Thermal stability of HfO2 high-k gate dielectric on GaAs is investigated. Compared to HfO2 gate dielectric, significant improvements in interfacial properties as well as electrical characteristics were found by constructing a Al2O3/HfO2/Al2O3 dielectric stack. At elevated temperatures, the amorphous Al2O3 layers were effective in inhibiting crystallization of HfO2. Since the passivating Al2O3 layers prevent interfacial oxide and trap charge formation, it aids in reducing the increasing rate of equivalent oxide thickness as well as capacitance-voltage hysteresis. Transmission electron microscopy and x-ray photoelectron spectroscopy data supported the improved electrical characteristic of GaAs metal-oxide-semiconductor capacitors with Al2O3/HfO2/Al2O3 gate dielectric stack.

The structural stability and electrical performance of SiO2 grown on SiC via direct plasma-assisted oxidation were investigated. To investigate the changes in the electronic structure and electrical characteristics caused by the interfacial reaction between the SiO2 film (thickness ~5 nm) and SiC, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), density functional theory (DFT) calculations, and electrical measurements were performed. The SiO2 films grown via direct plasma-assisted oxidation at room temperature for 300s exhibited significantly decreased concentrations of silicon oxycarbides (SiOxCy) in the transition layer compared to that of conventionally grown (i.e., thermally grown) SiO2 films. Moreover, the plasma-assisted SiO2 films exhibited enhanced electrical characteristics, such as reduced frequency dispersion, hysteresis, and interface trap density (Dit ≈ 1011 cm−2 · eV−1). In particular, stress induced leakage current (SILC) characteristics showed that the generation of defect states can be dramatically suppressed in metal oxide semiconductor (MOS) structures with plasma-assisted oxide layer due to the formation of stable Si-O bonds and the reduced concentrations of SiOxCy species defect states in the transition layer. That is, energetically stable interfacial states of high quality SiO2 on SiC can be obtained by the controlling the formation of SiOxCy through the highly reactive direct plasma-assisted oxidation process.

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Articles you may be interested inLow-temperature plasma-enhanced atomic layer deposition of HfO2/Al2O3 nanolaminate structure on Si J. Vac. Sci. Technol. B 33, 01A101 (2015); 10.1116/1.4895010Effects of rapid thermal annealing on the properties of HfO2/La2O3 nanolaminate films deposited by plasma enhanced atomic layer deposition

Slightly tapered SiGe nanowires (NWs) (x = 0.29-0.84) were synthesized via a vapor-liquid-solid procedure using Au as a catalyst. We measured the optically excited carrier dynamics of SiGe NWs as a function of Ge content using optical pump-THz probe spectroscopy. The measured -ΔT/T signals of SiGe NWs were converted into conductivity in the THz region. We developed a fitting formula to apply to indirect semiconductors such as SiGe, which explains the temporal population of photo-excited carriers in the band structure and the relationship between the trapping time and the defect states on an ultrafast time scale. From the fitting results, we extracted intra- and inter-valley transition times and trapping times of electrons and holes of SiGe NWs as a function of Ge content. On the basis of theoretical reports, we suggest a physical model to interpret the trapping times related to the species of interface defect states located at the oxide/NW: substoichiometric oxide states of Si(Ge), but not Si(Ge), could function as defect states capturing photo-excited electrons or holes and could determine the different trapping times of electrons and holes depending on negatively or neutrally charged states.

We investigated the dielectric characteristics of Hf-silicate films which were grown on Si͑100͒ substrates by atomic layer deposition. The X-ray photoelectron spectroscopy results indicated that the atomic concentrations of HfO 2 and SiO 2 in the Hf-silicate films were similar to the cycle ratio between the number of HfO 2 deposition cycles and that of SiO 2 deposition cycles. The flatband voltage of Hf-silicate films increased as the compositional deviation from the stoichiometric compound HfSiO 4 increased. For Hf-rich silicate films, the flatband voltages were lowered due to the increase of the positive fixed charge in SiO 2 with the increase of SiO 2 content. In addition, the crystallization temperatures were below 900°C after postannealing for 1 min in N 2 ambient and accompanied the phase-separation process as the Si content increased. However, in the case of Si-rich Hf-silicate films, the increase of the effective metal work function dominated and increased the flatband voltages as the Si composition increased. The crystallization and phase separation of Hf-silicate films were not observed even after annealing at 900°C.As the geometric dimensions of metal-oxide-semiconductor field effect transistor ͑MOSFET͒ devices are scaled down following the semiconductor industry's roadmap, the equivalent gate oxide thickness ͑EOT͒ must decrease below 1.2 nm for 90 nm node. However, as the thickness of the conventional thermally grown SiO 2 film is reduced down to ϳ2 nm range, the gate leakage current across the gate dielectric stack exponentially increases due to the inherent direct-tunneling mechanism. 1 Recently, metal-oxide systems are being widely investigated as an alternative solution to replace conventional SiO 2 films. Due to the high dielectric constants of those materials, it is possible to achieve a larger gate capacitance density with the identical physical thickness of SiO 2 film. In other words, the gate leakage current can be significantly reduced while maintaining the same capacitance value per unit area due to the increase in physical thickness of the gate dielectric layer. 2 Among many high-k materials, HfO 2 3,4 and ZrO 2 5,6 are quite promising candidates due to their high dielectric constant, large bandgap, and excellent thermal stability in contact with silicon. However, they are deposited as a polycrystalline state or suffer from the crystallization process during the postdeposition annealing, which may introduce high-leakage-current paths along the grain boundaries. 7 In addition, annealing in an oxygen-rich ambient may lead to a fast diffusion of oxygen through the HfO 2 and ZrO 2 layers, which are well known to have a large amount of oxygen vacancies, resulting in the growth of an uncontrollable interfacial oxide layer between the gate dielectric and silicon substrate. 8 Another problem with the high-k dielectrics is the Fermi level pinning at the interface between the poly-Si gate electrode and HfO 2 , causing high threshold voltages in MOSFET devices. Hobbs et al. reported that the pinning ...

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