Hydrogen sulfide plasma passivation of gallium arsenide

Improvement in the electrical properties of the GaAs surface has been accomplished using a room‐temperature hydrogen sulfide plasma. The surface has then been protected by a 300 °C plasma enhanced chemical vapor deposition (PECVD) SiO2 film. This treatment is highly reproducible due to computer control of process parameters and long‐lasting due to the SiO2 cap. Improved C‐V characteristics were observed, showing interface trap densities in the high 1011 cm−2 eV−1 range. Photoluminescence (PL) measurements on the sulfided samples showed increased intensity over the untreated samples.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71276/2/APPLAB-60-6-716-1.pd

A hybrid analysis of ellipsometry data from patterned structures

Rigorous coupled wave analysis (RCWA) has been used for modeling the polarization dependent reflection from periodic patterns for process monitoring and control. However, the computational load of this vector method is very heavy. In this paper, we will carefully examine a much simpler scalar method for reflection modeling. We also extend the application of the vector analysis to some special non-periodic structures by combining RCWA with the scalar model. We conclude that this hybrid approach is of significant promise for in situ IC production applications. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87397/2/373_1.pd

Interference fringe-free transmission spectroscopy of amorphous thin films

Based on optical fundamentals, we present in this article a practical method to obtain an interference fringe-free transmission spectrum for hydrogenated amorphous solid thin films. From this spectrum, reliable optical properties, such as the Urbach edge and optical band gap of the thin films, can be extrapolated directly. In terms of the Brewster angle accuracy, the margins of error of the proposed method due to material dispersion are less than ±1%±1% for hydrogenated amorphous silicon and less than ±1.2%±1.2% for hydrogenated amorphous silicon nitride. These figures are less than the detectable limit of the proposed method. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70510/2/JAPIAU-88-10-5764-1.pd

Analysis of reflectometry and ellipsometry data from patterned structures

Specular reflected light techniques, including both single wavelength and spectroscopic versions of ellipsometry and reflectometry, have been used for both etch and growth rate control. However, use of these techniques for process control on products has been limited due to the problems inherent in the analysis of reflected light from patterned structures. In this paper, we examine techniques for the quantitative analysis of data from both highly regular grating structures and from patterns with low local order. We find good quantitative agreement of vector diffraction theory to specular reflection data. We conclude that there is significant promise for the use of specular techniques for in situ monitoring of topography provided that computational speed issues can be improved. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87552/2/331_1.pd

Global forms and local forces : PhD enrollments and graduations in Australia, Canada, the Czech Republic, the United Kingdom, and the United States

 This chapter presents and discusses data from five different nations—Australia, Canada, the Czech Republic, the United Kingdom, and the United States—on doctoral candidates and graduates. These data are from governmental and institutional sources for the years 1998–2004, a sample that enables changes across a five-year span to be identified. They span important basic characteristics, such as gender, age, discipline, and study load (that is, full-time or part-time study). Therefore, readers can see national as well as international trends and differences in such characteristics and can match these to equivalent and/or contemporary data in their own nations. The five countries considered here are among those whose data were discussed at the 2007 CIRGE research synthesis meeting in Australia. Although these countries are not universally representative of doctoral education, their practices do offer a vivid sense of how vastly the enterprise of doctoral education differs in its scope and dimensions around the worl

Erratum: ‘‘Evidence for field enhanced electron capture by EL2 centers in semi‐insulating GaAs and the effect on GaAs radiation detectors’’ [J. Appl. Phys. 75, 7910 (1994)]

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69985/2/JAPIAU-77-3-1331-1.pd

Evidence for field enhanced electron capture by EL2 centers in semi‐insulating GaAs and the effect on GaAs radiation detectors

The performance of Schottky contact semiconductor radiation detectors fabricated from semi‐insulating GaAs is highly sensitive to charged impurities and defects in the material. The observed behavior of semi‐insulating GaAs Schottky barrier alpha particle detectors does not match well with models that treat the semi‐insulating material as either perfectly intrinsic or as material with deep donors (EL2) of constant capture cross section compensated with shallow acceptors. We propose an explanation for the discrepancy based on enhanced capture of electrons by EL2 centers at high electric fields and the resulting formation of a quasineutral region in the GaAs. Presented is a simple model including field enhanced electron capture which shows good agreement with experimental alpha particle pulse height measurements.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71231/2/JAPIAU-75-12-7910-1.pd

Membrane-initiated actions of estradiol (E2) in the regulation of LH secretion in ovariectomized (OVX) ewes

Abstract Background We demonstrated that E2 conjugated to BSA (E2BSA) induces a rapid membrane-initiated inhibition of LH secretion followed hours later by a slight increase in LH secretion. Whether these actions of E2BSA are restricted to the pituitary gland and whether the membrane-initiated pathway of E2BSA contributes to the up-regulation of the number of GnRH receptors during the positive feedback effect of E2 were evaluated here. We have shown that the suppression of LH secretion induced by E2 and E2BSA is the result of a decreased responsiveness of the pituitary gland to GnRH. In this study we further tested the ability of E2BSA to decrease the responsiveness of the pituitary gland to GnRH under the paradigm of the preovulatory surge of LH induced by E2. Methods For the first experiment GnRH and LH secretions were determined in samples of pituitary portal and jugular blood, respectively, in ewes treated with 12 mg E2BSA. In the second experiment, the number of GnRH receptors was quantified in ewes 12 h after administration of 25 micrograms E2 (the expected time for the increase in the number of GnRH receptors and the positive feedback effect of E2 in LH secretion) or 12 mg E2BSA. In the third experiment, the preovulatory-like surge of LH was characterized in ewes injected with 25 micrograms E2 alone or followed 8 h later (before the beginning of the LH surge) with 60 mg E2BSA. Results a) the decrease in LH secretion induced by E2BSA was not accompanied by changes in the pulsatile pattern of GnRH, b) E2BSA increased the number of GnRH receptors, and c) the presence of E2BSA in E2-treated ewes delayed the onset, reduced the length, and decreased the amount of LH released during the preovulatory surge of LH. Conclusions a) the rapid suppression of LH secretion induced by E2BSA is mediated only via a direct action on the pituitary gland, b) E2 acting via a membrane-initiated pathway contributes to increase the number of GnRH receptors and, c) administration of E2BSA near the beginning of the pre-ovulatory surge of LH delays and reduces the magnitude of the surge.http://deepblue.lib.umich.edu/bitstream/2027.42/112939/1/12958_2009_Article_665.pd

Improvement of integrated utrasonic transducer sensitivity

In this paper, we present a micromachined diaphragm structure for integrated ultrasound transducers. This structure greatly reduces the parasitic capacitance between the lower electrode and the conductive Si substrate in a nonmicromachined structure. The micromachining improves both sensitivity and minimum detectable signal. It also reduces crosstalk between transducer elements.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27930/1/0000354.pd

In situ measurements of HCl during plasma etching of poly-silicon using a diode laser absorption sensor

Tunable diode laser absorption spectroscopy is used to monitor hydrogen chloride (HCl) concentration in a commercial, high-density, low-pressure plasma reactor during plasma etching. A near-infrared diode laser is used to scan the P(4) transition in the first overtone of HCl near 1.79 µm to measure changes in HCl levels. A variety of HBr and Cl2 feedstock recipes are investigated at a process pressure of 10 mTorr as a function of rf power transformer coupled plasma, bias power and the total flow rate. Using 50 ms averaging and a signal modulation technique, we estimate a minimum detectivity of 4 × 10−6 in peak absorbance, which corresponds to an HCl number density of ∼2 × 1011 cm−3. The diode-laser based HCl sensor is sufficiently sensitive to detect small concentration variations and HCl concentration correlates with poly-Si etch rate for the conditions studied. These measurements demonstrate the feasibility of a real-time diode laser-based sensor for etch rate monitoring and the potential for process control.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49064/2/e30918.pd