Abstract
For detecting feeble Ultra-Violet (UV) signals it is essential that front-illuminated photodetector (PD) should havethick photo-absorbing layer with thin transparent metal electrodes and antireflective coating (ARC) so as to getmore photocurrent and low dark current.Since detector geometry influences its performance, so it is very important to optimize layer thickness parameters. In proposed work fixed area Al0.5Ga0.5N/AlN/ Sapphire based Metal-Semiconductor-Metal (MSM)PDbased has been analyzed for optimum value of active layer thickness and inter-electrode thickness.In addition to take benefit of large Schottky barrierGold material has beenutilized for electrodes. It has been illustrated in past research studies that with the increase in thickness of AlGaN layer, more incident energy can be absorbed for large EHPs generation which lead to increased responsivity.However, few research papers have related the effect of variations inthickness of active layerwith electron velocity which has significant effect on dark current density, recombination rateand additionally on efficiency.So for further development and widespread implementation of AlGaN/GaN based detectors there is need to study the effect of variation in photo-absorber layer thickness on closely related performance parameters so as to select its optimum value.Current Voltage (IV)-characteristics,recombination rate, current density plots and spectral response have been investigated using Atlas-Silvaco simulation tool.In addition for electrode thickness variation,transmission and absorptionplots are alsoinvestigated. For the proposed MSM structure, it has been observed that dark current density tends to increase
 
 beyond the optimum value of thickness of AlGaN layerwith specific absorption coefficient. Good transmission of light with high spectral response can be obtained with optimum value of electrode thickness.These observations can be suitable for improving the detectivity in support of various UV detection applications requiring good sensitivity and high signal to noise ratio.
Highlights
AlxGa1-xNalloy is a direct wide bandgap semiconductor material with tunable band gap from 3.4 eV to 6.2 eV has good stability and provides fast response for UV light detection [1]
That’s why thick photo-absorbing layer is suggested for improving quantum efficiency (QE) at the cost of lower bandwidth and speed of operation [20]. it was illustrated that the absorption coefficient of III-V material increasesat shorter wavelengths and absorption of incident light remains very close to the top surface [5]
It has been observed that photocurrent or responsivity of MSM detector tends to increase with the increase in AlGaN layer thickness the recombination rate is increasing
Summary
AlxGa1-xNalloy is a direct wide bandgap semiconductor material with tunable band gap from 3.4 eV to 6.2 eV has good stability and provides fast response for UV light detection [1]. AlGaN alloy based UV detectors have wide range of applications from UV astronomy, flame detection, UVcuring of different materials, water purification, bio-sensors to more advanced applications including combustion engine control, missile plume detection and secure space-to-space communications.For most of these applications, capability of sensing very weak UV signals is often required [2,3,4,5,6,7,8,9,10]. MSM PDs have been the focus of recent research as they exhibit low dark current and wide bandwidth. They can be designed using simple planar structurewithSchottkycontacts.Low capacitance is one of the important features of MSM PD which leads to very high speed operation [3]. Finding an operational way to improve the photocurrent or responsivity of AlGaN based detectors at low dark current comes to be significant
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