Comparative study of HVPE- and MOCVD-grown nitride structures for UV lasing application
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Comparative study of HVPE- and MOCVD-grown nitride structures for UV lasing application J. B. Lam, G. H. Gainer, S. Bidnyk1, Amal Elgawadi, G. H. Park, J. Krasinski, J. J. Song, D. V. Tsvetkov2, and V. A. Dmitriev2 Center for Laser and Photonics Research and Department of Physics, Oklahoma State University, Stillwater, OK 74078, USA 1
Zenastra Photonics, Inc., Ottawa, ON K1G 4J8, Canada
2
Technologies and Devices International, Inc., Gaithersburg, MD 20877, USA.
ABSTRACT We studied and compared the emission properties of optically excited (Al)GaN structures grown by two different techniques: hydride vapor phase epitaxy (HVPE) and metalorganic chemical vapor deposition (MOCVD). We successfully achieved stimulated emission (SE) in an HVPE-grown GaN epilayer and a GaN/AlGaN double heterostructure at 10 K and room temperature. We found that the SE threshold and photoluminescence efficiency of the HVPE-grown samples are similar to those of high-quality MOCVD-grown structures. Photoluminescence measurements from 10 to 300 K show that the HVPE GaN has a high density of non-radiative recombination channels, especially those activated below 100 K. This study represents the first demonstration of SE in HVPE-grown (Al)GaN heterostructures. INTRODUCTION With the commercial availability of InGaN-based laser diodes (LDs) and light emitting diodes (LEDs) [1], GaN related materials have proven to be important for the development of optoelectronic devices that operate in the blue to UV spectral range. For example, optically pumped lasing at room temperature was obtained in a GaN/AlGaN structure at 362 nm [2], which is shorter than the lowest emission wavelength of 376 nm reported for InGaN-based LDs [3]. Currently, most nitride LEDs and LDs are grown by MOCVD. However, HVPE has become an important growth technique for GaN, since it is a cost-effective way of growing thick, high quality GaN with growth rates of up to 100 µm/h [4] and dislocation densities on the order of 106 cm-2 [5]. Free-standing HVPE-grown GaN films with thicknesses of up to 300 µm have been produced via laser liftoff [6]. Nichia and NEC both have fabricated InGaN-based LDs on HVPE-grown GaN substrates [7,8]. Here, we compare the optical properties of HVPE-grown samples (a GaN epilayer and a GaN/AlGaN double heterostructure) with a high quality MOCVD-grown GaN epilayer. EXPERIMENTAL DETAILS The HVPE GaN epilayer and GaN/AlGaN double heterostructure (DH) used in this study were grown using ammonia, GaCl, and AlCl3 as the N, Ga, and Al sources, respectively. The GaN epilayer is 5 µm thick and was deposited on a 5 nm thick buffer layer on a sapphire G6.4.1
substrate. The GaN/AlGaN DH was grown on a SiC substrate and has a ~ 250 nm active GaN layer embedded between an Al0.06Ga0.94N layer on top and an Al0.16Ga0.84N layer below. Both AlGaN layers are 400 nm thick. This DH was designed for better optical confinement, and the top AlGaN layer has a smaller Al concentration than the lower AlGaN layer to facilitate p-doping the top layer, should we later choose to do
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