The optical constants of GaeslInu4sP have been determined from 0.8 to 5.0 eV using variable-angle spectroscopic ellipsometry measurements at room temperature. The metal-organic vapor-phase-epitaxy-grown samples were x-ray analyzed to confirm lattice matching to the GaAs substrate. The effects of the native oxide were numerically removed from the data to determine the intrinsic optical constants. This is important because the optical constants reported become generally useful for modeling multiple-layer structures. A Kramers-Kronig analysis was used to reduce interference-related fluctuations in the below-gap refractive index. Near the band edge a mathematical form for excitonic absorption was included. Critical point energies were extracted using a numerical second-derivative fitting algorithm. 0 1995 American Institute of Physics.
Pseudodielectric functions (E) = (et) + i(eZ) of GaAs were measured by spectroscopic ellipsometry (SE), in the range of 1.W.45 eV, at temperatures from room temperature (RT) to -610 "C. A very clean, smooth surface was obtained by first growing an epitaxial layer of GaAs on a GaAs substrate and immediately capping it with a protective layer of arsenic. The cap prevented surface oxidation during transport to the measurement chamber, where it was evaporated under ultrahigh vacuum at -350 "C. Room-temperature SE results from this surface are in good agreement with those in the literature obtained by wet-chemical etching. A quantitative analysis of the (E) spectrum was made using the harmonic-oscillator approximation (HOA). It is shown by the HOA that the El and El + A, energy-band critical points shift downward -300 meV as temperature increases from RT to -610 "C. An algorithm was developed, using the measured optical constants at a number of fixed temperatures, to compute the dielectric function spectrum at an arbitrary temperature in the range of 22-610 "C!. Therefore, the ellipsometer can be utilized as an optical thermometer to determine the sample surface temperature.
The ideal operation of CdZnTe devices entails having a uniformly distributed internal electric field. Such uniformity especially is critical for thick long-drift-length detectors, such as large-volume CPG and 3-D multi-pixel devices. Using a high-spatial resolution X-ray mapping technique, we investigated the distribution of the electric field in real devices. Our measurements demonstrate that in thin detectors, <5 mm, the electric field-lines tend to bend away from the side surfaces (Le., a focusing effect). In thick detectors, 21 cm, with a large aspect ratio (thickness-to-width ratio), we observed two effects: the electric field lines bending away from or towards the side surfaces, which we called, respectively, the focusing field-line distribution and the defocusing field-line distribution. In addition to these large-scale variations, the field-line distributions were locally perturbed by the presence of extended defects and residual strains existing inside the crystals. We present our data clearly demonstrating the non-uniformity of the internal electric field.
Anisotropic dielectric functions of sapphire have been determined by both reflection and transmission variable angle spectroscopic ellipsometry. The measurements were made on a-plane (21̄1̄0) sapphire substrates in the energy range of 0.75–6.5 eV at room temperature. The orientation of the optic axis of the a-plane sapphire sample was determined by polarized Raman scattering based on which the Euler angles are set for the fitting model. Two pairs of Cauchy user-defined functions were constructed to describe the optical constants of both ordinary n⊥(ω) and extraordinary n∥(ω) rays, respectively. As a result the optical constants from the generalized ellipsometry analysis are in good agreement with the reported data. The Kramers–Kronig (KK) relation between the real and the imaginary part have been carefully checked for both ordinary and extraordinary rays. The perfect fitting between the calculated and experimental ε1(ω) function indicates that both functions of ordinary and extraordinary rays are KK consistent. The refractive index difference between the ordinary and extraordinary rays is close to a constant (+0.008), which is determined mainly by the off-diagonal signal of the transmission ellipsometry data. The extinction coefficients are zero below 6 eV, and increase rapidly above 6 eV.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.