Indium bound exciton luminescence in silicon

A high-resolution photoluminescence study is presented of the bound exciton line and its 4 meV low energy satellite in Si:In. The excitation and temperature dependence and the decay times suggest that the satellite line originates from the decay of an exciton bound to the indium acceptor. We tentatively correlate this line with excitations of the final state indium acceptors into a vibrational excited level.     

Phase transitions in a system of coupled Boson oscillators on a sphere

The solutions of mean-field equations for a system of coupled Boson oscillators on an infinite k-dimensional sphere are discussed in the low density - high temperature region and high density — low temperature region. It is shown that for k = 2 the system exhibits only spatial condensation, whereas for k ⩾ 3 both spatial condensation and Bose-Einstein condensation.     

Influence of magnetic field on exciton luminescence

The magnetic field dependence of the exciton emission intensity I_ex(H) has been investigated in Ge crystals stressed along the direction near 〈100〉. In the low field limit the magnetic field correction has been evaluated to the wave functions of the ground and some excited states of an isotropic exciton. The calculated dependence I_ex(H) in the case of Ge is in a good agreement with the experimental one at H ? 0.5 T.     

Intensity-reversal in the donor bound exciton luminescence of GaAs

A self-reversal model is presented to explain the luminescence dependence of the donor bound exciton intensity. The line broadening mechanism is attributed to rotational interaction with non-rigid rotator states. Line reversal results from absorption by non-broadened states near the crystal surface. The absence of a similar excitation intensity dependence for acceptor bound excitons is explained.     

Bound exciton luminescence of Ar- and Al-implanted ZnO

Argon- and aluminum-implanted ZnO single crystals (N_impl=10¹⁶?10¹⁹cm^?3) were investigated at liquid helium temperature by photoluminescence. We obtained highly resolved emission spectra of implanted and thermally annealed samples. Maximum luminescence yield was achieved after annealing with an oxygen ambient at 800°C and an anneal time of 30 min. In Al-implanted ZnO crystals, we observed a strong emission line $\text{I}{}_{\mathrm{<mtext>5</mtext><mtext>6</mtext>}}\text{at λ = 3688}\text{A}\text{?}$. The intensity of this line is correlated with the implanted Al concentration. The I_{$\text{5}\text{6}$} line is interpreted as the recombination of a bound exciton at a polycentric Al complex.     

Bound exciton luminescence in GaP:Cu,O

Luminescence from Cu,O-diffused high-ohmic p-type GaP crystals exhibits hitherto unobserved complexity in the red spectral region (1.6−1.9 eV). The present investigation concerns the features of three different emission series, denoted by C, E₁ and E₂, simultaneously present in these crystals. From detailed measurements of emission and excitation spectra at different temperatures the properties of any of these emissions could be studied separately. The low-temperature spectra for the two line emission series E₁ (1.78−1.72 eV) and E₂ (1.67−1.62 eV) show strong resemblances to well-known properties of isoelectronic complexes such as, for example, Cd,O in GaP. The featureless broad C emission (1.81 eV) is probably of a similar physical origin as E₁ and E₂, so that all three emissions are believed to originate from excitons bound to different complexes involving Cu and possibly O. Further work to determine the chemical nature of these defects is suggested.     

Effects of optical activity on exciton luminescence of CdS

The luminescence spectra have been investigated in the vicinity of the B_n=1 exciton resonance in CdS at T = 2 K. The effect of “weak” optical activity on luminescence has been observed for the first time. The observed spectra are compared with the frequency dependences of the polariton transmission coefficients.     

Absorption and luminescence of the bound exciton in thallium doped silicon

We report the photoluminescence and absorption spectra of the bound exciton in Si:Tl. Four lines are observed in both spectra in contrast to three lines observed in the Al, Ga, In doped Si. The total oscillator strength is approximately 4x10^-4 continuing a trend of increasing oscillator strength with binding energy.     

Quenching of luminescence and exciton diffusion in KI at low temperature

Exciton—defect interaction in KI between 4 and 77 K is measured through the study of the intrinsic luminescence of irradiated crystals excited by both u.v. and electron irradiation. Results are interpreted by a possible athermal diffusion of the non-relaxed exciton at low temperature.     

Excitation intensity dependence of shallow donor bound exciton luminescence in n-GaAs

Luminescence measurements were performed on high purity epitaxial n-GaAs $\text{(}\text{1 × 10}{}^{14}\text{cm}{}^3\text{< n <}\text{3 × 10}{}^{15}\text{cm}{}^3\text{)}$ for various excitation intensities I₀ in the range $\text{8 mW}\text{cm}{}^2\text{< I}{}_0\text{<}\text{4 W}\text{cm}{}^2$. The luminescence line corresponding to the radiative decay of the shallow donor bound exciton, (D⁰, X), broadens with increasing I₀ and appears as a doublet for $\text{I}{}_0\text{? 1}\text{W}\text{cm}{}^2$, while the two-electron replica of the (D⁰, X) remains a single narrow line. The doublet structure of the (D⁰, X) at elevated excitation levels is due to missing luminescence intensity in the center of the line as a consequence of low (D⁰, X) concentration in a layer extending 1–2 μm from the sample surface into the bulk. The low concentration of (D⁰, X) is attributed to capture of (D⁰, X) quanta into surface states, extending to lower energies from the Fermi level fixed by the shallow donors. Comparison of the present results with luminescence spectra obtained by various authors reveals, that unexplained spectral features in the (D⁰, X) region of n-GaAs reported in the literature are a consequence of high excitation intensity and correspond to the effect reported here. In partly compensated p-GaAs with donor concentrations as given above, the (D⁰, X) did not transform into a doublet structure even at $\text{W}\text{cm}{}^2$ excitation intensity.     

Free exciton luminescence lineshape of Hg0.3Cd0.7Te

The photoluminescence spectrum of Hg_0.3Cd_0.7Te at 77K includes a narrow, high energy free exciton line. This experimental spectrum is in good agreement with the theoretical free exciton lineshape, the Gaussian broadening of this line is due to alloy inhomogeneity, and the binding energy of the bound exciton with respect to the free exciton at 77K is 13 ± 4 meV.     

Dynamic stark effect in strongly coupled microcavity exciton polaritons

We present experimental observations of a nonresonant dynamic Stark shift in strongly coupled microcavity quantum well exciton polaritons-a system which provides a rich variety of solid-state collective phenomena. The Stark effect is demonstrated in a GaAs/AlGaAs system at 10?K by femtosecond pump-probe measurements, with the blueshift approaching the meV scale for a pump fluence of 2 mJ?cm^{-2} and 50?meV red detuning, in good agreement with theory. The energy level structure of the strongly coupled polariton Rabi?doublet remains unaffected by the blueshift. The demonstrated effect should allow generation of ultrafast density-independent potentials and imprinting well-defined phase profiles on polariton condensates, providing a powerful tool for manipulation of these condensates, similar to dipole potentials in cold-atom systems.     

Analysis of LO and TO phonon assisted free exciton luminescence in silicon

Linefits are made of LO and TO phonon assisted free exciton luminescence spectra in silicon. The temperature range covered is 1.55–4.0 K. Values of the recombination rates, the phonon energy splitting, the intrinsic line broadening, and the exciton ground state splitting are deduced. The splitting of the indirect ground state is found to be 0.31±0.03 meV.     

Second harmonic generation and two-photon luminescence in the exciton region of CuCl

The wavelength dependence of second harmonic generation and two-photon induced luminescence in the region of the first and second exciton absorption peaks in CuCl has been measured to determine the variation of the nonlinear optical susceptibility in that region.     

Determination of the exciton formation in quantum wells from time-resolved interband luminescence

We present the results of a detailed time-resolved luminescence study carried out on a very high quality InGaAs quantum well sample where the contributions at the energy of the exciton and at the band edge can be clearly separated. We perform this experiment with a spectral resolution and a sensitivity of the setup, allowing us to keep the observation of these two separate contributions over a broad range of times and densities. This allows us to directly evidence the exciton formation time, which depends on the density as expected from theory. We also denote the dominant contribution of excitons to the luminescence signal, and the lack of thermodynamical equilibrium at low densities.     

Coherence length of cold exciton gases in coupled quantum wells

A Mach-Zehnder interferometer with spatial and spectral resolution was used to probe spontaneous coherence in cold exciton gases, which are implemented experimentally in the ring of indirect excitons in coupled quantum wells. A strong enhancement of the exciton coherence length is observed at temperatures below a few Kelvin. The increase of the coherence length is correlated with the macroscopic spatial ordering of excitons. The coherence length at the lowest temperature corresponds to a very narrow spread of the exciton momentum distribution, much smaller than that for a classical exciton gas.     

Theory of resonant secondary radiation via an exciton strongly coupled with phonons

Abstract

Recent progress in the theory of resonant secondary radiation from a strongly-coupled excitonphonon system is briefly reviewed. Implication of some calculated results on the self-trapping process of hot excitons is discussed.     

Mechanism of photooxide quenching of exciton luminescence of anthracene and tetracene

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 52, No. 5, pp. 758–763, May, 1990.