a high quantum efficiency (up to 40%) and a low supply voltage (10—20 V). Their disadvantage for fluorescence detection is the small active area compared to the much larger cathode area of photomultipliers [4.114-4.115]. 

Another type of avalanche diode is the "diac." This also has a characteristic curve that is the same in both directions, because it is a symmetrical design with a PNP structure. It can be thought of as two PN diodes, back to back. Each one is designed to be able to avalanche at about 1 ma of current without being damaged. Breakdown can be as low as about 6 volts, and this goes lower after the avalanche has started, even more so than in the neon bulb. We will make use of this device in Chapter 21. As an optional experiment, it can be inserted into the curve tracer to give a curve like that in Fig. 14.4. 

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