With Al2O3 passivation on the surface of Cu(In,Ga)Se2, the integrated photoluminescence intensity can achieve two orders of magnitude enhancement due to the reduction of surface recombination velocity. The photoluminescence intensity increases with increasing Al2O3 thickness from 5 nm to 50 nm. The capacitance-voltage measurement indicates negative fixed charges in the film. Based on the first principles calculations, the deposition of Al2O3 can only reduce about 35% of interface defect density as compared to the unpassivated Cu(In,Ga)Se2. Therefore, the passivation effect is mainly caused by field effect where the surface carrier concentration is reduced by Coulomb repulsion.

Thin-film ferromagnetic semiconductors Sb 2−x V x Te 3 with the Curie temperature as high as 177 K were prepared on sapphire ͑0001͒ substrates by molecular-beam epitaxy. Films of Sb 2−x V x Te 3 with x up to 0.35 display robust, out-of-plane ferromagnetic ordering that depends on the concentration of vanadium in the structure. The Curie temperature was determined from magnetization measurements and Arrott plots. Ferromagnetic order is manifested by hysteresis loops observed in magnetization, magnetoresistivity, and the anomalous Hall effect.

We report ultrafast surface pump and interface probe experiments on photoexcited carrier transport across single crystal bismuth films on sapphire. The film thickness is sufficient to separate carrier dynamics from lattice heating and strain, allowing us to investigate the time-scales of momentum relaxation, heat transfer to the lattice and electron-hole recombination. The measured electron-hole (e − h) recombination time is 12-26 ps and ambipolar diffusivity is 18-40 cm 2 /s for carrier excitation up to ∼ 10 19 cm −3 . By comparing the heating of the front and back sides of the film, we put lower limits on the rate of heat transfer to the lattice, and by observing the decay of the plasma at the back of the film, we estimate the timescale of electron-hole recombination. We interpret each of these timescales within a common framework of electron-phonon scattering and find qualitative agreement between the various relaxation times observed. We find that the carrier density is not determined by the e − h plasma temperature after a few picoseconds. The diffusion and recombination become nonlinear with initial excitation > ∼ 10 20 cm −3 .

No abstract

No abstract

Semiconductor trilayer structures with ferromagnetic Sb 2−x Cr x Te 3 layers separated by a nonmagnetic Sb 2 Te 3 layer of different thickness have been fabricated by molecular beam epitaxy. Ferromagnetic out-of-plane exchange coupling between the SbCrTe layers was found and the coupling strength, which can be represented by a saturation field H S , depends on both the Sb 2 Te 3 spacer thickness and temperature.