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Smoothing of patterned gallium arsenide surfaces during epitaxial growth Ballestad, Anders


Control over the surface structure of semiconductor films during growth is critical for devices of recent technological importance. Typically the length scales of interest range from nanometers to micrometers. Examples include the size and spacing of quantum dots in quantum dot lasers, and the pitch and amplitude of grating structures for distributed Bragg reflectors. Elastic light scattering has atomic height sensitivity to this surface structure, on lateral length scales as low as half the incident wavelength, and is easily implemented for in-situ monitoring during film growth [1]. For the smooth surfaces of interest here, the distribution of the scattered light intensity as a function of scattering angle directly maps out the power spectral density (PSD). The PSD gives the 'root mean square' roughness of the surface structure as a function of inverse length scale, or spatial frequency. Here we present in-situ light scattering measurements performed during III-V semiconductor film growth by molecular beam epitaxy (MBE). We have used the technique to monitor the smoothing of one-dimensional grating structures during regrowth. For the regrowth experiments, the grating pitch was chosen such that the detection angle of the in-situ measurement coincided with the scattering peak associated with a harmonic of the grating periodicity. Because the initial shape of the patterned surface is known, it is possible to reconstruct the shape of the grating from the PSD as it evolves in time during growth. We find that for homoepitaxy of gallium arsenide (GaAs) on textured substrates, the time evolution follows the Kardar-Parisi-Zhang (KPZ) model [2].

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