Transparent conducting metal oxides (TCO) are unusual semiconducting materials displaying transparency to visible light. TCO materials are used for electrostatic shielding, antistatic screens, transparent heating devices, solar cells and even organic light emitting diodes. However, most TCOs are n-type, while p-type TCOs are scarce. SrCu2O2 is a leading candidate as a p-type transparent conductive oxide. In this paper, we report theoretical calculations and experimental studies on the vibrational, optical and microstructural properties of both bulk and thin films of polycrystalline undoped SrCu2O2 obtained by pulsed laser deposition (PLD). Barium doping of the SrCu2O2 by substitution of Sr atoms is also reported. The simulated crystal structures of both SrCu2O2 and BaCu2O2 materials, obtained through a state-of-the-art implementation of the Density functional theory, are compared with experimental X-ray diffraction data of undoped and Ba-doped SrCu2O2 bulk materials. Raman spectra of both SCO and BCO materials are simulated from the derivatives of the dielectric susceptibility and a symmetry analysis of the optical phonon eigenvectors at the Brillouin zone center is proposed. Good agreement with Raman scattering experimental results is demonstrated.
Lattice-matched GaP-based nanostructures grown on silicon substrates is a highly rewarded route for coherent
integration of photonics and high-efficiency photovoltaic devices onto silicon substrates. We report on the structural and
optical properties of selected MBE-grown nanostructures on both GaP substrates and GaP/Si pseudo-substrates. As a
first stumbling block, the GaP/Si interface growth has been optimised thanks to a complementary set of thorough
structural analyses. Photoluminescence and time-resolved photoluminescence studies of self-assembled (In,Ga)As
quantum dots grown on GaP substrate demonstrate a proximity of two different types of optical transitions interpreted as
a competition between conduction band states in X and Γ valleys. Structural properties and optical studies of
GaAsP(N)/GaP(N) quantum wells coherently grown on GaP substrates and GaP/Si pseudo substrates are reported. Our
results are found to be suitable for light emission applications in the datacom segment. Then, possible routes are drawn
for larger wavelengths applications, in order to address the chip-to-chip and within-a-chip optical interconnects and the
optical telecom segments. Finally, results on GaAsPN/GaP heterostructures and diodes, suitable for PV applications are
reported.
During the recent years, there has been a growing interest on the physical properties of zirconium dioxide (ZrO2) for its possible use as high-k material and its application in optical coatings technology as high-refractive index material. In the present work we study the optical and structural properties of ZrO2 thin films obtained by plasma ion-assisted deposition (PIAD) on silicon wafers, in their as-deposited state and after annealing of the samples at different temperatures. The optical properties were studied by variable angle spectroscopic ellipsometry in the visible spectral range, while the structural properties were analyzed with grazing-incidence x-ray diffraction and x-ray reflectometry. The experimental results show a clear correlation between the optical properties and the variations of the structural properties due to the annealing. Thus, the as-deposited layers show a poor crystalline state, with a low refractive index and energy band-gap. As the annealing temperature was augmented, the degree of crystallinity was increased, as well as the refractive index and the band-gap. Moreover, the annealing also induced a reduction of the layer thickness and a slight increase of the surface roughness.
Mircea Modreanu, P. Hurley, B. O'Sullivan, Breda O'Looney, Jean-Pierre Senateur, H. Rousell, F. Rousell, M. Audier, C. Dubourdieu, Ian Boyd, Q. Fang, T. Leedham, S. Rushworth, A. Jones, Hywel Davies, C. Jimenez
The optical properties of a set of high-k dielectrics HfO2 thin films obtained by two different modified metal organic chemical vapour deposition (MOCVD) techniques were studied using spectroscopic ellipsometry (SE). HfO2 thin films with thickness varying from 10-40 nm were formed over a range of temperatures (300-425°C). After deposition the sample were annealed by Rapid Thermal Annealing (RTP) at 800°C in an oxygen/argon ambient and UV annealing at 400°C in oxygen. The films were analysed physically using XRD and FTIR. The XRD results show that as-deposited HfO2 films microstructure strongly depends on deposition temperature. Both polycrystalline (T>365°C) and amorphous films (T<320oC) were formed. The polycrystalline structure is identified as monoclinic. The SE results demonstrate that as-deposited amorphous HfO2 thin films have a high degree of porosity. After annealing at 800oC in oxygen and in nitrogen ambient, due to the solid phase crystallisation, as-deposited amorphous HfO2 thin films become crystalline and the film porosities are strongly reduced. In addition, an increase of the refractive index and a decrease of the film thickness are also obtained. Optical properties of the as-deposited polycrystalline HfO2 are also improved after annealing and an increase of the refractive index and a decrease of the film thickness is also obtained.
In this work we report the application of optical spectroscopic techniques namely photoreflectance (PR), ellipsometry and photoluminescence (PL) for qualification of InGaP/GaAs multi-layer heterojunction bipolar transistor (HBT) material. These techniques reveal important information regarding the quality of the different InGaP and GaAs layers for the emitter, base, collector and surface cap regions. In particular PR studies of non-optimal HBT material reveals InGaP (emitter) layer sub-lattice ordering effects, as correlated with selective area electron diffraction patterns. Moreover, comparison of the emitter/base interface field levels and InGaP ordering data reveals further evidence of a non-abrupt InGaP/GaAs heterojunction, proving to have adverse consequences for HBT current gain characteristics and consistent with measured reduced common emitter current gain. Supporting evidence for such non-optimal, strained emitter/base region is provided from x-ray (004) & (002) diffraction but mainly from cleaved edge (g=002) dark field TEM, revealing significant interfacial non-uniformity, also likely correlated to the emitter layer ordering present. PR spectral information is compared with PL lineshape data - including Arrhenius (thermal) plots, while extracted interfacial electric field data are also supported by device finite-element (ANSYS) modelling. In summary this paper demonstrates the application of non-destructive and rapid techniques for evaluation and control of compound semiconductor materials for HBT technology.
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