P. Selvam

Bio: P. Selvam is an academic researcher. The author has contributed to research in topic(s): Annealing (metallurgy). The author has an hindex of 1, co-authored 1 publication(s) receiving 6 citation(s).

A detailed calculation of the auger lifetime in p-type HgCdTe

Abstract: There has been recent experimental evidence that showed, in heavily doped p-type HgCdTe, the lifetime may be limited by the Auger 7 recombination mechanism. We have performed a detailed calculation of both the Auger 7 and Auger 1 lifetimes as a function of Cd composition (x), temperature (T), and doping (NA). Compared with those done 20 years ago, the depth and breadth of these calculations result in a significant increase in the accuracy of the predictions. We present here the Auguer 7 lifetime for two different compositions, x=0.305 and x=0.226 over a range of temperature extending from 60 K to 300 K and for acceptor doping from 1015 cm−3 to 1018 cm−3. The calculated results for MWIR (x=0.305) are in reasonably good agreement with recent experiments performed on MWIR HgCdTe at 77 K over a range of doping. In addition, we calculated γ (≡ τA7 /τA1) with the same doping, composition (x ≈ 0.22), for a range of temperatures (40–80 K) and found γ=3–6.

Fundamental materials studies of undoped, In-doped, and As-doped Hg1-xCdxTe

Abstract: Variable magnetic-field Hall and transient photoconductance-lifetime measurements were performed on a series of undoped, In-doped, and As-doped HgCdTe samples grown by molecular beam epitaxy (MBE). Use of quantitative mobility-spectrum analysis (QMSA) combined with multiple carrier-fitting (MCF) techniques indicates that the majority of samples contain an interfacial n-type layer that significantly influences the interpretation of the electrical measurements. This n-type layer completely masks the high-quality electrical properties of undoped or low n-type In-doped HgCdTe, as well as complicating the interpretation of activation in As-doped p-type HgCdTe. Introduction of an intentional n-type background, typically created through doping with In to “recover” high mobility, is actually shown to increase the “bulk” layer conductivity to a level comparable to the interface layer conductivity. Photoconductance-lifetime measurements suggest that In-doping may introduce Shockley-Read-Hall (SRH) recombination centers. Variable-field Hall analysis is shown to be essential for characterizing p-type material. Photoconductance-lifetime measurements suggest that trapping states may be introduced during the incorporation and activation of As. Two distinctly different types of temperature dependencies were observed for the lifetimes of As-doped samples.

The vortex path model and angular dependence of Jc in thin YBCO films deposited from undoped and BaZrO3-doped targets

Abstract: The vortex path model is applied to Jc(?) data of YBa2Cu3O6+x (YBCO) thin films with different densities and types of columnar defects. The films were prepared by laser deposition from micro-?and nanograined undoped and BaZrO3-doped nanograined targets. It is found that in the ab-axis direction the model gives parameters which can be interpreted in terms of vortices trapped in the Cu?O spacer layers. In the c direction the model gives estimates of average vortex path shapes and explains the shoulders close to the ab peak frequently observed in the Jc(?) data without the need for assuming changes in the electronic mass anisotropy.

Enhanced Jc and improved grain-boundary properties in Ag-doped YBa2Cu3O7−δ films

Abstract: A large increase (∼8×) in critical current density, Jc, was achieved for in situ laser ablated YBa2Cu3O7−δ–Ag films. High-resolution Auger electron spectroscopic investigation indicates that the Ag-doped films are stoichiometric with a relatively low grain-boundary extension (8 nm) in contrast to undoped YBa2Cu3O7−δ films (32 nm). Further analysis suggests that the doped film contains a much lower silver content (<0.15 wt %) than in the target material (5 wt %). These observations are in excellent agreement with the temperature dependence of Jc, the room-temperature resistivity, and the surface resistance results. Thus, Jc enhancement in Ag-doped films can be attributed to their superior properties, viz., improved microstructure characteristics and the reduced resistive grain boundaries.

Reason for high critical current in thin YBCO films prepared by laser ablation from nanostructured target

Abstract: Thin YBCO films prepared by laser ablation from a nanocrystalline target have a high critical current density Jc≈107 A cm-2 at 77 K. To clarify the reason for the high value of Jc, the composition and structure of these films are compared with those deposited from a typical coarse-grained target. According to energy-dispersive x-ray and photoelectron spectroscopic analysis the contents of Y, Ba and Cu are similar in the films of both origins, despite some differences in the compositions of the targets. It is concluded that the high value of Jc in the films prepared from the nanocrystalline target can be explained by pinning of magnetic flux vortices to extended structural defects.