Direct laser patterning of GaAs(001) surfaces
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Direct laser patterning of GaAs(001) surfaces Haeyeon Yang1 * 1
Department of Nanoscience and Nanoengineering, South Dakota School of Mines and Technology, Rapid City, SD 57701, U.S.A. ABSTRACT Analysis of surface images indicates that GaAs(001) surfaces can be patterned directly by applying interferential irradiation of high power laser pulses on the surface. Atomic force microscopy (AFM) was used to image the patterned surfaces. The patterned surface shows strips that have the same separation as the interference period used. The direct laser patterning leaves the surface with trenches. The depth of trenches increases with the laser intensity and can be varied from few nanometers to a few hundred nanometers. At low laser intensity, strip shaped mound appears at the both edges of a trench, leaving a plateau area between them. The width of mound increases with the laser intensity, making the plateau area smaller. With a higher laser intensity, the plateau area disappear as the mounds merge together, forming a single strip between the adjacent trenches. AFM images from the patterned surface indicate that direct laser patterning can be used to fabricate nanostructures with a period smaller than that of the interference period as well as the wavelength of the laser used. INTRODUCTION The ability to pattern surfaces in nanoscale has numerous applications such as magnetic data storage, efficient energy storage, photovoltaic cells, and other electronic devices.[1] Lithography has been successful in patterning surfaces over a large area. Unlike lithography, direct laser patterning via interferential irradiation of laser pulses (IILP) is a simple and low-cost technique as it does not require processes involving photomasks, photoresist materials, and chemical etching.[2] Furthermore, real time patterning is possible when the laser patterning is integrated into epitaxial growth process so that three dimensional features can be grown directly on top of laser patterned epitaxial surfaces. For example, direct laser heating has been used to create and align self-assembled metallic nano dots on glass substrates.[3, 4] The dots are aligned along interference lines due to mass transport arising from selective heating in nanoscale. IILP has been used to selectively ablate surfaces. GaN nano lines[5] has been reported due to the ablation at interferential maxima lines when two beam interference is applied on the surface. Self-assembled nano dots created by applying IILP on semiconductor surfaces have been reported recently[6] and self-assembled metallic gallium nano dots were reported due to laserdissociated desorption from GaAs(110).[7] In this paper, we present our recent results of direct laser patterning of GaAs(001) surfaces. EXPERIMENT In order to pattern the surface, transient thermal grating was created on the irradiated interferentially by high power laser pulses in air GaAs(001) wafers with miscut angle of ±0.5°. Although there are complications in interpreting the surface images due to interaction with ambient gas molecules
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