Anisotropic high‐field diffusion of holes in silicon

Anisotropy of the silicon valence band leads to a strong dependence of charge carrier transport properties, upon the orientation of the electric field. A detailed anisotropic Monte Carlo method has been applied to the calculation of the hole diffusion coefficient in silicon, studying its dependence on field magnitude and orientation. The longitudinal diffusion coefficient is found to have a dependence on the field orientation which is similar in degree to the more familiar dependence of the drift velocity on field orientation. However, it is found that the transverse diffusion coefficient has a substantially stronger dependence on field orientation. At the highest field which has been studied, 50 kV/cm, the transverse diffusion coefficient almost doubles as one shifts from a field oriented in the [100] direction to one in the [101] direction and considers the [101] transverse direction. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70410/2/APPLAB-66-20-2727-1.pd

Rugged, low-conductance, heat-flow probe

Lightweight, compact probe structure has low thermal conductance to enable accurate measurement of slight temperature gradients. Probe combines ruggedness, high precision, accuracy, and stability. Device can withstand vibration, shock, acceleration, temperature extremes, and high vacuums, and should interest industrial engineers and geologists

High‐field thermal noise of holes in silicon: The effect of valence band anisotropy

The effects of valence band anisotropy on longitudinal and transverse high‐field differential mobilities, diffusivities, and thermal noise temperatures were theoretically investigated. The effects were examined for holes in silicon and in several hypothetical materials having systematically varied degrees of valence band anisotropy. The results show a pronounced dependence of the transverse high‐field differential mobility and of the longitudinal high‐field noise temperature upon the degree of anisotropy. This suggests that thermal noise measurements may provide an alternative to magnetotransport methods as a valence bandstructure measurement technique. The results also imply that thermal noise in semiconductor devices can be mitigated by choosing a semiconductor with a low degree of valence band anisotropy and, for a given semiconductor, by properly aligning the device layout with respect to the material crystallographic axes. © 1996 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70685/2/JAPIAU-80-12-6766-1.pd

Anisotropic high‐field transverse differential mobility of holes in silicon

Anisotropy of the silicon valence band does not lead to any significant anisotropy in the longitudinal hole transport properties, but we find that the transverse mobility is quite anisotropic. The transverse mobility represents the response of charge carriers to a small transverse electric field in the presence of a strong longitudinal field. A detailed, anisotropic Monte Carlo method has been applied to the calculation of the hole transverse differential mobility in silicon. The transverse differential mobility is studied both with regard to variations in the orientation, with respect to the crystalline axes, of the high longitudinal electric field, and with regard to variations in the transverse direction of the mobility, taken in the plane perpendicular to the high electric field. The anisotropy of the valence band causes the transverse differential mobility to strongly vary with respect to the electric field orientation. Symmetry considerations show that the transverse differential mobility is isotropic in the {100} and {111} planes and has twofold rotational symmetry in the {101} planes. Our calculations bear this out. Furthermore, we show that the transverse mobility can be much different from the chordal mobility, in distinction to the case for isotropic band structures. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69866/2/APPLAB-67-20-2966-1.pd

Monte Carlo studies of ohmic hole mobility in silicon and germanium: Examination of the optical phonon deformation potential

Monte Carlo methods which have been widely used for studying high field electron and hole transport, so far have not been applied to the complex problem of Ohmic hole transport. We present a versatile generalization of the Monte Carlo approach for Ohmic hole mobility studies and apply it to pure silicon and germanium. In particular, we examine the role of the optical phonon deformation potential d0 in controlling the temperature dependence of the mobility.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70383/2/JAPIAU-76-7-4192-1.pd

Dependence of pseudomorphic semiconductor band gap on substrate orientation

For a given misfit we examine the band‐gap variation of a pseudomorphic overlayer on a thick substrate as a function of substrate orientation. The strain tensor is found to be a strong function of the substrate orientation. For both direct and indirect band‐gap overlayers, this results in a significant variation in the band gap as the substrate orientation is changed. However, for indirect band‐gap layers, such as SiGe alloys grown on Si substrates, the change in band gap is accompanied by a lifting of conduction‐band‐edge degeneracies. The magnitude of this splitting may be as large or larger than the change in the band gap. Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69642/2/JAPIAU-69-4-2694-1.pd

Late Pregnancy Exposures to Disinfection By-products and Growth-Related Birth Outcomes

Toxicologic studies have demonstrated associations between growth-related birth outcomes and exposure to high concentrations of disinfection by-products (DBPs), including specific tri-halomethane (THM) and haloacetic acid (HAA) chemical subspecies. Few prior investigations of DBPs have evaluated exposure during the third trimester of pregnancy, the time period of gestation when fetal growth may be most sensitive to environmental influences. We conducted a retrospective cohort study to examine the effects of exposure to THMs and HAAs during the third trimester and during individual weeks and months of late gestation on the risks for term low birth weight, intrauterine growth retardation, and very preterm and preterm births. The study population (n = 48,119) included all live births and fetal deaths occurring from January 1998 through March 2003 to women whose residence was served by one of three community water treatment facilities. We found evidence of associations between exposure to specific HAAs and term low birth weight as well as intrauterine growth retardation and for exposure to the five regulated HAAs (HAA5) and term low birth weight. Our findings suggest a critical window of exposure with respect to fetal development during weeks 33–40 for the effects of dibromoacetic acid and during weeks 37–40 for the effects of dichloroacetic acid. Adjustment for potential confounders did not affect the conclusions

The White River Oligocene Rodent \u3ci\u3eDIPLOLOPHUS\u3c/i\u3e

The rich and varied nature of the mammalian faunas of the White River Oligocene has been recognized for many years, but the exact geologic succession is only now becoming known. In these faunal assemblages the rodents and lagomorphs appear to have been important elements, perhaps numerically as abundant in the Oligocene as are these same groups at present