Origin of photoluminescence peaks in Ge–SiO2 thin films

Ge–SiO₂ thin films were prepared by the RF magnetron sputtering technique on p–Si substrates from a Ge–SiO₂ composite target. The asdeposited films were annealed in the temperature range of 300–10000C under nitrogen ambience. The structure of films was evaluated by X–ray diffraction, X-ray photoemission spectroscopy and Fourier transform infrared absorption spectroscopy. Results show that the content of Ge and its oxides in thefilms change with increasing annealing temperature (Ta), the photoluminescence (PL) characteristics are closely dependent on the contents of Ge and its oxides in SiO₂ matrix. The dependence observed strongly suggests that the PL peak at 394 nm is related to the existenceof GeO and 580 nm to that of Ge nanocrystal (nc-Ge) in the films. © 2002 Elsevier Science Ltd. All rights reserved.     

Origin of photoluminescence peaks in Ge–SiO2 thin films

Ge–SiO₂ thin films were prepared by the RF magnetron sputtering technique on p-Si substrates from a Ge–SiO₂ composite target. The as-deposited films were annealed in the temperature range of 300–1000 °C under nitrogen ambience. The structure of films was evaluated by X-ray diffraction, X-ray photoemission spectroscopy and Fourier transform infrared absorption spectroscopy. Results show that the content of Ge and its oxides in the films change with increasing annealing temperature (T_a), the photoluminescence (PL) characteristics are closely dependent on the contents of Ge and its oxides in SiO₂ matrix. The dependence observed strongly suggests that the PL peak at 394 nm is related to the existence of GeO and 580 nm to that of Ge nanocrystal (nc-Ge) in the films.     

Charging effects in Ge nanocrystals embedded in SiO2 matrix for non volatile memory applications

Charging effects in germanium nanocrystals (nc-Ge) embedded in SiO₂ matrix fabricated by low pressure chemical vapor deposition have been studied by the mean of capacitance–voltage (C–V) combined with current–voltage (I–V) analysis. The C–V measurements showed hysteresis phenomena indicating holes charging in the Ge islands. The I–V measurements at ambient temperature exhibited an N-shaped form attributed to screening effects of positive charges stored in the nc-Ge. The same measurement at low temperatures shows that the hole trapping is a thermally activated process and the I–V analysis with different ramp rates were used in order to investigate the charging phenomena.     

Quantum confinement effect in SiO2 films containing Ge microcrystallites

SiO₂ thin films embedded with Ge microcrystallites (Ge-SiO₂ films) were prepared by RF-magnetron co-sputtering method from a composite target of Ge and SiO₂. The average size of Ge crystallites can be modulated by the experiment parameters. The optical absorption and non-linear optical properties of Ge-SiO₂ films were measured. The blue shift of the optical absorption edge, the saturated absorption and two-photon absorption under the condition of resonant absorption have been observed, and are discussed according to the quantum confinement effect.     

Synthesis of SiOF nanoporous ultra low-k thin film

In this work, we have investigated the effect of annealing temperature on physical, chemical and electrical properties of Fluorine (F) incorporated porous SiO₂ xerogel low-k films. The SiO₂ xerogel thin films were prepared by sol–gel spin-on method using tetraethylorthosilicate as a source of Si. The hydrofluoric acid was used as a catalyst for the incorporation of F ion in the film matrix. The thickness and refractive index (RI) of the films were observed to be decreasing with increase in annealing temperature with minimum value 156 nm and 1.31 respectively for film annealed at 400 °C. Based on measured RI value, the 34 % porosity and 1.53 gm/cm³ density of the film annealed at 400 °C have been determined. The roughness of the films as a function of annealing temperature measured through AFM was found to be increased from 0.9 to 1.95 nm. The Electrical properties such as dielectric constant and leakage current density were evaluated with capacitance–voltage (C–V) and leakage current density–voltage (J–V) measurements of fabricated Al/SiO₂ xerogel/P–Si metal–insulator-semiconductor (MIS) structure. Film annealed at 400 °C, was observed to be with the lowest dielectric constant value (k = 2) and with the lowest leakage current (3.4 × 10^?8 A/cm²) with high dielectric breakdown.     

Sol–gel deposited ceria thin films as gate dielectric for CMOS technology

In this work, cerium oxide thin films were prepared using cerium chloride heptahydrate, ethanol and citric acid as an additive by sol–gel spin-coating technique and further characterized to study the various properties. Chemical composition of deposited films has been analysed by FTIR which shows existence of CeO₂. The samples have been optically characterized using ellipsometry to find refractive index of 2·18 and physical thickness which is measured to be 5·56 nm. MOS capacitors were fabricated by depositing aluminum (Al) metal using the thermal evaporation technique on the top of CeO₂ thin films. Capacitance–voltage measurement was carried out to calculate the dielectric constant, flat-band voltage shift of 18·92, 0·3–0·5 V, respectively and conductance–voltage study was carried out to determine the D_it of 1·40 × 10¹³ eV^???1 cm^???2 at 1 MHz.     

Dielectric enhancement of BaTiO3/BaSrTiO3/SrTiO3 multilayer thin films deposited on Pt/Ti/SiO2/Si substrates by sol–gel method

Polycrystalline BaTiO₃/Ba_0.6Sr_0.4TiO₃/SrTiO₃ (BT/BST/ST) multilayer thin films with different periodicities have been deposited on Pt/Ti/SiO₂/Si substrates by using a sol–gel method. The multilayer thin films were crack free, compact and crystallized in a perovskite structure. The dielectric constant of the multilayer thin films was significantly increased and the dielectric loss was almost the same as those of uniform BT, ST and BST thin films. The dielectric constant increased with increasing stacking periodicity as the thickness of each individual layer decreased. The multilayer thin films showed excellent dielectric properties and can be promisingly used for the dielectric layer of silicon-based embedded capacitors in package substrate.     

Structural and photoluminescence investigation of ZnSe nanocrystals dispersed in organic and inorganic matrices

In this work, we report on the investigation of the effect of dispersion of zinc selenide (ZnSe) nanocrystallites into polystyrene (PS) and silica (SiO₂) thin films on their structural, morphological and photoluminescence properties. The ZnSe/PS nanocomposites thin films were synthesized by a direct dispersion of ZnSe crystallites into polymers solution, whereas the ZnSe–SiO₂ films were prepared on glass substrates by the sol–gel dip-coating technique. X-ray diffraction (XRD), Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-rays (EDX), UV–visible spectrophotometry and photoluminescence spectroscopy (PL) techniques have been used to study the structural, morphological and optical properties of the prepared nanocomposite thin films. XRD patterns have demonstrated the incorporation of cubic ZnSe in both organic and inorganic matrices. SEM micrographs have indicated that ZnSe dispersion in the films is homogeneous. UV–visible absorption spectra of the nanocomposite thin films have put into evidence that the dispersion of ZnSe nanocrystals in the thin film matrices improved their optical absorption. Room temperature PL spectra have shown that the addition of ZnSe enhanced the UV emission of PS and all the emission of SiO₂ thin films.     

Bottom electrodes dependence of microstructures and dielectric properties of compositionally graded (Ba1−xSrx)TiO3 thin films

Compositionally graded (Ba_1−xSr_x)TiO₃ (BST) thin films, with x decreasing from 0.3 to 0, were deposited on Pt/Ti/SiO₂/Si and Ru/SiO₂/Si substrates by radio frequency magnetron sputtering technology. The microstructure and dielectric properties of the graded BST thin films were investigated. It was found that the films on Ru electrode have better crystallization, and that RuO₂ is present between the Ru bottom electrode and the graded BST thin films by X-ray diffraction and SEM analysis. Dielectric measurement reveals that the graded BST thin films deposited on Ru bottom electrode have higher dielectric constant and tunability. The enhanced dielectric behavior is attributed to better crystallization as well as smaller space charge capacitance width and the formation of RuO₂ that is more compatible with the BST films. The graded BST films on Ru electrode show higher leakage current due to lower barrier height and rougher surface of bottom electrode.     

Improved dielectric properties of chemical solution derived Pb0.5Sr0.5TiO3 thin films by a layer-by-layer annealing method

Pb_0.5Sr_0.5TiO₃ thin films were prepared on Pt/TiO₂/SiO₂/Si and LaNiO₃ (LNO)/Si substrates by using chemical solution deposition technique, and a layer-by-layer annealing method was used in an attempt to improve the dielectric properties of the thin films. The structure, dielectric, and ferroelectric properties of the thin films were investigated. Improved dielectric properties of the thin films were clearly confirmed: the dielectric constant and dielectric loss for the films on Pt/TiO₂/SiO₂/Si substrates annealed at 650 °C were 1064 and 0.027, respectively, at 1 kHz, with a dielectric tunability of more than 50%; similarly, the films prepared on LNO/Si substrates, showed a high dielectric constant of 1280 and a low dielectric loss of 0.023, at 1 kHz. P-E hysteresis loop measurements indicated that the remanent polarization and coercive field for the films on Pt/TiO₂/SiO₂/Si substrates annealed at 650 °C were 15.7 μC/cm² and 51 kV/cm, respectively.     

High-quality spin-on glass-based oxide as a matrix for embedding HfO<Subscript>2</Subscript> nanoparticles for metal-oxide-semiconductor capacitors

By using a low cost, simple, and reproducible spin-coating method, thin films of SOG (spin-on-glass)-based oxides with electrical characteristics resembling those of a dry thermal oxide have been obtained. The superior electrical characteristics of Metal-Oxide-Semiconductor (MOS) capacitors based on SOG-oxides come from both (1) reducing the organic content of the SOG solutions after dilution with deionized water and (2) passivation of the silicon surface by a thin chemical oxide. Fourier transform infrared spectroscopy analysis shows that the organic content in H₂O-diluted SOG-oxides is reduced compared to undiluted SOG after N₂ annealing. In addition, by chemically embedding HfO₂ nanoparticles (np-HfO₂) to these SOG-based oxides, an effective increase in the accumulation capacitance of MOS capacitors is observed and this is related to the increase in the final dielectric constant of the resulting oxide after annealing so that potential use of SOG as a glass matrix for embedding HfO₂ nanoparticles and produce higher-k oxide materials is demonstrated.     

Optical and electrical properties of E-Beam deposited TiO<Subscript>2</Subscript>/Si thin films

In this paper, optical and electrical properties of E-Beam deposited TiO₂/Si thin films have been studied and investigated extensively. The films were deposited on p-type (100) silicon wafer by using electron beam evaporation technique. The thickness of the thin films was measured by a spectroscopic reflectometer, which is about 216 nm. The fabricated titanium oxide (TiO₂) thin films were annealed at 800 °C for 1 h under N₂ ambient. X-ray diffraction measurements were performed to study the structure and phase identification of the fabricated TiO₂ thin films. For the optical properties, reflection, transmittance, refractive index and absorption coefficient were obtained and analyzed. The photocurrent and dark current of the fabricated films were measured by I–V measurements. The measurement of the current–voltage (I–V) characteristics possesses good ohmic contact. The electrical characterizations of the films were performed in the range of the low frequencies (50 and 100 kHz) and high frequencies (750 kHz and 1 MHz) by the capacitance–voltage and conductance–voltage measurements at room temperature. The capacitance of the fabricated TiO₂ MOS capacitor at both high and low frequencies increases with the decrease in frequencies. The obtained conductance curves (peaks) increase with the decreasing in the frequencies. This can be due to the interface state density, series resistance and interfacial dielectric of the fabricated MOS capacitors. The variation in the characteristics of the fabricated film shows that TiO₂ is a promising candidate to be used in the optoelectronic and future UV detector applications as a switch, such as an optical amplifier, emitter, and UV light detectors.     

Influence of Ge addition on the morphology and properties of TiN thin films deposited by magnetron sputtering

Thin films of TM-X-N (TM stands for early transition metal and X = Si, Al, etc.) are used as protective coatings. The most investigated among the ternary composite systems is Ti-Si-N. The system Ti-Ge-N has been chosen to extend the knowledge about the formation of nanocomposite films. Ti-Ge-N thin films were deposited by reactive magnetron sputtering on Si and WC-Co substrates at T_s = 240 °C, from confocal Ti and Ge targets in mixed Ar/N₂ atmosphere. The nitrogen partial pressure and the power on the Ti target were kept constant, while the power on the Ge target was varied in order to obtain various Ge concentrations in the films. No presence of Ge-N bonds was detected, while X-ray photoelectron spectroscopy measurements revealed the presence of Ti-Ge bonds. Transmission Electron Microscopy investigations have shown important changes induced by Ge addition in the morphology and structure of Ti-Ge-N films. Electron Energy-Loss Spectrometry study revealed a significant increase of Ge content at the grain boundaries. The segregation of Ge atoms to the TiN crystallite surface appears to be responsible for limitation of crystal growth and formation of a TiGe_y amorphous phase.     

Preparation of regularly ordered Ge quantum dot lattices in amorphous matrices

We compare structural and optical properties of Ge quantum dot lattices in amorphous silica matrix obtained by two recently published techniques for the preparation of regularly ordered quantum dot lattices in amorphous matrices. The first technique is self-ordering growth of (Ge + SiO₂)/SiO₂ multilayer at an elevated substrate temperature where diffusion and surface morphology effects drive the self-ordering. The second one is irradiation of (Ge + SiO₂)/SiO₂ multilayer by oxygen ions. The multilayer used for the irradiation is grown at room temperature in this case, resulting with no Ge clusters after the deposition process. The irradiation causes clustering of Ge and ordering of Ge quantum dots in the irradiation direction. We show that the size of the dots and their arrangement can be easily manipulated by the preparation parameters. The structural properties of the films prepared by these methods affect the quantum confinement of the charge carriers which is visible in the absorption properties of the films.     

Measurement of the interlayer between aluminum and silicon dioxide using ellipsometric,capacitance-voltage and auger electron spectroscopy techniques

Ellipsometric and capacitance-voltage measurements were combined to detect both the AlSiO₂ interlayer and the SiSiO₂ interlayer for the Si/SiO₂/Al system. The AlSiO₂ interlayer was characterized by Auger electron spectroscopy (AES), combined with argon ion sputter profiling, of the Al/SiO₂/Si structure and also of the remaining SiO₂/Si structure after the aluminum had been chemically removed. An effective interlayer thickness is defined as the product of the interlayer thickness and the fractional change in the dielectric SiO₂ constant. The results of these experiments indicate that the Alz.sbnd;SiO₂ effective interlayer thickness has a range of 0.1–0.5 nm. The AES data can be readily interpreted if it is assumed that collision cascade mixing and recoil implantation occur as a consequence of sputter depth profiling through the aluminum.     

Enhanced dielectric and piezoelectric properties of (100) oriented Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–BaTiO<Subscript>3</Subscript>–SrTiO<Subscript>3</Subscript> thin films

The (100) oriented and random oriented 0.755Bi_0.5Na_0.5TiO₃–0.065BaTiO₃–0.18SrTiO₃ (BNT–BT–ST) thin films were deposited on LaNiO₃ (LNO) buffered Pt(111)/Ti/SiO₂/Si substrates by the sol–gel processing technique. The orientation is controlled by the concentration of solution. The structure, dielectric and piezoelectric properties of the thin films are significantly affected by the crystallographic orientation. The (100) oriented BNT–BT–ST thin film has improved dielectric and piezoelectric properties. For the (100) oriented and random oriented BNT–BT–ST thin films, the dielectric constants are 660 and 550, the dielectric losses are 0.045 and 0.076 and the effective piezoelectric coefficients are 140 and 110 pm/V, respectively. The large piezoelectric response is attributed to the uniform microstructure and increased lattice distortion along (100) direction.     

Electrical, optical and structural characterization of high-k dielectric ZrO2 thin films deposited by the pyrosol technique

High-k dielectric zirconium oxide (ZrO₂) thin films have been deposited on silicon substrates at temperatures from 400 to 600 °C using the spray pyrolysis technique. The films were deposited from two spraying solution concentrations (0.033 and 0.066 M) of zirconium acetylacetonate dissolved in N,N-dimethylformamide. These films were stoichiometric, transparent and with a very low surface roughness (5–40 ). The refractive index of these films was of the order of that obtained for a bulk material (2.12). Films deposited with high molar concentration presented the best electrical characteristic, have a dielectric constant in the range 12.5–17.5, depending on the deposition temperature, and can stand electric fields up to 3 MV cm^–1 without observing destructive dielectric breakdown. Transmission electron microscopy measurements, indicate that the films consist of nano-crystallites of the tetragonal ZrO₂ crystalline phase embedded into an amorphous matrix. Infrared spectroscopy measurements of the films show peaks associated with ZrO₂ and a peak related to silicon dioxide (SiO₂). The analysis of spectroscopic ellipsometry measurements on these films indicates the existence of a layer at the ZrO₂/Si interface composed of SiO₂ as well as ZrO₂ and crystalline silicon.     

Dielectric properties of (Ba,Ca)(Zr,Ti)O3/CaRuO3 heterostructure thin films prepared by pulsed laser deposition

(Ba_0.90Ca_0.10)(Zr_0.25Ti_0.75)O₃ (BCZT) thin films were grown on Pt/Ti/SiO₂/Si substrates without and with a CaRuO₃ (CRO) buffer layer using pulsed laser deposition (PLD). The structure and surface morphology of the films have been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). At room temperature and 1 MHz, the dependence of dielectric constant and tunability of the films with electric field were investigated; the dielectric constant and tunability are 725 and 47.0%, 877 and 50.4%, respectively, for the BCZT film on Pt/Ti/SiO₂/Si substrates without and with the CRO buffer layer at 400 kV/cm. The tunability of the BCZT/CRO heterostructure thin films on Pt/Ti/SiO₂/Si substrates was higher than that of the BCZT thin films on Pt/Ti/SiO₂/Si substrates. The high constant likely results from the oxide electrode (CRO).     

Structural and electrical characteristics of chemical solution derived (Bi3.2La0.4Nd0.4)Ti3O12 thin films

(Bi_3.2La_0.4Nd_0.4)Ti₃O₁₂ (BLNT) thin films were prepared on Pt/Ti/SiO₂/Si substrates by using chemical solution deposition technique, and the effects of annealing temperatures in the range of 550-750 °C on structure and electrical properties of the thin films were investigated. X-ray diffraction analysis shows that the thin films have a bismuth-layered perovskite structure with preferred (117) orientation. The surface morphology observation by field-emission scanning electron microscopy confirms that films are dense and smooth with uniformly distributed grains. The grain size of the thin films increases with increasing annealing temperature; meanwhile, the structural distortion of the thin films also increases. It was demonstrated that the thin films show good electrical properties. The dielectric constant and dielectric loss are 191 and 0.028, respectively, at 10 kHz for the thin film annealed at 600 °C, and the 2Pr value of the thin film annealed at 700 °C is 20.5 μC/cm² at an electric field of 500 kV/cm.     

Thermal stability of hafnium silicate dielectric films deposited by a dual source liquid injection MOCVD

The hafnium and silicon precursors, Hf(NMe₂)₄ and Bu^tMe₂SiOH, have been investigated for the MOCVD of high-κ hafnium silicate, (HfO₂)_1–x –(SiO₂) _x films for gate dielectric applications. Control of the silica concentration in the hafnium silicate can be achieved by varying the relative precursor ratios up to a saturation level of 35–40% SiO₂. The thermal stability of the resulting hafnium silicate films in air has been investigated using medium energy ion scattering. Internal oxidation of the underlying silicon substrate is discernable when the films are annealed in dry air for 15 min over the temperature range 800–1000 °C.