This paper describes the development of a nitrogen-based passivation technique for interface states near the conduction band edge [Dit(Ec)] in 4H-SiC/SiO2. These states have been observed and characterized in several laboratories for n- and p-SiC since their existence was first proposed by Schorner, et al. [1]. The origin of these states remains a point of discussion, but there is now general agreement that these states are largely responsible for the lower channel mobilities that are reported for n-channel, inversion mode 4H-SiC MOSFETs. Over the past year, much attention has been focused on finding methods by which these states can be passivated. The nitrogen passivation process that is described herein is based on post-oxidation, high temperature anneals in nitric oxide. An NO anneal at atmospheric pressure, 1175°C and 200–400sccm for 2hr reduces the interface state density at Ec-E ≅0.1eV in n-4H-SiC by more than one order of magnitude - from > 3×1013 to approximately 2×1012cm−2eV−1. Measurements for passivated MOSFETs yield effective channel mobilities of approximately 30–35cm2/V-s and low field mobilities of around 100cm2/V-s. These mobilities are the highest yet reported for MOSFETs fabricated with thermal oxides on standard 4H-SiC and represent a significant improvement compared to the single digit mobilities commonly reported for 4H inversion mode devices. The reduction in the interface state density is associated with the passivation of carbon cluster states that have energies near the conduction band edge. However, attempts to optimize the the passivation process for both dry and wet thermal oxides do not appear to reduce Dit(Ec) below about 2×1012cm−2eV−1 (compared to approximately 1010cm−2eV−1 for passivated Si/SiO2). This may be an indication that two types of interface states exist in the upper half of the SiC band gap – one type that is amenable to passivation by nitrogen and one that is not. Following NO passivation, the average breakdown field for dry oxides on p-4H-SiC is higher than the average field for wet oxides (7.6MV/cm compared to 7.1MV/cm at room temperature). However, both breakdown fields are lower than the average value of 8.2MV/cm measured for wet oxide layers that were not passivated. The lower breakdown fields can be attributed to donor-like states that appear near the valence band edge during passivation.

The impact of two implant parameters, namely the implant substrate temperature and implant beam current, on the physical and electrical properties of SIMOX buried oxide are investigated. Three implant substrate temperatures, 540 °C, 590 °C, and 640 °C and three beam current, 45 mA, 55 mA, 65 mA, are investigated. Results from thermal conductivity and surface photovoltage measurements show no apparent differences between samples. Results from interface roughness shows a decreasing trend as the substrate temperature and beam current increases. For the samples with different implant temperatures, the high‐field conduction shows an opposite dependence for top‐interface versus substrate injection. This behavior can be explained by the conservation of silicon in the buried oxide. Correlation of surface photovoltage and high‐field conduction shows weak positive dependency while that of interface roughness and high‐field conduction shows dependency only when the sets of temperature variation and beam current variation are decoupled.

The effect of hydrogen plasma on the electrical properties of low-temperature-grown GaAs (LT-GaAs) is reported. LT-GaAs epitaxial layers, 2μm thick were grown on a <100>, semi-insulating GaAs (SI GaAs) substrate using molecular beam epitaxy (MBE) at 300°C. Some of the samples were annealed in- situ at 600°C for 1 hour. These LT-GaAs samples were then subjected to hydrogen plasma at 300°C in a parallel-plate, low-frequency (30KHz) system for varying times up to a maximum of 13 hours. Current through the LT-GaAs layers as a function of voltage (I-V), temperature (I-T), and time (I-t) was measured between two surface contacts formed by thermal evaporation of Au. Evidence of partical defect passivation found in the electrical characteristics of hydrogenated LT GaAs is presented. These include reduced current at low temperature (<210K) and reduced current activation energy at high temperature (>320K).

It is shown that the nilpotency of a derivation on a 2-torsion free semiprime ring is always an odd number. Examples are provided to show the necessity of the assumptions.

There has been a great deal of work recently concerning the relationship between the commutativity of a ring JR and the existence of certain specified derivations of R. Bell, Herstein, Procesei, Schacher, Ligh, Martindale, Putcha, Wilson, and Yaqub [1, 2, 6, 8, 9, 10, 11, 12, 14] have studied conditions on commutators which imply the commutativity of rings.

Let R be a prime ring possessing a nontrivial automorphism T such that xTx = ±xxT. If R is not of characteristic 3 or R has nonzero center, then R is a commutative integral domain.