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International audience; Optical and structural properties of ceramics based on Mn-doped magnesium titanates synthesized by sintering in air at 1200 °C of MgO and TiO$_2$ powders of different molar ratio ranging from MgTiO$_3$ to Mg$_2$TiO$_4$ stoichiometric compositions were studied. The influence of excess MgO on Mn incorporation in crystal lattice of MgTiO$_3$ was also investigated. The Mn$^{4+}$ ions substituted Ti$^{4+}$ sites were controlled by the photoluminescence (PL) and diffuse reflectance spectroscopy, and the Mn$^{2+}$ ions on Mg$^{2+}$ sites were monitored by electron paramagnetic resonance (EPR). The ceramics produced using equimolar ratio of MgO and TiO$_2$ composed of a major MgTiO$_3$ and a minor MgTi$_2$O$_5$ crystal phases, and those made with excess MgO contained MgTiO$_3$ and Mg$_2$TiO$_4$ phases in different proportions. The EPR study showed that Mn incorporated in MgTiO$_3$ synthesized under 1:1 molar ratio as Mn$^{2+}$ ion mainly. This agreed with low intensity of Mn$^{4+}$ red PL ascribed to low concentration of Mn$^{4+}$ centers and partial absorption of the UV excitation light by the MgTi$_2$O$_5$ phase. The Mn-doped MgTiO$_3$ synthesized with excess MgO of 19 and 50 mol.% showed increased Mn$^{4+}$ red PL by a factor 30-50, enhanced Mn$^{4+}$ optical absorption and more than ten times decreased Mn$^{2+}$ EPR signal. The Mg$_2$TiO$_4$ phase was found to be under compressive strains attributed to the presence of Mg vacancies and demonstrated Mn$^{4+}$ red PL with modified spectrum shape and decay behavior. It is concluded that in MgTiO$_3$ the excess MgO facilitates the incorporation of Mn onto Ti$^{4+}$ site and can be used for the increasing of Mn$^{4+}$ PL intensity.

International audience; The influence of magnesium oxide (MgO) content on the intensity of red photoluminescence (PL) of Mn4+ ions in Mn-doped phosphors Mg2TiO4:Mn produced by solid-state reaction at 1200 °C has been investigated by PL, optical absorption, X-ray diffraction, and electron paramagnetic resonance methods. The phosphors synthesized with excess MgO show an increase of Mn4+ red emission compared with those of stoichiometric composition. The magnitude of this increase depends on both MgO and Mn content. The largest increase of PL intensity is found for the phosphors synthesized under 3:1 molar ratios of MgO to TiO2. For these phosphors, the PL intensity increases from time 1.1 to time 3 when Mn concentration decreases from 1.0 to 0.0001 mol%. The phosphors produced under 6:1 molar ratios demonstrate a decrease of PL intensity at any Mn concentration. It is shown that excess MgO promotes stabilization of Mg2TiO4 phase against decomposition, hinders formation of Mn2+ centers, and enhances Mn4+ ions incorporation in the Mg2TiO4 crystal lattice. The latter together with reduced concentration quenching are supposed to be the main reasons of PL enhancement, which leads to the conclusion that excess MgO is necessary to produce an efficient red phosphor.

International audience; The effect of thermal annealing on optical, electrical and structural properties of Tb and Eu co-doped ZnO films grown by magnetron sputtering on Si and Al2O3 substrates was investigated by X-ray diffraction, photoluminescence, micro-Raman and IR reflection methods. It is shown that incorporation of rare earth ions in ZnO is accompanied by the formation of intrinsic defects. The as-deposited and annealed at 600 °C films demonstrate Tb3+ emission and no Eu3+ one. Higher intensity of Tb3+ photoluminescence in the films on Al2O3 substrate as compared with that on Si is ascribed to higher content of Tb3+ emitting centers. The model of these centers including the substitutional Tb and interstitial oxygen is proposed. In the excitation spectra of Tb3+ emission, no features connected with light absorption in ZnO are observed. An annealing at 900 °C is found to result in the formation of crystalline terbium oxide and silicate phases. In the photoluminescence spectra, the decrease of Tb3+ emission and the appearance of two sets of Eu3+ related bands caused by energy transfer from Tb3+ to Eu3+ ions are found. This is ascribed to segregation of rare earth ions in the additional phases and the decrease of the distance between the ions.

The relaxation of built-up strain in the heteroepitaxial GaN/AlN superlattices (SLs) leads to defect-related undesirable changes of the optical and electrical properties of SL-based devices. In the present study, the influence of lattice misfit between the GaN/AlN SL and GaN(0001) substrate on the mechanism of strain relaxation in the SLs is comprehensively analyzed. A strain/thickness-dependent effect on the densities of threading dislocations (TDs) and cracks in the SLs is observed. At the initial stage of growth of the SLs with relatively small lattice misfit, the formation of TDs dominates over the post-grown cracking triggered by the thermal stress during the sample cooling. Cracking during the growth is the main mechanism of strain relaxation for the SLs with large lattice misfit. It is established that for the GaN/AlN SLs with thicknesses >115 ± 15 nm, which corresponds to a SL relaxation degree >40 ± 5%, the density of defects drastically decreases. This result offers an essential guidance for excluding the strong influence of the substrate on generation of a large number of defects in the SLs. The quantitative interpretation and discussions of the presented results are important toward the design of a high-quality heteroepitaxial GaN/AlN SLs. Keywords: GaN/AlN superlattice, XRD, Microstructure, Strain relaxation, Dislocations, Cracks

Systematic study of mercury cadmium telluride thin films subjected to the ion beam bombardment was carried out. The evolution of surface morphology of (111) Hg1 − x Cd x Te (x ~ 0.223) epilayers due to 100 keV B+ and Ag+ ion irradiation was studied by AFM and SEM methods. X-ray photoelectron spectroscopy and X-ray diffraction methods were used for the investigation of the chemical compound and structural properties of the surface and subsurface region. It was found that in the range of nanoscale, arrays of holes and mounds on Hg0.777Cd0.223Te (111) surface as well as the polycrystalline Hg1 − x Cd x Te cubic phase with alternative compound (x ~ 0.20) have been fabricated using 100 keV ion beam irradiation of the basic material. Charge transport investigation with non-stationary impedance spectroscopy method has shown that boron-implanted structures are characterized by capacity-type impedance whereas for silver-implanted structures, an inductive-type impedance (or “negative capacitance”) is observed. A hybrid system, which integrates the nanostructured ternary compound (HgCdTe) with metal-oxide (Ag2O) inclusions, was fabricated by Ag+ ion bombardment. The sensitivity of such metal-oxide-semiconductor hybrid structure for sub-THz radiation was detected with NEP ~ 4.5 × 10−8 W/Hz1/2at ν ≈ 140 GHz and 296 K without amplification.

International audience; The effect of substrate material (Si, SiO2, Al2O3) on structural, optical and electrical properties of terbium doped ZnO films (Tb-ZnO) has been investigated by the X-ray diffraction, Raman scattering, atomic force microscopy, photoluminescence and infrared reflection methods. All films consist of micron size clusters of closely packed ZnO grains separated by deep trenches. The width of the trenches depends on the substrate material, being the largest in the Tb-ZnO/Al2O3 one. It is shown that the film on Al2O3 substrate contains the largest amount of extended and point defects. This film also demonstrates the highest intensity of Tb3+-related photoluminescence, while the film on Si substrate shows the lowest. On the contrary, the largest free carrier concentration evaluated from the infrared reflection spectra is found for Tb-ZnO/Si film and the lowest one is for the Tb-ZnO/Al2O3 film.

The influence of conditions occurring at the pulsed laser deposition of films with gold nanoparticles on the film porosity has been studied, by using the X-ray reflectometry. The films of two types were obtained by depositing particles (i) from the direct high-energy flow of erosion-torch particles and (ii) from the backward low-energy one. In both cases, the films were deposited either at the residual air pressurep = 10^−2 Pa or in the argon atmosphere with the pressures pAr = 5–100 Pa. In case (i), the film porosity was 0.1% atp = 10^−2 Pa and 1% at pAr ≤ 5 Pa. The plasmon properties of those films are associated with the propagation of surface plasmon-polariton waves. As the argon pressure grew further up to 100 Pa, the porosity increased to approximately 30%. In case (ii), the porosity of films deposited at pAr = 5–100 Pa onto substrates located in the target plane equaled 30 to 70% and depended on the distance from the film to the torch axis. All films with the porosity higher than 20% turned out nanocomposite structures with arrays of gold nanoparticles, which enabled us to observe the excitation of local surface plasmons., Вивчено вплив умов формування iмпульсним лазерним осадженням плiвок з наночастинками золота на їх пористiсть iз застосуванням рентгенiвської рефлектометрiї. Одержано плiвки двох типiв: з прямого високоенергетичного та зворотного низькоенергетичного потокiв частинок ерозiйного факела при залишковому тискуp =10^−2 Па i тиску аргону pAr =5–100 Па. Встановлено, що пористiсть плiвок першого типу, одержаних приp = 10^−2 та pAr 65 Па, становить 0,1 i 1%. Для цих плiвок плазмоннi властивостi пов’язанi з поширенням поверхневих плазмон-поляритонних хвиль. З подальшим пiдвищенням тиску аргону до 100 Па пористiсть зростає до ≈30%. Показано, що для плiвок другого типу, осаджених при pAr =5–100 Па на пiдкладку, яка розташована в площинi мiшенi, пористiсть становить 30–70% та залежить вiд положення дiлянки плiвки вiдносно осi факела. Всi плiвки з пористiстю бiльшою за 20% є нанокомпозитними структурами з масивами наночастинок золота. На них спостерiгається збудження локальних поверхневих плазмонiв.

International audience; The effect of Li+ co-doping on crystal phase formation and photoluminescence (PL) of Mn4+ activated magnesium titanate films produced by a solid state reaction method at different temperatures (800–1200 °C) has been investigated by using X-ray diffraction (XRD), diffuse reflectance and PL spectroscopy. The chemical composition of sintered films was estimated by energy dispersive X-ray spectroscopy. The concentration of Mn impurity estimated by Electron spin resonance was about 5 × 1016 cm−3. The XRD study of the annealed films revealed several magnesium titanate crystal phases, such as Mg2TiO4, MgTiO3 and MgTi2O5. The contribution of each phase depended strongly on the annealing temperature and the presence of Li+ additive. Furthermore, Li+ co-doping facilitated the formation of both MgTiO3 and Mg2TiO4 phases, especially at lower annealing temperatures. The PL spectra showed two bands centered at 660 and 710 nm and ascribed to the $^{2}E$ → ${^4}$A$_{2}$ spin-forbidden transition of the Mn4+ ion in the Mg2TiO4 and MgTiO3, respectively. In Li co-doped films, the integrated intensity of Mn4+ luminescence was found several times stronger compared to Li-undoped films that was ascribed mainly to flux effect of lithium.

A detailed XRD analysis of AlN/GaN multiple quantum well (MQW) structures grown on AlN(0001) substrates is proposed. The effect of roughness on the 2θ-ω scans measured in Bragg diffraction for symmetrical reflections is investigated together with the effect of depth variation of the well and barrier thickness. As shown, the magnitude of depth variation of the well and barrier thickness results in an asymmetrical broadening of the satellite peaks of the 2θ-ω scans. Roughness causes their symmetrical expansion that allows separating the influence of both effects. Several reasons of asymmetrical broadening of satellite peaks are considered: variation of the thickness period, variation of the average lattice parameter inherent to the period, which depends on the thickness ratio of the layers in the period, and their combination. The efficiency of the described method is illustrated in detail by numerical simulations. В работе предложен детальный рентгенодифракционный анализ структур с множественными квантовыми ямами (МКЯ) AlN/GaN, выращенными на подложках AlN(0001). Было исследовано влияние шероховатости и вариации толщины слоёв квантовых ям и барьеров на 2θ-ω-сканы, полученные в геометрии отражения по Брэггу для симметричных рефлексов. Показано, что наличие вариации толщины слоёв AlN и GaN по глубине приводит к появлению асимметрии сателлитных пиков МКЯ на 2θ-ω-сканах. Наличие шероховатости приводит к симметричному расширению сателлитных пиков, что позволяет разделить влияние этих эффектов. Рассмотрено несколько причин асимметричного расширения сателлитных пиков: изменение толщины периода, изменение среднего параметра решётки периода, который зависит от соотношения толщин слоёв в периоде, и их комбинации. Эффективность разработанного метода показана с помощью численного моделирования. В роботі проведено детальну аналізу структур із множинними квантовими ямами (МКЯ) AlN/GaN, вирощених на підкладинках AlN(0001). Було досліджено вплив шерсткости та зміни товщини шарів структури з МКЯ по глибині на 2θ-ω-скани, виміряні в Бреґґовій геометрії дифракції для симетричних рефлексів. Показано, що зміна товщини квантових ям і бар’єрів по глибині приводить до асиметричного розширення сателітних піків МКЯ на 2θ-ω-сканах. Шерсткість спричинює симетричне розширення піків, що уможливлює розрізнити вплив цих ефектів. Розглянуто кілька причин асиметричного розширення сателітних піків: зміну товщини періоду, зміну середнього параметра ґратниці періоду, який залежить від співвідношення товщин шарів періоду, та їх комбінації. Ефективність розробленої методи показано шляхом числового моделювання рентґенівських спектрів.

International audience; This work deals with the effect of Cu doping on thermal stability of the structural properties ofY-stabilized ZrO2 nanopowders and dopants’ spatial distribution. The powders were synthesized by a co-precipitation technique, calcinated at Tc = 500–1100 °C during 2 h and studied by x-ray diffraction (XRD) and transmission electron microscopy. Calcination at Tc = 500 °C results in the formation of ZrO2 nanocrystals with tetragonal phase predominantly. The shifts of XRD peak positions of Cu-doped powders to larger angles in comparison with those of Cu-free ones testify to the Cu presence inside nanocrystals. The Tc increase results in two main processes: (i) the nonmonotonic shift of XRD peak positions and (ii) the phase transformation (tetragonal to cubic and both of them to monoclinic). This observation was explained by, at first, Cu atoms incorporation into the nanocrystal volume from the surface complexes (Tc = 500–700 °C) and then their outward diffusion followed by the formation of crystalline CuO (Tc > 700 °C). Phase transformation sets in at Tc = 700 °C, when monoclinic phase appears. Its contribution rises till Tc = 1000 °C. The mechanism of monoclinic phase formation is supposed to be consisted of the out-diffusion of interstitial Cu ions due to their shift from lattice sites. This promotes an appearance of the channels for Y out-diffusion via cation vacancies and results in phase transformation. The sintering process stimulated by CuO formation is proposed to be responsible for appearance of cubic phase at 1000–1100 °C.

Radio-frequency (RF) hydrogen plasma treatment, thermal annealing in a furnace, and rapid thermal annealing of high-dose P+ ion implanted p-type Ge layers have been studied by Raman scattering spectroscopy, atomic force microscopy, secondary ion mass spectrometry, electrochemical capacitance–voltage profiling, four-point probes method, and x-ray reflectometry. It was shown that low-temperature RF plasma treatment at temperature about 200 °C resulted in full recrystallization of amorphous Ge layer implanted by P+ ions and activation of implanted impurity up to 6.5 × 1019 cm−3 with a maximum concentration at the depth of about 20 nm. Rapid thermal annealing (15 s) and thermal annealing (10 min) in nitrogen ambient required considerably higher temperatures for the recrystallization and activation processes that resulted in diffusion of implanted impurity inside the Ge bulk. It was demonstrated that RF plasma treatment from the samples with front (implanted) side resulted in considerable stronger effects of r...

This paper describes the in-situ synthesis in polymer films of the nanocrystals (NCs) of the ternary semiconductors Cd1 – xCuxS and Cd1 – xZnxS as well as the results of investigations of their structure and optical properties. It has been established that, in case of Cd1 – xCuxS in a large range of Cu to Cd ratios, the hexagonal structure is dominating in NCs synthesized, while in case of Cd1 – xZnxS the dominating crystalline structure of NCs corresponds to cubic structure of CdS. However in both cases formation of separate phases of either CdS and CuS or CdS and ZnS has not been revealed, confirming formation of ternary semiconductor compounds. It has been revealed an opposite effect of increasing concentrations of Cu and Zn cations in ternary compounds on intensity of an impurity photoluminescence, for the former this intensity decreases, but for latter it increases. The possible reasons for these phenomena are discussed. У роботі описується синтез in-situ в полімерних плівках нанокристалів (НК) потрійних напівпро- відників Cd1 – xCuxS і Cd1 - xZnxS, а також результати досліджень їх структури і оптичних властивостей. Встановлено, що у разі Cd1 – xCuxS у широкому діапазоні співвідношень Cu-Cd у синтезованих НК до- мінує гексагональна структура, тоді як у разі Cd1 - xZnxS домінуюча кристалічна структура НК відпові- дає кубічній структурі CdS. Разом з тим, в обох випадках утворення окремих фаз CdS і CuS або CdS і ZnS не було знайдено, що підтверджує утворення потрійних напівпровідникових сполук. Було вияв- лено протилежний вплив збільшення концентрації катіонів Cu і Zn в потрійних сполуках на інтенси- вність домішкової фотолюмінесценції, якщо для перших ця інтенсивність зменшується, то для остан- ніх вона зростає. Обговорюються можливі причини цих явищ. В работе описывается синтез in-situ в полимерных пленках нанокристаллов (НК) тройных полу- проводников Cd1 – xCuxS и Cd1 - xZnxS, а также результаты исследований их структуры и оптических свойств. Установлено, что в случае Cd1-xCuxS в большом диапазоне отношений Cu-Cd в синтезирован- ных НК доминирует гексагональная структура, тогда как в случае Cd1 - xZnxS доминирующая кри- сталлическая структура НК соответствует кубической структуре CdS. Тем не менее, в обоих случаях образование отдельных фаз CdS и CuS или CdS и ZnS не было найдено, что подтверждает образова- ние тройных полупроводниковых соединений. Было выявлено противоположное влияние увеличения концентрации катионов Cu и Zn в тройных соединениях на интенсивность примесной фотолюминес- ценции, если для первых эта интенсивность уменьшается, то для последних она возрастает. Обсуж- даются возможные причины этих явлений.

The depth distribution of strain and composition in graded Al x Ga1 − x N films and nanowires (NWs) are studied theoretically using the kinematical theory of X-ray diffraction. By calculating $$ \left(20\overline{2}5\right) $$ reciprocal space maps (RSMs), we demonstrate significant differences in the intensity distributions from graded Al x Ga1 − x N films and NWs. We attribute these differences to relaxation of the substrate-induced strain on the NWs free side walls. Finally, we demonstrate that the developed X-ray reciprocal space map model allows for reliable depth profiles of strain and Al composition determination in both Al x Ga1 − x N films and NWs.

The results of X-ray, scanning electron microscopy and atomic force microscopy studies of near-surface re- gions of (111) Hg1..xCdxTe (x = 0:223) structures are presented. These structures were obtained by low-energy implantation with boron and silver ions. TRIM calculation of the depth dependences of impurity concentration and implantation-induced mechanical stresses in the layer near-surface regions has revealed that the low-energy implantation of HgCdTe solid solution with elements of different ionic radiuses (B+ and Ag+) leads to the formation of layers with significant difference in thickness (400 nm and 100 nm, respectively), as well as with maximum me- chanical stresses differing by two orders of magnitude (1:4-103 Pa and 2:2-105 Pa, respectively). The structural properties of the Hg1..xCdxTe epilayers were investigated using X-ray high-resolution reciprocal space mapping.

In this paper, we investigate the structural properties of AlGaN/GaN heterostructures grown by metal organic chemical vapor deposition on sapphire substrates with different thicknesses using high-resolution x-ray diffraction and Raman scattering methods. We discuss the microscopic nature of spatial-inhomogeneous deformations and dislocation density in the structures. Microdeformations within mosaic blocks and the sizes of regions of coherent diffraction are determined. We reveal a gradient depth distribution of deformations in the mosaic structure of nitride layers, as well as at the interface regions of the sapphire substrate on the microscale level using confocal micro-Raman spectroscopy. We determine that an increase in substrate thickness leads to a reduction in dislocation density in the layers and an increase in the elastic deformations. The features of the block structure of nitrides layers are shown to have a significant influence on their elastic properties.

Kinetics of recrystallization in screen-printed polycrystalline CdS films has been investigated by X-ray structure analysis and optical microscopy. The relation between the crystallite size, crystallite orientation and the macrostrain, as well as their dependence on heat treatment regimes is established. It is shown that single-phase CdS films having a thick- ness of some tens microns, large grain size and low residual strain can be produced at opti- mum technological regimes. The films obtained are suitable for fabrication of CdS/CdTe solar cells.

We present a comparative study of thermal donor (TD) center formation mechanisms as a result of carbon ion implantation into float zone (FZ-Si) and Czochralski (Cz-Si) silicon crystals. The kinetics of the TD center formation and transformation of their structure during annealing have been investigated. Also, the TD center formation takes place after additional oxygen implantation into FZ/Cz-Si, and an important role of recoil oxygen atoms (from the screen oxide) has been demonstrated for the FZ-Si case. Their concentration in the Si surface layer depends on the implantation dose and the screen oxide thickness, reaching up to values 10(18) to 10(19) cm(-3), which is comparable with the oxygen concentration in Cz-Si. These oxygen atoms can lead to additional thermal donor centers generation, especially in the FZ-Si.34.50.Dy; 61.10.-i; 68.35.Dv.