Effect of In as Surfactant on the Growth of AlN/GaN Distributed Bragg Reflectors by Metal Organic Vapor Phase Epitaxy

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1108-A09-18

Effect of In as surfactant on the growth of AlN/GaN Distributed Bragg Reflectors by Metal Organic Vapor Phase Epitaxy L. E. Rodak1 and D. Korakakis1,2 1. Lane Department of Computer Science and Electrical Engineering, West Virginia University, Morgantown, WV 26506-6109 2. National Energy Technology Laboratory, 3610 Collins Ferry Road, Morgantown, WV 265070880 ABSTRACT Nitride based distributed Bragg reflectors (DBRs) have several important applications in current nitride based optoelectronic devices. DBRs can be implemented in resonant cavity light emitting diodes (RCLEDs) to improve light extraction and obtain a more directional emission and in vertical cavity surface emitting lasers (VCSELs) to achieve a lower threshold current. Due the large contrast in refractive index, AlN/GaN DRBs are practical for obtaining high reflectivity and wide bandwidth using relatively few periods. Cracking of the samples is typical for AlN/GaN DRBs due to the tensile strain which results from the 2.4% lattice mismatch and to the difference in thermal expansion coefficients. In addition to cracks, v-shaped defects may also arise in the surface due to surface undulation from stored elastic misfit strain or from threading dislocations that result in scattering and diffraction. Several techniques to reduce the number of cracks and defects have been investigated to obtain smooth surface morphology and high reflectivity, e.g. superlattices to reduce the strain or the growth of AlInGaN/GaN DBRs that offer less lattice mismatch but also lower refractive index contrast. In this work, results of the use of Indium (In) as a surfactant in Metal Organic Vapor Phase Epitaxy (MOVPE) will be discussed. This study addresses AlN/GaN DBR structures designed for peak reflectivity around 465 nm. During the AlN layers’ growth, trimethylindium was introduced to the system and resulted in a reduction of surface cracks. Results of growths at In flow rates are reported and discussed. INTRODUCTION III-Nitride based semiconductors are of significant interest for the fabrication of optoelectronic devices, such as Light Emitting Diodes (LEDs) and Laser Diodes (LDs), primarily due to the ability to engineer the emission across the visible spectrum and into the ultra violet regime by adjusting the molar concentration. As research efforts are focusing on the fabrication of vertical structures such as Resonant Cavity LEDs (RCLEDs)1 and Vertical Cavity Surface Emitting Lasers (VCSELs)2, considerable attention is being paid to the epitaxial growth of high quality Distributed Bragg Reflectors (DBRs)3,5,6 for use as wavelength specific mirrors in such structures. Within the III-Nitride material system, Aluminum Nitride (AlN) and Gallium Nitride (GaN) have the largest contrast in refractive index and enable high reflectivity to be achieved with the fewest number of DBR periods. Furthermore, the large contrast in refractive index results in a larger bandwidth. As the emission wavelength of Indium Gallium Nitride (InxGa1xN)/GaN Multi Quantum Wells (MQWs) can be