The main direction of the development of modern technology is the miniaturization of the element base of micro-and optoelectronics. Any device with nanoscale features inevitably displays some types of quantum behavior and the main task is to exploit quantum-based ideas, to seek a radical technology, with wholly novel quantum components operating alongside existing silicon and optical technologies.Spin is a purely quantum object and spin properties begin to play a decisive role in the creation of nanoscale device structures. Magnetic resonance is the most direct method for studying spin processes. Electron paramagnetic resonance (EPR) is a method of choice for the study of intrinsic and impurity centers in condense matter, which makes it possible to determine the chemical and charge states of a paramagnetic center, its local symmetry, the composition of the nearest environment, the structure of energy levels, the specific features of the interaction with the crystal lattice, wave function distribution etc. However, conventional radio spectroscopy techniques are hardly applicable for low dimensional systems because of a small active volume and the not high enough sensitivity and the absence of special selectivity. This difficulty can be overcome by optically detected magnetic resonance (ODMR). High sensitivity, extreme resolution and spatial selectivity of ODMR make this technique very suitable for a study of defects, carriers and excitons in quantum wells (QWs), superlattices (SLs), quantum dots (QDs) and nanocrystals. In ODMR a microwave-induced repopulation of spin sublevels is detected optically, i.e., there is a giant gain in sensitivity since an energy of optical quantum is by several orders of magnitude higher compared with microwave one, it becomes possible to detect a very small number of spins down to single spin! ODMR is a “trigger detection” in that the absorption of a resonance microwave photon triggers a change in emission (absorption) of an optical photon due to the selective feeding of the magnetic sublevels. The detection of photons is thus displaced from the microwave domain to the far more sensitive optical domain.
The report will present the results of studies of various types of semiconductor nanostructures, as well as experimental methods and techniques of research.
The results of EPR, electron spin echo (ESE), electron–nuclear double resonance (ENDOR) and ODMR studies on colloidal ZnO nanocrystals doped with shallow donors (SD), deep acceptors, transition metal ions will be presented. The attraction of ZnO quantum dots is that the confinement of the electronic wave function allows the tuning of the optical and electronic properties.
ODMR has been intensively applied for studying diluted magnetic semiconductors (DMSs) and DMS-based nanostructures. Anisotropy of ODMR spectra was found in CdMnSe quantum dots and sub-monolayer quantum wells and explained by the fine structure splitting of Mn2+, which appears because of low dimensionality. New anisotropic ODMR spectra with different angular variations were reported on (CdMn)Te quantum wells containing 2D hole gas. These spectra were ascribed to the exchange coupled complexes consisting of manganese and holes.
The nitrogen–vacancy (NV) defects in diamond have a wonderful properties which make it the pet subject of modern research and applications. NV defect consisting of a nitrogen atom (N) and a vacancy (V) in adjacent lattice sites is the only known solid-state system where there exist possibility of detecting and manipulating the spin states (S = 1) of a single localized electron at room temperature. Coupling between the NV and N spins in NV –N pair due to a cross-relaxation gives rise to new possibilities for spin manipulation.A giant concentration of nitrogen vacancy defects (up to 0.1%) has been revealed by the EPR, ESE and ODMR methods in a detonation nanodiamond sintered at high pressure and temperature. The results presented are opening new perspectives of NV-containing diamond fabrication, especially taking into account the high-density of single nitrogen atoms integrated in crystalline lattice and high coherence of the spin system.
The unique quantum properties of the nitrogen–vacancy defect in diamond have motivated efforts to find defects with similar properties in bulk and nano silicon carbide (SiC), which is a material with highly developed device technologies and can extend the functionality of such systems not available to the diamond. Depending on the defect type, temperature, SiC polytype, and crystalline position, two opposite schemes have been observed for the optical alignment of the ground state spin sublevels population of the Si-vacancy related defects upon irradiation with unpolarized light. Optically induced spin polarization of the ground-state spin sublevels (S = 3/2) of a family of Si-vacancy related defects in SiC has been shown to persist up to the room temperature and spin ensemble can be prepared in a long-lived coherent superposition of the spin states at room temperature. ODMR shows the possibility to manipulate of the ground state spin population by applying radiofrequency field. The unique properties of the defects make them a promising quantum system for single-defect and single-photon spectroscopy in the infrared region. These properties can be used to implement high-power masers and low-noise radio-frequency amplifiers with optical or electrical pumping. SiC light-emitting diode is shown to be a perspective room temperature source of single photons and electrically driven alignment of the ground state spin sublevels with inverse population at room temperature. As these defects can potentially be generated at a low or even single defect level, electrically driven single photon source for quantum telecommunication and information processing can be realized. These altogether make the Si-vacancy related defects in SiC very favourable candidate for spintronics, quantum optics, quantum information processing, nanoscale magnetometry, biolabelling.
This work was supported by the Government of the Russian Federation, Agreement № 14.Z50.31.0021.