Electron-hole plasma expansion in the direct-band-gap semiconductors CdS and CdSe

Majumder, F. A.; Swoboda, H.-E.; Kempf, Karl G.; Klingshirn, C.

doi:10.1103/physrevb.32.2407

Cited by 100 publications

(16 citation statements)

References 35 publications

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“…While the absolute energy of the 1s exciton stays nearly unchanged in bulk samples over a wide range of carrier densities its oscillator strength disappears due to band gap shrinkage. This was proved in many experiments [1][2][3] and explained qualitatively by strong compensation of gap shrinkage and weakening of the Coulomb interaction due to screening inspecting the effective Wannier equation of an exciton embedded in a thermal plasma [4][5][6][7]. The situation is rather different in quantum wells, where a blueshift of the exciton with increasing density was observed [8,9].…”

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confidence: 84%

Density Dependence of the Exciton Energy in Semiconductors

et al. 1998

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We investigate both experimentally and theoretically the excitonic absorption in ZnSe in a temperature range between 2 and 60 K with increasing densities of carriers. For higher temperatures a weak redshift of the exciton resonance is found which turns into a blueshift for lower temperatures. While the widely used simplified treatment of the scattering processes within a static screening approximation fails completely to describe this thermally induced crossover, it can be explained by the interplay between Coulomb-Hartree-Fock renormalizations and carrier-carrier and carrier-polarization scattering including the dynamical screening. [S0031-9007 (98)06251-6] PACS numbers: 71.35.CcThe nonlinear behavior of the excitonic absorption is one of the most investigated manifestations of many-particle effects in a highly excited narrow-gap semiconductor. For instance the Mott transition observed for increasing excitation densities is well understood as a consequence of screening of the Coulomb interaction between charge carriers. While the absolute energy of the 1s exciton stays nearly unchanged in bulk samples over a wide range of carrier densities its oscillator strength disappears due to band gap shrinkage. This was proved in many experiments [1-3] and explained qualitatively by strong compensation of gap shrinkage and weakening of the Coulomb interaction due to screening inspecting the effective Wannier equation of an exciton embedded in a thermal plasma [4][5][6][7]. The situation is rather different in quantum wells, where a blueshift of the exciton with increasing density was observed [8,9]. Qualitatively, this behavior is caused by the reduced dimensionality, which leads to a reduction of the Coulomb interaction between carriers [10] as was confirmed by more elaborated calculations for a dense exciton gas model [11]. In GaAs͞Ga 12x Al x As quantum wells the transition from quasi-2D to 3D behavior was found to occur at well widths of 19 nm, i.e., already at less than two exciton Bohr radii [9,12].The present situation is characterized by two aspects. At first, recent experimental results shed new light on the commonly accepted view that the excitonic resonance stays nearly constant in a large density region. In GaAs͞Ga 12x Al x As quantum wells of 21 nm width the exciton shift was found to change from a weak blueshift under resonant excitation to a weak redshift under nonresonant excitation [13]. Also in bulk ZnSe, where the influence of many-particle effects on the exciton can be observed much more pronounced than in the III-V semiconductors (GaAs) due to the larger exciton binding energy, a weak blueshift of the exciton [14] at resonant excitation and low temperatures has been found recently. Second, substantial progress has been achieved during the last few years to find out which many-particle effects have to be included into the semiconductor-Bloch equations (SBE) in order to describe the nonlinear absorption features of laser pulses. In particular, inclusion of carrier-polarization scattering processes was sh...

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confidence: 84%

Density Dependence of the Exciton Energy in Semiconductors

et al. 1998

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“…With increasing stripe length or increasing carrier concentration, g(hw) deviates from I,,(hw) along with q and the gain becomes negative on the high-energy side Next, we considered the gain spectrum (curve 5 in Fig. l b ) at higher excitation (1.1 MW/cm2) but for the same stripe length as above and fitted it with the electron-hole plasma model described in [3]. The optical amplification g(ho) in a direct-band gap semiconductor, where all excitonic correlations are screened in an EHP of sufficiently high carrier concentration, can be described simply by the square-root dependence of the combined density of states above the reduced band gap Ei(np), modulated by the Fermi functions of electrons and holes, j , and f,, as given in [3],…”

Section: 34mentioning

confidence: 99%

“…A gain spectrum calculated according to (3) and modified with the k concervation model and energy-depending damping as described in [3] is shown in Fig. 3a together with the experimental one where the exciton-exciton scattering processes are strongly saturated.…”

Section: 34mentioning

confidence: 99%

Gain Processes in ZnTe Epilayers on GaAs

Majumder¹,

Klingshirn²,

Westphäling

et al. 1994

Physica Status Solidi (b)

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Optical gain processes in ZnTe epitaxial layers grown by MOVPE on GaAs substrates are reported. Depending on the excitation conditions, optical gain related to exciton-exciton scattering or due to recombination in an electron-hole plasma is identificd by means of the variable-stripe-length method. The experimental gain spectra are compared to model calculations for the respective gain processes. Stimulated emission up to room temperature is observed under intense picosecond excitation.Optische Verstarkungsprozesse in ZnTe/GaAs-Epitaxieschichten, die mittels MOVPE gezuchtet wurden, werden untersucht. Die optische Verstarkung, die auf Exdton-Exziton-Streuung oder Rekombination im Elektronen-Loch-Plasma beruht, wird in Abhangigkeit von den Anregungsbedingungen mittels der Strichlangen-Methode beobachtet. Die experimentellen Verstarkungsspektren werden mit Modellrechnungen fur die entsprechenden Verstarkungsprozesse verglichen. Stimulierte Emission wird unter starker ps-Anregung sogar bis Zimmertemperatur beobachtet.

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“…[8,13]) have been reported. With respect to the plasma expansion velocity, u p , one can distinguish two kinds of behaviour:`slow' expansion with u p µ 10 6 cm s ¡1 [6,7,12,17,21,22] or`fast' , with u p > 10 6 cm s ¡1 [8± 10, 13± 16, 23]. In the latter case a mechanism of stimulated emission recombination, optical transport and reabsorption has been proposed to explain the observed ultrafast carrier diå usion.…”

Section: Introductionmentioning

confidence: 98%

“…Expansion lengths as low as ¹20 mm (e.g. [6,12]) and as high as ¹100 mm (e.g. [8,13]) have been reported.…”

Section: Introductionmentioning

confidence: 98%

Plasma-expansion induced absorption and refraction changes in ZnSe epilayers

Bakarezos

Blewett

Galbraith

et al. 2000

Journal of Modern Optics

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A novel transient-grating technique with a well-de® ned and moveable optical probe is used to investigate the spatial extent of any optical changes arising from optically-driven electron± hole plasma expansion in molecular-beam-epitaxially grown ZnSe. We present experimental data demonstrating that optically-driven plasma expansion does not extend signi® cantly beyond the originally excited area when pumped to carrier densities appropriate to lasing action in these materials (10 18 cm ¡3 ).

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Electron-hole plasma expansion in the direct-band-gap semiconductors CdS and CdSe

Cited by 100 publications

References 35 publications

Density Dependence of the Exciton Energy in Semiconductors

Density Dependence of the Exciton Energy in Semiconductors

Gain Processes in ZnTe Epilayers on GaAs

Plasma-expansion induced absorption and refraction changes in ZnSe epilayers

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