High-κ Al2O3−HfTiO Nanolaminates With Less Than 0.8-nm Equivalent Oxide Thickness

High quality nanolaminate stacks consisting of five Al₂O₃-HfTiO layers with an effective dielectric constant of about 22.5 are reported. A dielectric constant for binary HfTiO thick films of about 83 was also demonstrated. The electrical characteristics of as-deposited structures and ones which were annealed in an O₂ atmosphere at up to 950 degC for 5-10 min were investigated. Two types of gate electrodes: Pt and Ti were compared. The dielectric stack which was annealed up to 500 degC exhibits a leakage current density as small as ~1times10^-4 A/cm² at an electric of field 1.5 MV/cm for a quantum-mechanical corrected equivalent oxide thickness of ~0.76 nm. These values change to ~1times10^-8 A/cm² and 1.82 nm, respectively, after annealing at 950 degC     

The correlation of the electrical properties with electron irradiation and constant voltage stress for MIS devices based on high-k double layer (HfTiSiO:N and HfTiO:N) dielectrics

This paper describes the influence of e-beam irradiation and constant voltage stress on the electrical characteristics of metal-insulator-semiconductor structures, with double layer high-k dielectric stacks containing HfTiSiO:N and HfTiO:N ultra-thin (1 and 2 nm) films. The changes in the electrical properties were caused by charge trapping phenomena which is similar for e-beam irradiation and voltage stress cases. The current flow mechanism was analyzed on the basis of pre-breakdown, soft-breakdown and post-breakdown current-voltage (J-V) experiments. Based on α-V analysis (α=d[ln(J)]/d[ln(V)]) of the J-V characteristics, a non-ideal Schottky diode-like current mechanism with different parameters in various ranges of J-V characteristics is established, which limits the current flow in these structures independent of irradiation dose or magnitude of applied voltage during stress.     

The influence of electron-beam irradiation on electrical characteristics of metal-insulator-semiconductor capacitors based on a high-k dielectric stack of HfTiSiO(N) and HfTiO(N) layers

We describe the influence of electron irradiation (at 30 kV with a dose of up to 100 μC/cm²) on the electrical characteristics of metal-insulator-semiconductor structures based on a high-k dielectric stack of HfTiSiO(N) and HfTiO(N). The capacitance-voltage (C-V) and current-voltage characteristics were investigated after irradiation and compared to those of unirradiated samples. To better understand the irradiation effect, the capacitance-voltage (C-V) and current-voltage characteristics were also characterized for structures which were stressed at constant voltages. The irradiation induces a parallel shift of the C-V curves towards negative bias due to the introduction of positive charges in the bulk dielectric and semiconductor-dielectric interface. Annealing at 300 °C restored the C-V characteristics to those of the untreated state. A small decrease of the dielectric constant, from 11.7 to 10.7, was observed after irradiation. No measurable change in leakage current due to irradiation was observed.     

Gain and noise saturation of wide-band InAs-InP quantum dash optical amplifiers: model and experiments

We present a theoretical model for gain and noise saturation in quantum dash (QDash) semiconductor optical amplifiers. The model is based on the density matrix formalism and addresses static saturation spectra. The calculations are confirmed by a series of experiments which highlight the unique properties of these amplifiers. We demonstrate a high gain, a wide bandwidth, and high saturation power. The saturation spectrum is shown to be asymmetric, emphasizing saturation at short wavelength. The asymmetry stems from the high energy tail of the density of state function in those quantum wire (QWire) like gain media as well as from the interactions with the wetting layer.     

Optical and electrical characterization of the electron beam gun evaporated TiO2 film

We report measured evolutions of the optical band gap, refractive index and relative dielectric constant of TiO₂ films obtained by electron beam gun evaporation and annealed in an oxygen environment. A negative shift of the flat band voltage with increasing annealing temperatures, for any film thickness, is observed. A dramatic reduction of the leakage current by about four orders of magnitude to 5×10⁻⁶ A cm⁻² (at 1 MV cm⁻¹) after 700°C and 60 min annealing is found for films thinner than 15 nm. The basic carrier transport mechanisms at different ranges of applied voltage such as hopping, space charge limited current and Fowler–Nordheim is established. An equivalent SiO₂ thickness in order of 3.5 nm is demonstrated.     

Electrical properties of MIS capacitor using low temperature electron beam gun—evaporated HfAlO dielectrics

A low effective oxide thickness of 1.45 nm was achieved in HfAlO films deposited by an electron beam gun evaporator on unheated p-Si substrate. A reduction of the leakage current density from 1 × 10⁻⁴ to 4.5 × 10⁻⁷ A/cm², at an electric field 3 MV/cm, with annealing temperature and a breakdown electric field of 10 MV/cm were demonstrated for ultra thin films.     

Solid-state dewetting of Pt on (100) SrTiO3

Continuous thin films of Pt on (100) SrTiO₃ substrates were dewetted to form Pt particles at 1,150 °C, using an oxygen partial pressure of 10^?20 atm. After retraction of thick (50 or 100 nm) Pt films, SrTiO₃ anisotropic rods, slightly depleted in Ti, were found on the surface of the substrate. Rods did not form after dewetting of thinner (10 nm) Pt films. After dewetting, a ~10 nm thick interfacial phase was found between the Pt and the SrTiO₃. The interfacial phase, based on Sr and containing ~25 at% oxygen, is believed to be a transient state, formed due to Ti depletion from the substrate, resulting in a Pt(Ti) solution in the particles. The interfacial phase forms due to the low oxygen partial pressure used to equilibrate the system, and is expected to influence the electrical properties of devices based on Pt–SrTiO₃.     

The effect of light irradiation on electrons and holes trapping in nonvolotile memory capacitors employing sub 10 nm SiO2-HfO2 stacks and Au nanocrystals

We demonstrate the possibility to control charge trapping in the memory stacks comprised of metal nanocrystals (NCs) sandwiched between SiO₂ and high-k dielectric films by light irradiation. Non-equilibrium depletion effects in the state of the art charge trapping memories are reported for the first time. The studied nonvolatile memory devices employ Au NCs, thermal SiO₂ tunnel layer, atomic layer deposited HfO₂ blocking layer and Au/Pt metal gate. The memory windows are 3 V and 10.5 in the dark and under illumination for ±10 V programming voltages. Reliability limitations of the studied structure, in particular leakage currents and effects in high electric fields have been investigated in detail and are discussed in view of the mentioned device application. Low programming voltages and currents, and high light sensitivity make suggested NVM structures promising for developing digital imagers with ultra-low power consumption.     

Reversible Charge Transfer in Liquids at High Excitation Power

We discuss the influence of high excitation power on reversible charge transfer kinetics. The kinetics depends on the excited donor concentration, on the parameters of the rate constants, and on the boundary conditions for the Smoluchowski equation in liquids. The nonlinear effects of the excitation power are determined by the geometry of molecular spectra of emission and absorption. They disappear with the acceptor concentration, with the decrease in the forward rate constant. The role of Coulomb interaction of ions increases with increase of diffusion constant. Nonlinear effects for our theory of reversible charge transfer in liquids are compared with those of Dorfman and coworkers (J. Chem. Phys. 1989 , 90, 159). The difference of the effects between the two theories vanishes when the probability of the donor's excited state approaches unity.     

Charge Transfer at High Excitation Power of Solids

Electron transfer between excited donor molecules followed by the back reaction is treated theoretically for a solid solution at high excitation power. An expression for the average donor cation probability P⁺(t) is derived. Calculations of the time dependence for P⁺(t) are presented. The results indicate that the maximum value of P⁺(t) in the nonlinear quenching process is less than the corresponding values of P⁺(t) for the linear quenching at a low excitation power due to the depletion of the acceptors with time t. The restriction of the reaction volume slows down the charge separation if the back charge transfer takes place.