No abstract

The decay of excess minority carriers produced in a silicon wafer of thickness d by a laser pulse is analyzed. A comprehensive theory based on this analysis is presented for the determination of bulk lifetime τb and surface recombination velocity S. It is shown that, starting with an exponential spatial profile, the carrier profile assumes a spatially symmetrical form after approximately one time constant of the fundamental mode of decay. Expressions for the spatial average of the carrier density as a function of time are derived for three temporal laser pulse shapes: impulse, square, and Gaussian. Particular attention is paid to the time constants of the fundamental and higher modes of decay. The ratios of the time constants of the higher modes to the fundamental mode, as well as the time constant of the fundamental mode, are presented over wide ranges of values of S and d. Two complementary methods applicable for values of the product Sd≳40 cm2/s are proposed to determine τB and S, without having to invoke the usual stringent requirement of either S→∞ or d→∞, and thus permit the determination of τb and S for a greater variety of wafer characteristics. For Sd≲40 cm2/s, a two-wafer method is developed to determine τb and S; it is also shown that the requirement of d/τb ≳20S is sufficient to adequately guarantee that the asymptotic value of the instantaneous observed lifetime differs from the bulk lifetime by no more than 10%.

The annealing behavior and the uniaxial stress response of the radiation-induced defects causing the 1.8-, 3.3-, and 3.9-p, infrared absorption bands were studied after 45-MeV-electron and fast-neutron irradiation. The results indicate that these three bands all arise from the same defect. The defect exhibits two kinds of stress response, as evidenced by the dichroism induced in the bands: one due to electronic redistribution and the other due to atomic redistribution among the allowable orientations. We determine that the defect has an atomic symmetry along a (111)direction and a transition dipole close to a perpendicular (110) direction. The activation energies for atomic reorientation and for annealing of the defect are the same, about 1.2 eV. Correlation of these results with the previous EPR studies indicates that the defect giving rise to these bands is the divacancy. Using the one-electron molecular-orbital model deduced for the divacancy from the EPR studies, some suggestions are given as to the nature of the optical transitions involved.

Acupuncture is a popular but controversial treatment option for low back pain. In China, it is practised as traditional Chinese medicine; other treatment strategies for low back pain are commonly practised as Western medicine. Research on patient preference for low back-pain treatment options has been mainly conducted in Western countries and is limited to a willingness-to-pay approach. A stated-preference, discrete choice experiment was conducted to determine Chinese patient preferences and trade-offs for acupuncture and low frequency infrared treatment in low back pain from September 2011 to August 2012 after approval from the Department of Scientific Research in the study settings. Eight-six adult outpatients who visited the ‘traditional medicine department’ at a traditional Chinese medicine hospital and the ‘rehabilitation department’ at a Western medicine hospital in Guangdong Province of China for chronic low back pain during study period participated in an interview survey. A questionnaire containing 10 scenarios (5 attributes in each scenario) was used to ask participants' preference for acupuncture, low frequency infrared treatment or neither option. Validated responses were analysed using a nested-logit model. The decision on whether to receive a therapy was not associated with the expected utility of receiving therapy, female gender and higher out-of-pocket payment significantly decreased chance to receive treatments. Of the utility of receiving either acupuncture or low frequency infrared treatment, the treatment sensation was the most important attribute as an indicator of treatment efficacy, followed by the maximum efficacy, maintenance duration and onset of efficacy, and the out-of-pocket payment. The willingness-to-pay for acupuncture and low frequency infrared treatment were about $618.6 and $592.4 USD per course respectively, demonstrated patients' demand of pain management. The treatment sensation was regarded as an indicator of treatment efficacy and the most important attribute for choosing acupuncture or low frequency infrared treatment. The high willingness-to-pay demonstrated patients' demand of pain management. However, there may be other factors influencing patients' preference to receive treatments.

The production and annealing behavior of the divacancy and the A center in Gssion-neutron-irradiated silicon was studied by infrared absorption, using the 1.8-, 3.9-, and f2-p, bands. The production rate of the divacancy was found to be high, about 5.7 cm ', and to be enhanced by the presence of boron (~2 X 10" atoms per cm'), but not by the presence of oxygen ( 1X10"atoms per cm'). The annealing of divacancies in neutron-irradiated Si required an activation energy of 1.25 eV, as in electron-irradiated Si, indicating that most of the divacancies were removed by diffusion to sinks. The annealing results also indicate that the local defect concentrations in the damaged regions can be as high as 10'0 defects cm 3, in which the divacancies still retain their individual properties as far as their infrared absorption and annealing properties are concerned. The production rate of the A center was found to be extremely low. The near-edge absorption band was also studied. About 95% of the near-edge band disappeared upon annealing in the same broad temperature range as did the divacancies. From these results, it was concluded that the majority of the total volume in localized damage regions produced by the ission-neutron irradiation of silicon is rich in divacancies and is still crystalline.