We report on the electrical properties of germanium oxynitride and its interface with germanium prepared by nitriding the germanium oxide/germanium surface by irradiating a nitrogen plasma stream generated by an electron-cyclotron-resonance plasma source without substrate heating. Excellent leakage current characteristics were obtained for a metal–insulator–semiconductor capacitor with a gate stack consisting of a silicon nitride sputter-deposited on germanium oxynitride with an interface trap density of ∼2×1011 cm-2·eV-1. Moreover, the equivalent oxide thickness of the germanium oxynitride was found to be about 30% smaller than that of germanium oxide. The reported germanium oxynitride is suitable as a beneficial interlayer between high-dielectric-constant gate insulators and germanium.

Using an ultrasonic technique, the diffusion of Cu, Ag and Au in lowresistivity single-crystal CdS was studied. For Cu and Ag over the temperature range 300-700 "C, the diffusion coefficients (cme s-I) were found to be and for Au over the range 500-800 "C, the diffusion coefficient was No significant anisotropy was found in diffusion coefficients of Ag measured parallel or perpendicular to the c axis. The activation energy of diffusion was found to increase linearly with the atomic mass of the diffusing element.

Power devices are operated under harsh conditions, such as high currents and voltages, and so degradation of these devices is an important issue. Our group previously found significant increases in reverse leakage current after applying continuous forward current stress to GaN p–n junctions. In the present study, we identified the type of threading dislocations that provide pathways for this reverse leakage current. GaN p–n diodes were grown by metalorganic vapor phase epitaxy on freestanding GaN(0001) substrates with threading dislocation densities of approximately 3 × 105 cm−2. These diodes exhibited a breakdown voltage on the order of 200 V and avalanche capability. The leakage current in some diodes in response to a reverse bias was found to rapidly increase with continuous forward current injection, and leakage sites were identified by optical emission microscopy. Closed-core threading screw dislocations (TSDs) were found at five emission spots based on cross-sectional transmission electron microscopy analyses using two-beam diffraction conditions. The Burgers vectors of these dislocations were identified as [0001] using large-angle convergent-beam electron diffraction. Thus, TSDs for which b = 1c are believed to provide current leakage paths in response to forward current stress.

A novel process for fabricating a high-k dielectric/Si structure is proposed. The structure is fabricated by ultrahigh vacuum (UHV) sputtering of Hf metal followed by postannealing in atmospheric oxygen ambient. In the fabrication of structures by this method, an interfacial layer such as SiO2 is scarcely formed because the Si surface is already covered with Hf metal from UHV sputtering, before heating in oxygen ambient. Also a postoxidation condition is set up so that the metal Hf, but not the substrate Si, is oxidized completely. Consequently, the HfO2/Si structure was fabricated with an interfacial layer thickness of as low as 0.2 nm. In addition, thermal stability of the HfO2 film fabricated by this method was maintained up to 800°C for 30 min, which is a standard thermal budget for the impurity activation process. These experimental facts show that this novel process is effective for fabricating the high-k dielectric/Si stacked structure with ultrasmall equivalent oxide thickness (EOT) for the next-generation metal-oxide-semiconductor field effect transistor (MOSFET).

Reliability tests involving the application of high electrical stresses were employed to assess GaN-based vertical p-n junctions fabricated on freestanding GaN substrates with threading dislocation densities less than 104 cm−2. Electric field crowding at the device edges was eliminated by employing a shallow bevel mesa structure, thus allowing an evaluation of the reliability of the internal p-n junctions. The p-n diodes exhibited reproducible avalanche breakdown characteristics over the temperature range of 25–175 °C. No degradation was observed even during tests in which the devices were held under a reverse bias near the breakdown voltage. Despite this high degree of reliability in response to reverse bias stress, a small number of diodes were degraded during continuous forward current tests, although the majority of diodes remained unchanged. The reverse leakage current exhibited by degraded diodes was increased with an increase in the forward current density within the range of 50–500 A/cm2, while the breakdown voltages were unchanged in response to current stress. The leakage level increased exponentially with an increase in the total amount of injected carriers but eventually plateaued. In the degraded p-n diode, a luminous point in an emission microscope corresponded to one of the threading dislocations observed in the synchrotron x-ray topography, indicating that a specific dislocation played as a leakage path after injecting carriers.