Selectively excited photoluminescence of GaAs1-xNx single quantum wells

GaAsN bulk and GaAsN/GaAs single quantum wells grown by molecular beam epitaxy are studied by selectively excited photoluminescence (PL) measurements. A significant difference is observed in the PL spectra when the excitation energy is set below or above the band gap of GaAs for the GaAsN/GaAs quantum well samples, while the spectral features of GaAsN bulk are not sensitive to the excitation energy. The observed difference in PL of the GaAsN/GaAs quantum well samples is attributed to the exciton localization effect at the GaAsN/GaAs interfaces, which is directly correlated with the transfer and trap processes of the photogenerated carriers from GaAs into GaAsN through the heterointerfaces. This interface-related exciton localization effect can be greatly reduced by a rapid thermal annealing process, making the PL be dominated by the intrinsic delocalized transition in GaAsN/GaAs. (C) 2003 American Institute of Physics.

Occupation modulation of higher subbands in a three-barrier tunnelling structure with a magnetic field

We verify that the magnetic suppression of intersubband LO or LA phonon scattering can give rise to a noticeable nonthermal occupation in higher-lying subbands. This is clearly determined by the relative intensity ratio of the interband photoluminescence spectra for the E-2 - HH1 and E-1 - HH1 transitions. The observed phenomenon may provide an effective method to control the intersubband scattering rate, which is a key factor of the so-called quantum cascade lasers. This is helpful for the population inversion between both the subbands in quantum wells.

Photoluminescence study of CdSexS1-x quantum dots in a glass spherical microcavity

The photoluminescence (PL) of CdSexS1-x semiconductor quantum dots (QDs) in a glass spherical microcavity is investigated. The CdSexS1-x semiconductor clusters embedded in a glass matrix are fabricated by using the heat treatment method. Periodical structures consisting of sharp spectral lines are observed in the PL spectra of CdSexS1-x QDs, which can be well explained by the coupling with the whispering gallery modes of the spherical microcavity based on Mie scattering theory.

Quantum dots in glass spherical microcavity

Glass spherical microcavities containing CdSexS1-x semiconductor quantum dots (QDs) are fabricated. The coupling between the optical emission of embedded CdSexS1-x QDs and spherical cavity modes is realized. When the luminescence of QDs is excited by a laser beam, the strong whispering gallery mode resonance with high Q factors is achieved in the photoluminescence spectra. (C) 2001 American Institute of Physics.

Experimental measurement of microwave-induced electron spin-flip time

The electron spin resonance (ESR) is optically detected by monitoring the microwave-induced changes in the circular polarization of the neutral exciton (X) and the negatively charged exciton (X-) emission in CdTe quantum wells with low density of excess electrons. We find that the circular polarization of the X and X- emission is a mapping of the spin polarization of excess electrons. By analyzing the ESR-induced decrease in the circular polarization degree of the X emission, we deduce the microwave-induced electron spin-flip time >0.1 mus, which is much longer than the recombination time of X and X-. This demonstrates that the optically detected ESR in type I quantum wells with low density of excess electrons does not obey the prerequisite for the conventional optically detected magnetic resonance. (C) 2001 American Institute of Physics.

The intrinsic temperature effect of the Raman spectra of graphite

The Raman spectra of ion-implanted highly oriented pyrolytic graphite (HOPG) are reported, in which an additional mode at 1083 cm(-1) and three doublet structures in the positions of similar to 1350, similar to 2450, and similar to 2710 cm(-1) are revealed. Noticeable frequency shifts are observed for all the Raman bands between the spectra excited with different laser powers, which are interpreted as the pure temperature effect and a downshift in the C-C stretching frequency induced by the thermal expansion. Moreover, the pure temperature effect (d omega/dT)(V) without anharmonic contribution is achieved in pristine HOPG. The results suggest that the pure temperature effect without anharmonic contribution plays an important role in the frequency shifts with temperature. (C) 1999 American Institute of Physics. [S0003-6951(99)01313-3].