Fabrication of mid-infrared plasmonic antennas based on heavily doped germanium thin films

Abstract

Fabrication of mid-infrared plasmonic antennas based on heavily doped germanium thin films, Thin Solid Films (2015Films ( ), doi: 10.1016Films ( /j.tsf.2015 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ) germanium was used to fabricate dipole antennas of 800 nm width with a gap spacing of 300 nm which demonstrate resonance frequencies around 13 µm and 13.5 µm for 2 µm and 3 µm long structures, respectively. This technology has the potential to be used for midinfrared sensing applications of hazardous gases and liquids. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT

Nanomaterial‐Based Plasmon‐Enhanced Infrared Spectroscopy

“…From the perspective of device integration, we need to rely on semiconductors (especially group-IV semiconductors), which additionally can be used to dynamically adjust the resonance frequency through chemical doping or electrical gating. Thus, a wide range of doped semiconductors have been explored as mid-IR plasmonic materials, such as group-IV semiconductors (e.g., Si, [27,101,102] Ge, [28][29][30] and SiC [103] ), group III-V semiconductors (e.g., GaAs, [104,105] InAs, [32,33] InAsSb, [35] GaN, [106] and GaP [107] ), and oxide semiconductors (e.g., indium tin oxide (ITO), [108] aluminum-doped zinc oxide (AZO), [109] and gallium-doped zinc oxide (GZO) [110] ). For example, silicon, the most widely used semiconductor, can be highly doped to achieve a free-carrier concentration as high as 10 20 cm −3 using various approaches (e.g., ion implantation) [27,101] that is promising for IR plasmonics.…”

“…[112] In contrast to Si, doped Ge has a smaller effective electron mass (cf. m*  0.12 for Ge [29] and m*  0.26 for Si [113] ), leading to a higher plasma frequency for a given doping level, according to Equation 1. Additionally, Ge can be grown epitaxially with great quality (thus contributing to displaying improved plasmon performance), a method that is compatible with Si-based CMOS technology, and therefore amenable to integration in compact microchips.…”

“…[9,10] Subsequently, numerous SEIRA nanoscale morphologies [5,[16][17][18] have been proposed and experimentally demonstrated to significantly enhance the resonance signals for an expanding range of applications. [7,8,19,20] Most recently, renewed interest in new IR plasmonic materials (e.g., graphene, [21][22][23][24][25][26] Si, [27] Ge, [28][29][30][31] InAs, [32,33] InSb, [34] InAsSb, [35] oxides, [36,37] and carbon nanotubes (CNTs) [38,39] ) has arisen within the community, extensively pushing the development of SEIRA. [40,41] Among these materials, graphene has been a central focus of attention because of its unique plasmonic properties when it is highly doped.…”

Mid-Infrared Sensing Using Heavily Doped Germanium Plasmonics on Silicon Substrates

“…Subsequently, an inductively coupled plasma tool was used to etch the antennas using SF6 and C4F8 in a mixed chemistry process [9] which has been demonstrated to produce low electrical damage in the fabrication of Si nanowire devices [10]. Figure 1(a) demonstrates a scanning electron microscope (SEM) image of fabricated 1 μm thick double n-Ge antennas with lengths of 2 μm and a gap of 300 nm [11]. The MIR response of the fabricated antenna structures has been characterized by Fourier transform infra-red (FTIR) spectroscopy.…”

Mid-Infrared Sensing Using Heavily Doped Germanium Plasmonics on Silicon Substrates

“…Subsequently, an inductively coupled plasma tool was used to etch the antennas using SF6 and C4F8 in a mixed chemistry process [9] which has been demonstrated to produce low electrical damage in the fabrication of Si nanowire devices [10]. Figure 1(a) demonstrates a scanning electron microscope (SEM) image of fabricated 1 μm thick double n-Ge antennas with lengths of 2 μm and a gap of 300 nm [11]. Figure 1 The MIR response of the fabricated antenna structures has been characterized by Fourier transform infra-red (FTIR) spectroscopy.…”