Photodiodes frequency response

FIGURE 9.77 Waveguide photodiode frequency response with 10-mW optical power incident on the detector and at various detector bias voltages Vj,. 

Emmons, R.B. 1967. Avalanche-photodiode frequency response. /. Appl. Phys. 38(9) 3705-3714. 

In one of the most common types of photodiodes used for time-resolved work, the p-i-n photodiode (see Figure 12.24), the depletion layer thickness (i for intrinsic) is fabricated to obtain this optimum performance. Manufacturers usually give full specification sheets detailing, active area, time/frequency response, responsivity amps/watt (AAV) at a given wavelength, dark current, depletion layer capacitance, and bias volts such that with minimal external electronics devices can be made operative. 

A simple example of how the frequency response of an opto-electronic system is defined by its transfer function is provided by the equivalent circuit for a conventional photodiode shown in Fig. 1. 

Here i = /M. 0(g>) corresponds to the quantum efficiency of the photodiode, and except at very high frequencies where electron transport effects become important, it is effectively constant so that the frequency response is determined only by A o ). The product / C is referred to as the RC time constant, trc- The complex attenuation factor A co) = Real[A aj)] -f i Imaginary[A co) can be plotted in the complex plane as shown in Fig. 2a, noting that it has real and imaginary components given by... 

Figure 5.40. Measured frequency responses erf several PMTs and a fast photodiode 0>D). Data ire from Refs. KB and 104 and litenluie...

Not all semiconductors can be prepared in both n- and p-types. Schottky barrier photodiodes are of special interest in those materials in which p — n junctions cannot be formed. They also find application as UV and visible radiation detectors, especially for laser receivers where their high frequency response (in the gigahertz range in many cases) is of particular usefulness. See Ahlstrom and Gartner [2.41], Schneider [2.42] and Sharpless [2.43] for more detailed descriptions. 

The theoretical analysis describes the microstrip connection between the PIN photodiode and the input of the HBT amplifier by the small signal equivalent circuit. For frequency response analysis we used the small signal equivalent circuit of the OE receiver input Fig. 4. 

The PIN photodiode (C30606ECER from Judson Technologies) chip connection to the microstrip waveguide is composed from compensation inductance made by gold microstrip on the alumina carrier Li and gold wire connection L2. For calculation frequency response limit it was counted inductance L given by (3). 

In the typical setup, excitation light is provided by a pulsed (e.g., nanosecond) laser (emitting in the visible range, e.g., at 532 nm, if Mb is investigated), while the probe is delivered by a continuous-wave (cw) laser. The two beams are spatially overlapped in the sample, and the temporal changes in the optical properties (such as optical absorption or frequency shift) that follow the passage of the pump pulse are registered by a detector with short response time (relative to time scale of the processes monitored), such as a fast photodiode. 

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