Luminescence and microstructure of Er/O co-doped Si structures grown by MBE using Er and SiO evaporation

Er and O co-doped Si structures have been prepared using molecular-beam epitaxy (MBE) with fluxes of Er and O obtained from Er and silicon monoxide (SiO) evaporation in high-temperature cells. The incorporation of Er and O has been studied for concentrations of up to 2×10²⁰ and 1×10²¹ cm⁻³, respectively. Surface segregation of Er can take place, but with O co-doping the segregation is suppressed and Er-doped layers without any indication of surface segregation can be prepared. Si_1−xGe_x and Si_1−yC_y layers doped with Er/O during growth at different substrate temperatures show more defects than corresponding Si layers. Strong emission at 1.54 μm associated with the intra-4f transition of Er³⁺ ions is observed in electroluminescence (EL) at room temperature in reverse-biased p–i–n-junctions. To optimize the EL intensity we have varied the Er/O ratio and the temperature during growth of the Er/O-doped layer. Using an Er-concentration of around 1×10²⁰ cm⁻³ we find that Er/O ratios of 1 : 2 or 1 : 4 give higher intensity than 1 : 1 while the stability with respect to breakdown is reduced for the highest used O concentrations. For increasing growth temperatures in the range 400–575°C there is an increase in the EL intensity. A positive effect of post-annealing on the photoluminescence intensity has also been observed.     

AFM observation of OMVPE grown ErP on InP (0 0 1), (1 1 1)A and (1 1 1)B substrates

ErP has been grown on InP (0 0 1), (1 1 1)A and (1 1 1)B substrates by low-pressure organometallic vapor-phase epitaxy. The morphological change with growth temperature has been explored by atomic force microscope. On all the substrates, ErP is grown in island structure. Height and area size of the ErP islands on (1 1 1)A substrate exhibit an obvious dependence on growth temperature. ErP islands grown at 540°C, that is the suitable temperature for ErP formation, gather to step edges to make wires.     

XRD and EXAFS studies of crystallisation in films

This paper reports a detailed structural study on the nucleation of t-HfO₂ nanocrystals in thin films of 70SiO₂–30HfO₂ prepared by sol–gel route on v-SiO₂ substrates. Thermal treatment was performed at different temperatures ranging from 900 to 1200 °C for short (30 min) or long (24 h) time periods. Crystallisation and microstructure evolutions were traced by X-ray diffraction (XRD). The local structure around hafnium ions was determined from Hf L₃-edge extended X-ray absorption fine structure (EXAFS) measurements carried out at the BM08-GILDA Beamline of ESRF (France). XRD shows the nucleation of HfO₂ nanocrystals in the tetragonal phase after heat treatment at 1000 °C for 30 min, and a partial phase transformation to the monoclinic phase (m-HfO₂) starts after heat treatment at 1200 °C for 30 min. The lattice parameters as well as the average crystallites size and their distributions were determined as a function of the heat treatment. EXAFS results are in agreement with the XRD ones, with hafnium ions in the film heat treated at 1100 °C for 24 h are present in mixed phases.     

Er~(3+)离子及ErP_5O_(14)晶体的光谱性质

根据ErP_5O_(14)的吸收和荧光光谱,用Judd—Ofelt理论计算了在此晶体中Er~(3+)的强度参数Ω_λ(或τ_λ),由此计算了激光能级辐射跃迁速率、辐射寿命、荧光分支比和积分发射截面等光谱参数。提出了在Peap与强度参数的总和之间存在直线关系的经验公式。讨论了ErP_5O_(14)作为激光材料的可能性。     

Etch pits observation and etching properties of β-FeSi2

We have investigated the etching properties of p- and n-type β-FeSi₂ crystals grown from solution. Characteristic shapes of etch pits depending on the surface orientation was observed on the etched surface by using diluted hydrofluoric acid (5% of HF) and HF:HNO₃:H₂O=1:1:(2–8) solutions. However, the shapes of etch pits were independent of the conduction type and carrier density of the crystals. We also found the anisotropy of etch rates. The etch rates of the HF:HNO₃:H₂O=1:1:2 solution at 22°C were approximately 1.57, 1.43 and 1.09 μm/min on {1 1 1}, {1 0 0} and {0 0 1} faces of p-type β-FeSi₂ crystals, respectively.     

Properties of low temperature Sn–Ag–Bi–In solder systems

The metallurgical and mechanical properties of Sn–3.5 wt%Ag–0.5 wt%Bi–xwt%In (x = 0–16) alloys and of their joints during 85 °C/85% relative humidity (RH) exposure and heat cycle test (−40–125 °C) were evaluated by microstructure observation, high temperature X-ray diffraction analysis, shear and peeling tests. The exposure of Sn–Ag–Bi–In joints to 85 °C/85%RH for up to 1000 h promotes In–O formation along the free surfaces of the solder fillets. The 85°C/85%RH exposure, however, does not influence the joint strength for 1000 h. Comparing with Sn–Zn–Bi solders, Sn–Ag–Bi–In solders are much stable against moisture, i.e. even at 85 °C/85%RH. Sn–Ag–Bi–In alloys with middle In content show severe deformation under a heat cycles between −40 °C and 125 °C after 2500 cycles, due to the phase transformation from β-Sn to β-Sn + γ-InSn₄ or γ-InSn₄ at 125 °C. Even though such deformation, high joint strength can be maintained for 1000 heat cycles.     

Optical properties of Zn1−xMgxO nanorods using catalysis-driven molecular beam epitaxy

We report on the optical properties of (Zn,Mg)O nanorods grown by catalyst-driven molecular beam epitaxy. The process is site-specific, as single crystal (Zn,Mg)O nanorod growth is realized via nucleation on Ag films or islands that are deposited on a SiO₂-terminated Si substrate surface. Growth occurs within a flux of Zn, Mg, and O₂/O₃ mixture at substrate temperatures of 400–500 °C. With the addition of Mg, the nanorod morphology becomes more uniform relative to the pure ZnO nanomaterials synthesized under similar conditions. The (Zn,Mg)O nanorods are cylindrical, exhibiting diameters of 15–40 nm and lengths in excess of 1 μm. The (Zn,Mg)O nanorods exhibit a strong photoluminescence response, showing a slight shift to shorter wavelengths due to Mg incorporation.     

1.54 μm Near-infrared photoluminescent and electroluminescent properties of a new Erbium (III) organic complex

The crystal structure of Er(PM)₃(TP)₂ [PM = 1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone, TP = triphenyl phosphine oxide] was reported and its photoluminescence properties were studied by UV–vis absorption, excited, and emission spectra. The Judd–ofelt theory was introduced to calculate the radiative transition rate and the radiative decay time of 3.65 ms for the ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ ion in this complex. The antenna-effect and phonon-assisted energy-transfer were introduced to discuss the intramolecular energy transfer from ligands to Er³⁺ ion. Based on this Er(III) complex as the emitter, the multilayer phosphorescent organic light emitting diode was fabricated with the structure of ITO/NPB 20 nm/Er(PM)₃(TP)₂ 50 nm/BCP 20 nm/AlQ 40 nm/LiF 1 nm/Al 120 nm, which shows the typical 1.54 μm near-infrared (NIR) emission from Er³⁺ ion with the maximum NIR irradiance of 0.21 μW/cm².     

Effects of the electrical stress on the conduction characteristics of metal gate/MgO/InP stacks

The degradation dynamics and post-breakdown current–voltage (I–V) characteristics of magnesium oxide (MgO) layers grown on n and p-type indium phosphide (InP) substrates subjected to electrical stress were investigated. We show that the current–time (I–t) characteristics during degradation can be described by a power-law model I(t) = I₀t^−α, where I₀ and α are constants. It is reported that the leakage current associated with the soft breakdown (SBD) failure mode follows the typical voltage dependence I = aV^b, where a and b are constants, for both injection polarities but in a wider voltage range compared with the SiO₂/Si system. It is also shown that the hard breakdown (HBD) current is remarkably high, involving large ON–OFF fluctuations that resemble the phenomenon of resistive switching previously observed in a wide variety of metal oxides.     

Local crystal structural modifications in pulsed laser deposited high-k dielectric thin films on silicon and germanium

The thin film growth conditions are correlated with the local structures formed in Hf_xZr_1−xO₂ (x=0.0–1.0) high-k dielectric thin films on Si and Ge substrates during deposition. Pulsed laser deposition (PLD) technique has been used in the synthesis of the thin films with systematic variations of substrate temperature, Zr content of the targets and substrate selection. The local structural information acquired from extended X-ray absorption spectroscopy (EXAFS) is correlated with the thin film growth conditions. The response of the local structure around Hf and Zr atoms to growth parameters was investigated by EXAFS experiments performed at the National Synchrotron Light Source of Brookhaven National Laboratory. The competing crystal phases of oxides of Hf were identified and the intricate relation between the stabilized phase and the parameters as: the substrate temperature; Hf to Zr ratio; have been revealed. Specifically, HfO₂ thin films on Si(1 0 0) exhibit a tetragonal to monoclinic phase transformation upon increase in the substrate temperature during deposition whereas, HfO₂ PLD films on Ge(1 0 0) substrates remain in tetragonal symmetry regardless of the substrate temperature.     

Hooge parameter of InGaAs bulk material and InGaAs 2DEG quantum well structures based on InP substrates

The 1/f noise of various InGaAs layers lattice matched to InP is investigated systematically at room temperature. To elucidate the origin of the 1/f noise in this type of III–V compound semiconductor, thick n-type doped InGaAs layers, typical InP based InAlAs/InGaAs or InP/InGaAs heterostrucuture field-effect transistor (HFET) structures, respectively, as well as InP based InAlAs/InGaAs quantum well structures with doped InGaAs two-dimensional electron gas (2DEG) channel are analysed. From the experiments it is found that mobility fluctuation is the only origin for the 1/f noise observed both in InGaAs bulk material and in 2DEG heterostructures of high quality. A Hooge parameter attributed to phonon scattering α_Hphon in the bulk material is found to be about 7×10⁻⁶ and agrees with those obtained from HFET structures with the highest mobilities (α_H≈1.5×10⁻⁵). Furthermore, the Hooge parameter of 2DEG structures strongly depends on the channel design and on the doping concentration in the n-type doped 2DEG channels.     

Vibrational spectroscopy characterization of low-dielectric constant SiOC:H films prepared by PECVD technique

Low-dielectric constant SiOC:H films were prepared by plasma enhanced chemical vapour deposition (PECVD) from trimethyl-silane (H–Si–(CH₃)₃) and ozone (O₃) gas mixture. The samples were preliminarily annealed at 400 °C in N₂ atmosphere and then in N₂+He plasma. Afterwards, they were treated in vacuum at some fixed temperatures in the range between 400 and 900 °C. Structural investigations of the annealed films were carried out by means of vibrational spectroscopy techniques. FT-IR spectrum of a preliminarily treated sample shows absorption bands due to stretching modes of structural groups like Si–CH₃ at 1270 cm⁻¹, Si–O–Si at 1034 cm⁻¹ and C–H_x in the region between 2800 and 3000 cm⁻¹. No significant spectral change was observed in the absorption spectra of samples annealed up to 600 °C, indicating that the preliminarily treated film retains a substantial structural stability up to this temperature. Above 600 °C, absorption spectra show a strong quenching of H-related peaks while the band due to Si–O–Si anti-symmetric stretching mode shifts towards higher energy, approaching the value observed for thermally grown SiO₂. Raman spectra of samples treated at temperatures T500 °C exhibit both D and G bands typical of sp²-hybridised carbon, due to the formation of C–C bonds within the film which is accompanying the release of hydrogen. The intensity of D and G bands becomes more pronounced in samples annealed at higher temperatures, thus suggesting a progressive precipitation of carbon within the oxide matrix.     

Influence of oxygen on the photoluminescence intensity of erbium (at 1.54 µm) in erbium-doped a-Si:H films

The influence of oxygen on the photoluminescence (PL) of erbium (at 1.54 μm) in erbium-doped hydrogenated amorphous silicon (c-Si〈Er〉) is investigated. The a-Si:H〈Er〉 films studied are fabricated by cosputtering Si and Er targets using the technology of dc silane decomposition in a magnetic field. The oxygen concentration is varied from 10¹⁹ to 10²¹ cm⁻³ by increasing the partial pressure of oxygen in the chamber. It is shown that, as in the case of erbium-doped crystalline silicon (c-Si〈Er〉), oxygen has an effect on the intensity of the 1.54 μm photoluminescence in a-Si:H〈Er〉 films. The values of the erbium and oxygen concentrations at which the maximum Er PL intensity is observed are two orders of magnitude higher than in crystalline silicon. The increase in the Er PL intensity at room temperature and the weaker temperature dependence of the Er PL in comparison to c-Si〈Er,O〉 attest to the prospect of using a-Si:H〈Er〉 films in optoelectronic applications. Fiz. Tekh. Poluprovodn. 32, 1384–1389 (November 1998)     

Local structures around Er atoms doped in GaAs by low-temperature molecular beam epitaxy

Er-doped GaAs samples were grown by molecular beam epitaxy at 400°C and 590°C. The samples were investigated by photoluminescence (PL) and fluorescence extended X-ray absorption fine structure (EXAFS) measurements in order to find the relationship between the local structures around the Er atoms and the PL properties. Er-related PL peaks were observed only for the samples grown at a low temperature (400°C). The fluorescence EXAFS measurements showed the Er atoms were located on tetrahedral interstitial site when the growth temperature was low. On the other hand, when the growth temperature was high (590°C), the Er atoms substituted the Ga site in GaAs lattice.     

Effect of rapid thermal annealing of sputtered aluminium nitride film in an oxygen ambient

Aluminium nitride (AlN) thin films were deposited by radio frequency (RF) magnetron sputtering on p-type silicon (Si) substrate of (1 0 0) orientation using only argon (Ar) gas at substrate temperature of 300 °C. In order to achieve improved electrical properties, we performed post-deposition rapid thermal annealing (RTA). Sputtered AlN films were annealed in an oxygen ambient at temperatures of 600, 700, and 800 °C using RTA for 30 min. The orientation of the AlN crystal in the film was investigated using X-ray diffraction (XRD). The characteristic spectra by functional group were analyzed by Fourier transformation infrared (FTIR) spectroscopy. The electrical properties of the AlN thin films were studied through capacitance–voltage (C–V) characteristics in metal–insulator–semiconductor (MIS) device using the films as insulating layers. The flatband voltages (V_FB) in C–V curves were found to depend on crystal orientations. Negative V_FB was found in the case when AlN (1 0 0) peak was found. Also, when AlN (1 0 3) peak was observed upon increasing the annealing temperature, the value of V_FB was positive and after annealing at 700 °C, AlN (1 0 3) peak intensity was found to be maximum and V_FB was as high as+6.5 V.     

Ballistic electron emission microscopy studies of the temperature dependence of Schottky barrier height distribution in CoSi2/n-Si(1 0 0) diodes formed by solid phase reaction

Ballistic electron emission microscopy (BEEM) and ballistic electron emission spectroscopy have been performed on polycrystalline and epitaxial CoSi₂/n-Si(1 0 0) contacts at temperatures ranging from −144°C to −20°C. The ultra-thin CoSi₂ films (10 nm) were fabricated by solid state reaction of a single layer of Co (3 nm) or a multilayer of Ti (1 nm)/Co (3 nm)/amorphous-Si(1 nm)/Ti (1 nm) with a Si substrate, respectively. The spatial distribution of barrier height over the contact area obeys a Gaussian function at each temperature. The mean barrier height increases almost linearly with decreasing temperature with a coefficient of −0.23±0.02 meV/K for polycrystalline CoSi₂/Si diodes and −0.13±0.03 meV/K for epitaxial diodes. This is approximately equal to one or one-half of the temperature coefficient of the indirect energy gap in Si, respectively. It suggests that the Fermi level is pinned to different band positions of Si. The width of the Gaussian distribution is about 30–40 meV, without clear dependence on the temperature. The results obtained from conventional current–voltage and capacitance–voltage (I–V/C–V) measurements are compared to BEEM results.     

Electrical characterization of hafnium oxide and hafnium-rich silicate films grown by atomic layer deposition

An electrical characterization comparative analysis between Al/HfO₂/n-Si and Al/Hf-Si-O/n-Si samples has been carried out. Hafnium-based dielectric films have been grown by means of atomic layer deposition (ALD). Interface quality have been determined by using capacitance–voltage (C–V), deep level transient spectroscopy (DLTS) and conductance transient (G-t) techniques. Our results show that silicate films exhibit less flat-band voltage shift and hysteresis effect, and so lower disordered induced gap states (DIGS) density than oxide films, but interfacial state density is greater in Hf–Si–O than in HfO₂. Moreover, a post-deposition annealing in vacuum under N₂ flow for 1 min, at temperatures between 600 and 730 °C diminishes interfacial state density of Hf–Si–O films to values measured in HfO₂ films, without degrade the interface quality in terms of DIGS.     

Epitaxial growth of metallic ErP, ErSb and lattice-matched ErP/sub x/Sb/sub (1-x)/ layers on

ErP and ErSb compounds have been demonstrated to have metallic behaviour ( rho /sub ErP/=150 mu Omega cm; rho /sub ErSb/=60 mu Omega cm). The authors show that they can be epitaxially grown on InP and GaAs in an MBE system and that many matched systems (metallic layer)/(III-V semiconductor) can be built using ternary compounds of rare-earth and V elements.<>     

Phase Formation during the Surface-Diffusion Growth of Ti–Co–Si–N and Ti–Co–N Thin Films on Si and SiO2

The kinetics of phase formation in Ti–Co–Si–N and Ti–Co–N thin films on Si and SiO₂is investigated experimentally. With the deposition on Si, rapid thermal annealing (T 900°C) is shown to cause phase separation that ends in a TiN/CoSi₂/Si structure. If SiO₂is used, the alloy reacts with the substrate to produce compounds that are difficult to remove with selective etchants. This limits the potential uses of this process in the fabrication of contact systems for CMOS devices. It is shown that structure- and phase-dissimilar films can be formed on Si and SiO₂by means of the surface-diffusion reactions between a Ti–Co–Si–N or Ti–Co–N alloy and the substrate at 650–700°C. The effect of a TiN, Ti, or CoSi₂thin layer at the alloy–substrate interface on the phase separation is investigated.     

The formation and growth of intermetallic compounds and shear strength at Sn–Zn solder/Au–Ni–Cu interfaces

The microstructures and shear strength of the interface between Sn–Zn lead-free solders and Au/Ni/Cu interface under thermal aging conditions was investigated. The intermetallic compounds (IMCs) at the interface between Sn–Zn solders and Au/Ni/Cu interface were analyzed by field emission scanning electron microscopy and transmission electron microscopy. The results showed the decrease in the shear strength of the interface with aging time and temperature. The solder ball with highly activated flux had about 8.2% increased shear strength than that with BGA/CSP flux. Imperfect wetting and many voids were observed in the fracture surface of the latter flux. The decreased shear strength was influenced by IMC growth and Zn grain coarsening. In the solder layer, Zn reacted with Au and then was transformed to the β-AuZn compound. Although AuZn grew first, three diffusion layers of γ-Ni₅Zn₂₁ compounds were formed after aging for 600 h at 150 °C. The layers divided by Ni₅Zn₂₁ (1), (2), and (3) were formed with the thickness of 0.7 μm, 4 μm, and 2 μm, respectively.