Atomic force microscopy study of sapphire surfaces annealed with a H2O flux from a baffled molecular-beam epitaxy effusion cell loaded with Al(OH)3

Abstract

Stable nonplanar surface formed on patterned GaAs (311)A substrate by molecular-beam epitaxyWe present an atomic force microscopy ͑AFM͒ study of sapphire surfaces that contain scratches with various severities. The objective was to observe the effects of substrate annealing at 850°C for 200 min with a H 2 O-based overpressure resulting from an Al͑OH͒ 3 powder that was thermally cracked at 1200°C. The Al͑OH͒ 3 was decomposed into Al 2 O 3 and H 2 O according to a partial Bayer process in a modified molecular-beam epitaxy ͑MBE͒ effusion cell, which was equipped with homemade baffles placed at its outlet. These homemade, simple-to-construct tantalum baffles allow for the selective outfluxing of gaseous species, from those that are solid based. A UTI™ 100C-model mass spectrometer was used to monitor the species present at the sapphire surface during annealing. Any aluminum-based solid species from the Al͑OH͒ 3 were not observed in the mass spectrum, although the H 2 O-based species were. The sapphire substrates were annealed in a Varian Gen II™ MBE system, with H 2 O beam equivalent pressures ͑BEPs͒ of 5 ϫ 10 −6 and 2 ϫ 10 −5 Torr, as well as with no H 2 O flux at all. The AFM images show that the samples annealed with a higher H 2 O BEP of 2 ϫ 10 −5 Torr had noticeably less severe surface scratches than the samples that were annealed with lower H 2 O BEPs.