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Carrier recombination under one-photon and two-photon excitation in GaN epilayers
|Saulius Miasojedovas 1, Mantas Butkus 1, Saulius Jursenas 1, Bolesław Łucznik 2, Izabella Grzegory 2, Tadeusz Suski 2|
1. Institute of Material Science and Applied Research, Sauletekio 9, III bld., Vilnius LT-10222, Lithuania
III-nitride semiconductors are successfully applied for blue and UV optoelectronic devices such as light emitting and laser diodes, as well as high-voltage and high-power electronic devices. Although these devices are commercially available, there are a lot of unsolved problems related to the high density of nonradiative traps in GaN epilayers. The conventional heteroepitaxial growth of GaN films results in high dislocation densities (108 – 1010 cm-2) which affect both optical and electrical device properties. One of the ways to reduce threading dislocations in the film is growth of the homoepitaxial layers of large thickness by hydride vapor phase epitaxy (HVPE).
In recent decade, significant progress has been achieved in growth of GaN layers, which has an impact on dominating luminescence decay processes. For the surface excited high quality GaN layers, due to efficient diffusion created carriers rapidly escapes from the excited region, thus luminescence lifetime cannot be treated as materials quality factor anymore. Recently, we proposed application of two-photon excitation conditions for luminescence characterization of high quality GaN.
Here we present time-resolved luminescence properties of ~100-μm thick GaN epilayers grown by HVPE over three different substrates excited under one-photon (1P) and two-photon (2P) conditions. The excited sample area is much bigger than carrier diffusion depth and we can neglect carrier diffusion processes. Experimental data was fitted with consideration to theoretical spatial-temporal distribution of the plasma density.
We show that the investigation of luminescence transients obtained for 1P and 2P excitations allows for the estimation of carrier lifetime, related to the density of nonradiative traps, and of the carrier bipolar diffusion coefficient. The impact of the equilibrium carrier density on the luminescence dynamics of highly excited GaN is discussed.
Presentation: Poster at E-MRS Fall Meeting 2007, Symposium J, by Saulius Miasojedovas
See On-line Journal of E-MRS Fall Meeting 2007
Submitted: 2007-05-14 09:06 Revised: 2009-06-07 00:44