Preparation of epiready gallium antimide substrates with gas cluster ion beams.

摘要

One of the key problems to producing mid-infrared optoelectronic and low-power electronic devices in the GaSb material system is the lack of substrates with appropriate surfaces for epitaxial growth. Chemical mechanical polishing (CMP), which is a standard polishing technique for the semiconductor industry, produces GaSb substrates with scratches, subsurface damage, and an inappropriate oxide layer on its surface. In this work, novel gas cluster ion beam (GCIB) etching techniques were developed to remove CMP induced damage in order to produce wafers with atomically smooth surfaces and uniformly-thick thermally desorbable surface oxides. As compared to CMP finished GaSb wafer surfaces, dual energy step CF4/O2 and/or O2 cluster beam processes with a 10keV etch step and 3keV smoothing step produced significantly improved surfaces that, when overgrown by molecular beam epitaxy, exhibited smooth transitions from the substrate to the epitaxial layer. This is the first time that GCIB processed GaSb wafers were overgrown with MBE. Furthermore, only the overgrown cluster ion beam processed substrates produced epitaxial surfaces with uniform step-terrace formation with mono-atomic steps and wide terraces. As part of this work, a chemical model was developed for the formation of cluster beam induced surface oxides on GaSb and a new method for characterizing the roughness of substrate/oxide interfaces was demonstrated. Statistical analysis was also used for the first time to determine the fractal characteristics of CMP- and GCIB-finished GaSb surfaces, substrate/oxide interfaces, and episurfaces. This new method of post processing CMP-finished GaSb wafers advances the state-of-the-art one step closer to being able to produce "epi-ready" GaSb wafers.