The role of MBE in recent Quantum Hall Effect physics discoveries
01 December 2003
Much of the experimental progress in Quantum Hall and Composite Fermion physics over the past seventeen years has depended on the continuous improvement of the carrier mobility of the two dimensional systems at the semiconductor heterojunction. During this time the highest reported 2D electron mobility has increased by over a factor six from the value, 5 x 106 cm2/Vsec set by Gossard and English 1 in 1986, to our current record 2 of 31 x 106 cm2/Vsec. Remarkably over this entire time we find that the electron mobility of the best samples has always scaled approximately as the 2D electron density to the 0.7 power. For our current best samples we find that this relationship continues to hold over the entire electron density range from 1 x 109cm-2 to 3 x 1011cm-2. This result is independent even of gross structural issues such as whether the electron carriers are induced by modulation-doping or by an external electric field. We will discuss some of the physics issues that are encountered in maintaining the heterostructural quality as the electron density approaches the extremes of this range, and will review some recent Quantum-Hall-Effect experiments where the sample mobility has had an especially significant impact.