Y. W. Jung

InAs critical-point energies at 22 K from spectroscopic ellipsometry

We report dielectric function data from 0.74 to 6.54 eV for InAs at 22 K, obtained by spectroscopic ellipsometry. Critical-point (CP) structures are blueshifted and significantly sharpened relative to those seen at room-temperature (RT). The E0′, E2Δ, E2, E0′+Δ0′, and E2′ features in the E2 energy range of 4.0 to 5.6 eV cannot be resolved at RT but are clearly separated at 22 K. The energies of the CPs giving rise to these structures are determined by line shape fitting to numerically calculated second energy derivatives, and their Brillouin-zone locations identified by band structure calculations using the linear augmented Slater-type orbital method.

Effect of overlayers on critical-point parameters in the analysis of ellipsometric spectra

As the complete removal of overlayers may not be possible in general, the authors investigate the effect of incomplete removal on critical-point parameters in the analysis of ellipsometric data. Using an approximate analytic expression, they show that energies and broadening parameters are much less affected by overlayers than amplitudes and phases. These conclusions are confirmed by false-data calculations for GaAs and overlayer-removal data for CdTe.

Model dielectric functions for AlxGa1−xAs alloys of arbitrary compositions

Many optical models have been used to construct analytic composition-dependent dielectric functions of AlxGa1−xAs alloys. However, these models incorporate various unphysical assumptions to improve their fits to data. Here, we provide the parameters needed to calculate dielectric functions of AlxGa1−xAs for 1.5≤E≤6.0 eV and 0≤x≤1 by means of the parametric model of Johs et al. [Thin Solid Films 313–314, 137 (1998)], which eliminates these problems. A representative example concerning interface analysis is discussed, where it is necessary to construct a dielectric function of an alloy of essentially arbitrary composition.

Dielectric response of AlSb from 0.7 to 5.0 eV determined by in situ ellipsometry

We present pseudodielectric function data ⟨e⟩=⟨e1⟩+i⟨e2⟩ from 0.7 to 5.0 eV of oxide-free AlSb that are the closest representation to date of the intrinsic bulk dielectric response e of the material. Measurements were done on a 1.5 μm thick film grown on (001) GaAs by molecular beam epitaxy. Data were obtained with the film in situ to avoid oxidation artifacts. Overlapping critical-point (CP) structures in the E2 energy region were identified by means of band-structure calculations done with the linear augmented Slater-type orbital method. Calculated CP energies agree well with those obtained from data, confirming the validity of the calculations.

Dielectric functions and interband transitions of In1−xAlxSb alloys

Pseudodielectric functions ⟨e⟩ of In1−xAlxSb ternary alloy films were determined from 1.5 to 6.0 eV by spectroscopic ellipsometry. Overlayer effects were minimized by performing in situ chemical etching to more accurately determine intrinsic bulk dielectric responses. Critical-point (CP) energies of structures were determined from numerically calculated second energy derivatives. Where necessary, Brillouin-zone origins were identified by electronic band structure calculations done with the linear augmented Slater-type orbital method. These calculations also showed increasing separation of the E2 and E2′ CP structures with increasing Al-composition

Overlayer effects in the critical-point analysis of ellipsometric spectra: Application to InxGa1−xAs alloys

We investigate the effect of incomplete removal of semiconductor overlayers on critical-point (CP) parameters determined from the analysis of ellipsometric spectra. An approximate analytic expression shows that CP energies and broadening parameters should be relatively unaffected for isolated CPs if the dielectric response of the overlayer varies slowly with energy. The results are confirmed by model calculations for InAs, which show that the energies of the E1 and E1+Δ1 CP structures that are commonly used for compositional analysis of semiconductor alloys are relatively unaffected. We also analyze overlayer-removal data for a series of InxGa1−xAs alloy samples. Consistent with the above, the amplitudes and phases are affected significantly for all CPs, while the energies of the well-separated E1 and E1+Δ1 transitions are relatively invariant. The results show that accurate values of composition can be obtained from the analysis of the E1 and E1+Δ1 CP structures, even if complete removal of overlayers is...