2.?The photo effect and photodiode modelAccording to Graeme [1], light entering a semiconductor material produces an electrical current URL List 1|]# by releasing hole-electron pairs. There, photons transfer energy to the atoms of the radiated material, moving these hole and electron carriers to the radiated material, moving these hole and electron carriers to their conductions states. Once there, the individual carriers may or may not contribute to current flow.Carriers released within the depletion region of a semiconductor junction produce the majority of this current due to the electric field of this region. That region contains ionized or depleted atoms that support a voltage differential across the junction.

The associated electric field accelerates the carriers toward the terminals of the diode, adding conduction energy to the carriers and reducing the probability of recombination.

Applying reverse bias to the junction expands the depletion region to encompass more of the material of the diode within the accelerating field [1].Forward bias narrows the depletion region and lowers the barrier to carrier injection. Diffusion component of current greatly increases and drift component decreases. Carrier density is large (exponential), making the junction conductive and allowing a large forward current.In photodiodes, semiconductor doping levels and the junction depth are two of the most important parameters.

The depth and extent of the junction determines the location of the depletion region and the light wavelengths that produce an efficient response.

Photons generate carriers at a range of depths with a given range proportional Dacomitinib to the photon wavelength [1].The most important characteristics of a photodiode are the following [1, 16, 17]:Spectral responseRadiometric sensitivityResponsitivityQuantum efficiencySensitivityLinearityDark currentShunt resistanceJunction capacitanceReverse breakdown voltageOpen circuit voltageResponse timeNoise currentAngular responsePackage styleAlso, according to [1, 16, 17], the equivalent circuit for a photodiode is shown in Fig. 1, where IP is light generated photocurrent, IN is noise current, RSH is the shunt resistance, RS is the series resistance, CJ is the junction capacitance, and RL is an external load resistance connected to the photodiode.

Figure 1.Equivalent circuit for a photodiode connected to a load resistance3.?The photometer circuitsDue to their excellent Brefeldin_A linearity, gain accuracy, high input resistance, high open-loop gain, low noise, low offsets and wide bandwidth, among other characteristics, operational amplifiers are commonly used in monitoring photodiodes [1, 16-18].