Modified MBE hardware and techniques and role of gallium purity for attainment of two dimensional electron gas mobility > 35 x 106 cm2/V s in AlGaAs/GaAs quantum wells grown by MBE

We provide evidence that gallium purity is the primary impediment to attainment of ultra-high mobility in a two-dimensional electron gas (2DEG) in AlGaAs/GaAs heterostructures grown by molecular beam epitaxy (MBE). The purity of gallium can be enhanced dramatically by in-situ high temperature out gassing within an operating MBE. Based on analysis of data from an initial growth campaign in a new MBE system and modifications employed for a 2nd growth campaign, we have produced 2DEGs with low temperature mobility mu in excess of 35 x 10(6) cm(2)/V s at density n=3.0 x 10(11)/cm(2) and mu=18 x 10(6) cm(2)/ V s at n=1.1 x 10(11)/cm(2). Our 2nd campaign data indicate that gallium purity remains the factor currently limiting mu < 40 x 10(6) cm(2)/V s. We describe strategies to overcome this limitation. (C) 2016 Elsevier B.V. All rights reserved.