Advanced substrate/buffer layer polishing techniques to optimize the growth and performance of 6.1Angstrom InAs HBTs

Summary form only given. The metamorphic InP/In_xAl_1-x/As/InAs or InP/In_xAl_1-x/As/In_0.85Al_0.15As graded system provides a virtual substrate with semi-insulating properties for the growth of InAs based device structures. We demonstrate that through graded buffer growth and chemical polishing, structures are produced using fully relaxed template layers with surface r.m.s roughness of about 0.5 nm. The composition of the InAlAs film is initially latticematched to the semi-insulating M substrate and graded to InAs during molecular beam . epitaxial growth. High growth temperatures help exploit the high dislocation velocities in this materials system. This approach allowed for enhanced dislocation propagation in the buffer along with a minimization of surface roughness. Plan view and cross-section transmission electron microscopy images show a crosshatch pattern of long interfacial misfit dislocations and a surface threading dislocation density of less than lo6 cm" (below the detection limit of plan view TEM). To reduce the surface roughness of the completely relaxed structures, chemicalmechanical polishing (CMF) was used. An optimized NaOCl based solution was found to produce a smooth surface with minimal surface scratches and subsurface damage. Triple axis x-ray rocking curve measurements on separate CMP-processed InAs substrates confirmed that very little polishing damage was introduced. Epitaxial regrowth of device structures shows a considerable enhancement of the surface quality when the CMF process is used. This improved surface roughness may be important. Initial materials and device results from regrowth of device structures on these buffer layers will be described.