Raman Back-scattering study of Damaged and Strain Subsurface Layers in GaAs Wafers

The damaged and strain subsurface layers of semi insulating(SI) GaAs substrate were characterized non destructively by Raman back scattering.The study shows that the thicknesses of the damaged and strain layers are less than 3μm.The damaged and strain layer can be removed after being etched in H 2SO 4·H 2O 2·H 2O for 1.5 min.

Hot electron effects on the operation of potential well barrier diodes

A study has just been carried out on hot electron effects in GaAs/Al0.3Ga0.7As potential well barrier(PWB)diodes using both Monte Carlo(MC)and drift-diffusion(DD)models of charge transport.We show the operation and behaviour of the diode in terms of electric field,mean electron velocity and potential,mean energy of electrons andΓ-valley population.The MC model predicts lower currents flowing through the diode due to back scattering at anode(collector)and carrier heating at higher bias.At a bias of 1.0 V,the current density obtained from experimental result,MC and DD simulation models are 1.35,1.12 and1.77μA/μm^2 respectively.The reduction in current over conventional model,is compensated to a certain extent because less charge settles in the potential well and so the barrier is slightly reduced.The DD model results in higher currents under the same bias and conditions.However,at very low bias specifically,up to 0.3 V without any carrier heating effects,the DD and MC models look pretty similar as experimental results.The significant differences observed in the I-V characteristics of the DD and MC models at higher biases confirm the importance of energy transport when considering these devices.

Achieving ultra-high strength in Mg-Gd-Ag-Zr wrought alloy via bimodal-grained structure and enhanced precipitation

Mg-13.1 Gd-1.6 Ag-0.4 Zr(wt%)alloy was either iso-thermally extruded at 350℃ or differentialthermally extruded with respectively pre-heated billet at 500℃ and die at 350℃.The iso-thermal extrusion leads to a near fully recrystallized structure and a[0001]//ED(extrusion direction)texture.In contrast,the differential-thermally extruded alloy develops a bimodal-grained structure composed of fine equiaxed recrystallized grains and coarse elongated unrecrystallized grains with a0110//ED texture.The differential-thermally extruded alloy has a higher number density of precipitates after postextrusion ageing than that of the iso-thermally extruded counterpart.Moreover,precipitation in the differential-thermally extruded alloy is further enhanced with cold rolling before ageing.Finally,the alloy obtains room temperature tensile yield strength of 421 MPa and ultimate tensile strength of 515 MPa via differential-thermal extrusion,cold rolling and ageing,mainly ascribed to the coupled strengthening from the bimodal-grained structure and enhanced precipitation.Strength of the alloy is noticeably higher than those of Mg-Gd(-Y)-Ag extruded alloys with similar compositions reported previously and is comparable to those of other high-strength Mg wrought alloys.The findings suggest that differentialthermal extrusion plus strain ageing is a suitable approach for achieving high strength in age-hardenable Mg alloys.

<110> Fiber Texture Evolution of Ferrite Wires during Drawn-torsion and Drawn-annealing-torsion Process

In this paper, the texture and microstructure evolution of drawn-torsion and drawn-annealing-torsion ferrite wires are studied by electron back scattering diffraction （EBSD） in order to investigate the special torsion texture evolution. Compared to the simulation results, the stable texture components {110}〈 110 〉 and {110}〈112〉 in both drawn-torsion and drawn-annealing-torsion wires display different evolution processes. The texture of the drawn-annealing-torsion wire fits to the Taylor model. A special texture evolution is found in drawn-torsion wires, related to the grain shape, and the heterogeneous deformation. A new plastic deformation viewpoint is suggested based on the special microstructure of drawn ferrite wire.