Application of picosecond four-wave mixing and photoluminescence techniques for investigation of carrier dynamics in bulk crystals and heterostructures of GaN

Kestutis Jarasiunas 1T. Malinauskas 1Arunas Kadys 1M. Sudzius 1R. Aleksiejunas 1Saulius Miasojedovas 1Saulius Jursenas 1A. Zukauskas 1Daniela Gogova 2A. Kakanakova-Georgieva 2E. Janzen 2H. Larsson 2Bo Monemar 2P. Gibart 3B. Beaumont 3

1. Vilnius University, Institute of Materials Science and Applied Research (IMSAR, VU), Sauletekio 9, building III, Vilnius LT-2040, Lithuania
2. Linköping University, Dept. of Physics and Meas. Techn., Linkoping, Sweden
3. LUMILOG, 2720, Chemin Saint Bernard, Les Moulins I, F-06220 Vallauris, France, Vallauris, France

Abstract

We studied defect-density governed photoelectric parameters in GaN heterostructures and bulk crystals by using the time-resolved techniques of picosecond four-wave mixing (FWM) and photoluminescence (PL). A few mm-thick GaN layers were grown on 6H-SiC or 4H-SiC substrates by hot-wall MOCVD with varied growth parameters, while the 270-mm-thick free-standing bulk crystal was grown by HVPE on a two-step epitaxial lateral overgrown GaN template on sapphire. FWM was realized by recording transient free carrier gratings at interband excitation at 355 nm wavelength and probing their kinetics by the delayed probe beam at 1064 nm. For spectrally and temporally resolved PL, the samples were excited at 266 nm and luminescence was measured in backward geometry. The excitation density varied up to a few mJ/cm2, what allowed us to study effects at nonequilibrium carrier density from 1018 up to 5x1019 cm-3.
Simple correlation between photoelectrical and nonlinear optical properties of FWM allowed us to determine carrier lifetimes τR and diffusion coefficients D in differently grown samples. The τR increased value from 100-300 ps in the epilayers up to 3 ns in the bulk crystal, while the D value varied from 1.5-1.7 cm2/s up to 2-2.8 cm2/s, correspondingly. We attribute the enhanced values of D and τR to screening of potential barriers around dislocations and ability of carriers to avoid nonradiative recombination at dislocations.
We observed a novel feature of FWM in GaN, namely a complete saturation of its diffraction efficiency at the excitation energy 0.5 - 2 mJ/cm2, dependent on sample. This peculiarity of FWM correlated with the spectra and intensity of stimulated PL, and pointed out that the origin of the FWM saturation is the favorable conditions for ultrafast stimulated recombination. The kinetics and spectra of PL are compared with the features of FWM to develop complementary characterization of the highly-excited nitrides.

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Presentation: oral at E-MRS Fall Meeting 2004, Symposium C, by Kestutis Jarasiunas
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-04-28 13:52
Revised:   2009-06-08 12:55
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