Apurba Laha

Influence of interface layer composition on the electrical properties of epitaxial Gd2O3 thin films for high-K application

The authors report on the impact of interface layer composition on electrical properties of epitaxial Gd2O3 thin films on Si(001) substrates. The electrical properties of epitaxial Gd2O3 thin films were improved significantly by controlled modification of interface layer composition. The minimum capacitance equivalent thickness estimated for Pt∕Gd2O3∕Si metal oxide semiconductor structures was as low as 0.76nm with leakage current density of 15mA∕cm2 at (Vg−VFB)=1V. The corresponding density of interface states was found to be 2.3×1012cm−2eV−1. The authors also find that a change in the interface layer composition significantly alters band alignment of Gd2O3 layer with respect to Si substrates.

Investigation of the electronic structure at interfaces of crystalline and amorphous Gd2O3 thin layers with silicon substrates of different orientations

Internal photoemission, photoconductivity, and spectroscopic ellipsometry experiments were carried out to characterize the electronic structure of interfaces of (001) and (111)-oriented Si with crystalline (epitaxially grown) and amorphous Gd2O3 insulators. The energy barriers for electrons and holes (3.2 and 3.9eV, respectively) appear to be sensitive neither to the orientation of the Si crystal surface nor to the oxide phase (crystalline or amorphous). This result indicates that despite the difference in Si–O bond density in going from (001) to (111)Si, the interface dipoles do not ensue any measurable effect on the electronic structure of the interface and the associated band offsets.

Crystalline ternary rare earth oxide with capacitance equivalent thickness below 1 nm for high-K application

Ternary neodymium-gadolinium oxide (NGO) thin films were grown epitaxially on Si(001) substrates using modified molecular beam epitaxy. The electrical properties of NGO thin films demonstrate that this ternary oxide could be one of the most promising candidates to replace the conventionally used SiO2 or SiOxNy in complementary metal oxide semiconductor devices. The films were characterized with various methods. The capacitance equivalent oxide thickness of 4.5nm thin films extracted from capacitance-voltage (C-V) characteristics was 0.9nm. For such films, leakage current density and the density of interface traps were 2.6×10−4A∕cm2 at ∣Vg−VFBV∣=1V and 1.4×1012∕cm2eV−1, respectively.

Impact of Si substrate orientations on electrical properties of crystalline Gd2O3 thin films for high-K application

The authors compare the properties of epitaxial Gd2O3 thin films grown on silicon substrates with three different orientations for high-K application. Pt∕Gd2O3∕Si(111) and Pt∕Gd2O3∕Si(110) metal oxide semiconductor heterostructures show promising electrical properties and hence, could be considered for future generation of complementary metal oxide semiconductor devices. Capacitance equivalent oxide thicknesses estimated from capacitance versus voltage characteristics are 0.97, 1.12, and 0.93nm for the films grown on Si(001), Si(111), and Si(110) substrates, respectively. The films exhibit good insulating property with leakage current densities of 0.4, 0.5, and 4.5mA∕cm2, respectively, at (Vg−VFBV)=−1V.

Effective passivation of slow interface states at the interface of single crystalline Gd2O3 and Si(100)

The as-grown single crystalline Gd2O3 thin film on Si(100) substrate suffers from flatband voltage instability and large hysteresis which are possibly due to the intrinsic dangling bonds induced by the existing binding mismatch at the Gd2O3∕Si(100) interface. The instability of flatband voltage and hysteresis of Pt∕Gd2O3∕Si and W∕Gd2O3∕Si structures can be fully eliminated by the introduction of traditional forming gas annealing with proper process optimization. Both optimized metal-oxide-semiconductor structures show negligible hysteresis with the interface state at the magnitude order of 1011∕cm2eV at the midgap of silicon and can be considered for the future of complementary metal oxide semiconductor devices.

Role of La0.5Sr0.5CoO3 template layers on dielectric and electrical properties of pulsed-laser ablated Pb(Nb2/3Mg1/3)O3–PbTiO3 thin films

Relaxor ferroelectric thin films of 0.7Pb(Mg1/3Nb2/3)O-3-0.3PbTiO(3) (PMN-PT) deposited on platinized silicon substrates with and without template layers were studied. Perovskite phase (80% by volume) was obtained through proper selection of the processing conditions on bare Pt/Ti/SiO2/Si substrates. The films were initially grown at 300 degreesC using pulsed-laser ablation and subsequently annealed in a rapid thermal annealing furnace in the temperature range of 750-850 degreesC to induce crystallization. Comparison of microstructure of the films annealed at different temperatures showed change in perovskite phase formation and grain size etc. Results from compositional analysis of the films revealed that the films initially possessed high content of lead percentage, which subsequently decreased after annealing at temperature 750-850 degreesC. Films with highest perovskite content were found to form at 820-840 degreesC on Pt substrates where the Pb content was near stoichiometric. Further improvement in the formation of perovskite PMN-PT phase was obtained by using buffer layers of La0.5Sr0.5CoO3 (LSCO) on the Pt substrate. This resulted 100% perovskite phase formation in the films deposited at 650 degreesC. Dielectric studies on the PMN-PT films with LSCO template layers showed high values of relative dielectric constant (3800) with a loss factor (tan delta) of 0.035 at a frequency of 1 kHz at room temperature

Dielectric response and impedance spectroscopy of 0.7Pb(Mg1/3Nb2/3)O3 /0.3PbTiO3 thin films

Dielectric response of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN–PT) thin films deposited by pulsed laser deposition has been studied as a function of frequency over a wide range of temperatures. The films exhibited maximum frequency dispersion in both real and imaginary part of dielectric susceptibility near and below the dielectric transition temperature. The relaxor behavior in the films was confirmed from the diffused phase transition (DP) together with frequency dependent of transition temperature (Tm). The frequency dependence of transition temperature Tm (temperature of the maximum of dielectric constant) was studied in terms of Vogel–Fulcher relation. The dielectric relaxation of PMN–PT thin films was studied at different temperatures using the complex impedance (Z*) and electric modulus (M*) formalism. The shape of complex impedance curve inferred that only one type of dielectric relaxation was involved in the present case. This was attributed to the contribution of bulk grain of the films while the other probable sources, such as grain boundaries, film electrode interfaces were negligible. The films exhibited Debye type dielectric relaxation at temperature sufficiently above the temperature of permittivity maximum (Tm), while a multi-Debye relaxation was observed at lower temperatures (<200 °C), which was confirmed from the broad spectrum of dielectric relaxation. The average relaxation times estimated from Cole–Cole plots varied with temperature according to the V–F relation.

Analysis of leakage current conduction phenomenon in thin SrBi2Ta2O9 films grown by excimer laser ablation

The dc conduction behavior of thin films of SrBi2Ta2O9 (SBT) has been investigated on the basis of space-charge limited current theory. The theory was generalized to account for the traps, which were inevitably present in this case. The relative percentage of trapped injected charge and the free injected charge was seen to follow a dynamical equilibrium instead of the true thermal equilibrium as the temperature of the sample was raised during the measurement. The onset voltage of the trap filled region (VTFL) showed a decreasing trend with the increase of temperature. This reduction of VTFL was ascribed to the appearance of some excess charge in the conduction band. It was seen that the thermodynamically stable distribution of charges among the energy levels could not be taken to explain such a situation. A dynamic model was proposed to explain this kind of a nonequilibrium distribution of trapped and free charges.

Leakage current conduction of pulsed excimer laser ablated BaBi2Nb2O9 thin films

The leakage current behavior of the BaBi2Nb2O9 (BBN) thin films was investigated over a wide range of temperatures. The current density, calculated from current–voltage (I–V) characteristics at room temperature, was 4.02×10−9 A/cm2 at an electric field of 3×105 V/m. The I–V characteristics of the films showed ohmic behavior for electric field strength lower than 1 MV/m. Nonlinearity in the current density–voltage (J–V) behavior was observed at an electric field above 1 MV/m. Different conduction mechanisms were brought into picture to explain the I–V characteristics of BBN thin films. The J–V behavior of BBN thin films was found to follow the Lampert’s theory of space charge limited conduction in an insulator with traps. Three different regions, i.e., ohmic, trap filled limited, Child’s law were explicitly observed in J–V characteristics. The activation energies in the ohmic region calculated from the Arrhenius plot were 0.46, 0.48, and 0.51 eV, respectively. These energies were attributed to the shallow ...

Growth and characterization of excimer laser-ablated BaBi2Nb2O9 thin films

The pulsed-laser ablation technique has been employed to deposit polycrystalline thin films of layered-structure ferroelectric BaBi2Nb2O9 (BBN). Low-substrate-temperature growth (Ts = 400 °C) followed by ex situ annealing at 800 °C for 30 min was performed to obtain a preferred orientation. Ferroelectricity in the films was verified by examining the polarization with the applied electric field and was also confirmed from the capacitance–voltage characteristics. The films exhibited well-defined hysteresis loops, and the values of saturation (Ps) and remanent (Pr) polarization were 4.0 and 1.2 μC/cm2, respectively. The room-temperature dielectric constant and dissipation factor were 214 and 0.04, respectively, at a frequency of 100 kHz. A phase transition from a ferroelectric to paraelectric state of the BBN thin film was observed at 220 °C. The dissipation factor of the film was observed to increase after the phase transition due to a probable influence of dc conduction at high temperatures. The real and imaginary part of the dielectric constant also exhibited strong frequency dispersion at high temperatures.