Employing the Keldysh diagram technique, we calculate the electron-phonon energy relaxation rate in a conductor with the vibrating and static ␦-correlated random electron-scattering potentials. If the scattering potential is completely dragged by phonons, this model yields the Schmid's result for the inelastic electronscattering rate e-ph Ϫ1. At low temperatures the effective interaction decreases due to disorder, and e-ph Ϫ1 ϰT 4 l ͑l is the electron mean-free path͒. In the presense of the static potential, quantum interference of numerous scattering processes drastically changes the effective electron-phonon interaction. In particular, at low temperatures the interaction increases, and e-ph Ϫ1 ϰT 2 /l. Along with an enhancement of the interaction, which is observed in disordered metallic films and semiconducting structures at low temperatures, the suggested model allows us to explain the strong sensitivity of the electron relaxation rate to the microscopic quality of a particular film.

Since the original invention by Samuel P. Langley in 1878 5 , bolometers have gone a long way of improving the sensitivity and expanding the frequency range, from X-rays and optical/UV radiation to the submillimeter waves. The latter range contains approximately half the total luminosity of the Universe and 98% of all the photons emitted since the Big Bang 6 .Because the performance of ground-based THz telescopes is severely limited by a strong absorption of THz radiation in the Earth atmosphere, the development of space-based THz telescopes will be crucial for better understanding of the Universe evolution. Active cooling of primary mirrors on these telescopes will reduce the mirror emission below the cosmic background level (Fig. 1) and greatly expand the range of observable faint objects. The development of advanced detectors with background-limited sensitivity for such telescopes poses a significant challenge. Indeed, the photon flux N ph , which corresponds to the cosmic background fluctuations, is very weak: at ν > 1 THz, the photon flux in a diffraction-limited beam does not exceed 100 photons/s for typical extragalactic emission lines with ν/δν ~ 1000. The noise equivalent power (NEP) of a background-limited detector should be less than NEP ph = hν 2N ph ~ 10 -20 W/Hz 1/2 , which is a factor of 100 lower than that of state-of-the-art bolometers.Although new detector concepts are coming into play nowadays 7,8 , bolometers still have a great potential for achieving the most challenging goals. Realization of the ultra-high sensitivity requires an unprecedented thermal isolation of a bolometer. Indeed, in the fluxintegrating regime (the bolometric time constant τ >> N ph -1 ), the minimum NEP is determined by the thermal energy fluctuations in a bolometer, and the corresponding value ofG is controlled by the thermal conductance G between the bolometer and its environment. In a traditional (the so-called "geometrically isolated") bolometer, G is determined by the number of relevant phonon and photon "channels" (modes) participating in thermal transport between the sensor and its environment. It has been shown recently for both photons 3,9 and phonons 10 that the thermal conductance of a short single channel is determined by the universal value G Q = π Despite a relatively small size of this micromachined device, the heat capacity C was still rather large, which resulted in a slow bolometric response with the time constant τ = C/G =1-10 s.Here we present a novel approach that enables a significant increase of the bolometer sensitivity and, at the same time, reduction of its response time. Fast response in a well isolated bolometer requires a very small heat capacity C and, thus, the nanoscale dimensions of a sensor.To overcome the limitation of fast phonon exchange, we realized the hot-electron regime 11, , 12 13 in superconducting nanobolometers at sub-Kelvin temperatures. In this case, a weak electronphonon coupling, which governs the effective thermal conductance, dramatically improves the thermal isola...

We report a 50% increase in the power conversion efficiency of InAs/GaAs quantum dot solar cells due to n-doping of the interdot space. The n-doped device was compared with GaAs reference cell, undoped, and p-doped devices. We found that the quantum dots with built-in charge (Q-BIC) enhance electron intersubband quantum dot transitions, suppress fast electron capture processes, and preclude deterioration of the open circuit voltage in the n-doped structures. These factors lead to enhanced harvesting and efficient conversion of IR energy in the Q-BIC solar cells.

We study the electron-phonon relaxation (dephasing) rate in disordered semiconductors and low-dimensional structures. The relaxation is determined by the interference of electron scattering via the deformation potential and elastic electron scattering from impurities and defects. We have found that in contrast with the destructive interference in metals, which results in the Pippard ineffectiveness condition for the electron-phonon interaction, the interference in semiconducting structures substantially enhances the effective electron-phonon coupling. The obtained results provide an explanation to energy relaxation in silicon structures.

Layered van der Waals heterostructures have attracted considerable attention recently, due to their unique properties both inherited from individual two-dimensional (2D) components and imparted from their interactions. Here, a novel few-layer MoS /glassy-graphene heterostructure, synthesized by a layer-by-layer transfer technique, and its application as transparent photodetectors are reported for the first time. Instead of a traditional Schottky junction, coherent ohmic contact is formed at the interface between the MoS and the glassy-graphene nanosheets. The device exhibits pronounced wavelength selectivity as illuminated by monochromatic lights. A responsivity of 12.3 mA W and detectivity of 1.8 × 10 Jones are obtained from the photodetector under 532 nm light illumination. Density functional theory calculations reveal the impact of specific carbon atomic arrangement in the glassy-graphene on the electronic band structure. It is demonstrated that the band alignment of the layered heterostructures can be manipulated by lattice engineering of 2D nanosheets to enhance optoelectronic performance.