First-Principles Study for Evidence of Low Interface Defect Density at Ge/GeO2_2 Interfaces

We present the evidence of the low defect density at Ge/GeO$_2$ interfaces in terms of first-principles total energy calculations. The energy advantages of the atom emission from the Ge/GeO$_2$ interface to release the stress due to the lattice mismatch are compared with those from the Si/SiO$_2$ interface. The energy advantages of the Ge/GeO$_2$ are found to be smaller than those of the Si/SiO$_2$ because of the high flexibility of the bonding networks in GeO$_2$. Thus, the suppression of the Ge-atom emission during the oxidation process leads to the improved electrical properties of the Ge/GeO$_2$ interfaces

Interface and oxide trap states of SiO2/GaN metal–oxide–semiconductor capacitors and their effects on electrical properties evaluated by deep level transient spectroscopy

The relationship between the electrical properties and the carrier trap properties of the SiO2/GaN metal–oxide–semiconductor (MOS) capacitors was investigated using electrical measurements and deep level transient spectroscopy (DLTS). The capacitance–voltage (C–V) measurement showed that the frequency dispersion of the C–V curves became smaller after an 800 °C annealing in O2 ambient. DLTS revealed that before the annealing, the interface trap states, in a broad energy range above the midgap of GaN, were detected with the higher interface state density at around 0.3 and 0.9 eV below the conduction band minimum (Ec) of GaN. Moreover, the oxide trap states were formed at around 0.1 eV below the Ec of GaN, plausibly indicating a slow electron trap with a tunneling process. Although both trap states affect the electrical reliability and insulating property of the SiO2/GaN MOS capacitors, they were found to drastically decrease after the annealing, leading to the improvement of the electrical properties.Shingo Ogawa, Hidetoshi Mizobata, Takuma Kobayashi, Takayoshi Shimura, Heiji Watanabe; Interface and oxide trap states of SiO2/GaN metal–oxide–semiconductor capacitors and their effects on electrical properties evaluated by deep level transient spectroscopy. J. Appl. Phys. 7 September 2023; 134 (9): 095704. https://doi.org/10.1063/5.016589

Control on the density and optical properties of color centers at SiO2/SiC interfaces by oxidation and annealing

Color centers in solids can serve as single photon emitters (SPEs) those are important in many quantum applications. Silicon carbide (SiC) is a promising host for color centers because of its well-established crystal growth and device technologies. Although color centers with extremely high brightness were found at the silicon dioxide (SiO2)/SiC interface, controlling their density and optical properties remains a challenge. In this study, we demonstrate control over the color centers at the SiO2/SiC interface by designing the oxidation and annealing conditions. We report that post-oxidation CO2 annealing has the ability to reduce the color centers at the interface and form well-isolated SPEs with bright emission. We also discuss the correlation between the color centers and electrically active defects.Takato Nakanuma, Kosuke Tahara, Katsuhiro Kutsuki, Takayoshi Shimura, Heiji Watanabe, Takuma Kobayashi; Control on the density and optical properties of color centers at SiO2/SiC interfaces by oxidation and annealing. Appl. Phys. Lett. 4 September 2023; 123 (10): 102102. https://doi.org/10.1063/5.016674

Insight into enhanced field-effect mobility of 4H-SiC MOSFET with Ba incorporation studied by Hall effect measurements

Improved performance in 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) by incorporating Ba into insulator/SiC interfaces was investigated by using a combination of the Hall effect and split capacitance-voltage measurements. It was found that a moderate annealing temperature causes negligible metal-enhanced oxidation, which is rather beneficial for increments in field-effect mobility (μFE) of the FETs together with suppressed surface roughness of the gate oxides. The combined method revealed that, while severe μFE degradation in SiC-MOSFETs is caused by a reduction of effective mobile carriers due to carrier trapping at the SiO2/SiC interfaces, Ba incorporation into the interface significantly increases mobile carrier density with greater impact than the widely-used nitrided interfaces

Excellent electrical properties of TiO2/HfSiO/SiO2 layered higher-k gate dielectrics with sub-1 nm equivalent oxide thickness

Equivalent oxide thickness (EOT) scaling, as well as improved interface properties, of metal/higher- k gate stacks for the sub- 1 nm region was achieved using a TiO_2/HfSiO/SiO_2 layered dielectric structure. Ti diffusion into the bottom oxides was found to form electrical defects, which lead to an increase of leakage current, fixed charge, interface trap density (Dit), and reliability degradation of the gate stacks. By controlling Ti diffusion and terminating Ti-induced defects using forming gas annealing, we successfully obtained a superior interface property (Dit =9.9× 10^{10} eV^{-1} cm^{-2}) and reduced gate leakage (Jg =7.2× 10^{-2} A/cm^2) at the 0.71-nm -EOT region.Hiroaki Arimura, Naomu Kitano, Yuichi Naitou, Yudai Oku, Takashi Minami, Motomu Kosuda, Takuji Hosoi, Takayoshi Shimura and Heiji Watanabe, "Excellent electrical properties TiO_2/HfSiO/SiO_2 of higher-k gate dielectrics with sub-1nm equivalent oxide thickness", Appl. Phys. Lett. 92, 212902 (2008) https://doi.org/10.1063/1.292968

Annealing behavior of open spaces in AlON films studied by monoenergetic positron beams

The impact of nitridation on open spaces in thin AlONx films deposited by a reactive sputtering technique was studied by using monoenergetic positron beams. For AlONx films with x = 0%–15%, positrons were found to annihilate from trapped states in open spaces, which coexist intrinsically in an amorphous structure with three different sizes. Nitrogen incorporation into the Al2O3 film increased the size of the open spaces, and their density increased as the post-deposition annealing temperature increased. The effect of nitrogen incorporation, however, diminished at x = 25%. The observed change in the network structure was associated with the formation of a stable amorphous structure, which we could relate to the electrical properties of AlONx/SiO2/Si gate stacks

Humidity-dependent stability of amorphous germanium nitrides fabricated by plasma nitridation

Katsuhiro Kutsuki, Gaku Okamoto, Takuji Hosoi, Takayoshi Shimura and Heiji Watanabe, "Humidity-dependent stability of amorphous germanium nitrides fabricated by plasma nitridation", Appl. Phys. Lett. 91, 163501 (2007) https://doi.org/10.1063/1.2799260