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spot on the surface is exposed to an average of 200 pulses. Figures 3a and 3b show
electron micrographs of the silicon surface following irradiation at a fluence of 4 kJ/m2.
The resulting surface is covered with microstructures that are 2-3 pm tall and spaced by
2-3 pm (Figure 3a). The microstructures are crystalline silicon covered with a few-
hundred nanometer thick laser-altered surface layer (Figure 3b) [7]. Hall measurements
of this surface layer show n-doping with a higher electron concentration than the
substrate and an electron mobility on the order of 100 cm2V-is 1. The microstructuring
thus creates an n/n+ heterojunction between the undisturbed substrate and the disordered
surface layer. Following microstructuring, we thermally anneal the samples in vacuum
for thirty minutes. Next we thermally evaporate Cr/Au (3 nm/75 nm) contacts on either
side of the heterojunction. Figure 3c shows a schematic diagram of a finished device; our
devices have an active area of approximately 5 mm2.
Spectral responsivity and diode characteristics of prototype p-i-n detector. The spectral
responsivity of a photodetector is a measure of the wavelength dependence of
- 20p 1p
C
y m rostructured Si
c-Si
Figure 8. (a) Scanning electron micrograph of a silicon surface microstructured with 100-fs laser
pulses at a fluence of 4 kJ/m2. The micrograph is at a 450 angle to the surface. (b) Transmission
electron micrograph of thin cross section of the sample in a. The uppermost few hundred
nanometers of each microstructure is a highly disordered, nano-crystalline silicon layer. (c)
Schematic diagram of a microstructured silicon photodiode. The disordered surface layer is
approximately 300 nm thick and the substrate wafer is 250 um thick.
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Carey, JE & Mazur, E. Microtextured Silicon Surfaces for Detectors, Sensors & Photovoltaics, report, May 19, 2005; United States. (https://digital.library.unt.edu/ark:/67531/metadc780018/m1/4/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.