Self-powered Broadband and Ultrafast Photoresponse using InN and InGaN grown on AlN/Si (111) by Plasma-assisted Molecular Beam Epitaxy
Group III-nitride semiconductors have enabled revolution in solid-state lighting and high-power/high-frequency electronics. Now-a-days, III-nitride based photodetectors are of great importance because of their various applications from everyday consumer electronics such as compact disc players, smoke detectors, remote control etc. to more elegant applications such as environmental monitoring, space research and in optical communications. Materials such as AlN and AlGaN have been used as solar blind photodetectors, whereas AlGaN and GaN based devices have been extensively used as UV photodetectors that depend on the concentration of Ga. On the other hand, InGaN and InN based devices are well-established for broad band and infrared photodetection applications, respectively. The key point of a broad band photodetector is that it occupies multiple wavelength region and therefore, allows much higher throughput over a single medium. Furthermore, along with broad band detection, the infrared detection in the optical telecommunication range (1550 nm) is also a demanding research area in the scientific community. Most of the photodetectors require an applied bias for appreciable detectivity, which needs a constant electrical power source. However, a self-powered photodetector can operate at zero bias without any external power source. The self-powered photodetectors such as p-n junction, heterojunction, Schottky junctions and organic/inorganic hybrid junctions can immediately separate the electron-hole pairs due to the built-in electric field, exhibiting faster photo response and higher responsivity at zero bias. Therefore, InN and InGaN based self-powered photodetectors in the present work will enthuse the scientific community considering the recent energy crisis. In our work, we have optimised InN epilayer on AlN/Si (111) template and achieved the self-powered infrared photoresponse with appreciable responsivity. Furthermore, InGaN epilayers were grown on AlN template to realize the UV and visible photodetection. We had grown three InGaN epilayers on AlN template with different Indium concentration. The point defects dominate on lower indium content sample due to hydrostatic strain and trench and sub-interfacial extended defects dominate on higher indium content sample due to in-plane biaxial strain. Moreover, the localised states dominate on higher indium content sample over electron-phonon interaction and therefore, we have chosen the InGaN sample with low In content for UV-Visible photodetection. The InGaN/AlN/n-Si (111) devices exhibit excellent self-powered photoresponse under UV-Visible (300-800 nm) light illumination. Furthermore, to cover the broad band range and as well as the infrared optical fibre communication range (1550 nm) with the help of binary (InN) and ternary (InGaN) compounds we have combined the InN binary layer with InGaN ternary layer in the form of nanorods and epilayer junction. The InN nanorods and InGaN epilayers were grown on AlN/n-Si (111) template by using plasma-assisted molecular beam epitaxy. The device structure displays outstanding self-powered photodetection from UV, visible to infrared (300 – 800 nm and 1550 nm) wavelength range. This work is thus believed to make a great impact in nanoelectronics, optoelectronics and in optical fibre communication due to its superior device structure.