Structure‐Dependent Spectrum Characteristics of Infrared Radiation from Metal–Semiconductor Surface Microstructures

Abstract

The thermal radiation at 8.5 THz resonating with the longitudinal optical (LO) phonon is emitted from surface Au-GaAs microstripe structures on undoped GaAs wafers. The emission spectrum comprises a component originating from the LO phonon resonant electric dipole and another one of blackbody-like emission subject to Planck's law for structures without or low mesa height. Narrow GaAs window yields thermal emission spectra with deep-and wideintensity drop at the higher-energy side of the LO phonon energy. This intensity drop is formed by the absorption of the emitted radiation by generating surface phonon polaritons and forms the weak background emission in the region of 260-350 cm À1 . An additional emission peak is observed at %350 cm À1 for highmesa structures. This peak is attributed to phonon-polariton-related emission, for which electric dipoles are yielded by pairs of polarization charges in Au-GaAs-Au mesa structures.

Mid-infrared thermal radiation resonating with longitudinal-optical like phonon from n++-doped GaN–semi-insulating GaN grating structure

“…This represents the property of a material with a wide Reststrahlen bandwidth of 170 cm -1 . This result contrasts with the property of structures on undoped GaAs wafers with the Reststrahlen bandwidth of 30 cm -1 , which results in the emission resonating with the LO-phonon energy [28,29]. These spectrum features reveal that n ++ -GaN stripes can replace metal stripes.…”

“…the line widths reflect their intrinsic emission property. This reflectance result contrasts with the decrease in LO-phonon resonant reflectance at the LO-phonon energy for structures on GaAs [28,29]. Table 1 shows that peaks β and γ have nearly the same intensity within the fitting error.…”

“…In comparison, a longer lifetime of 3 ps was reported for GaN [44]. At a high temperature of 630 K, the observed emission line width of the Au-u-GaAs stripe structures was in the range of 11-13 cm -1 [28,29]. Assuming the observed line width of 22 cm -1 for line β of sample A as homogeneous width, the lifetime of the LO phonon is calculated as 250 fs.…”

“…Tani et al reported that the dispersion of the refractive index affects the emission spectrum when the LO phonon is excited by an ultrashort-pulse light [39]. However, this effect is minor in the case of the emission from Au-GaAs surface stripe structures exhibiting emission line widths of 11-13 cm −1 [28,29]. In contrast, the emission spectrum of n ++ -GaN-SI-GaN comprises four or five lines covering a range of approximately 50 cm −1 .…”

“…In contrast, Schubert et al [27] ascribed this phenomenon to the effects of guided wave mode and IPhP, including SPhP or phononplasmon polariton. However, when lateral structures of metal line-and-space designs were introduced on the surface of an undoped (u-) GaAs wafer, an LO phonon resonant thermal radiation peak was observed at 8.5 THz (285 cm -1 ) with a width of 0.4 THz (12 cm -1 ) at 628 K [28,29]. This emission was obtained only for the emission window width of less than 10 µm, where partial coherence of the LO phonon was preserved.…”