Diffusion of boron, aluminum, and oxygen was conducted at temperatures 1600 - 1700 <$E symbol Р>C. Very pure original n-SiC crystal (6H-SiC) specially grown by the Lely method annealed in oxygen during 2 h at 1700 <$E symbol Р>C, in argon during 2 h at 1700 <$E symbol Р>C, with aluminum and silicon oxide powder during 2 h, and with boron oxide and aluminum during 0,5 h. Electrical characterization of the silicon carbide samples was done by the Hall effect measurements using the square van der Pauw method to determine the sheet resistance, mobility, and free carrier concentration. The model of deep donor level as a complex of nitrogen atom replacing carbon with adjacent silicon vacancy is suggested.

Recently developed ac ZnS-powder electroluminescence devices have flexibility (thickness is about 60 <$E mu>m) 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.

The reliability of AC thick-film electroluminescent (EL) devices has been studied. The AC thick-film EL devices were fabricated by Novatech Inc. using the industrial print screen technology. The analysis of reasons for failure has been proposed. The dependence of EL lamp parameters on physical properties of the device EL layers was found. Our analysis of the breakdown spot showed that improvement of reliability can be reached using the additional dielectric layer between the phosphor layer and transparent electrode, high concentration of phosphor powder 70 % and binder 30 %, balanced resistance between the electric circuit and EL lamp. The thickness of the phosphor layer was equal to <$E H~=~(1~+~sqrt {3 "/" 2} )D> (hexagonal packing), where D is the mean diameter of phosphor particles. The reliability dependence of EL lamp on a water adsorption property of packaging material was revealed.

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.

Індекс рубрикатора НБУВ: В345.3 + В379.24

Рубрики:

Фотолюмінесценція

Оптичні властивості напівпровідників

Шифр НБУВ: Ж16425 Пошук видання у каталогах НБУВ 
Повний текст  Наукова періодика України 

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 <$E symbol Р>C. 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.

Perfect pure (concentration of donors ~10<^>16 cm<^>-3 ) single crystals with joint polytypes (hexagonal-cubic) or heterojunction investigated using low temperature (4,2 К and 77 K) photoluminescence. Phase transformation started exactly from lamella between polytypes. <$Ebeta ~symbol О~ alpha> (3C-6H) SiC transformation distributes from lamella as from nuclear. Photoluminescence spectra are similar to the spectrum demonstrated by pure perfect 3C-SiC crystal in the field of mechanical deformation. In the zone of joint polytypes and zone of the plastic deformation in perfect 3C-SiC crystal after bending, the same stacking faults are localized. Luminescence in the disordered <$Ealpha>-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 micro- and nano-SiC structures. Solid-phase transformations <$Ebeta ~symbol О~ alpha> are related with the same intermediate metastable microstructure that take place in the transformation <$Ealpha ~symbol О~ beta>.

Зміни в електронних спектрах поглинання фулерена C₆₀ у видимій та ближній УФ області було перевірено в процесі асоціації молекул у розчині та твердих плівках на скляній підкладці. Знайдено, що піки поглинання на 2,73 еВ та 3,35 еВ з'являються виключно завдяки агрегації молекул. Передбачено, що перша смуга з'являється завдяки взаємодії молекул в агрегаті, а друга - завдяки взаємодії самих агрегатів. Було також знайдено діхроїзм смуги поглинання на 3,35 еВ у зразках з анізотропною структурою.

Influence of plastic deformation and high-temperature annealing (<$ET~=~2100~symbol Р roman 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.

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.

In this work, the results of investigations of DLi spectra in alpha-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 ~ <$E(2~-~8)~cdot~10 sup 16 ~roman cm sup -3>, ND ~ <$E(5~-~8)~cdot~10 sup 17 ~roman cm sup -3>, and <$EN sub D ~-~N sub A ~>>~3~cdot~10 sup 17 ~roman cm sup -3>, <$EN sub D ~symbol У~1~cdot~10 sup 18 ~roman cm sup -3> (NDL-samples) 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 alpha-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.

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 High-Frequency 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 E_Tauc, 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 n-types 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.

The luminescence spectra of SiC crystals and films with grain boundaries (GB) on the atomic level were observed. The GB spectra are associated with luminescence centers localized in areas of specific structural abnormalities in the crystal, without no reference to the one-dimensional layer-disordering. The zero-phonon part of GB spectra is always within the same energy range (2,890 - 2,945 eV) and does not fit in the dependence of its position in the energy scale on the percent of hexagonality as in the case of stacking faults (SFi) and deep level (DLi) spectra. The zero-phonon part 2,945 - 2,890 eV with a fine structure is better observed in crystals with the centers of origin growth of crystal, if ND - NA ~ <$E(2~-~8)~cdot~10 sup 16> cm<^>-3, ND ~ <$E(2~-~7)~cdot~10 sup 17> cm<^>-3. The edge phonons of the Brillouin zone TA-46 meV, LA-77 meV, TO-95 meV and LO-104 meV are involved in development of the GB spectrum. This spectrum may occur simultaneously with the DLi and SFi ones. The GB spectra also occur after high temperature processing the <$Ebeta>-phase (in the 3C-SiC) with appearance of the <$Ealpha>-phase. The temperature range of observation is 4,2 - 40 K. There is synchronous thermal quenching of all elements in the fine structure. The thermal activation energy of quenching is <$EE sub a sup T> ~ 7 meV.

Проаналізовано фотолюмінесцентні спектри кристалів SiC з дефектами, що виникають під час вирощування. Показано, що дефекти упаковки та глибокі рівні люмінесцентного спектра відображають закономірності політичної структури SiC. Аналіз спектра нульових фотонів дефектів упаковки, глибоких рівнів і границь зерен в фотолюмінесцентному спектрі надає змогу контролювати процеси фазових перетворень під час вирощування кристалів та плівок, а також у разі проведення технологічних операцій. Більш того, це також надає змогу в наноструктурованому карбіді кремнію визначати положення або зсув атомів, що беруть участь у фотолюмінесценції з точністю до 0,0787 Ангстрем (або 1,075 меВ).