High-excitation photoluminescence in GaN: Hot-carrier effects and the Mott transition

Binet, F.; Duboz, J.-Y.; Off, J.; Scholz, F.

doi:10.1103/physrevb.60.4715

Cited by 110 publications

(76 citation statements)

References 24 publications

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“…Especially in three dimensions (3D), studies exist that argue to evidence the first-order nature of the MT [5,6], while others point toward a second-order transition [7][8][9]. However, note that in optically-probed bulk systems, the exponential absorption profile leads to an emission signal that mixes inhomogeneously injected regions and may conceal certain characteristics of the MT.…”

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confidence: 99%

High-temperature Mott transition in wide-band-gap semiconductor quantum wells

et al. 2014

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The crossover from an exciton gas to an electron-hole plasma is studied in a GaN/(Al,Ga)N single quantum well by means of combined time-resolved and continuous-wave photoluminescence measurements. The twodimensional Mott transition is found to be of continuous type and to be accompanied by a characteristic modification of the quantum well emission spectrum. Beyond the critical density, the latter is strongly influenced by band-gap renormalization and Fermi filling of continuum states. Owing to the large binding energy of excitons in III-nitride heterostructures, their injection-induced dissociation could be tracked over a wide range of temperatures, i.e., from 4 to 150 K. Various criteria defining the Mott transition are examined, which, however, do not lead to any clear trend with rising temperature: the critical carrier density remains invariant around 10 12 cm −2 . At sufficiently low temperature T and carrier density n, free electrons and holes in a semiconductor bind and form neutrally charged quasiparticles. These so-called excitons represent the fundamental electronic excitation of a semiconductor and obey Bose statistics in the low-density limit. However, when increasing T or n beyond a certain limit, the exciton complexes get ionized and the system switches from an insulating state to a conductive electron-hole plasma (EHP)-the Mott transition (MT) [1]. While exciton dissociation induced by a hot phonon bath represents a classical process and occurs when the thermal energy becomes of the order of the exciton binding energy E b X ≈ k B T , the breakup of excitons due to an increasing carrier population relies on much more complex mechanisms. In simplified terms, when n approaches the hard-sphere limit, that is, when the interparticle distance is reduced to the order of the exciton Bohr radius a B , the fermionic properties of the exciton constituents become dominant: Coulomb screening and phase-space filling cause a reduction of E b X and eventually the dissociation of the excitonic bound state around a certain critical density n crit [2]. Note that the latter is usually overestimated by the simple hard-sphere criterion [3].Whereas the MT was initially claimed to be a first-order phase transition [1,4], later experiments led to partially conflicting results. Especially in three dimensions (3D), studies exist that argue to evidence the first-order nature of the MT [5,6], while others point toward a second-order transition [7][8][9]. However, note that in optically-probed bulk systems, the exponential absorption profile leads to an emission signal that mixes inhomogeneously injected regions and may conceal certain characteristics of the MT. This drawback can be circumvented in 2D systems. Here, most of the studies suggest a rather smooth MT [10][11][12][13]. On the contrary, experimental studies concerning the T dependence of the MT are extremely scarce. In a simple framework, an increasing Debye-screening length gives reason to expect a rise in n crit with T . Even if such a behavior was claimed for bulk ...

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High-temperature Mott transition in wide-band-gap semiconductor quantum wells

et al. 2014

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“…Luminescence spectra of GaN epilayers are formed by high-density electron-hole plasma (EHP) emission that occurs under intense photoexcitation with the excitonic states screened by the nonequilibrium carrier system [7,8]. All spectra consist of one broad emission band.…”

Section: Resultsmentioning

confidence: 99%

Luminescence of Highly Photoexcited GaN Epilayers and Heterostructures Grown on Different Sapphire Crystal Planes

et al. 2005

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GaN epilayers and AlGaN/GaN multiple quantum wells grown by metalorganic chemical vapor deposition on different crystal planes (c, a, and r) of the sapphire substrate were studied by excitation intensity dependent and time-resolved photoluminescence. In polar multiple quantum wells grown on a-and c-planes, a blueshift of the luminescence band with increasing the excitation energy was observed, indicating that screening of built-in field by free carriers takes place, whereas in nonpolar r-plane grown multiple quantum wells, the luminescence band maintained an almost constant peak position. Full screening of built-in field was achieved at the excitation densities higher than 0.3 mJ/cm 2 . Under conditions of screened built-in electric field the structures were characterized by carrier lifetime. It was shown that nonpolar multiple quantum wells suffer from high density of nonradiative traps that can be due to substrate related threading dislocations.

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“…Figure 1a shows some typical time-integrated PL spectra of the GaN layer for various excitation densities. The spectra are seen to contain the main emission band peaked in the vicinity of the bandgap energy (∼ 3.4 eV), which is typical of the radiative recombination of high-density electron-hole plasma (EHP) [6,7]. An increase in the pump energy density (I p > 1 mJ/cm…”

Section: Methodsmentioning

confidence: 99%

Transients of Carrier Recombination and Diffusion in Highly Excited GaN Studied by Photoluminescence and Four-Wave Mixing Techniques

et al. 2005

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Time-resolved photoluminescence and four-wave mixing techniques have been combined for studies of carrier relaxation dynamics in a highly photoexcited GaN epilayer. For a moderate excitation density below 1 mJ/cm 2 , carrier recombination was due to free carrier capture by deep traps. The characteristic time of carrier capture, τ e = 550 ps, was measured under deep trap saturation regime. The ambipolar diffusion coefficient for free carriers, D = 1.7 cm 2 /s, was estimated from the analysis of the transients of the light-induced gratings of various periods. A complete saturation of the four-wave mixing efficiency was observed for the excitation energy density exceeding 1.5 mJ/cm 2 . The latter saturation effect was shown to be related to electron-hole plasma degeneration, which results in a significant enhancement of carrier recombination rate due to onset of stimulated emission.

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High-excitation photoluminescence in GaN: Hot-carrier effects and the Mott transition

Cited by 110 publications

References 24 publications

High-temperature Mott transition in wide-band-gap semiconductor quantum wells

High-temperature Mott transition in wide-band-gap semiconductor quantum wells

Luminescence of Highly Photoexcited GaN Epilayers and Heterostructures Grown on Different Sapphire Crystal Planes

Transients of Carrier Recombination and Diffusion in Highly Excited GaN Studied by Photoluminescence and Four-Wave Mixing Techniques

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