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The article analyses the flatband voltage shift of ruthenium (Ru) gated metal-oxide-semiconductor stacks and its effects on the formation of thin Ru oxide layer at the dielectric interface after a thermal treatment with oxygen. It reveals that an increase in the voltage shifts for Ru gated stacks is the result of the formation of the thin Ru-oxide layer, which is found to be thermodynamically very much similar to the bulk Ru[O.sub.2].

Spectral analysis of optically excited currents in single-crystal (100)InAs/amorphous (a-)Al2O3/metal structures allows one to separate contributions stemming from the internal photoemission (IPE) of electrons into alumina and from the trapping-related displacement currents. IPE spectra suggest that the out-diffusion of In and, possibly, its incorporation in a-Al2O3 lead to the development of ≈0.4eV wide conduction band (CB) tail states. The top of the InAs valence band is found at 3.45±0.10eV below the alumina CB bottom, i.e., at the same energy as at the GaAs/a-Al2O3 interface. This corresponds to the CB and the valence band offsets at the InAs/a-Al2O3 interface of 3.1±0.1eV and 2.5±0.1eV, respectively. However, atomic-layer deposition of alumina on InAs results in additional low-energy electron transitions with spectral thresholds in the range of 2.0-2.2eV, which is close to the bandgap of AlAs. The latter suggests the interaction of As with Al, leading to an interlayer containing Al-As bonds providing a lower barrier for electron injection. [ABSTRACT FROM AUTHOR]

In this article, we investigate extensively the bipolar-switching properties of Al2O3- and HfO2- based resistive-switching memory cells operated at low current down to <1 μA. We show that the switching characteristics differ considerably from those typically reported for larger current range (>15 μA), which we relate as intrinsic to soft-breakdown (SBD) regime. We evidence a larger impact of the used switching-oxide in this current range, due to lower density of oxygen-vacancy (Vo) defects in the SBD regime. In this respect, deep resetting and large memory window may be achieved using the stoichiometric Al2O3 material due to efficient Vo annihilation, although no complete erasure of the conductive-filament (CF) is obtained. We finally emphasize that the conduction may be described by a quantum point-contact (QPC) model down to very low current level where only a few Vo defects compose the QPC constriction. The large switching variability inherent to this latter aspect is mitigated by CF shape tuning through adequate engineering of an Al2O3\HfO2 bilayer. [ABSTRACT FROM AUTHOR]

The hydrogen interaction kinetics of the GePb1 defect, previously identified by electron spin resonance (ESR) as an interfacial Ge dangling bond (DB) defect occurring in densities ~7×1012 cm-2 at the SiGe/SiO2 interfaces of condensation grown (100)Si/a-SiO2/Ge0.75Si0.25/ a-SiO2 structures, has been studied as function of temperature. This has been carried out, both in the isothermal and isochronal mode, through defect monitoring by capacitance-voltage measurements in conjunction with ESR probing, where it has previously been demonstrated the defects to operate as negative charge traps. The work entails a full interaction cycle study, comprised of analysis of both defect passivation (pictured as GePb1-H formation) in molecular hydrogen (~1 atm) and reactivation (GePb1-H dissociation) in vacuum. It is found that both processes can be suitably described separately by the generalized simple thermal (GST) model, embodying a first order interaction kinetics description based on the basic chemical reactions GePb1+H2→GePb1H+H and GePb1H→GePb1+H, which are found to be characterized by the average activation energies Ef=1.44±0.04 eV and Ed=2.23±0.04 eV, and attendant, assumedly Gaussian, spreads σEf=0.20±0.02 eV andσEf=0.15±0.02 eV, respectively. The substantial spreads refer to enhanced interfacial disorder. Combination of the separately inferred kinetic parameters for passivation and dissociation results in the unified realistic GST description that incorporates the simultaneous competing action of passivation and dissociation, and which is found to excellently account for the full cycle data. For process times ta ~35 min, it is found that even for the optimum treatment temperature ~380°C, only ~60% of the GePb1 system can be electrically silenced, still far remote from device grade level. This ineffectiveness is concluded, for the major part, to be a direct consequence of the excessive spreads in the activation energies, ~2-3 times larger than for the Si DB Pb defects at the standard thermal (111)Si/SiO2 interface which may be easily passivated to device grade levels, strengthened by the reduced difference between the average Ef and Ed values. Exploring the guidelines of the GST model indicates that passivation can be improved by decreasing Tan and attendant enlarging of ta, however, at best still leaving ~2% defects unpassivated even for unrealistically extended anneal times. The average dissociation energy Ed~2.23 eV, concluded as representing the GePb1-H bond strength, is found to be smaller than the SiPb-H one, characterized by Ed~2.83 eV. An energy deficiency is encountered regarding the energy sum rule inherent to the GST-model, the origin of which is substantiated to lie with a more complex nature of the forward passivation process than basically depicted in the GST model. The results are discussed within the context of theoretical considerations on the passivation of interfacial Ge DBs by hydrogen. [ABSTRACT FROM AUTHOR]

Monitoring oxidation steps is an important factor during the fabrication of semiconductor devices, because transistor performance can be greatly affected by defects in the passivation layer. As an example, we discuss the formation of a gate stack in metal oxide semiconductor (MOS) devices using Ge as an alternative channel material. Building an MOS gate stack on Ge requires passivation of the interface between the dielectric (typically a high-k material such as Al2O3 or HfO2, grown by means of atomic layer deposition (ALD)) and the Ge channel. Such passivation can be obtained from a very thin Si layer, epitaxially grown on Ge. The Si surface receives an oxidizing clean (O3 or wet chemical clean) before the ALD step. In this work, second-harmonic generation (SHG) data are presented for silicon layers with varying thickness, grown with either trisilane (Si3H8) or silane (SiH4) and with various cleaning steps. The trend in second-harmonic response upon azimuthal rotation of the samples was comparable for both silane and trisilane as a Si precursor. Our results show that upon oxidation, the SHG intensity reduces, most likely due to a reduction of the amount of crystalline Si, which is converted to SiO2. [ABSTRACT FROM AUTHOR]

Analysis of electron states in nanometer-thin NiO layers grown by metallo-organic chemical vapor deposition on SiO2 or Al2O3 by means of spectroscopic ellipsometry and internal photoemission measurements points to the presence of a metal-like electron density, in correlation with the enhanced electrical conductivity of the films. These metallic states are suggested to be related to Ni clusters formed by partial reduction of NiO by hydrogen-containing by-products of the deposition reaction. [ABSTRACT FROM AUTHOR]

Traps at the (110)Si/SiO2 interface are investigated by combining electrical methods with electron spin resonance (ESR) measurements, and the results are compared to the well studied (100) and (111)Si/SiO2 interfaces. At all three Si crystal faces, the interface trap density Dit as function of energy E in the Si band gap exhibits two peaks at about 0.25 and 0.85 eV above the Si valence band, found to be well correlated with Pb(0) centers (Si3≡Si• defects). By comparing capacitance-voltage (CV) curves at 300 and 77 K of both n- and p-type samples, the Pb(0) defects are confirmed to be amphoteric. Effective passivation of interface traps by H2 annealing suggests that Pb0 defects are responsible for most of interface traps observed in (110)Si/SiO2. The truly amphoteric behavior, implying that one Pb0 defect delivers two interface trap levels, was observed for the (100) and (111)Si faces but not for the (110) face. The estimated interface trap density Nit at the (110)Si/SiO2 interface oxidized at 930 °C is (6.7±0.5)×1012, while the Pb0 density as determined by ESR is about (6±1)×1012 cm-2. Lowering of the oxidation temperature leads to further reduction in the electrically active Pb0 centers fraction at the (110)Si/SiO2 interface. [ABSTRACT FROM AUTHOR]

An electron spin resonance study has been carried out on heteroepitaxial Si/insulator structures obtained through growth of epi-Lu2O3 films on (111)Si (∼4.5% mismatch) by molecular-beam epitaxy, with special attention to the inherent quality as well as the thermal stability of interfaces, monitored through occurring paramagnetic point defects. This indicates the presence, in the as-grown state, of Pb defects (∼5×1011 cm-2) with the unpaired sp3 Si dangling bond along the (111) interface normal, the archetypical defect (trap) of the standard thermal (111)Si/SiO2 interface, directly revealing, and identified as the result of, imperfect epitaxy. The occurrence of Pb defects, a major system of electrically detrimental interface traps, is ascribed to lattice mismatch with related introduction of misfit dislocations. This interface nature appears to persist for annealing in vacuum up to a temperature Tan∼420 °C. Yet, in the range Tan∼420-550 °C, the interface starts to "degrade"to standard Si/SiO2 properties, as indicated by the gradually increasing Pb density and attendant appearance of the EX center, an SiO2-associated defect. At Tan∼700 °C, [Pb] has increased to about 1.3 times the value for standard thermal (111)Si/SiO2, to remain constant up to Tan∼1000 °C, indicative of an unaltered interface structure. Annealing at Tan>1000 °C results in disintegration altogether of the Si/SiO2-type interface. Passivation anneal in H2 (405 °C) alarmingly fails to deactivate the Pb system to the device grade (sub) 1010 cm-2 eV-1 level, which would disfavor c-Lu2O3 as a suitable future high-∼ replacement for the a-SiO2 gate dielectric. Comparison of the thermal stability of the c-Lu2O3 / (111)Si interface with that of molecular-beam deposited amorphous-Lu2O3 / (100)Si shows the former to be superior, yet unlikely to meet technological thermal budget requirements. No Lu2O3-specific point defects could be observed. [ABSTRACT FROM AUTHOR]

To explore the possibility of bandgap engineering in binary systems of oxide insulators we studied photoconductivity of nanometer-thin Hf oxide layers containing different concentrations of cations of different sorts (Si, Al, Sr, or Ce) deposited on (100)Si. The lowest bandgap of the Hf:Al oxide is close to the value 6–6.2 eV of elemental amorphous Al2O3 and insensitive to the Al content for concentrations of Al exceeding 36%. This result suggests that the Al oxide subnetwork with the largest bandgap preserves this energy width while development of a narrower gap of HfO2 is prevented possibly by dilution of the second cation subnetwork. When Ce is admixed to HfO2 an intermediate bandgap value (between the CeO2 and HfO2 bandgap widths) of 5.3+0.1 eV is observed for all concentrations of Ce, suggesting that the electronic structure of both elemental oxide subnetworks which form the binary metal oxide system, is affected. In Hf:Si oxide samples photoconductivity thresholds of 5.6–5.9 eV corresponding to the bandgap of HfO2 are observed for all studied Si concentrations, suggesting phase separation to occur. The photoconductivity of SrHfO3 exhibits two thresholds at 4.4 and 5.7 eV, which are close to the bandgaps of elemental SrO and HfO2, respectively, indicating, again, phase separation. Through this work we have illustrated photoconductivity as a feasible method to trace phase separation in nanometer-thin layers of binary systems of metal oxides. [ABSTRACT FROM AUTHOR]