Optical monitoring of nonequilibrium carrier lifetime in freestanding GaN by time-resolved four-wave mixing and photoluminescence techniques

Abstract

Optical monitoring of nonequilibrium carrier dynamics was performed in freestanding GaN. Four-wave mixing kinetics directly provided carrier lifetime of 5.4ns in the layer, while complementary measurements by photoluminescence technique revealed the fast transients with subnanosecond decay time. Numerical modeling of photoluminescence decay taking into account the carrier spatial-temporal dynamics allowed us to attribute an origin of the fast photoluminescence transients to carrier diffusion to the bulk and to reabsorption of the backward emission. The studies demonstrated carrier diffusion limited applicability of the time-resolved photoluminescence technique for carrier lifetime measurements in a high quality thick III-nitride layers.

Carrier dynamics under two‐ and single‐photon excitation in bulk GaN

“…The thickness of the photoexcited region under 2P excitation was estimated using the determined 2P-absorption coefficient b which led to a penetration depth of a at P 0 ¼ 1 GW/cm 2 power density. This is some 100-1000 times higher when compared to the 1P injection case (a À1 1P % 100 nm with diffusion-expanded photoexcited region to a few micrometers [4]). …”

“…Subsequent spatial redistribution of the carriers by diffusion from the surface into the bulk, trapping at surface states, radiative and nonradiative recombination rates were treated as critical parameters contributing to the fast initial decay of already thermalized carriers. The fast transients with few nanoseconds decay times were observed in GaN heterostructures grown by metalorganic chemical vapor deposition on various substrates as well as in hydride vapor phase epitaxy (HVPE) crystals using time-resolved photoluminescence (TRPL), picosecond light-induced transient grating (LITG), and a variety of other techniques [1][2][3][4].…”

“…These techniques enabled us to examine the changes in refractive index, Dn, and absorption coefficient, Da, at wavelengths far below E g (at 1053 nm), which are well described by the DrudeLorentz theory through the simple relationships: Dn ¼ n eh DN and Da ¼ s eh N, where DN is the nonequilibrium carrier density, n eh is the refractive index change per one electronhole pair in cm À3 , and s eh is the FCA cross-section [4,5]. Spatial modulation of Dn with grating period L (i.e., recording of a transient free-carrier grating) was realized for carrier injection by the light interference pattern.…”

“…LITG [4] and FCA [5] techniques were used to monitor the spatial and temporal carrier dynamics. These techniques enabled us to examine the changes in refractive index, Dn, and absorption coefficient, Da, at wavelengths far below E g (at 1053 nm), which are well described by the DrudeLorentz theory through the simple relationships: Dn ¼ n eh DN and Da ¼ s eh N, where DN is the nonequilibrium carrier density, n eh is the refractive index change per one electronhole pair in cm À3 , and s eh is the FCA cross-section [4,5].…”

A diffraction-based technique for determination of interband absorption coefficients in bulk 3C-, 4H- and 6H-SiC crystals

“…A deeper understanding of these processes in high-density carrier plasma can be obtained by applying time-resolved optical techniques, which allow the injection of an excess carriers by a short laser pulse and subsequent monitoring of the recombination and diffusion processes [1][2][3][4][5][6][7]. Therefore knowledge of absorption coefficent at commonly used laser wavelengths is an important issue for more precise determination of injected carrier density profile and related plasma parameters in SiC, e.g.…”