N. N. Zinov’ev

Terahertz electroluminescence under conditions of shallow acceptor breakdown in germanium

The spectrum of spontaneous terahertz electroluminescence was obtained near the breakdown threshold of a shallow acceptor (Ga) in germanium. The emission spectra were recorded by the Fourier spectroscopy method at a temperature of ∼5.5–5.6 K. The emission spectrum exhibits narrow lines with maxima at ∼1.99 THz (8.2 meV) and ∼2.36 THz (9.7 meV), corresponding to the optical transitions of nonequilibrium holes from the excited impurity states to the ground state of impurity center. A broad line with a maximum at ∼3.15 THz (13 meV) corresponding to the hole transitions from the valence band to the impurity ground state is also seen in the spectrum. The contribution of the hole transitions from the states of the valence band increases upon an increase in the electric-field strength. Simultaneously, the optical transitions of nonequilibrium holes between the subbands of the valence band appear in the emission spectrum. The integral terahertz-emission power is ∼17 nW per 1 W of the input power.

Terahertz photoluminescence from GaAs doped with shallow donors at interband excitation

We report on the observation of efficient generation of terahertz radiation at continuous-wave interband excitation of n-GaAs at low temperatures. The radiative transitions, accompanying relaxation and trapping of photoexcited electrons to localized donor states or to empty states in impurity subband, lead to the emission of terahertz photons with a relatively high external quantum yield up to 0.3%.

Terahertz luminescence in strained GaAsN:Be layers under strong electric fields

The authors report on the experimental studies of terahertz emission from strained GaAsN∕GaAs microstructures doped with beryllium at the conditions of electric breakdown of the shallow impurity. The terahertz emission spectrum demonstrates several distinctive signatures that are related to spontaneous optical transitions between resonant and localized states of the acceptor. The energy spectrum calculated for the Be acceptor in the GaAsN∕GaAs heterostructure fits reasonably well with the experimentally observed peaks.The authors report on the experimental studies of terahertz emission from strained GaAsN∕GaAs microstructures doped with beryllium at the conditions of electric breakdown of the shallow impurity. The terahertz emission spectrum demonstrates several distinctive signatures that are related to spontaneous optical transitions between resonant and localized states of the acceptor. The energy spectrum calculated for the Be acceptor in the GaAsN∕GaAs heterostructure fits reasonably well with the experimentally observed peaks.

Electroluminescence from AlGaAs/GaAs quantum-cascade structures in the terahertz range

Electroluminescence from a quantum-cascade structure comprising 40 periods of GaAs/Al0.15Ga0.85As tunnel-coupled quantum wells (QW) was studied. A terahertz emission band in the range 1.0–1.8 THz is observed under bias exceeding 1.5–2.0 V. The emission band peak shifts linearly to higher frequency with the increasing bias. The effect is accounted for by spatially indirect electron transitions between states in the neighboring QWs.

Confocal terahertz imaging

We report on a configuration of confocal spatial filtering applied to terahertz imaging. Theoretical analysis of the confocal terahertz imaging layout agrees fairly well with the experimental observations of the enhancement of optical resolving power, both lateral and axial, leading to three-dimensional optical slicing, in comparison with the image properties obtained with a generic terahertz imaging.

Interaction of terahertz electromagnetic radiation with a probe-object system in a terahertz apertureless near-field microscope

The mechanism of the interaction of coherent terahertz radiation with a probe-nanoobject system has been experimentally investigated in a terahertz apertureless near-field microscope. It has been found that the type of the material of a sample under the probe, as well as the geometry of the probe, determines the form of the dependence of the differential signal of the terahertz field on the distance between the probe and sample. The amplitude of the modulation of the probe height significantly affects the spectral composition of the differential terahertz signal, which is directly related to the amplitude and phase of a terahertz wave scattered by the probe-nanoobject system.

Time-resolved photoluminescence of polycrystalline GaN layers on metal substrates

The low-temperature time-resolved photoluminescence of polycrystalline GaN layers grown by molecular beam epitaxy on metal substrates (Mo and Ta) was investigated. The photoluminescence spectra observed include two emission bands in the ultraviolet spectral region. We assign one of these bands to recombination processes inside cubic nanocrystallites, which are formed in the hexagonal polycrystalline GaN host. The recombination radiation of cubic nanocrystallites is enhanced due to predominant trapping of the nonequilibrium electron-hole pairs in these crystallites.

Contrast and Resolution Enhancement in a Confocal Terahertz Video System

The effect of image contrast enhancement without the loss of the spectral composition of the radiation under investigation has been experimentally demonstrated for a terahertz far-field video system. The result has been obtained by using a confocal aperture placed in the intermediate-focus region of the optical system. The result is a fundamental advance towards the achievement of subwavelength resolution and the contrast of microscopy video systems in the terahertz spectral range.

Emission of terahertz radiation from GaN under impact ionization of donors in an electric field

The emission of terahertz radiation from epitaxial n-GaN layers in lateral electric field was found and studied for the first time. Radiation emission was observed in fields exceeding the impurity breakdown threshold. The highest -intensity radiation lines may be associated with intracenter electron transitions between donor levels (Si and O) and electron transitions from the conduction band to donor ground levels. Compact emitters of terahertz radiation operating at temperatures from 4 to 80 K can be created on the basis of n-GaN.

Terahertz injection electroluminescence in multiperiod quantum-cascade AlGaAs/GaAs structures

Terahertz electroluminescence in the range ≈1.5 THz was observed in a quantum-cascade GaAs/AlGaAs structure containing 40 periods of tunnel-coupled wells. The luminescence is caused by the spatially indirect optical electron transitions between the ground states of neighboring quantum wells.