Subcycle Wannier-Stark Localization by Mid-Infrared Bias in Gallium Arsenide

The fundamental interband absorption in gallium arsenide shows a strong blue shift when biased by mid-infrared transients exceeding 10 MV/cm. This subcycle feature is induced by the localization of electronic wavefunctions from 3D to 2D.

Trans influence of triphenylphosphines and pseudohalogens on Ni-S bonds: Synthesis, spectral and single crystal X-ray structural studies on NiS2PN and NiS2PC chromophores

Trans influence of triphenylphosphines and pseudohalogens on Ni-S bonds of NiS2PN and NiS2PC chromophores has been investigated by synthesizing and characterizing them. The complexes show the characteristic thioureide IR band at ∼ 1530 cm−1. Electronic spectrum of the cyanide analogue shows a strong blue shift relative to others. X-ray structures of [Ni(pipdtc)(4-MP)(NCS)] (1), [Ni(pipdtc)(PPh3)(NCS)] (2) and [Ni(pipdtc)(PPh3)(CN)] (3) (pipdtc = piperidinecarbodithioate anion, 4-MP = tri(4-methylphenyl)phopshine) are reported. Ni-S bond distance trans to 4-MP(1) is longer than the distances in (2) and (3) and Ni-S bond distances trans to Ni-NCS/CN decrease as follows: (3) > (2) > (1). Particularly, 4-MP shows a highly significant trans influence than triphenylphosphine on Ni-S bond. Similarly, CN− exerts a marginally significant trans influence compared to NCS-. Thioureide C-N distances are relatively very short due to the drift of electron density towards the metal. The Ni-N-C angle (163.5(2)°) observed in (2) indicates deviation from linearity to a larger extent compared to that in (1) (176.3(3)°) due to the steric effect of the 4-methyl group. The reduction potentials (CV) for the mixed ligand complexes are much less compared to that of the parent NiS4 chromophore due to the π-acidic phosphines.

Effect of Thermal Annealing on the Photoluminescence Properties of a GaInNAs/GaAs Single Quantum Well

ABSTRACTWe report on the effect of thermal annealing on the photoluminescence properties of a Ga0.65In0.35N0.02As0.98/GaAs single quantum well. Thermal annealing is shown to decrease the strong nitrogen-induced localization effects observed at low temperatures and to reduce the full width at half maximum of the emission peak. It also induces a strong blue shift of the emission peak energy, which is thought not to arise from an In-Ga interdiffusion alone, as it is much larger than in a nitrogen-free reference single quantum well.

Depth Profile of the Excitonic Luminescence in Gallium-Nitride Layers

ABSTRACTWe present results of spatially-resolved photoluminescence and Raman measurements on a 200 μm thick GaN layer grown on sapphire by hydride vapor phase epitaxy. Our microphotoluminescence measurements reveal that the peak position of the excitonic and donoracceptor-pair transitions strongly depends on the distance to the substrate interface. We observed a strong blue shift near the interface and discuss the influence of strain, which we quantified by micro-Raman experiments.

Strain Effects in InP Dots in between Barriers of GaInP

We have investigated the photoluminescence emission energy of InP dots as a function of cap layer thickness. We find a strong blue-shift with increasing cap layer thickness. The strain tensor in the dot as well as in the surrounding matrix has been modelled using finite element methods and the band-gap has been calculated using deformation potential theory. We find good agreement between calculation and experiment. For uncapped dots we find that the emission energy is lower than for biaxially strained InP, and is indeed close to unstrained InP.

Photoluhi Nescence of Inas/InAsPSb and InAs/Heterojunctions

ABSTRACTPhotol uminescence of p-P InAs/InAsPSb and InAs/InAl AsSb heterojunctions grown by LPE method was studied at liquid helium temperature. The recombination spectra contained a new broad band lying between the substrate and the layer lines which was identified as an emission from the interface. This line is characterized by a strong blue shift when the excitation intensity increases. The intensities of bulk and interface lines show an unusual dependence on the pumping power. On the basis of experimental findings the interface line is attributed to emission from electrons confined at the interface due to reflection of elecctrons moving above the barrier.