Aug 28, 2014

Large-depth defect profiling in GaAs wafers after saw cutting

Positron lifetime measurements and Doppler-broadening spectroscopy using slow positrons were combined to investigate open-volume defects created by sawing wafers from GaAs ingots introduced by a diamond saw cutter. The depth distribution represents a large-depth (up to 9.5 μm), wedge-like profile. This was found during step-by-step etching and assembling the respective individual S(E) curves. The depth and the concentration of the defects introduced by the diamond saw depend on the advance of the saw blade. The thermal stability of the detected defects was studied by an isochronal annealing experiment. It was concluded from the positron lifetime measurements and from the Doppler-broadening parameters as well as from the annealing behavior that small vacancy aggregates consisting of at least two vacancies are created by the sawing procedure. More extended defects such as microcracks were analyzed by scanning electron microscopy (SEM). Rutherford-backscattering spectroscopy shows that there is no amorphous material in the near-surface region.

Keywords:GaAs wafers; Saw cutting; Positron;DB; GD; PM


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Aug 15, 2014

Photoelastic characterization of residual strain in GaAs wafers annealed in holders of different geometry

The spatial distribution of residual strain in undoped 2 inch GaAs wafers multi-step annealed in holders of different geometry was characterized by the scanning infrared polariscope (SIRP) method. The SIRP maps reveal that the distribution of strain is significantly influenced by the symmetry of annealing, in particular by the points of contact between wafer and holder. In contrast to the as-grown state, the annealed wafers show fine patterns of slip lines. The lowest level and the most homogeneous distribution of residual strain were achieved by annealing in a vertically positioned holder of graphite rings. The radial temperature differences in the wafers caused by heating and cooling were checked by means of thermocouples on dummies of graphite. Temperature gradients up to 30 K cm−1 were measured depending upon the rates of cooling and heating.

Keywords:Annealed; GaAs wafers; Residual strain

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