Low-loss plasmonic metals from heavily doped InAs for infrared optoelectronic devices

Plasmonic enhancements of optoelectronic devices, such as emitters and detectors, have traditionally used metals such as gold and aluminum. However, these materials are susceptible to high losses in the infrared region, limiting their usefulness for infrared devices, a field with growing interest. To address this problem, we use heavily doped III-V semiconductors to produce low-loss plasmonic epilayers that can be monolithically integrated with traditional III-V infrared optoelectronic devices using well established semiconductor foundries. We show that heavily tellurium-doped and a heavily silicon-doped indium arsenide (InAs) epilayers exhibit plasma frequencies as high as 4.5 microns for an electron concentration of 7x10¹⁹ cm^-3. We also show through spectroscopic ellipsometry that losses are dopant dependent. In the case of silicon-doped InAs the losses increase with increasing doping. Conversely, in the case tellurium-doped InAs the losses decrease with higher electron concentrations. Fabricated one-dimensional gratings with pitches and linewidths from 1 to 5 microns show strong resonances (absorption up to 95%) with quality factors as high as 7. Electromagnetic models based on finite element solvers confirm experimental results using permittivity functions determined from spectroscopic ellipsometry.