Effect of the Load Resistance in the Linearity and Sensitivity of MIS Position Sensitive Detectors
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A15.6.1
Effect of the Load Resistance in the Linearity and Sensitivity of MIS Position Sensitive Detectors H. Águas, L. Pereira, L. Raniero E. Fortunato, R. Martins Departamento de Ciência dos Materiais/CENIMAT, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516 Caparica, Portugal ABSTRACT It is experimentally known that the linearity and sensitivity of the position sensitive detectors (PSD) are dependent on the resistance of the collecting layer and of the load resistance, mainly if the detection is based on the measurement of the photo-lateral voltage. To determine the value of the load resistance to be used in metal - insulator - semiconductor (MIS) PSDs structures that lead to the maximum value of sensitivity and linearity, we propose an electrical model through which it is able to simulate the proper sensor response and how the load resistance influence the results obtained. This model is valid for PSDs where the resistance of the collecting resistive layer is quite low (≤ 500 Ω), leading to a low output impedance. Under these conditions we conclude that the value of the load resistance should be of about 1 kΩ in order to achieve a good compromise between the linearity and the sensitivity of the PSD. This result is in agreement with the set of experiments performed. INTRODUCTION Position Sensitive Detectors (PSD) are optoelectronic devices that allow the determination of the position of a striking light beam on the sensor surface. There are several types of PDS’s based both on crystalline and amorphous silicon (a-Si:H) technology [1]. The a-Si:H technology presents several advantages, like low cost, easiness of device fabrication and higher sensitivity in the visible range of the spectrum [2,3]. Due to these advantages, several research works appeared in the last two decades [4-8]. The main goals in the PSD research are the increase in sensor length, its sensitivity and resolution, for which different types of device structures, ranging from the classical p-i-n to a multilayer system (MLS) of a-Si:H/Ti have been proposed. In the present work we investigate one dimensional PSD’s fabricated with a Metal – Insulator – Semiconductor (MIS) structure similar to the one proposed by Arimoto et. al. [9] that reported a sensor with a length of 1 cm length. In this work we report sensors with an active linear length of 6 cm, exhibiting a high sensitivity and linearity. The objective of this study was to understand the role of the load resistance RL on the final static PSD performances, function of the characteristics of the of the resistance of the top collecting layer that for the MIS sensors is several orders of magnitude lower than the one due to typical p-i-n sensors [1]. THEORETICAL MODEL Figure 1 shows a scheme of the sensor where the width (W) and the length (L) of the active region are indicated. It is also shown the external connections, where the load resistances (RL) and the voltmeter (V) used to measure the lateral photo-voltage is indicated. Figure 2 shows the equiv
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