Abstract
Platinum germanides (PtGe) were investigated for infrared plasmonic applications. Layers of Pt and Ge were deposited and annealed. X-ray diffraction identified PtGe(2) and Pt(2)Ge(3) phases, and x-ray photo-electron spectroscopy determined vertical atomic composition profiles for the films. Complex permittivity spectra were measured by ellipsometry over the 2 to 15 μm wavelength range. Surface plasmon polariton (SPP) characteristics such as propagation length and field penetration depth were calculated. Photon-to-SPP couplers in the form of 1D lamellar gratings were fabricated and characterized in the range 9 - 10.5 μm via wavelength-dependent specular reflection spectra for multiple angles of incidence. The observed resonances compare well with calculated spectra for SPP excitation on PtGe(2). Platinum germanides are CMOS compatible and may serve as SPP hosts for on-chip mid-IR plasmonic components with tighter field confinement than noble-metal hosts.
Highlights
Plasmonic devices confine and guide electromagnetic waves at sub-wavelength dimensions
We report here the investigation of germanides as new Surface plasmon polariton (SPP) host materials with plasma wavelengths in the near-infrared and at shorter wavelengths that doped semiconductors can offer
We suppose that the SPP host material is useful when the field penetration depth into the dielectric Lair is less than three times the wavelength; e.g. for PtGe2, we see from Fig. 5 that this holds for wavelengths smaller than about 6.9 μm
Summary
Plasmonic devices confine and guide electromagnetic waves at sub-wavelength dimensions. Sub-wavelength mode confinement requires that the plasma frequency be closer to the operational frequencies Doped semiconductors, such as Si, Ge, and related alloys [1, 5, 6], InAs [7], and metal oxides [8, 9] have been investigated as design-tunable plasmonic materials for the infrared. We report here the investigation of germanides as new SPP host materials with plasma wavelengths in the near-infrared and at shorter wavelengths that doped semiconductors can offer. These may help bridge the gap between the doped semiconductors and metals. Platinum germanide is the subject of this paper, though other metals like Pd, Ni, and Cu, can be used readily to create germanides with expected performance similar to that of PtGe in the same way that Pd-, Ni-, and Cusilicides demonstrate similar optical properties to PtSi [12]
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