Observation of hot-electron energy loss through the emission of phonon-plasmon coupled modes in GaAs

Overcoming the Fermi-Level Pinning Effect in the Nanoscale Metal and Silicon Interface

Silicon-based photodetectors are attractive as low-cost and environmentally friendly optical sensors. Also, their compatibility with complementary metal-oxide-semiconductor (CMOS) technology is advantageous for the development of silicon photonics systems. However, extending optical responsivity of silicon-based photodetectors to the mid-infrared (mid-IR) wavelength range remains challenging. In developing mid-IR infrared Schottky detectors, nanoscale metals are critical. Nonetheless, one key factor is the Fermi-level pinning effect at the metal/silicon interface and the presence of metal-induced gap states (MIGS). Here, we demonstrate the utilization of the passivated surface layer on semiconductor materials as an insulating material in metal-insulator-semiconductor (MIS) contacts to mitigate the Fermi-level pinning effect. The removal of Fermi-level pinning effectively reduces the Schottky barrier height by 12.5% to 16%. The demonstrated devices exhibit a high responsivity of up to 234 μA/W at a wavelength of 2 μm, 48.2 μA/W at 3 μm, and 1.75 μA/W at 6 μm. The corresponding detectivities at 2 and 3 μm are 1.17 × 108 cm Hz1/2 W-1 and 2.41 × 107 cm Hz1/2 W-1, respectively. The expanded sensing wavelength range contributes to the application development of future silicon photonics integration platforms.

Hot carrier relaxation in CdTe via phonon-plasmon modes

Carrier and lattice dynamics of laser excited CdTe was studied by time-resolved reflectivity for excitation fluences spanning about three orders of magnitude, from 0.064 to 6.14 mJ cm^-2. At fluences below 1 mJ cm^-2 the transient reflectivity is dominated by the dynamics of hybrid phonon-plasmon modes. At fluences above 1 mJ cm^-2 the time-dependent reflectivity curves show a complex interplay between band-gap renormalization, band filling, carrier dynamics and recombination. A framework that accounts for such complex dynamics is presented and used to model the time-dependent reflectivity data. This model suggests that the excess energy of the laser-excited hot carriers is reduced much more efficiently by emitting hybrid phonon-plasmon modes rather than bare longitudinal optical phonons.

Upconverted hot-luminescence spectroscopy investigation of nonradiative relaxation in forsterite

Upper-state nonradiative relaxation in the 3.2-1.9-eV energy region of the excited-state manifold of Cr(4+)-doped forsterite is investigated. Measurements of the upconverted hot-luminescence spectra reveal two electronic bottlenecks and several phonon modes involved in the initial steps of the vibrational relaxation at different portions of the excited-state manifold.