Ellipsometric characterization of doped Ge_095Sn_005 films in the infrared range for plasmonic applications

Abstract

GeSn as a group-IV material opens up new possibilities for realizing photonic device concepts in Si-compatible fabrication processes. Here we present results of the ellipsometric characterization of highly p- and n-type doped Ge_0.95Sn_0.05 alloys deposited on Si substrates investigated in the wavelength range from 1 to 16 μm. We discuss the suitability of these films for integrated plasmonic applications in the infrared region.

Photonic-Plasmonic Mode Coupling in Nanopillar Ge-On-Si Pin Photodiodes

“…The integration volume dV spans the intrinsic region of the NP by following the procedure from [21]. The wavelengthdependent refractive index of Ge nGe(λ) used in simulation was extracted from ellipsometry measurements on the material used for diode fabrication (permittivity values were derived from this data as well; for data acquisition procedures see [22]). The active layers of the Ge PIN photodiode were grown in a molecular beam epitaxy (MBE) system under coevaporation of the dopants.…”

On-chip liquid sensing using mid-IR plasmonics

“…Unfortunately, it is not always useful for mid-IR liquid-sensing applications, where coupling to active or passive on-chip components on the wavelength-scale is needed. For avoiding those limitations of metalbased mid-IR plasmonics, lower-plasma-frequency materials have been demonstrated, including highly-doped epitaxial semiconductors (Taliercio and Biagioni, 2019;Ehlers and Mills, 1987;Gómez Rivas et al, 2004;Ginn et al, 2011;Law et al, 2012;N'tsame Guilengui et al, 2012;Augel et al, 2016;Frigerio et al, 2016;Pellegrini et al, 2018), such as Ge, Si, III-Vs (e.g., GaP and GaN) or II-VIs (Barker, 1968;Harima et al, 1998;Streyer et al, 2014;Zhong et al, 2015;Taliercio and Biagioni, 2019), transparent conductive oxides (Zhong et al, 2015;Castellano, 2022), silicides (Soref et al, 2008;Naik et al, 2013;Zhong et al, 2015), transition metal nitrides (Zhong et al, 2015) and graphene (Fei et al, 2012;Grigorenko et al, 2012;Zhong et al, 2015;Constant et al, 2016). However, they mainly fit to Si-photonics integration or to implementation into CMOS-structures and lack simple fabrication and implementation protocols, compatible with mid-IR technology.…”

Ex situ n+ doping of GeSn alloys via non-equilibrium processing

“…The heavily P implanted GeSn has an average effective carrier concentration in the range of 5×10 19 cm −3 . Highly n-type doped group-IV semiconductors Ge and GeSn are particularly interesting materials for mid-infrared plasmonic applications which cannot be realized using conventional plasmonic materials like metals [8,38]. Figure 5 shows the room temperature reflectivity as a function of the wavenumber of the incident light for an un-doped GeSn film, a P implanted layer and an in situ Sb doped GeSn with a similar active carrier concentration in the range of 5×10 19 cm −3 .…”

“…The small separation of only 134 meV between the direct band gap at the Γ point and the indirect band gap at the L point allows for the possibility to convert Ge from an indirect to a direct band gap material [1][2][3]. This approach can be realized by: (i) ultrahigh n-type doping, (ii) introducing biaxial tensile strain and (iii) alloying with Sn [4][5][6][7][8][9]. The n-type Ge becomes a direct band gap material for an electron concentration higher than 8×10 19 cm −3 .…”