Lateral redistribution processes of excitons localized in CdSe/ZnSe quantum dot structures are investigated by time-integrated and time-resolved spectroscopy. The photoluminescence properties are governed by lateral energy transfer within a dense ensemble of quantum dots. The quantum dots differ in size and Cd concentration and provide a complex potential landscape with localization sites for excitons. At low temperatures, lateral transfer by tunneling leads to a redshift with increasing delay after pulsed excitation. The mobility edge was determined to 2.561 eV. Above 100 K, thermally activated escape and recapture of excitons cause a strong redshift of the PL maximum in the first 500 ps.

The radio-frequency plasma-assisted molecular beam epitaxy of cubic AlyGa1−yN/GaN heterostructures on GaAs(001) substrates is reported. Rutherford backscattering spectroscopy, high resolution x-ray diffraction, and first-order micro-Raman spectroscopy measurements were used to characterize the structural and vibrational properties of the alloy epilayers. The Al content of the alloy is in the range from 0.07<x<0.20. X-ray diffraction reciprocal space maps demonstrate the good crystal quality of the cubic (Al, Ga)N/GaN films. The measured Raman shift of the TO phonon mode of the AlyGa1−yN alloy is in good agreement with theoretical calculations.

Articles you may be interested inEfficient long-range collisional energy transfer between the E0 g +(3 P 2) and D0 u +(3 P 2) ion-pair states of I2, induced by H2O, observed using high-resolution Fourier transform emission spectroscopy Rydberg and ionpair state mixing in the 11Σ+ u and 23Π u vibronic states of Cl2 as studied by vacuum ultraviolet laser spectroscopy High-resolution vacuum ultraviolet fluorescence excitation spectra of the D( 0 + ) ion-pair state of 12 have been obtained using a pulsed supersonic jet. Tunable vacuum ul~raviolet radiation in the region 184-200 nm was produced by Raman shifting (fifth and sixth anti-S~okes) t~e output from a tunable excimer pumped dye laser. Vibrational constants valid up to v = 201m the D(O;:) state have been determined.

We investigated the optical properties of two monolayers of CdSe sandwiched by ZnSe layers grown by molecular-beam epitaxy on GaAs substrates with a vicinal tilt of 2° in the [111] direction. By varying the spatial resolution from 10 μm down to 500 nm, sharp photoluminescence lines due to the recombination of excitons confined into quantum dots could be observed at low temperature. The dot density could be as low as ≈109 dots/cm2, which is smaller than previously reported values by at least one order of magnitude.

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