Light Emission Properties of GaN-Based Double Heterostructures and Quantum Wells
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ABSTRACT Edge emission characteristics of optically pumped GaN-AlGaN double heterostructures and quantum wells are examined. The samples, which were grown by metalorganic vapor phase epitaxy, are photoexcited with light from a pulsed nitrogen laser. The pump light is focused to a narrow stripe on the sample surface, oriented perpendicular to a cleaved edge, and the edge luminescence is collected and analyzed. We first compare emission characteristics of highly excited GaN-AlGaN double heterostructures grown simultaneously on SiC and sapphire substrates. Polarization resolved spectral properties of edge luminescence from both structures is studied as a function of pump intensity and excitation stripe length. Characteristics indicative of stimulated emission are observed, particularly in the sample grown on SiC. We then present results demonstrating laser emission from a GaN-AIGaN separate-confinement quantum-well heterostructure. At high pump intensities, band edge emission from the quantum well exhibits five narrow (HIA)modes which are evenly spaced by 10 to within the resolution of the spectrometer. This represents the first demonstration of laser action in a GaN-based quantum-well structure. INTRODUCTION The III-V nitrides are important candidate materials for short-wavelength optical emitters. Light-emitting diodes based on InGaN have been reported [1,2] and are commercially available. While injection lasers based on the III-V nitrides have yet to be realized, recent results from a number of groups bode well for GaN-based lasers. Photoluminescence features characteristic of stimulated emission, such as line narrowing and superlinear input/output power dependence at high intensity, have been observed in GaN [3-5] and InGaN [6] films, InGaN-AlGaN [7] and GaN-
AlGaN double heterostructures [8], and GaN-AlGaN superlattices [9]. Laser modes have been clearly observed in the edge emission from optically pumped GaN films grown on sapphire [10] and SiC [11] substrates. Most recently, we have demonstrated an optically pumped GaN-AlGaN vertical-cavity surface emitting laser grown on sapphire [12]. In this work, we study the polarization and spectral properties of edge luminescence from optically excited GaN-A1GaN double heterostructures and quantum wells. The excitation geometry and high excitation intensities used in these experiments are selected to provide information relevant to laser structures. Our results include what we believe to be the first observation of laser action from a HI-V nitride quantum-well heterostructure. CRYSTAL GROWTH AND OPTICAL CHARACTERIZATION The samples studied in this work were grown by metalorganic vapor phase epitaxy (MOVPE) in a vertical reactor operating at 100 Torr. Trimethylgallium (TMGa), trimethylaluminum (TMA1), and ammonia were used as precursors, with H 2 as the carrier gas. In all samples, growth of the GaN and AlGaN layers was performed at 1100 0 C following deposition of a 150 A AIN buffer layer at 5500C. Two types of structures were grown: The first is a double heterostructur
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