In the specific case of a photodetector, it measures the electrical output per optical input. A photodetector’s responsivity is usually expressed in units of amperes or volts per watt of incident radiant power. , the wavelength of the optical signal, and has units of amperes per watt (A/W).

What is the responsivity of a light detector?

Responsivity is defined as the output signal (typically voltage or current) of the detector produced in response to a given incident radiant power falling on the detector.

How is responsivity of photodiode calculated?

A photodetector should ideally be operated in a spectral region where its responsivity is not far below the highest possible value, because this leads to the lowest possible detection noise and thus to a high signal-to-noise ratio and high sensitivity….

How is responsivity of detector measured?

Photodetector responsivity (defined by Equation 1.2. 2 in Chapter 1) is a measure of optical-to-electrical conversion efficiency of a photodetector and is usually expressed by the value of the photocurrent (mA) generated by each milliwatt of optical signal.

How is responsivity calculated?

You need to know the spectral irradiance which is the incident irradiation power per wavelength interval at the different wavelength of the measurement range. Assuming this power is P(lambda) watt/ um , Then you obtain the responsivity by dividing the total current to the total power.

What is detector response time?

In case of a pulsed source of light, the detector response time is considered as either the rise time or fall time required for the output signal to change from 10% to 90% of its final value or vice versa.

What is the cutoff wavelength of a photodetector?

The long end of the spectral response of GaAs photodiodes is limited by the bandgap energy of GaAs which is 1.42eV (corresponding to about 870nm).

Why does responsivity increase with wavelength?

With the increase of wavelength, the energy per photon becomes smaller, and each photon is still able to generate a carrier but with a lower energy. Therefore the responsivity becomes higher at longer wavelengths.

What are the requirements of a photo detector?

Depending on the application, a photodetector has to fulfill various requirements: It must be sensitive in a certain spectral region (range of optical wavelengths). In some cases, the responsivity should be constant or at least well defined within some wavelength range.

What is photodiode response time?

Photodiode response time is the root mean square sum of the charge collection time and the RC time constant arising from series plus load resistances and the junction and stray capacitances. Charge collection time is voltage dependent and is made up of a fast and a slow component.

What is the difference between sensitivity and responsivity?

As nouns the difference between responsivity and sensitivity is that responsivity is a measure of responsiveness while sensitivity is the quality of being sensitive.

What is the relation between quantum efficiency and responsivity *?

Quantum Efficiency is defined as the ratio of number of electrons collected to the number of incident photons. It is also defined as ratio of generated current flux to input photon flux. Responsivity: It represents the sensitivity of a photodetector.

How do you find the responsivity of a photodiode?

As an example, for a photodiode operating at 1550 nm wavelength, if the quantum efficiency is η = 0.85, the responsivity can be easily found with Eq. (4.2.1), as ℜ ≈ 1.06 [mA/mW]. As a rule of thumb, for a typical photodiode, 1 mW of optical power should produce about 1 mA photocurrent. View chapter Purchase book.

What is the photovoltaic effect on silicon detectors?

Through the photovoltaic effect, silicon detectors provide a means of transforming light energy to an electrical current. The root of the theory behind this phenomenon is a small energy gap between the valence and conduction bands of the detector.

How do you calculate the quantum efficiency of a photodiode?

It can be calculated according to. where h ν is the photon energy, η is the quantum efficiency, and e the elementary charge. For example, a photodiode with 90% quantum efficiency at a wavelength of 800 nm, the responsivity would be ≈ 0.58 A/W.

What are the advantages and disadvantages of a photodiode?

This makes it ideal for low signal detection. One disadvantage is the slightly lower responsivity at higher wavelengths (see graph). Photoconductive (biased): During photoconductive (PC) operation, a reverse bias on the photodiode results in a number of response advantages, such as a faster rise time.