Growth and Characterization of LED Structures Grown by MOCVD on HVPE‐Grown GaN Templates

Abstract

PACS: 68.55.Jk; 68.65.AcOptical and structural properties of light emitting diode (LED) structures grown by MOCVD on both GaN/sapphire templates and sapphire substrates are presented. The GaN/sapphire 3-5 mm thick templates were grown by HVPE on c-plane sapphire. Si-doping can alter defect formation in the templates. Depending on the LED structure design and growth conditions, the EL peak position varied in the range of 380 to 430 nm. MOCVD deposition improved the morphology of the HVPE-grown surface. The LED structures grown on GaN/sapphire templates had similar or superior EL intensity compared to samples grown on sapphire substrates.Introduction One of the challenges remaining in the epitaxial growth of III-N materials is the absence of a suitable lattice-matched substrate. Currently, sapphire and SiC substrates are widely used in nitride-based technology [1,2]. Device quality III-nitride materials are commonly grown on sapphire by metal organic chemical vapor deposition (MOCVD) utilizing a two-step method that includes nucleation layer deposition at a low temperature followed by annealing and epilayer growth at a higher temperature. Subsequently, a buffer layer and the device structure are grown. Despite these shortcomings, blue, green and white light emitting diodes (LEDs), violet laser diodes (LDs), field effect transistors, and ultraviolet photodiodes have been developed. However, the structures suffer from a high density of threading dislocations and strain-induced problems that strongly affect device performance. GaN grown on sapphire with a low temperature nucleation layer still has a dislocation density as high as 10 8 to 10 10 cm --2 . These dislocations are a major cause of device degradation, particularly for LDs, which operate at high current density [3].Alternatively, due to its high growth rate and high material quality, hydride vapor phase epitaxy (HVPE) is an approach for fabricating GaN quasi-bulk material and GaN templates to be used as substrates for III-N device structure growth. A growth procedure on III-N templates does not require a nucleation layer and a thick GaN buffer layer. The homoepitaxial nature of growth on templates can improve crystal quality, and thus, device performance. Other benefits of GaN and AlGaN templates are reduced growth time and precursor consumption, reduced downtime and maintenance, and increased productivity in MOCVD reactors.