Optical Characterization of GaAs/Si Layers Grown by the Conformal Method (Confined Lateral Epitaxial Growth)

Abstract

Optical studies of conformal GaAs layers grown on silicon substrates were carried out by cathodoluminescence, photoluminescence imaging, and micro-Raman spectroscopy. These techniques revealed, in the conformal GaAs layers, local variations of the luminescence intensity with the shape of stripes both parallel and perpendicular to the GaAs seed, associated with local variations of tensile stress. The cathodoluminescence and micro-Raman spectra suggest that this distribution of tensile stress plays an important role in the formation of mid-gap states responsible for the variations of the luminescence intensity. The high luminescence emission of the conformal GaAs layers compared to the emission of the GaAs seed grown directly on the Si substrate is consistent with the high quality of the conformal layers.

Stress distribution mapping of GaAs on Si conformal layers

“…In fact, luminescence spectra, as well as R data, indicated a different level of stress in the bright areas with respect to the dark ones, 6 with an increase of the tensile stress in the dark regions. This was attributed to the presence of nonradiative centers, accumulated in the dark areas, probably due to the existence of different stress levels in the layers.…”

“…6 The dislocation density in the conformal layers was estimated to be lower than 10 5 cm −2 using transmission electron microscopy ͑TEM͒ and Abrams-Buiocchi ͑AB͒ etching; furthermore, a low dislocation density was confirmed by the efficiency of light-emitting diodes ͑LEDs͒ obtained by epitaxial regrowth on conformal layers. 6 The dislocation density in the conformal layers was estimated to be lower than 10 5 cm −2 using transmission electron microscopy ͑TEM͒ and Abrams-Buiocchi ͑AB͒ etching; furthermore, a low dislocation density was confirmed by the efficiency of light-emitting diodes ͑LEDs͒ obtained by epitaxial regrowth on conformal layers.…”

“…The large lattice mismatch leads to the formation of misfit dislocations that propagate through the layers producing poor quality GaAs material, unable for optical devices. 6 The layers elastically accommodate the residual stress resulting from the lattice and thermal mismatches with the Si substrate and the top dielectric layer. Conformal growth is one of the proposed methods.…”

Cathodoluminescence study of Si complex formation in self-doped and intentionally Si-doped GaAs conformal layers

“…In spite of the high quality of the GaAs/Si conformal layers some detrimental features in the layers obtained by this procedure have been observed by previous Raman and CL studies, such as the existence of strain modulations [8], the appearance of a doped stripe near the seed in unintentionally doped layers [8,9] or the formation of Si-based complexes in the doped regions [10]. In particular, the presence of such complexes is expected to reduce the effective free carrier concentration, also producing a decrease of the carrier mobility, which would negatively affect the transport properties of the devices.…”