Shinji Fujieda

Low Temperature Growth of GaN and AlN on GaAs Utilizing Metalorganics and Hydrazine

The growth and characterization of AlN and GaN on GaAs are presented. Trimethylgallium (TMG) and trimethylaluminum (TMA) were used as group III sources and hydrazine as a nitrogen source. It was found for both nitrides that mass-transport-limited growth took place at high temperature, and that at low temperature the surface catalyzed decomposition of respective metalorganics manifested itself. Deposition of AlN film was observed at as low as 220°C and that of GaN at 450°C both on GaAs substrates. A distinct proof of cubic-form GaN grown on GaAs is obtained from results of the X-ray precession measurement. The direction of GaN on (100) GaAs, however, is slightly tilted from that of the substrate. It is speculated that this tilt results from the very large lattice-mismatch existing between GaN and GaAs.

Interface defects responsible for negative-bias temperature instability in plasma-nitrided SiON/Si(100) systems

Interface defects generated by negative-bias temperature stress (NBTS) in an ultrathin plasma- nitrided SiON/Si(100) system were characterized by using D2 annealing, conductance-frequency measurements, and electron-spin resonance measurements. D2 annealing was shown to lower negative-bias temperature instability (NBTI) than H2 annealing. Interfacial Si dangling bonds (Pb1 and Pb0 centers), whose density is comparable to an increase in interface trap density, were detected in a NBTS-stressed sample. The NBTI of the plasma-nitrided SiON/Si system was thus shown to occur through Pb depassivation. Furthermore, the nitridation was shown to increase the Pb1/Pb0 density ratio and modify the Pb1 structure. Such a predominance and structural modification of Pb1 centers are presumed to increase NBTI by enhancing the Pb–H dissociation. Although we suggest that NBTS may also induce non-Pb defects, nitrogen dangling bonds do not seem to be included in them.

Structure Control of GaN Films Grown on (001) GaAs Substrates by GaAs Surface Pretreatments

Two types of cubic and hexagonal GaN films were deposited on (001) GaAs substrates. The film structure proved to be controlled by GaAs pretreatments. By performing a N2H4 (hydrazine) pretreatment of GaAs substrates, the GaN films, which were otherwise hexagonal similarly to ordinary films on sapphire substrates, became cubic. A surface cubic nitride layer was found to be formed on the pretreated GaAs by a RHEED (reflection high-energy electron diffraction) observation, which is thought to be the substantial substrate for the following growth of a cubic GaN film.

Structural defects working as active oxygen-reduction sites in partially oxidized Ta-carbonitride core-shell particles probed by using surface-sensitive conversion-electron-yield x-ray absorption spectroscopy

We analyzed the local structure of the surface Ta-oxide phase of TaCN/Ta2O5 core-shell particles that have a high oxygen reduction activity by using surface-sensitive conversion-electron-yield x-ray absorption spectroscopy, suppressing the contribution from the TaCN cores. The radial structure analysis revealed that the catalytically-active Ta2O5 phase in the TaCN/Ta2O5 particle surface contains oxygen-vacancy defects with shorter Ta–O bonds leading to the slight expansion of the first Ta–O shell. Such oxygen defects are likely responsible for the oxygen reduction capability by creating electronically favorable oxygen adsorption sites and electron conduction pathways.

Growth Characterization of Low-Temperature MOCVD GaN?Comparison between N2H4 and NH3?

The reaction mechanisms of the low-temperature growth of GaN using TMG (trimethylgallium) and two different nitrogen sources, i.e., N2H4 and NH3, are presented. Quite the same temperature dependence of the growth rate for both N sources was found, suggesting that the transport and decomposition of TMG are growth-rate limiting. A different behavior between the two N sources, on the other hand, is that the flow rate of NH3 that was required to obtain a specular surface of the film was much larger than that of N2H4. This surface specularity could be well described in terms of V/III (input gas molar ratio between N source and TMG) for the case of N2H4, whereas for the NH3 case, V/H2(NH3 partial pressure) was important. A discussion of the detailed growth mechanism, especially the difference in the two N sources, is presented.

Influence of H2-annealing on the hydrogen distribution near SiO2/Si(100) interfaces revealed by in situ nuclear reaction analysis

Employing hydrogen depth-profiling via 1H(15N,αγ)12C nuclear reaction analysis (NRA), the “native” H concentration in thin (19–41.5 nm) SiO2 films grown on Si(100) under “wet” oxidation conditions (H2+O2) was determined to be (1–2)×1019 cm−3. Upon ion-beam irradiation during NRA this hydrogen is redistributed within the oxide and accumulates in a ∼8-nm-wide region centered ∼4 nm in front of the SiO2/Si(100) interface. Annealing in H2 near 400 °C introduces hydrogen preferentially into the near-interfacial oxide region, where apparently large numbers of hydrogen trap sites are available. The amount of incorporated H exceeds the quantity necessary to H-passivate dangling Si bonds at the direct SiO2/Si(100) interface by more than one order of magnitude. The H uptake is strongly dependent on the H2-annealing temperature and is suppressed above 430 °C. This temperature marks the onset of hydrogen desorption from the near-interfacial oxide trap sites, contrasting the thermal stability of the native H, which pre...

Improvement of the Electrical Properties of the AlN/GaAs MIS System and Their Thermal Stability by GaAs Surface Stoichiometry Control

The GaAs surface pre-treatment conditions for the MOCVD-AlN/GaAs MIS diodes are investigated. An AsH3 pre-treatment just prior to the AlN deposition degraded the C-V characteristics of AlN/n-GaAs MIS diodes in the accumulation side. The characteristics and their stability were drastically improved by a pure H2 pre-treatment at 500°C. It was confirmed that the free As at the interface generates surface states near the conduction band edge and that control of the surface stoichiometry and atomic structure is necessary to improve the MIS characteristics.

Single silicon vacancy-oxygen complex defect and variable retention time phenomenon in dynamic random access memories

The variable retention time phenomenon has recently been highlighted as an important issue in dynamic random access memory (DRAM) technology. Based on electrically detected magnetic resonance and simulation studies, we suggest that a single Si vacancy-oxygen complex defect is responsible for this phenomenon, when the defect is embedded in the near surface drain-gate boundary of a DRAM cell.

Single-crystal Al growth on Si(111) by low-temperature molecular beam epitaxy

Al films were formed by low temperature molecular beam epitaxy on Si(111) surfaces. The substrates were pretreated in a NH4F solution to obtain a nearly atomically flat surface by anisotropic etching. Planview transmission electron microscopy observation demonstrates that single‐crystal Al films are successfully grown on the 7×7 surface structure. Such single‐crystal growth is arrested on a disordered or hydrogen‐terminated surface.

Interfacial Superstructure of AlN/n-GaAs(001) System Fabricated by Metalorganic Chemical Vapor Deposition

The superstructures at the insulator/semiconductor interface were observed for the first time by grazing incidence X-ray diffraction. The insulating AlN was deposited on the n-GaAs(001) substrate by the metalorganic chemical vapor deposition utilizing TMA and N2H4 as source gases in a H2 ambient gas at a pressure of 0.1 atm. At the beginning of AlN deposition at 220°C, either TMA or N2H4 was initially introduced before both of them were supplied together, resulting in two different diffraction patterns. For the TMA case, the diffraction pattern showed a 1×4 superstructure and for the N2H4 case, on the other hand, the diffraction pattern showed a 1×6 superstructure. It is suggested that superstructures should appear even at a pressure of 0.1 atm of a H2 gas.