Hardness tests on irradiated pressure vessel steel

http://www.worldcat.org/oclc/703482

Proceedings of the International Conference on Metastable Metallic Alloys, Brela, 1970

The contributions in this Supplement are invited papers and communications at the “Conference on Metastable Metallic Alloys” held in Brela, September 28-30, 1970. After the Conference the following Committee agreed that all the contributions may be published in this Supplement

Fusion materials semiannual progress report for the period ending March 31, 1995

This is the eighteenth in a series of semiannual technical progress reports on fusion materials. This report combines research and development activities which were previously reported separately in the following progress reports: {sm_bullet} Alloy Development for Irradiation Performance. {sm_bullet} Damage Analysis and Fundamental Studies. {sm_bullet} Special Purpose Materials. These activities are concerned principally with the effects of the neutronic and chemical environment on the properties and performance of reactor materials; together they form one element of the overall materials programs being conducted in support of the Magnetic Fusion Energy Program of the US Department of Energy. The other major element of the program is concerned with the interactions between reactor materials and the plasma and is reported separately. The Fusion Materials Program is a national effort involving several national laboratories, universities, and industries. The purpose of this series of reports is to provide a working technical record for the use of the program participants, and to provide a means of communicating the efforts of materials scientists to the rest of the fusion community, both nationally and worldwide. This report has been compiled and edited under the guidance of A.F. Rowcliffe by Gabrielle Burn, Oak Ridge National Laboratory. Their efforts, and the efforts of the many persons who made technical contributions, are gratefully acknowledged

Effect of Annealing on Photoluminescence from Defects in GaN

Annealing is a critical process in modern GaN technology, essential for achieving p-type conductivity by activating the MgGa acceptor, as first demonstrated by Shuji Nakamura in the early 1990s. Despite the omnipresence of hydrogen as an impurity in GaN crystals, the precise mechanisms governing hydrogen diffusion and acceptor passivation remain only partially understood. The presented research investigates the effects of annealing-induced activation and hydrogen passivation on C and Be acceptors in GaN grown by MOCVD, HVPE, and MBE methods. We explored these effects by using several annealing techniques, gas compositions, and thermal regimes. A transient behavior between the CN and CN-Hi complex was observed when samples were annealed in N2 and N2 + H2 atmospheres. Annealing in vacuum ambient revealed an unexpected behavior in acceptor-related PL bands, demonstrating that passivation of CN and BeGa can occur at temperatures as low as 200 °C and 350 °C, respectively. Both CN and BeGa exhibited a U-shaped pattern of passivation and activation, suggesting a common mechanism of hydrogen diffusion. In Be-doped MBE samples, high-temperature passivation involving VN was observed. Finally, using UHPA, activation of a shallow Be-related acceptor at an energy level 0.113 eV above the VBM, corresponding to the UVLBe peak at 3.38 eV, was achieved for the first time in Be-implanted samples

Defects in transition-metal-hyperdoped Si and their role in near-infrared light detection

The bandgap of Si makes it transparent to light with wavelengths longer than 1.1 um. This includes most of the technologically useful telecommunication bands in the near-infrared (NIR). Conversely, InGaAs, HgCdTe, or Ge-based detectors are ideal in this spectral range but integration onto a Si platform for efficient signal processing can be complicated and expensive. Thus, there is a strong incentive to develop a Si-based NIR detection capability to reduce these costs, enhance scalability, and leverage the mature manufacturing infrastructure of the Si industry. This is expected to have a significant impact on the fields of photovoltaics, optical computing, and infrared imaging to name a few. Hyperdoped Si has been identified as a promising material for Si-based NIR detection. It involves high dose implantation of deep level impurities such as Au, Ti, and Ag followed by nanosecond pulsed laser melting (PLM). Above a critical concentration (N_C = 6e19 per cubic cm), an intermediate impurity band forms in the Si bandgap, enabling efficient sub-bandgap light absorption in the NIR. However, despite the high NIR absorption levels, NIR photodetectors do not show a correspondingly high performance and suffer from extremely low external quantum efficiencies (less than 0.01%). This thesis explores the role of process-induced defects in first generation hyperdoped Si NIR detectors. A focus is placed on Au-hyperdoped Si. A combination of electrical and optical techniques is first used to characterise the diode properties and then gauge the possible impact of defects on the NIR response. Deep level transient spectroscopy (DLTS) reveals a range of defects within the active device region with appreciable defect densities (~1e15 per cubic cm). These defects exist in the Si substrate well beyond the implanted and PLM region, and are generated from the implantation and PLM processes. The most prominent defect is a deep electron trap located at E_C-0.35 eV in the Si bandgap. Collectively referred to as the process-induced defects, they are also found to contribute to the NIR photocurrent together with photo-generated carriers from the Au-hyperdoped regions. Based on these results, routes to an optimised device design are explored with a number of factors identified for areas of improvement such as the carrier lifetime, device geometry, surface properties, and metal-hyperdoped Si electrical contacts. In particular, further experiments aimed at improving contact quality uncovered some surprising results. The Au hyperdoped layer was not heavily p-type as previously assumed in the literature but semi-insulating and n-type. Furthermore, a thick surface oxide layer and segregated Au gave rise to an effective p+ surface layer, presumably arising from acceptor states at the surface. Finally, the ability to hyperdope silicon with Ag and Ti is explored. Structural characterisation indicates that, unlike Au, Si cannot be hyperdoped with these impurities. Surface segregation and filamentary breakdown were identified as competing processes which inhibit reaching a hyperdoped regime. This study highlights the limitations but also the opportunities in utilising hyperdoped Si as a material for NIR detection

The materials processing research base of the Materials Processing Center

The investigation and evaluation of materials processing techniques in metals, alloys, polymers, and crystal growth are described