Publisher Summary A refractive index can be increased by ion implantation by changes in density and structure, by the addition of high-polarizability impurity ions, by a reduction of the plasma effect that increases the index and that is most important in the wavelength region far from the energy gap, and by absorption changing in the index in the region of the gap, that is, via the Kramers–Kronig relation. This chapter discusses the optical properties of implanted semiconductors, electrooptic components formed by ion implantation, general principles that determine most luminescent systems, effects of implantation temperature, luminescence centers in LiF-Mg-Ti radiation dosimeters, and use of line spectra in defect studies. In the LiF system, the luminescence bands are broad, and if alternative versions of the same complex exist, they cannot be resolved from the spectra. The addition, by implantation, of ions with incomplete inner electron shells opens up new possibilities as the lattice distortions of the free-ion energy levels are strongly perturbed by the defects in the neighborhood of the ion.

Optical Effects of Ion Implantation

By using reflectivity and absorption measurements in the region 5 to 35 micron, the effect of free carriers on the optical constants has been determined for $n$- and $p$-type germanium, silicon, and indium antimonide, and for $n$-type indium arsenide. The contribution of the free carriers to the electric susceptibility is obtained from the optical constants. A carrier effective mass, ${m}_{s}$, is defined in terms of the susceptibility, and the significance of ${m}_{s}$ is considered for four different types of energy band structure. The experimental values of ${m}_{s}$ are compared with those calculated by using data from other experiments. Good agreement was found for $n$- and $p$-type silicon, $n$-type germanium, and $p$-type indium antimonide. In $p$-type germanium, the susceptibility due to transitions between the overlapping bands in the valence band was taken into account. However, the resulting ${m}_{s}$, for a sample of \ensuremath{\sim}${10}^{19}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ impurity concentration, is larger by a factor of 1.8 than that calculated by using cyclotron resonance data. In $n$-type indium antimonide ${m}_{s}$ increases with carrier concentration. If one assumes ${m}_{s}$ to be energy-dependent, the shape of the conduction band calculated is consistent with previously reported measurements of the shift of the intrinsic absorption edge with electron concentrations. In the case of $n$-type indium arsenide, ${m}_{s}$ differs from the effective mass reported from thermoelectric measurements but gives good agreement with the values determined from the shift of the intrinsic absorption edge for an impure specimen.

Determination of Optical Constants and Carrier Effective Mass of Semiconductors

In an investigation of the fundamental optical absorption edge of indium oxide at room temperature, transitions identified as direct‐allowed have been observed with an energy gap (probably at k=0) of 3.75 eV. Indirect‐forbidden transitions have also been observed with an energy gap of 2.619 eV and an assisting phonon of 0.069 eV. It is proposed that the minimum of the conduction band is at k=0 and the maximum of the valence band is at k≠0.

Optical Properties of Indium Oxide

The optical absorption of dispersions of gold particles is studied as a function of particle size, temperature, and method of preparation. The absorption spectra for gold sols in glass and water with small spread in particle size are compared to spectra calculated from Mie theory and the most reliable of recently measured optical constants of gold. The comparisons indicate that the real part of the dielectric constant e1 for particles from 85 to 200 A in diameter is the same as for bulk gold, and that the imaginary part e2 is similar for particles and bulk, although some discrepancies exist. Gold sols in glass have optical properties closer to bulk gold than sols in water, probably because of defects and adsorbed material on the particles in water. Between wavelengths of about 0.40 and 0.45 μ the optical properties of the particles in glass are unchanged down to particles containing very few atoms. The optical absorption peak at 0.525 μ is unaffected by particle size down to a particle diameter of about 8...

Optical Properties of Small Gold Particles

Infrared transmission and reflectivity measurements from 1 to 25 \ensuremath{\mu} (microns) have been made on several samples of green alpha (hexagonal) SiC. The residual ray bands have been observed for the ordinary and extraordinary rays. The resonance frequencies are 2.380\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ (12.60 \ensuremath{\mu}) and 2.356\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ (12.73 \ensuremath{\mu}), respectively. From the reflectivity the high-frequency dielectric constant is found to be 6.7. A careful analysis shows that the residual ray bands can be fitted within experimental error by the classical dispersion theory within the correct choice of the dispersion parameters. From the parameters the value 10.0 is obtained for the low-frequency dielectric constant. The effective charge is $0.94e$. Complete description of the residual ray band for the extraordinary ray required, in addition to the main resonance, a weak resonance at 2.647\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ (11.33 \ensuremath{\mu}). A study on the effects of several different surface treatments shows the reflectivities reported here are an intrinsic property of the crystal. The room-temperature absorption coefficient as a function of wavelength in the range 1 to 10 \ensuremath{\mu} has been determined from transmission measurements. A number of weak lattice bands are observed between 5 and 10 \ensuremath{\mu}.

Infrared Properties of Hexagonal Silicon Carbide

Infra-red absorption in semiconductors is classified into four different types according to the mechanism: (i) intrinsic absorption associated with electron excitation across the energy gap; (ii) absorption due to the presence of free carriers; (iii) absorption associated with impurities or lattice defects; and (iv) absorption associated with lattice vibration. A general introduction is followed by some theoretical discussions. Electron excitation between different energy bands is discussed with emphasis on the intrinsic absorption edge. For the absorption by free carriers, the effects of electron scattering by lattice vibration and by impurity centres are considered. Absorption associated with localized electronic states is briefly discussed. Experimental results are discussed for four different semiconductors: germanium, silicon, indium antimonide, and tellurium. All four types of absorption have been investigated to some extent for germanium and silicon. The work done on these materials provides a pattern for infra-red studies on semiconductors. The absorption edge in indium antimonide is affected by the carrier concentration. Long wave-length absorption shows interesting behaviour, and the observed effects attributed to lattice vibration have provided information regarding the type of binding in the crystal. Tellurium, having an optical axis, is doubly refracting. Both the absorption edge and the absorption associated with free carriers depend on the direction of polarization of the radiation.

http://iopscience.iop.org/article/10.1088/0034-4885/19/1/304/pdf

H Y Fan

Papers

Infra-red Absorption in Semiconductors