Internal modification of intrinsic and doped silicon using infrared nanosecond laser
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We report experimental results of three-dimensional (3D) modification inside intrinsic and doped silicon wafers using laser pulses with 1.55 µm wavelength and 3.5 ns pulse duration. Permanent modification in the form of lines is generated inside silicon by tightly focusing and continuously scanning the laser beam inside samples, without introducing surface damage. Cross sections of these lines are observed after cleaving the samples and are further analyzed after mechanical polishing followed by chemical etching. With the objective lens corrected for spherical aberration, tight focusing inside silicon is achieved and the optimal focal depth is identified. The laser-induced modification has triangular shape and appears in regions prior to the geometrical focus, indicating significant absorption in those regions. Experiments with doped samples show similar modification for doping concentrations (and corresponding initial free carrier densities) in the range of 1013–1016 cm−3. At carrier densities of 1018 cm−3, linear absorption of light becomes significant and the modification is reduced in size.
KeywordsPulse Energy Carrier Density Focal Depth Linear Absorption Spherical Aberration
Finance support for the author C. T-H and laser support are provided by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, US Department of Energy (DOE) under Grant No. DE-FG02-86ER13491. Partial financial support for this work by the National Science Foundation under Grant No. CMMI-1537846 is also gratefully acknowledged.
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