Band Gap Engineering of Nano Scale AlGaN Epitaxial Layers by Swift Heavy Ion Irradiation
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Band gap engineering of nano scale AlGaN epitaxial layers by Swift Heavy Ion irradiation N Sathish1, G Devaraju1, N Srinivasa Rao1, A P Pathak*1, A Turos2, S A Khan3, D K Avasthi3, E.Trave4 and P. Mazzoldi4 1
School of Physics, University of Hyderabad, Hyderabad – 500 046,India Institute of Electronic Materials Technology, 01-919 Warsaw, ul. Warsaw, Poland. 3 Inter-University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110 067, India 4 Dip. Fisica “G.Galilei”, Università di Padova, via Marzolo 8, 35131 Padova, Italy 2
ABSTRACT Epitaxial AlGaN/GaN layers grown by MBE on SiC substrates were irradiated with 150 MeV Ag ions at a fluence of 5x1012 ions/cm2. AlGaN/GaN Multi Quantum Wells (MQWs) were grown on Sapphire substrate by Metal Organic Chemical Vapour Deposition (MOCVD) and irradiated with 200 MeV Au8+ ions at a fluence of 5x1011 ions/cm2. These samples were used to study the effects of Swift Heavy Ions (SHI) on optical properties of AlGaN/GaN based nano structures. Rutherford Back Scattering (RBS) /Channelling measurements were carried out at off normal axis on irradiated and unirradiated samples to extract strain. In as grown samples, AlGaN layer is partially relaxed with a small compressive strain. After irradiation this compressive strain increases by 0.22% in AlGaN layer. Incident ion energy dependence of dechannelling parameter shows E1/2 dependence, which corresponds to the dislocations. Defect densities were calculated from the E1/2 graph. As a result of irradiation defect density increased on both GaN and AlGaN layer. Optical properties of AlGaN/GaN MQWs before and after irradiation have been analyzed using PL. In this study, we present some new results concerning high-energy irradiation on AlGaN/GaN heterostructures and MQWs characterized by RBS/Channelling and Photo Luminescence (PL).
----------------*Corresponding author. Tel.: +91 40 23010181 / 23134316 Fax: +91 40 23010181 / 23010227. & [email protected] (A.P. Pathak). E-mail address: [email protected]
INTRODUCTION III- Nitride semiconductors are a novel class of materials for optoelectronics & high power, high temperature device applications and are used in wide range of optical devices like Blue Light Emitting Diode (LED) to violet laser diode (LD) & UV photo detectors and High Electron Mobility Transistors (HEMTs). These materials are the best candidates for microwave electronics for base stations of cell phones. AlGaN/GaN MQWs also have numerous optoelectronic applications including semiconductor photodiodes. Quantum well interdiffusion technology has become increasingly important in the drive towards fabrication of photonic integrated circuits due to its versatile band gap tuning process [1,2]. SHI beam deposits energy via Electronic energy loss mechanism and create defects into the quantum well active region, which allows atomic diffusion to take place between the quantum well and barrier materials. Recently we have demonstrated strain modification in lattice-matched heterostructures using SHI and extensively strain
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