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Raman spectroscopy has been widely used as a non-destructive surface characterization method for the Cu2ZnSnS4 (CZTS) thin films. Secondary phases, which often co-exist with CZTS, are detrimental to the device performance. In this work, removal of the secondary phases using sodium sulfide (Na2S) aqueous solution etching in various time durations was investigated. Raman scattering mapping provides a direct visualization of phase distribution in CZTS-based materials on a relatively large scale (1mm x 10mm). Both as-grown and etched CZTS absorber layers were examined by Raman spectroscopy with a 532 nm excitation laser light in the range of 50-500 cm-1. A clear reduction of the secondary phases (mainly SnS) at the surface after etching was confirmed by Raman spectroscopy and scanning electron microscopy. Room temperature photoluminescence (PL) reveals a pronounced correlation between the amount of secondary phases and photoluminescence peak position. The PL spectra of the regions with more Sn-rich secondary phases show clearly a shift to high wavelength of the peak position, in comparison with regions with less Sn-rich secondary phases. These observed PL changes could be due to Sn-rich defects which may cause recombination processes. [ABSTRACT FROM AUTHOR]

The light enhancement phenomena in InGaN/GaN multi-quantum wells (MQWs) infiltrated with metal nanoparticles (NPs) are studied using resonant and off-resonant localized plasmon interactions. The emission and recombination characteristics of carriers in InGaN/GaN MQW structures with inverted hexagonal pits (IHPs) are modified distinctly depending on the nature of their interaction with the metal NPs and with the pumping and emitted photons. It is observed that the emission intensity of light is significantly enhanced when the emission energy is off-resonant to the localized plasmon frequency of the metal nanoparticles. This results in enhanced emission from MQW due to Au nanoparticles and from IHPs due to Ag nanoparticles. At resonant-plasmon frequency of the Ag NPs, the emission from MQWs is quenched due to the re-absorption of the emitted photons, or due to the drift carriers from c-plane MQWs towards the NPs because of the Coulomb forces induced by the image charge effect. [ABSTRACT FROM AUTHOR]

Comparable microcavities with 3λ/2 (∼240 nm) active regions containing distributed (In,Ga)N quantum wells, grown on GaN substrates and bounded by two dielectric mirrors, have been fabricated by two different routes: one using laser lift-off to process structures grown on GaN-on-sapphire templates and the second using freestanding GaN substrates, which are initially processed by mechanical thinning. Both exploit the properties of an Al0.83In0.17N layer, lattice matched to the GaN substrate and spacer layers. In both cases cavity quality factors >400 are demonstrated by measurements of the cavity-filtered room-temperature excitonic emission near 410 nm. [ABSTRACT FROM AUTHOR]

A technique based on the Fresnel diffraction effect for the fabrication of nano-scale site-controlled ring structures in InGaN/GaN multi-quantum well structures has been demonstrated. The ring structures have an internal diameter of 500 nm and a wall width of 300 nm. A 1 cm-1 Raman shift has been measured, signifying substantial strain relaxation from the fabricated structure. The 9 nm blueshift observed in the cathodoluminescence spectra can be attributed to band filling and/or screening of the piezoelectric field. A light emitting diode based on this geometry has been demonstrated. [ABSTRACT FROM AUTHOR]

This contribution is focused on Raman analysis of the InxGa1-xN alloy. It presents direct evidence that both strain and composition effects must be taken into account to interpret the Raman experimental results. Raman studies have been commonly discussed in view of composition inhomogeneity only, neglecting the possible existence of strain depth variations, recently shown to occur for layers grown above the critical layer thickness. The effects of this variation on the A1(LO) phonon frequency could only be investigated by combining both structural and Raman measurements. In this letter, a set of InxGa1-xN layers has been chemically etched during different periods, allowing the depth variation of the phonon frequency to be unambiguously evidenced. Comparing the Raman spectra before and after etching, two distinct InxGa1-xN regions, differing on their strain state, are identified: a relaxed one, found near the surface region; another one, grown coherently (i.e., pseudomorphic) to the GaN buffer layer. These results are in excellent agreement with an additional reciprocal space map analysis. [ABSTRACT FROM AUTHOR]

Ge:Ga blocked-impurity-band detectors having long-wavelength thresholds of 190 μm and peak quantum efficiencies of 4% have been fabricated. This performance approaches that of state-of-the-art discrete Ge:Ga photoconductors, with the additional benefit of good response at wavelengths longer than that obtained with unstressed photoconductors. [ABSTRACT FROM AUTHOR]

We have compared directly the performance of a Pb[sub 1-x]Sn[sub x]Te(In) photodetector with that of two other state-of-the-art far-infrared detectors: a Si(Sb) blocked impurity band (BIB) detector and a Ge(Ga) photoconductor in an integrating cavity. The Pb[sub 1-x]Sn[sub x]Te(In) photodetector has current responsivity S[sub I] several orders of magnitude higher than the Si(Sb) BIB at wavelength λ=14.5 μm. Persistent photoresponse with S[sub I]∼10[sup 3] A/W at 40 mV bias and 1 s integration time at the wavelengths λ=90 and 116 μm has also been observed in the Pb[sub 1-x]Sn[sub x]Te(In) photodetector. This is larger by a factor of ∼100 than the responsivity of the Ge(Ga) photoconductor in the same conditions. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]