Photoluminescence studies of GaN: A comparison between layers grown on sapphire and nitridated GaAs layers

Abstract

PACS 78.55.Cr, 81.15.Gh Gallium nitride layers were grown epitaxially on sapphire substrates in a LP-MOCVD reactor using trimethylgallium and ammonia. GaN films were also obtained by nitridation, exposing GaAs substrates to ammonia in the same reactor under similar conditions. The temperature ranged between 750 °C and 900 °C, while the pressure was adjusted between 75 and 585 Torr. Photoluminescence measurements were made on the samples using a 325 nm He -Cd laser; near band edge emission and subbandgap luminescence were observed. The luminescence color of the sapphire grown layers went from orange to yellow-green, while it ranged from yellow to blue-violet in the nitridated samples.

Light Enhanced MOCVD Growth of GaN

“…The first peak that appears when the amount of NH 3 is reduced is centered at 525 nm and has also been detected on layers grown by nitridation. This emission has been previously related to structural defects and is not associated to carbon (10). The appearance of a complex structure in YL on samples grown at a lower NH 3 flow indicates that at 750ºC the decomposition of ammonia is insufficient, following from the facts that thermal cracking decreases and that the power of the lamps is reduced.…”

Self‐Induced Nucleation Growth of GaN Columns by Chemical Vapor Deposition

“…The emission peak centered at 372 nm (3.34 eV) related with the band–band transition is observed. The crystalline quality is like the reported by Escobosa et al using a similar GaAs nitridation process.…”

“…[7,10,11] The GaAs nitridation is used as a buffer layer to reduce the lattice mismatch, to grow the zinc-blende or wurtzite GaN structure, or to enhance the photoluminescence. [12][13][14][15][16] Our interest in this method is based in the possible obtainment of auto-sustainable GaN, because it allows to remove the grown material from the substrate.…”

Luminescence study of grown sapphire: from starting material to single crystal

“…The comparison of obtained results for PL of starting materials and grown sapphire crystals, and literature [1][2][3][4][5][10][11][12][13][14][15][16][17] allowed us to do some assumption and conclusions concerning origins of observed PL. YGB might arise from the PL of some defects formed on the surfaces of the grain of starting materials, complex centers formed by interaction of F-type centers with defects and uncontrolled impurities or they originate from PL of micro precipitates as it was recently interpreted [18].…”

“…In this application, sapphire is the best and the most economical substrate to deposit GaN based compound, the material that produces blue light in LED devices. The problem encountered when sapphire is used is that sometimes 'parasite' yellow-red radiation arises caused by substrate [9,10]. One of the reasons for the existence of this "parasite" yellow-red emission might be photoluminescence (PL) of sapphire substrate due to its intense illumination from the light (from 400 to 600 nm depending on doping) produced by the material that constructs the LED device -compound based on GaN.…”