model of a low noise high quantum efficiency n+np Germanium Photodiode utilizing ion implantation technique and subsequent drive-in diffusion in the n layer is presented. Numerical analysis is used to study the influence of junction depth and bulk concentration on the electric field profile and quantum efficiency. The performance of the device is theoretically treated especially at the wave-length region 1. 55μ m where the Silica optical fiber has minimum attenuation loss. It has been found that at this wave-length and for the optimum device design the quantum efficiency approaches about 90%.

Introduction: Radiation imaging is one of the applicable methods in diagnostic medicine and nondestructive testing for industrial applications. In nondestructive 3D imaging, in addition to the radiation source, there is a requirement for a suitable detection system, data acquisition system, mechanical sections for moving objects, reconstruction algorithm and finally a computer for processing and control.Method and Materials: One of the most important components of a digital radiation imaging system is its detector. Light photodiode is a new light sensor which is used in digital imaging systems because of its high efficiency. In the present research, a photodiode grid has been implemented to design and make a detection system. The photodiode grid has an array of 10×10 photodiodes in a 50×50 mm2 area. Beside the photodiode grid, a control board has been designed. Furthermore, a mechanical system has been designed to move the objects in the horizontal and vertical directions, and also rotate it around its own axis. The maximum displacement in the horizontal and vertical directions is 60 cm with step accuracy of about 0.015 mm. Step accuracy of the rotational movement is about 0.9 degrees. Results: After the imaging system was constructed, background and uniformity of the system were tested. All the photodiodes in the imaging system showed good uniformity. The image data was transferred to a computer and processed using a MATLAB program to display the images on a monitor. As the physical resolution of the system is about the pixel size (5 mm), only the overall images of the object's dimensions were expected to be produced.Discussion and Conclusion: The fidelity of the detection system has been successfully tested using a visible light source and several test samples. The presented system is able to reconstruct 3D images and obtain cross-sectional images of the objects, by using the image processing algorithm specifically designed for it.

In this paper, the frequency and the time responses of a separated absorption and multiplication avalanche photodiode are studied by solving the carrier continuity equations, in the low gain regime. The discrepancy between the carrier velocities in different layers is considered for the first time. It is shown that considerable error occurs, if the device characteristics are calculated: assuming uniformly distributed velocities in the depletion layer, especially when the different layers have almost equal thickness

Using some simplifying assumptions in a separate absorption and multiplication avalanche photodiode (SAM-APD), in this paper we develop a circuit model. Then, using this circuit model, we calculate the gain and the quantum efficiency of the device. To examine the accuracy of the device, we compare the results obtained from the model with the experimental results. A fairly good correspondence between the model an the experimental results, shows that this model is capable of predicting the device behavior, while varying different parameters such as applied bias, device size, and hence the light wavelength.

Recently, research has shown that PIN photodiodes can be used in ionization radiation detection, especially in medical applications. In this research, three photodiode-based X-ray detectors have been implemented. The preamplifiers in these circuits have completely different structures,the number of pulse shaper stages and the bias of photodiodes are different. The first circuit benefits lower manufacturing costs due to its simple structure. The second circuit has a preamplifier with feedback impedance that generates pulses with a large amplitude. The third circuit has better noise than the second circuit due to the transistor preamplifier structure with a small feedback capacitor, and its gain is larger than the first circuit. The S1223-01 photodiode from Hamamatsu Corporation has been utilized in the experiments, which is excited using the 232Th. Comparing the conversion gain, dissipation power, and pulse period of these circuits, the second circuit with a gain of 66. 75-dB can be claimed to have the largest amplitude. Also, the first circuit with a noise power of 1. 215-nV2 and a dissipation power of 36. 6-mW, has recorded the lowest noise and energy consumption among others. The third circuit with a time period of 8. 2-μ, s has the lowest pulse duration and dead time.

The high-energy UV ray radiation on PIN Silicon photodiodes reduces the optimal parameters of these photodiodes. In this paper, by representing a model, we compare the effect of UV dose on the bright current in these two types of photodiodes and confirm the analytic relationships in order to simulate a model with the help of the Silvaco-Atlas software. In this model, Silicon photodiodes and Gallium Arsenide were investigated under the influence of 300nm UV source radiation in several reverse bias, and we arrived at a logical connection between the analytical and simulation results, and finally, in order to compare these two types of photodiodes, we have shown that the current of darkness in the photodiode has increased significantly with UV dose radiation. Also, the bright current in the Gallium Arsenide photodiodes is not much more than its Silicon model. This phenomenon indicates a higher sensitivity to Gallium Arsenide photodiodes.

This article is a report of calculation and measurements of a p+-n InSb photo-diode leakage current fabricated by mesa on the basis of the calculation and measurement of different leakage currents in InSb photo-diode along with its variation it shows that at relatively low reverse biases (up to about 300 mV) G-R and shunt current are dominant. But at high reverse biases the tunneling current dominates. In this article we investigate the relation between device parameters and rate of leakage currents and investigated this relation by fabricating high quality p+-n diode.