Dependency of Indium Concentration on Structural Defects in MOVPE-grown InGaN/GaN Heterostructures

Abstract

Indium Gallium Nitride (In_xGa_1-xN) alloys are currently playing an ever increasing role in optoelectronic devices as the bandgap of such alloys can theoretically be tuned between 0.7eV and 3.4eV–covering the entire visible spectrum. Although growth of high quality In_xGa_1-xN alloys with high indium mole fractions are difficult or presently unattainable, InGaN alloys are still a viable choice for light emitters and detectors over the visible (blue/green) to ultraviolet spectrum. However, many inherent problems during InGaN growth via Metal Organic Vapor Phase Epitaxy (MOVPE) arise due to the large lattice mismatch and low miscibility between GaN and InN–leading to the formation of Inverted Hexagonal Pyramid (IHP) defects at the termination of threading dislocations. Additionally, growth of InGaN at lower temperatures to promote increased indium incorporation results in poor surface morphology. Several methods such as strained layer superlattices and low mole fraction InGaN layers before the growth of the InGaN/GaN MQW structures have been shown to relive strain in the MQWs, thus reducing the density of IHP defects and/or improving the optical output characteristics. This work focuses on the application of GaN monolayer insertions during InGaN quantum well growth via Metal Organic Vapor Phase Epitaxy (MOVPE) as a means to reduce the IHP defect density and passivate effects on surface roughness while observing variations in indium concentration. Observations include the reduction of IHP defect density by nearly twofold as the number of GaN monolayer interruptions increase from zero to three while sustaining only slightly lower effective indium concentrations.