Characterization of differently grown GaN epilayers by time-resolved four-wave mixing technique

✍ Scribed by Jarašiūnas, K. ;Malinauskas, T. ;Aleksiejūnas, R. ;Sūdžius, M. ;Frayssinet, E. ;Beaumont, B. ;Faurie, J.-P. ;Gibart, P.

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 141 KB
• Volume: 202
• Category: Article
• ISSN: 0031-8965
• DOI: 10.1002/pssa.200460430

✦ Synopsis

Abstract

Room temperature time‐resolved four‐wave mixing has been performed in MOCVD GaN epilayers, grown on sapphire substrates by using either conventional or a 3D‐growth mode with Si/N treatment technique (micro‐ELO). Picosecond pulses at 355 nm were used to create light interference pattern and record a spatially modulated carrier distribution by interband transitions, while a delayed probe beam at 1064 nm monitored the carrier dynamics far from the bandgap. The determined values of the bipolar diffusion coefficient and the carrier lifetime were found equal to D~a~ = 1.7–1.8 cm^2^/s and τ~R~ ≈ 1.1 ns for standard grown epilayers, while in the samples with ultralow dislocation density they were found equal to 2.4 cm^2^/s and 2.7 ns. In the interface region of the epilayers with high dislocation density, a dependence of D and τ~R~ values on excitation intensity was found. The latter effect was attributed to a screening of potencial barriers around the charged dislocations by free carriers and an ability of the carriers to become less localized and thus avoid the nonradiative recombination at dislocations. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)