<title>Far-infrared absorption of Czochralski germanium and silicon</title>

Abstract

The current research demonstrates the effectiveness ofboth silicon and germanium as transmissive materials for use within the far infrared wavelength range of2O to 160 microns. This study involves samples with a wide range ofresistivities and temperatures including: n-type Si of4000, 2000, 160, 65, 12, and 2.6 ohm-cm and p-type Si of 500 and 60 ohm-cm within a temperature range of -100°C to 250°C and n-type Ge of39, 25, 14.5, 5.0, 2.5, and 0.5 ohm-cm within a temperature range of-100°C to 100°C. Far infrared absorption mechanisms are briefly discussed. The experimental absorption data are used to discuss the interaction between absorption by lattice resonance and free carrier absorption. Highly resistive germanium and silicon are both found to be excellent transmissive materials in the far infrared. These studies may be used to develop the feasibility of silicon and germanium as optical windows or lenses within an extraterrestrial environment.

Far-infrared transmission of diamond structure semiconductor single crystals—silicon and germanium

“…15͒. 3 This result suggests a primary scattering mechanism of acoustic phonons which has a theoretical wavelength dependence of 1.5 . Germanium is expected to be similar to silicon in the dependence of its absorption coefficient on wavelength as outlined in theoretical treatments.…”

“…Our recent paper treated the absorption spectra in this range. 3 This study investigates the wavelength range of 20 to 160 m and seeks to present insights into techniques which may allow engineering of specific transmission characteristics for applications such as inter-satellite communications.…”

Micromachined silicon grisms for infrared optics

“…When antireflection coated to reduce Fresnel losses, high-purity float-zone silicon transmits well between 1.2 and ∼8 μm and, as shown in Fig. 2, from ∼20 to 40 μm (and beyond) [21][22][23][24][25][26][27][28]. Between these regions, infrared lattice absorption due to phonons is observed [25][26][27][28][29][30] and limits usable optical path lengths to a few mm or less.…”

“…2, from ∼20 to 40 μm (and beyond) [21][22][23][24][25][26][27][28]. Between these regions, infrared lattice absorption due to phonons is observed [25][26][27][28][29][30] and limits usable optical path lengths to a few mm or less. By using highresistivity (ρ > 1000 Ω-cm) float-zone silicon, for which the absorption coefficient can be small (e.g., α < 10 −2 cm −1 for λ between 1.2 and 6:5 μm) [23,24], and by insuring that the fabrication process neither creates excessive damage to the silicon lattice nor introduces impurities that can scatter light, the absorption losses can be kept at acceptable levels.…”

“…In our case, this processing is achieved incidentally during the deposition of the LPCVD nitride layer. Other absorption features can occur to 40 μm [25][26][27][28]34,35] and beyond [25][26][27][28]36]. The short wavelength cutoff occurs at a wavelength of approximately 1.1 to 1:2 μm [37,38] at the silicon bandgap.…”