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This paper describes a method to optimally combine wide band gap Al2O3 with high dielectric constant (high-κ) Ta2O5 for gate dielectric applications. (Ta2O5)x(Al2O3)1-x thin films deposited by thermal atomic layer deposition (ALD) on GaN-capped AlxGa1-xN/GaN high electron mobility transistor (HEMT) structures have been studied as a function of the Ta2O5 molar fraction. X-ray photoelectron spectroscopy shows that the bandgap of the oxide films linearly decreases from 6.5 eV for pure Al2O3 to 4.6 eV for pure Ta2O5. The dielectric constant calculated from capacitance-voltage measurements also increases linearly from 7.8 for Al2O3 up to 25.6 for Ta2O5. The effect of post-deposition annealing in N2 at 600 °C on the interfacial properties of undoped Al2O3 and Ta-doped (Ta2O5)0.12(Al2O3)0.88 films grown on GaN-HEMTs has been investigated. These conditions are analogous to the conditions used for source/drain contact formation in gate-first HEMT technology. A reduction of the Ga-O to Ga-N bond ratios at the oxide/HEMT interfaces is observed after annealing, which is attributed to a reduction of interstitial oxygen-related defects. As a result, the conduction band offsets (CBOs) of the Al2O3/GaN-HEMT and (Ta2O5)0.16(Al2O3)0.84/GaN-HEMT samples increased by ~1.1 eV to 2.8 eV and 2.6 eV, respectively, which is advantageous for n-type HEMTs. The results demonstrate that ALD of Ta-doped Al2O3 can be used to control the properties of the gate dielectric, allowing the κ-value to be increased, while still maintaining a sufficient CBO to the GaN-HEMT structure for low leakage currents. [ABSTRACT FROM AUTHOR]

A comprehensive study of atomic-layer deposited thulium oxide (Tm2O3) on germanium has been conducted using x-ray photoelectron spectroscopy (XPS), vacuum ultra-violet variable angle spectroscopic ellipsometry, high-resolution transmission electron microscopy (HRTEM), and electron energy-loss spectroscopy. The valence band offset is found to be 3.0±60.2 eV for Tm2O3/p-Ge from the Tm 4d centroid and Ge 3p3/2 charge-corrected XPS core-level spectra taken at different sputtering times of a single bulk thulium oxide sample. A negligible downward band bending of ~0.12 eV is observed during progressive differential charging of Tm 4d peaks. The optical band gap is estimated from the absorption edge and found to be 5.77 eV with an apparent Urbach tail signifying band gap tailing at ~5.3 eV. The latter has been correlated to HRTEM and electron diffraction results corroborating the polycrystalline nature of the Tm2O3 films. The Tm2O3/Ge interface is found to be rather atomically abrupt with sub-nanometer thickness. In addition, the band line-up of reference GeO2/n-Ge stacks obtained by thermal oxidation has been discussed and derived. The observed low reactivity of thulium oxide on germanium as well as the high effective barriers for holes (~3 eV) and electrons (~2 eV) identify Tm2O3 as a strong contender for interfacial layer engineering in future generations of scaled high-κ gate stacks on Ge. [ABSTRACT FROM AUTHOR]

The present study analyzes the optimal price and quality decisions of a retailer for its different stores in a heterogeneous market. The consumers are also assumed to be heterogeneous in terms of their willingness to pay for quality who are non-uniformly distributed in the market. This type of heterogeneity which is identified based on income disparity can have important implications for a retailer's optimal policy. The main objective of this study is to determine how the distribution of different types of consumers in the market and how their travel costs affect the optimal setting of price and quality levels among different stores of a retailer. According to the findings of this study, the geographical disparity of willingness to pay plays a significant role in differentiation and targeting strategy of a retailer. Furthermore, a comparative analysis revealed that the widely adopted assumption of uniform distribution of consumers in the literature would lead to non-optimal decisions in which the distribution of consumers is non-uniform in a real-world situation. [ABSTRACT FROM AUTHOR]

A study into the optimal deposition temperature for ultra-thin La2O3 and Y2O3/Ge gate stacks has been conducted in this paper with the aim to tailor the interfacial layer for effective passivation of the Ge interface. A detailed comparison between the two lanthanide oxides ( La2O3 and Y2O3) in terms of band line-up, interfacial features, and reactivity to Ge using medium energy ion scattering, vacuum ultra-violet variable angle spectroscopic ellipsometry (VUV-VASE), X-ray photoelectron spectroscopy, and X-ray diffraction is shown. La2O3 has been found to be more reactive to Ge than Y2O3, forming LaGeOx and a Ge sub-oxide at the interface for all deposition temperature studied, in the range from 44 °C to 400°C. In contrast, Y2O3/Ge deposited at 400 °C allows for an ultra-thin GeO2 layer at the interface, which can be eliminated during annealing at temperatures higher than 525 °C leaving a pristine YGeOx/Ge interface. The Y2O3/Ge gate stack deposited at lower temperature shows a sub-band gap absorption feature fitted to an Urbach tail of energy 1.1 eV. The latter correlates to a sub-stoichiometric germanium oxide layer at the interface. The optical band gap for the Y2O3/Ge stacks has been estimated to be 5.7±0.1 eV from Tauc-Lorentz modelling of VUV-VASE experimental data. For the optimal deposition temperature (400 °C), the Y2O3/Ge stack exhibits a higher conduction band offset (∼2.3 eV) than the La2O3/Ge °2 eV), has a larger band gap (by about 0.3 eV), a germanium sub-oxide free interface, and leakage current (°10°7 A/cm2 at 1V) five orders of magnitude lower than the respective La2O3/Ge stack. Our study strongly points to the superiority of the Y2O3/Ge system for germanium interface engineering to achieve high performance Ge Complementary Metal Oxide Semiconductor technology. [ABSTRACT FROM AUTHOR]

Highly regio-regular poly(3-hexylthiophenes) (P3HT) thin films have been produced using the Tzrnadel method. They have head to tail counts approaching very close to 100% and high molecular mass. Thin-film transistors and Schottky diodes have been used to study the effects of counter ion and carrier density on field-effect and bulk mobility, respectively. The density of counter ions was increased using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and had a profound effect on both the field effect and bulk mobility with a ratio between the two of 10², in a similar way to DDQ in poly(β'-dodecyloxy-α,α',-α', α'terthienyl) (polyDOT[sub 3]), but with substantially higher drift mobilities. A method is described, using Schottky barriers, of simply and accurately determining carrier drift mobility. The effect of carrier density on hole mobility is believed to be indirect, filling traps in the regions separating the highly ordered domains until trap free conduction and hence high mobility is reached. [ABSTRACT FROM AUTHOR]

We present comprehensive experimental and theoretical work on tunnel-barrier rectifiers comprising bilayer (Nb2O5/Al2O3) insulator configurations with similar (Nb/Nb) and dissimilar (Nb/Ag) metal electrodes. The electron affinity, valence band offset, and metal work function were ascertained by X-ray photoelectron spectroscopy, variable angle spectroscopic ellipsometry, and electrical measurements on fabricated reference structures. The experimental band line-up parameters were fed into a theoretical model to predict available bound states in the Nb2O5/Al2O3 quantum well and generate tunneling probability and transmittance curves under applied bias. The onset of strong resonance in the sub-V regime was found to be controlled by a work function difference of Nb/Ag electrodes in agreement with the experimental band alignment and theoretical model. A superior low-bias asymmetry of 35 at 0.1V and a responsivity of 5 A/W at 0.25V were observed for the Nb/4 nm Nb2O5/1nm Al2O3/Ag structure, sufficient to achieve a rectification of over 90% of the input alternate current terahertz signal in a rectenna device. [ABSTRACT FROM AUTHOR]

The effect of fluorine doping on the switching stability of Ta2O5 resistive random access memory devices is investigated. It shows that the dopant serves to increase the memory window and improve the stability of the resistive states due to the neutralization of oxygen vacancies. The ability to alter the current in the low resistance state with set current compliance coupled with large memory window makes multilevel cell switching more favorable. The devices have set and reset voltages of <1V with improved stability due to the fluorine doping. Density functional modeling shows that the incorporation of fluorine dopant atoms at the two-fold O vacancy site in the oxide network removes the defect state in the mid bandgap, lowering the overall density of defects capable of forming conductive filaments. This reduces the probability of forming alternative conducting paths and hence improves the current stability in the low resistance states. The doped devices exhibit more stable resistive states in both dc and pulsed set and reset cycles. The retention failure time is estimated to be a minimum of 2 years for F-doped devices measured by temperature accelerated and stress voltage accelerated retention failure methods. [ABSTRACT FROM AUTHOR]

The role of nitrogen doping on the stability and memory window of resistive state switching in N-doped Ta2O5 deposited by atomic layer deposition is elucidated. Nitrogen incorporation increases the stability of resistive memory states which is attributed to neutralization of electronic defect levels associated with oxygen vacancies. The density functional simulations with the screened exchange hybrid functional approximation show that the incorporation of nitrogen dopant atoms in the oxide network removes the O vacancy midgap defect states, thus nullifying excess defects and eliminating alternative conductive paths. By effectively reducing the density of vacancy-induced defect states through N doping, 3-bit multilevel cell switching is demonstrated, consisting of eight distinctive resistive memory states achieved by either controlling the set current compliance or the maximum voltage during reset. Nitrogen doping has a threefold effect: widening the switching memory window to accommodate the more intermediate states, improving the stability of states, and providing a gradual reset for multi-level cell switching during reset. The N-doped Ta2O5 devices have relatively small set and reset voltages (<1V) with reduced variability due to doping. [ABSTRACT FROM AUTHOR]

A new three-pulse CV measurement technique has been developed to investigate the trapping and detrapping of negative and positive charges in SiO2/LaLuO3 gate dielectric stacks on p-type silicon. Two types of negative and positive trapped charges have been observed in these devices which are deemed to be related to electron and hole trapping, respectively. The technique has the advantage that trapping and detrapping of both types of charges can be measured independently. The concentrations of trapped charge types, their release times, and their relationship with measurement parameters such as pulse charging/discharging time and pulse amplitude have been investigated. A logarithmic universal relationship was found between the flat-band voltage shifts due to detrapping of positive charges with the discharging time. [ABSTRACT FROM AUTHOR]

The temperature dependence of leakage current for tantalum oxide metal-insulator-metal capacitors has been investigated over the temperature range 20-160 °C. The leakage current shows an increase with temperature and the conduction mechanism at medium to high electric fields is in agreement with the modified Poole-Frenkel model. The activation energy of the dominant deep trapping center in the oxide is calculated using this model. Constant voltage and constant current stress have been applied to the devices and the effect of stress conditions on leakage current, breakdown voltage, and high frequency capacitance-voltage have been investigated. Early oxide breakdown or time-dependent dielectric breakdown was observed during constant voltage and constant current stress, in which the former is a function of stress time and applied voltage or current. There is an increase in leakage current with time during the constant voltage stress, presumably due to generation of positive defect states. This is also apparent from the decrease in voltage with time during constant current stress. Degradation of the oxides by constant current stress and its effect on the oxide leakage current (or stress induced leakage current) at various constant current values and stress times has also been investigated and is discussed in this article. [ABSTRACT FROM AUTHOR]

Passivation of the germanium interface using native oxide results in a potential well at the interface of GeO2 and high-κ dielectric for n-channel metal-oxide-semiconductor field effect transistors. The well forms a potential trapping site for electrons, which could result in threshold voltage instability. We present calculations for the bound states and their occupancy in the well. The significance of threshold voltage shift in an 8-nm node field effect transistor and those with larger dimensions is investigated. The main conclusion is that charge storage in the well is insignificant at the 8-nm technology node but can have a significant effect on larger devices. [ABSTRACT FROM AUTHOR]

We present a detailed investigation on the nature of the interfacial layer (IL) in ultra-thin TiN/LaLuO3 (LLO) gate stacks, which is of importance to facilitate CMOS scaling. The molecular beam deposited LaLuO3 films are found to be amorphous by high-resolution transmission electron microscopy. A ∼9 Å thick LaLuO3/interlayer transition observed by medium energy ion scattering correlates with the presence of a dual silicate/SiO2-like interfacial layer derived from the analysis of photoelectron line positions and electron energy loss spectra. A theoretical model is used for the dielectric transition in a bi-layer LaLuO3/IL structure, linking physical and electrical characterization data. The obtained leakage current of 10-3 A/cm2 at 1.5 V and equivalent oxide thickness of 0.75 nm for TiN/LaLuO3 gate stacks are adequate for scaling in the 14-12 nm node. [ABSTRACT FROM AUTHOR]