“Higher-κ” dielectrics for advanced silicon microelectronic devices: A combinatorial research study

Combinatorial methodology is used to rapidly screen suitable ternary higher-κ dielectrics for future complementary metal oxide semiconductor (CMOS), and dynamic random access memory (DRAM) devices. Dielectric constant (κ) and leakage current (L_C) were mapped from capacitance–voltage (C–V) and current–voltage (I–V) measurements. HfO₂–TiO₂–Y₂O₃ library films, made by pulsed laser deposition (PLD), have been characterized. We found a band of compositions in the middle of the HfO₂–TiO₂–Y₂O₃ phase diagram that have dielectric constants in the range of 50–80, with reasonably low leakage currents, that are therefore promising for these applications.     

Effect of post-growth annealing on the structural,optical and electrical properties of V2O5 nanorods and its fabrication,characterization of V2O5/p-Si junction diode

We report the synthesis of V₂O₅ nanorods by utilizing simple wet chemical strategy with ammonia meta vanadate (NH₄VO₃) and polyethylene glycol (PEG) exploited as precursor and surfactant agent, respectively. The effect of post-annealing on structural, optical and electrical properties of V₂O₅ nanorods was characterized by XRD, HRSEM-EDX, TEM, FT-IR, UV (DRS), PL, TG–DTA and DC conductivity studies. The X-ray diffraction analysis revealed that the prepared sample annealed at 150 °C for 5 h which exhibited anorthic phase of V₅O₉ and annealed at 300–600 °C showed the anorthic phase change to orthorhombic phase of V₂O₅ due to the post-annealing effect. The surface morphology results indicated that increasing temperature caused a change from microrods to a nanorods shape in the morphology of V₂O₅. FT-IR spectrum confirmed that the presence of V₂O₅ functional groups and the formation of V–O bond. The optical band gap was found in the range 2.5–2.48 eV and observed to decreases with various annealed temperature. The DC electrical conductivity was studied as a function of temperature which indicated the semiconducting nature. Further, the potential of V₂O₅ nanostructures were grown on the p-Si substrate using the nebulizer spray technique. The junction properties of the V₂O₅/p-Si diode were evaluated by measuring current (I)–voltage (V) and AC characteristics.     

Comparative study of AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors with Al2O3 and HfO2 gate oxide

AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs) with Al₂O₃ gate oxide which was deposited by atomic layer deposition (ALD) were fabricated and their performance was then compared with that of AlGaN/GaN MOSHFETs with HfO₂ gate oxide. The capacitance (C)-voltage (V) curve of the Al₂O₃/GaN MOS diodes showed a lower hysteresis and lower interface state density than the C-V curve of the HfO₂/GaN diodes, indicating better quality of the Al₂O₃/GaN interface. The saturation of drain current in the I_D-V_GS relation of the Al₂O₃ AlGaN/GaN MOSHFETs was not as pronounced as that of the HfO₂ AlGaN/GaN MOSHFETs. The gate leakage current of the Al₂O₃ MOSHFET was five to eight orders of magnitude smaller than that of the HfO₂ MOSHFETs.     

Lanthanum germanate as dielectric for scaled Germanium metal–oxide–semiconductor devices

We report a study of La₂O₃ with lanthanum germanate (LGO) as interfacial layer, or LGO alone as a gate dielectric candidate for scaled germanium metal–oxide–semiconductor devices. Capacitance–voltage (C–V) analysis of as-deposited samples of various oxide thicknesses show a La₂O₃ with k value of ～24–27 with an interfacial LGO with k value of ～12. Upon O₂ annealing, the oxides fully transform into LGO without an interfacial layer. The paper also discusses flatband voltage (V_fb) shifts with oxide thickness, from which positive fixed charges in La₂O₃ can be deduced. It is also shown that these charges are strongly reduced upon the O₂ anneal and LGO formation.     

Evolution of oxide charge trapping under bias temperature stressing

Transient oxide-charge trapping and detrapping, commonly regarded as a parasitic effect in the interpretation of dynamic bias-temperature stress (BTS) data, may play an important role on the long term reliability of the gate oxide as revealed by recent studies on the SiON and HfO₂ gate dielectrics. Specifically, it is found that transient charge trapping (one which relaxes upon removal of the applied electrical stress) is transformed into more permanent trapped charge when the applied electrical cum thermal stress exceeds a certain threshold. Below the threshold, cyclical transient charge trapping and detrapping behavior is observed. The observations imply that the oxide structure may be modified by the applied stress, making it susceptible to permanent defect generation. In addition, it is found that when the transformation of hole trapping occurs under negative-bias temperature stress, a correlated increase of the gate current is always observed, which points to the transformation process being the origin for bulk oxide trap generation. However, when the transformation of electron trapping occurs under positive-bias temperature stress, an increase of the gate current is not always observed. From ab initio simulation, we show that an intrinsic oxide defect – the oxygen vacancy-interstitial (V_O − O_i) – could consistently explain the experimental observations. An interesting feature of the V_O − O_i defect is that it can exists in various metastable configurations with the interstitial oxygen O_i in different positions around the vacancy V_O, corresponding to different trap energy states in the oxide bandgap. This characteristic is able to account for the BTS induced generation of deep-level trapped charges as well as transformation of transient (or shallow) to permanent (or deep) charge trapping.     

Current saturation effect for pentacene-based static induction transistor under negative drain-source and gate voltages

Usually, the drain-source current (I_DS) increases with positive drain-source voltage (V_DS) for pentacene-based organic static induction transistor (OSIT) ITO(Source)/Pentacene/Al(Gate)/Pentacene/Au(Drain) and it shows an inherent rectifying property under negative gate voltages (V_G), i.e. the slope of I_DS vs. V_DS curve increases with V_DS but without any current saturation effect. In this paper, we investigated the electrical characteristics of pentacene-based OSIT ITO/Pentacene(80 nm)/Al(15 nm)/Pentacene(80 nm)/Au under negative V_DS and V_G, and found that I_DS changed from rectifying property to saturation effect when the magnitude of negative V_DS was increased from 0 V to −6 V under negative V_G, and the turn-on voltage (V_ON) moved to larger negative voltages when the magnitude of negative V_G increased and the movement step of V_ON gets smaller after keeping the device for a long time, and the possible mechanisms for such a kind of current modulation were discussed.     

Leakage current by Frenkel–Poole emission on benzotriazole and benzothiadiazole based organic devices

In this study three different organic semiconductors were used in the fabrication of ITO/PEDOT:PSS/Polymer:PCBM/LiF/Al configuration. Reverse current density–voltage (J_r–V) measurements of the samples were investigated to define the reverse-bias leakage current mechanisms on benzotriazole and benzothiadiazole based organic devices. Our results indicate that the J_r–V plot behaviors are given by linear dependence between In ( J_r) and V^1/2, where J_r is the reverse current density, and V is the applied voltage. This behavior is well known as the Poole–Frenkel (PF) effect where it is found to be dominating in the reverse-bias leakage current.     

Temperature-dependent resistive switching characteristics for Au/n-type CuAlOx/heavily doped p-type Si devices

Bipolar switching phenomenon is found for Au/n-type CuAlO_x/heavily doped p-type Si devices at temperatures above 220 K. For high or low resistive states (HRS or LRS), the electrical resistance is decreased with increasing temperature, indicating a semiconducting behavior. Carrier transport at LRS or HRS is dominated by hopping conduction. It is reasonable to conclude that the transition from HRS to LRS due to the migration of oxygen vacancies (V_O) is associated with electron hopping mediated through the V_O trap sites. The disappearance of the resistive switching behavior below 220 K is attributed to the immobile V_O traps. The deep understanding of conduction mechanism could help to control the device performance.     

Structural and Electrical Properties of Ta ax La(1−a)x O y Thin Films

Effect of annealing temperature on the characteristics of sol–gel-driven Ta _ax La_(1?a)x O _y thin film spin-coated on Si substrate as a high-k gate dielectric was studied. Ta _ax La_(1?a)x O _y thin films with different amounts of a were prepared (as-prepared samples). X-ray diffraction measurements of the as-prepared samples indicated that Ta_0.3x La_0.7x O_y film had an amorphous structure. Therefore, Ta_0.3x La_0.7x O _y film was chosen to continue the present studies. The morphology of Ta_0.3x La_0.7x O _y films was studied using scanning electron microscopy and atomic force microscopy techniques. The obtained results showed that the size of grain boundaries on Ta_0.3x La_0.7x O _y film surfaces was increased with increasing annealing temperature. Electrical and optical characterizations of the as-prepared and annealed films were investigated as a function of annealing temperature using capacitance–voltage (C–V) and current density–voltage (J–V) measurements and the Tauc method. The obtained results demonstrated that Ta_0.3x La_0.7x O _y films had high dielectric constant (≈27), wide band gap (≈4.5 eV), and low leakage current density (≈10^?6 A/cm² at 1 V).     

Numerical Simulation and Analytical Modeling of InAs nBn Infrared Detectors with p-Type Barriers

This paper presents finite-element one-dimensional numerical simulations and analytical modeling for ideal (diffusion current only) nBn detectors with p-type barrier layers. The simulations show that the current–voltage J(V) and the dynamic resistance versus voltage R _D(V) relations, both dark and illuminated, are in excellent agreement with the equations for ideal back-to-back photodiodes. We present a depletion approximation model for the nBn detector, analogous to that for the conventional p–n junction photodiode, based on new boundary conditions on the hole concentrations versus voltage at the edges of the nBn barrier layer. We show that these nBn boundary conditions are identical to those for ideal back-to-back photodiodes, justifying the applicability of back-to-back photodiode equations to describe the ideal nBn detector. The simulations for the space-charge regions show a low-bias-voltage regime and a high-bias-voltage regime. The integrated space-charge densities in the layers adjacent to the barrier layer vary linearly with bias voltage. Negative dynamic resistance occurs because the bias voltage changes the effective thickness of the thin-base layers that generate diffusion current. We present a new formulation of the model for ideal back-to-back photodiodes with a more elegant and transparent set of equations for J(V) and R _D(V).     

Control of Interface Traps in HfO2 Gate Dielectric on Silicon

The effects of postdeposition annealing (PDA) on the interface between HfO₂ high-k dielectric and bulk silicon were studied in detail. The key challenges of successfully adopting the high-k dielectric/Si gate stack into advanced complementary metal–oxide–semiconductor (CMOS) technology are mostly due to interfacial properties. We have proposed a PDA treatment at 600°C for several different durations (5 min to 25 min) in nitrogen or oxygen (95% N₂ + 5% O₂) ambient with a 5-nm-thick HfO₂ film on a silicon substrate. We found that oxidation of the HfO₂/Si interface, removal of the deep trap centers, and crystallization of the film take place during the postdeposition annealing (PDA). The optimal PDA conditions for low interface trap density were found to be dependent on the PDA duration. The formation of an amorphous interface layer (IL) at the HfO₂/Si interface was observed. The growth was due to oxygen incorporated during thermal annealing that reacts with the Si substrate. The interface traps of the bonding features, defect states, and hysteresis under different PDA conditions were studied using x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), transmission electron microscopy (TEM), and leakage current density–voltage (J–V) and capacitance–voltage (C–V) techniques. The results showed that the HfO₂/Si stack with PDA in oxygen showed better physical and electrical performance than with PDA in nitrogen. Therefore, PDA can improve the interface properties of HfO₂/Si and the densification of HfO₂ thin films.     

Electrical properties of vacuum annealed La2O3 thin films grown by E-beam evaporation

In this article, the conduction mechanisms of metal-oxide-semiconductor with vacuum annealed Lanthana (La₂O₃) oxide film are investigated. Lanthana films with thicknesses of 3.5, 4.7, and 11 nm were deposited by E-beam evaporation on n-Si (100), and annealed at various temperatures (300-500 °C) in ultra-high vacuum (10⁻¹⁰-10⁻⁹ Torr) for 90 min. From the measurement of spectroscopic ellipsometry, it is found that film thickness is increased with annealing temperature, which would be cause of flat-band voltage shift (ΔV_FB) due to the growth of interfacial layer. From the capacitance measurement, it is found that ΔV_FB of the film is reduced by post-deposition anneal (PDA) compared to that of as-deposited film, but increase again at high temperature annealing, especially in the case of thin film (3.5 nm). From the applied voltage and temperature dependence of the leakage current of the film, with different gate electrode materials (Ag, Al, and Pt), it is shown that the leakage currents are associated with ohmic and Poole-Frenkel (P-F) conductions when flat-band voltage (V_FB) is less than zero, and ohmic and Space-Charge-Limited Current (SCLC) conductions when V_FB is greater than zero. The dielectric constants obtained from P-F conduction for Al gate electrode case is found to be 11.6, which is consistent with the C-V result 11.9. Barrier height of trap potential well is found to be 0.24 eV from P-F conduction. Based on SCLC theory, leakage currents of 3.5 and 11 nm films with different PDA temperatures are explained in terms of oxide trap density.     

Electrical measurements of voltage stressed Al2O3/GaAs MOSFET

Electrical characteristics of GaAs metal–oxide–semiconductor field effect transistor with atomic layer deposition deposited Al₂O₃ gate dielectric have been investigated. The IV characteristics were studied after various constant voltage stress (CVS) has been applied. A power law dependence of the gate leakage current (I_g) on the gate voltage (V_g) was found to fit the CVS data of the low positive V_g range. The percolation model well explains the degradation of I_g after a high positive V_g stress. A positive threshold voltage (V_th) shift for both +1.5 V and +2 V CVS was observed. Our data indicated that positive mobile charges may be first removed from the Al₂O₃ layer during the initial CVS, while the trapping of electrons by existing traps in the Al₂O₃ layer is responsible for the V_th shift during the subsequent CVS.     

Investigation of Characteristics of Al2O3/n-In x Ga1−x As (x = 0.53, 0.7, and 1) Metal–Oxide–Semiconductor Structures

The electrical properties of Al₂O₃/n-InGaAs metal–oxide–semiconductor capacitors (MOSCAPs) with In content of 0.53, 0.7, and 1 (InAs) have been investigated. Results show small capacitance–voltage (C–V) frequency dispersion in accumulation (1.70% to 1.85% per decade) for these MOSCAPs, mostly being assigned to border traps in Al₂O₃. With higher In content, shorter minority-carrier response time and smaller C–V hysteresis are observed. The reduction of C–V hysteresis might be related to the reduction of Ga-bearing oxides in Al₂O₃/InGaAs interfaces as indicated by x-ray photoelectron spectroscopy.     

Temperature dependent electrical and dielectric properties of a metal/Dy2O3/n-GaAs (MOS) structure

This paper describes the structural properties, electrical and dielectric characteristics of thin Dy₂O₃ layer deposited on the n-GaAs substrate by electron beam deposition under ultra vacuum. Structural and morphological characterizations are investigated by atomic force microscopy (AFM) and X-ray diffraction measurements (XRD). The XRD shows that the elaborated Dy₂O₃ oxide has a cubic structure. The electrical and dielectric properties of Co/Au/Dy₂O₃/n-GaAs structure were studied in the temperature range of 80–500 K. The conductance and capacitance measurements were performed as a function of bias voltage and frequency. The dielectric constant (ε′), dielectric loss (ε″) and dielectric loss tangent (tanδ) of the structure are obtained from capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements. These parameters are found to be strong functions of temperature and bias voltage. A strong negative capacitance (NC) phenomenon has been observed in C–V; hence ε′–V plots for each temperature value take negative values. The following behavior of the C and ε′ in the forward bias region has been explained with the minority-carrier injection and relaxation theory. From DC conductance study, electronic conduction is found to be dominated by thermally activated hopping at high temperature. Activation energy is deduced from the variation of conductance with temperature. The interface state density (N_ss) of the structure is of the order 1.13×10¹³ eV⁻¹ cm⁻².     

Probing giant reduction of Tc in the Li(Ti1−xVx)2O4 spinel system

The doping effect of Vanadium in polycrystalline LiTi₂O₄ material is carefully analysed. We report on the detailed electrical and magnetic properties of Li(Ti_1−xV_x)₂O₄ system for 0⩽x⩽0.05 with an emphasis on the low Vanadium concentration. We have an interesting finding to report in that the doping of Vanadium in LiTi₂O₄, leads to a giant T_c reduction. The localized magnetic moments induced by the Vanadium doping seem to be responsible for the reduction in T_c.     

Elucidating the role of current injection on the influence of open-circuit voltage in small-molecule organic photovoltaic devices: From the aspects of charge transfer and electroluminescent spectrum

We demonstrate that the open-circuit voltage (V_OC) of organic photovoltaic (OPV) devices composed of rubrene and C₆₀ can be considerably different when the anode and active layer are changed. Two types of anodes and active layers were compared. In plasma-treated indium-tin-oxide (ITO) OPV devices, the parameter V_OC exhibits an improvement from 0.68 V to 0.76 V when the device structure is varied from a bilayer to a mixed structure. However, in the OPV devices that use ITO/MoO₃ as the anode, a similar V_OC is observed regardless of the device structure. A series of temperature-dependent measurements are conducted to investigate these results. The calculation of barrier height at the rubrene/C₆₀ (or rubrene:C₆₀) interface yields the prediction of V_OC, suggesting that an excess energetic loss occurs in the mixed structures. The electroluminescent (EL) spectra of these devices show that the mixed structure can completely quench the EL of rubrene single layer. A broad band of the charge transfer (CT) emission is observed clearly. A temperature-dependent measurement for the extracting injection barrier is conducted and shows that the mixed structure is favorable for the hole current injection. The CT properties are obtained using the external quantum efficiency and EL spectra of the OPV devices. We find that the nonradiative recombination loss is highly correlated with the injected current; the lower the injection barrier induced the less the nonradiative recombination loss. Therefore, the parameter V_OC can be improved when the injected current is increased.     

Investigation on a source of dominant donor in vanadium-doped ZnO films grown by reactive RF magnetron sputtering

The influences of O₂ gas addition in argon plasma on reactive RF magnetron sputtering deposition of vanadium-doped ZnO (VZO) films were examined. ZnO or VZO films with vanadium concentration of 2 at% were deposited on a quartz substrate. Vanadium doping caused oxygen deficiency in ZnO and formed a large number of zinc interstitials (Zn_i), oxygen vacancies (V_O), and zinc vacancies (V_Zn). Carrier density of VZO decreased from 9×10²⁰ to 9×10¹⁸ cm⁻³ between O₂ partial pressure ratio (α_O2) of 0.6% and 1.0% in spite of the increase in valence number of vanadium. This result suggests that Zn_i is the dominant donor in VZO since Zn_i is a shallow-level defect. Average optical transmittance (T_v) at wavelength between 450 and 800 nm of VZO was 61% while that of ZnO was 82% without oxygen addition. Although the optical transmittance of VZO was largely deteriorated by optical absorption of V_O, T_v of VZO improved by oxygen addition and reached 85% at α_O2 of 1.0% via suppression of V_O formation.     

Solution-processed vanadium oxide as an anode interlayer for inverted polymer solar cells hybridized with ZnO nanorods

Solution-processed vanadium oxide (V₂O₅) as an anode interlayer is introduced between the organic layer and the Ag electrode for improving the performance of the low-cost inverted polymer solar cells hybridized with ZnO nanorods. Our investigations indicate that the solution-processed V₂O₅ interlayer as an electron-blocking layer can effectively prevent the leakage current at the organic/Ag interface. The power conversion efficiency is improved from 2.5% to 3.56% by the introduction of the V₂O₅ interlayer. The V₂O₅ interlayer also serves as an optical spacer to enhance light absorption, and thereby increases the photocurrent. Compared to the vacuum-deposited techniques, the fabrication of the solution-processed V₂O₅ interlayer is simple and effective. The solution-based approach makes it attractive for applications to mass production and potentially printed organic electronics.     

Bistability and electrical activity of the vacancy-dioxygen complex in silicon

The methods of infrared absorption. Hall effect, and deep-level transient spectroscopy are used to study the complexes that consist of a vacancy and two oxygen atoms (the vacancy-dioxygen complexes, VO₂) in irradiated n-Si crystals with various levels of doping. The previously observed bistability of VO₂ is confirmed and evidence is provided for electrical activity of this defect in the metastable configuration VO*₂. It is established that the defect with this configuration features an acceptor level located at E _C ? 0.06 eV. It is shown that the absorption bands at 967 and 1023 cm^?1 are caused by the negatively charged VO*₂ state, while the bands peaking at 928 and 1004 cm^?1 correspond to the neutral charge state of the defect.