Volume 92, Issue 11, 01 December 2002
Index of content:
- DEVICE PHYSICS (PACS 85)
Near-field spectroscopic characterization of a 10 μm aperture selectively oxidized vertical cavity surface emitting laser92(2002); http://dx.doi.org/10.1063/1.1516624View Description Hide Description
We have characterized a 10 μm square aperture selectively oxidized 850 nm vertical cavity surface emitting laser(VCSEL) utilizing a near-field scanning optical microscope coupled to a spectrometer. We have obtained both spatially and spectrally resolved images of the VCSEL’s emission. The spatially resolved intensity distributions were measured for the transverse modes of the VCSELs in the near field and far field at three different excitation currents, at threshold as well as above threshold. We identify the modes as being Hermite–Gaussian. Two-dimensional maps of the total integrated intensity of the spectra reveal an inhomogeneous gain distribution. The relative intensities of the various individual modes as well as their spatial orientation reflect how the available gain of the cavity is used. The wavelengths of the transverse modes were observed to increase with increasing current; calculations show that a temperature-induced change in refractive index of the cavity is the factor contributing to this redshift.
Formation and thermal stability of ultra-shallow junctions in Si and formed by molecular beam epitaxy92(2002); http://dx.doi.org/10.1063/1.1518766View Description Hide Description
Ultra-shallow junction layers are required for deep-submicron complementary metal-oxide-semiconductor transistors and quantum devices. The use of low temperature Si molecular beam epitaxy(MBE) has been investigated for the formation of 10 nm ultra-shallow doped layers. Uniformly B-doped Si layers, B delta-doped Si, and uniformly B-doped 0.2, or 0.4) layers have been studied. Regardless of the growth technique (uniform versus delta-doped) or Ge concentration, the sheet resistance of the optimally-doped, as-grown samples were equivalent to idealized, box profiles having a carrier concentration equal to the B solid solubility limit in Si, which is a substantial improvement over the best reported, ion implanted shallow layers. The B in the as-grown, optimally-doped MBE layers is fully electrically active and does not require a post-growth anneal. The thermal budget of the layers was established so that the layers can be employed in a device fabrication process. The MBE-grown shallow-doped layers were not affected by 10 min thermal processing up to 700 °C. While substantial B redistribution occurred as a result of the 800 °C 10 min anneal, the sheet resistances of the MBE-grown layers are still less than ion implanted samples having the same junction depth. In addition, it was observed that the Ge alloy layers impeded the diffusion of B at 800 °C.
92(2002); http://dx.doi.org/10.1063/1.1516874View Description Hide Description
Passive magnetic bearings built with permanent magnets, such as NdFeB (neodynium–iron–boron) or SmCo (samarium–cobalt), are very reliable systems when used for industrial applications such as centrifuges or flywheels, as they do not require any electromagnetic coil supply. Nevertheless, during the rotational motion, gyroscopic effects (like precession) or inhomogeneous magnetization can lead to power losses created by eddycurrents flowing over the magnetic materials. This article provides a theoretical description and quantification of these phenomena by means of Ampere’s laws. For this purpose, the magnets are assumed to be ring-shaped and axially magnetized. Virtual surface and volume current densities are applied to the calculation of the time-dependent electric field, and consequently to the power loss. Numerical applications are presented for a typical bearing configuration.
A stable, single-chip, two-dimensional gradiometric device based on two superconducting quantum interference devices92(2002); http://dx.doi.org/10.1063/1.1519346View Description Hide Description
A planar gradiometric device for estimating current vectors in specimens, was fabricated as two orthogonal magnetic fieldgradiometers integrated on a 14.5-mm-square substrate. The gradiometers consist of superconducting quantum interference devices(SQUIDs) and pickup coils made from a low-critical-temperature superconductor. The two gradiometers (one for the x direction and one for the y direction) have exactly the same structure, and their gradiometric centers coincide at the center of the substrate. The gradiometric balance of each gradiometer is 1/2000–1/3700, the cross-talk ratio between the two gradiometers is less than 1% below a few hundred hertz, and their intrinsic noise is 2–3 pT/(m√Hz). The gradiometric configurations of both the pickup coils and the SQUIDs provide good gradiometric balance. The parallel-type gradiometric SQUIDs produced a simple yet effective structure, although the superconducting loops of such SQUIDs have conventionally been thought to lead to adverse effects in the presence of a changing magnetic field.Magnetic fields up to 1 mT, i.e., 20 times the geomagnetic field, applied to a zero-field cooled SQUID reduced the critical current, but did not affect the intrinsic noise. This result shows that the configuration of the SQUIDs kept the circulating current in the superconducting loop away from the Josephson junctions.