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

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

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

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

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

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

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

Nanograin boundaries and silicon carbide photoluminescence

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 ~ (2…8)•1016 cm–3, ND ~ (2…7)•1017 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 β-phase (in the 3C-SiC) with appearance of the α-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 ЕаТ ~ 7 meV