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

8H-, 10H-, 14H-SiC formation in 6H-3C silicon carbide phase transitions

In this paper the results of photoluminescence researches devoted to phase transitions in 6H-3C-SiC have been presented. High pure 6H-SiC crystals grown by Tairov’s method with and without polytype joint before and after plastic deformation at high temperature annealing were investigated using optical spectroscopy. Low temperature photoluminescence changes in the transition phase of SiC crystal represented with the stalking fault spectra within the temperature range 4.2 to 35 K. The stalking fault spectra indicate formation of metastable nanostructures in SiC crystals (14H₁ , 10H₂ , 14H₂ ). The phononless part of each stalking fault spectrum consists of two components of radiative recombination that are responsible for hexagonal and cubic arrangement of atoms. Each of radiative recombination components in the stalking fault spectrum has the width of entire band 34 meV and shifts relative to each other by 26 meV. The overlap area of those components equals to 8 meV. The super-fine structure of the recombination components in spectrum is observed, and it is related to different Si – Si or C – C and Si – C bonds. Behavior of all the stalking fault spectra is similar (temperature, decay of luminescence). The processes of the phase transition are explained by the mechanism of interfacial rearrangements in the SiC crystals

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

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

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

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

Silicon carbide phase transition in as-grown 3C-6H polytypes junction

Perfect pure (concentration of donors ~ 10¹⁶cm⁻³ ) single crystals with joint polytypes (hexagonal-cubic) or heterojunction investigated using low temperature (4.2 K and 77 K) photoluminescence. Phase transformation started exactly from lamella between polytypes. β → α ( 3C 6H ) SiC transformation distributes from lamella as from nuclear. Photoluminescence spectra are similar to the spectrum demonstrated by pure perfect 3C-SiC crystal in the field of mechanical deformation. In the zone of joint polytypes and zone of the plastic deformation in perfect 3C-SiC crystal after bending, the same stacking faults are localized. Luminescence in the disordered α-zone as a result of phase transformation is represented by a set of intensely pronounced stacking fault spectra. These spectra reside on more or less intense background band, which are emission of the donor-acceptor pairs in SiC. Excitation luminescence spectra confirm appearance of stacking faults which are responsible for metastable intermediate microand nano-SiC structures. Solid-phase transformations β → α are related with the same intermediate metastable microstructure that take place in the transformation α → β

Decomposition of dichloroethane vapor in barrierless discharge

Decomposition of dichloroethane vapor in the low-temperature plasma of barrierless gas discharge was investigated. High-voltage pulsed power supply forms high-voltage pulses of microsecond duration (1…2,2 ms) with a pulse repetition rate of 1…15 kHz and amplitude up to 15 kV. That voltage pulse shape was not changed by dichlorethane vapors in the air. At the same time, as dichlorethane vapor concentration was increased, so the amplitude of current pulse was decreased. Active radicals formed as a result of decomposition are easily oxidized by atomic oxygen and ozone, which are simultaneously synthesized from the air in barrierless discharge. It was shown, that dichlorethane decomposition reached 100% at the power of 100 W.Исследовалось разложение паров дихлорэтана в низкотемпературной плазме безбарьерного газового разряда. Высоковольтный источник питания позволяет формировать импульсы микросекундной длительности (1...2,2 мкс) с частотой 15 кГц и амплитудой до 15 кВ. Импульс напряжения не изменялся для смеси паров дихлорэтана с воздухом относительно чистого воздуха. В то же время при росте концентрации дихлорэтана в воздухе происходило снижение амплитуды импульса тока. Активные радикалы, которые формируются в результате разложения дихлорэтана, легко окисляются атомарным кислородом и озоном, параллельно образующемся в безбарьерном разряде из воздуха. Показано, что при вложенной мощности порядка 100 Вт степень разложения дихлорэтана достигает 100 %.Досліджувалося розкладання парів діхлоретану у низькотемпературній плазмі безбар’єрного газового розряду. Високовольтне джерело живлення дозволяє формувати імпульси мікросекундної довжини (1...2,2 мкс) з частотою 15 кГц та амплітудою до 15 кВ. Імпульс напруги не змінюється для суміши парів діхлоретана з повітрям відносно чистого повітря. В той же час при зростанні концентрації діхлоретана в повітрі відбувалося зниження амплітуди імпульса струму. Активні радикали, що формуються внаслідок розкладання діхлоретану, легко окислюются атомарним киснем та озоном, що паралельно синтезуются з повітря. Показано, що при вкладеній потужності порядку 100 Вт ступінь розкладання діхлоретану сягає 100%

Silicon carbide defects and luminescence centers in current heated 6H-SiC

At room temperature yellow photoluminescence with a broad peak of 2.13 eV is a well-known feature of boron-doped 6H-SiC. Usually yellow luminescence is regarded as recombination involving both the boron-related deep acceptor and donor level. But the nature of the deep level has not been clearly understood yet. We annealed 6H-SiC substrates by current in vacuum without boron injection at the temperature of 1350 and 1500 ºC. We received red and yellow luminescence in PL spectrum for the heated 6H-SiC. The luminescence was regarded as donor-acceptor pair recombination involving the deep aluminum acceptor related to the adjacent carbon vacancies and nitrogen donor or the formation of quantum well like regions of 3C-SiC in 6H-SiC matrix