19 research outputs found
Silicon carbide LED
Silicon carbide has been widely used as material for manufacturing yellow, red, green LED and optoelecronics devices (in¬dicators, screens). The silicon carbide LED technology has been in¬vestigated for improvement of their operational characteristics. This in¬cludes the influences of the surface processing (etching, annealing), the formation method for the p-n junctions and the contacts on the LED properties. Light-emitting devices used as light sources for optical-fiber communication lines. LED fabricated by Al⁺ ion-implanted in 6H-SiC and investigated their characteristics for an effective green LED. The brightness of the ion-implanted p-n junction was found to be two orders higher than that of diffusion p-n junction, and the best value was 2000-10000 cd/m² with passing current about 0.5 mA through area 50x50 mm and applied voltage about 2.6 ± 0.2 V. The ion-implanted structures showed a high stability of light in the temperature range of 77-600 K
Mechanism of 6H-3C transformation in SiC
Heavily doped by nitrogen single crystals of 6H-SiC were completely transformed into 3C-SiC ones by annealing in vacuum at presence of Si vapor for 1 hour at 2180 K or 4 hours at 2080 K. Mechanism of solid-to-solid transformation have been studied. Calculated nitrogen concentration from the Hall effect and EPR spectra for transformed crystals show its decreasing value in 3C-SiC. Data show appearance of new defects - donors and acceptors - that make nitrogen optically and electrically non-active. These defects accompany the process of transformation
Peculiarities of phase transformations in SiC crystals and thin films with in-grown original defects
Phase transformations of SiC crystals and thin films with in-grown original
defects have been studied. The analysis of absorption, excitation and low-temperature
photoluminescence spectra testifies to formation of new micro-phases during the growth.
The complex spectra can be decomposed into similar structure-constituting spectra
shifted against each other on the energy scale. These spectra are indicative of formation
of new nanophases. Taking into account the position of the short-wave edge in the zerophonon
part of the SF-i spectra as well as the position of corresponding excitation spectra
and placing them on the well-known linear dependence of the exciton gap (Egx) on the
percentage of hexagonally in different polytypic structures, one can obtain a hint to the
percentage of hexagonally in the new metastable structures appearing in the 6H (33)
matrix or in the growth process. The SF spectra are indicative of the appearance of these
metastable structures
Nanocrystalline silicon carbide films for solar cells
Nanocrystalline silicon carbide (nc-SiC) films as protective coating and as solar cell material for a harsh environment, high temperatures, light intensities and radiation, were investigated. p- and n-types 100-mm silicon wafers with (100) orientation were used as substrates for SiC films deposition. The films were deposited using HighFrequency Plasma Enhanced Chemical Vapor Deposition (HF-PECVD) with CH₃SiCl₃ gas as a silicon and carbon source. Hydrogen supplied CH₃SiCl₃ molecules in the field of HF discharge. Deposition was carried out on a cold substrate. The power density was 12.7 W/cm². Deposition conditions were explored to prepare films with a controlled band gap and a low defect density. Formation of nc-3C-SiC films has been confirmed by the high resolution-transmission electron microscopy analysis, optical band gap values ETauc, conductivity, charge carrier activation energy and Hall measurements. The efficiency of photoconductivity was calculated for evaluating the photoconductivity properties and for the correlations with technology. For p-n junction creation in solar cell fabrication, the ntypes nc-SiC films were doped with Al. Employing Al as a doping material of nc-n-SiC, the open-circuit voltage as high as 1.43 V has been achieved
Nanostructures in lightly doped silicon carbide crystals with polytypic defects
In this work, photoluminescence spectra of lightly doped SiC crystals with ingrown
original defects are reported. Undoped SiC single crystals with the impurity
concentration of ND – NA ~ (2…8)*10¹⁶ cm⁻³, NA ~ (2…8)*10¹⁷ cm⁻³, and ND – NA ~
(1…5)*10¹⁷ cm⁻³, ND = 10¹⁸ cm⁻³ were investigated. The analysis of absorption,
excitation and low temperature photoluminescence spectra suggests formation of a new
micro-phase during the growth process and appearance of the deep-level (DL) spectra.
The complex spectra of the crystals can be decomposed into the so-called DLi (i = 1, 2,
3, 4) spectra. The appearance of the DLi spectrum is associated with formation of new
nano-phases. Data of photoluminescence, excitation and absorption spectra show the
uniformity of different DLi spectra. Structurally, the general complexity of the DLi
spectra correlated with the degree of disorder of the crystal and was connected with onedimensional
disorder, the same as in the case of the stacking fault (SFi) spectra. The DLi
spectra differ from SFi spectra and have other principles of construction and behavior.
The DLi spectra are placed on a broad donor-acceptor pairs emission band in crystals
with higher concentrations of non-compensated impurities. The excitation spectra for the
DLi and SFi spectra coincide and indicate formation of nanostructures 14H₁,
10H₂, 14H₂, 8H<44
External impacts on SiC nanostructures in pure and lightly doped silicon carbide crystals
Influence of plastic deformation and high-temperature annealing (T = 2100 °C, t = 1 h) on SiC crystals with grown polytypic junctions demonstrating SF and DL spectra have been presented. SF-i and DL-i type luminescence are inherent to SiC crystals with distortions of the structure related with availability of packing defects that lead to onedimensional disordering (along the c-axis). They are a most expressed in doped crystals with original growth defects. DL luminescence appears in pure crystals at plastic deformation and in doped crystals at a hydrostatic pressure. It enhances at the high temperature annealing, too
3C-6H transformation in heated cubic silicon carbide 3C-SiC
Results of the research on the photoluminescence study of the 3C-6H-SiC
phase transformation are presented. 3C-SiC crystals with in grown 3C-6H transformation
and pure perfect 3C-SiC crystals grown by the Tairov-Tsvetkov method without a
polytypes joint after high temperature annealing were investigated. Fine structure at the
energy of E = 2.73, 2.79 eV, E = 2.588 eV, and E = 2.48 eV that appeared after annealing
was described. The role of stacking faults in the process of structure transformation was
investigated
Structure of photoluminescence DL-spectra and phase transformation in lightly doped SiC crystals and films
In this work, the results of investigations of DLi spectra in α-SiC crystals and films with a low impurity concentration have been presented. Photoluminescence spectra of lightly doped SiC single crystals and films with the impurity concentration of ND–NA ~ (2…8)∙10¹⁶ cm⁻³, ND ~ (5…8)∙10¹⁷ cm⁻³, and ND–NA >3∙10¹⁷ cm⁻³, ND ≥ 1∙10¹⁸ cm⁻³ (NDLsamples) were investigated within the temperature range 4.2…77 K. Complex spectroscopic study of one-dimensional disordered structures caused by solid phase transformations in SiC crystals was presented. Disordered growth D-layers in lightly doped crystals and α-SiC films were investigated using low temperature photoluminescence. The analysis testifies that DL and SF spectra hand-in-hand follow the structure transformations. It has been shown that the DL and SF spectra of luminescence reflect the fundamental logic of SiC polytypes structure. This allows to observe the structure changes at the phase transformations, the growth of SiC polytypes and to control their aggregates
Flexible electroluminescent panels
Recently developed ac ZnS-powder electroluminescence (EL) devices have
flexibility (thickness is about 60 µm) and can be multisegment, multicolor, as well as
rolled and bent. All colors (white, blue, blue-green, green, and orange) have been
investigated for improvement of their operational characteristics. Many factors including
the type of phosphor, formation method, contacts, initial input power (peak voltage and
frequency), type of input power, and environment safety which define the panel's
properties are discussed
Peculiarities of photoluminescence spectra behavior in SiC crystals and films during phase transformations
Peculiarities of photoluminescence spectra behavior in SiC crystals and thin films with in-grown defects during phase transformations have been studied. On the deep-level(DL)-spectra, as an example, their characteristics and behavior were investigated. It has been shown that all DL spectra have the same logic of construction and demonstrate identical behavior of the thin structure elements