Robin Nicholas

Abstract:

We have performed magnetotransport measurements on InAs/(Ga,In)Sb heterostructures under hydrostatic pressure. The system has a cross gap band alignment which leads to the formation of co-existent 2D electron-hole gases. The amount of overlap and thus the electron and hole concentrations can be tuned by the application of hydrostatic pressure. The samples studied here have nearly equal electron and hole concentrations and show large oscillatory quantum Hall features. Measurements of the band overlap Delta and its rate of change with pressure d(Delta)/dP provides evidence that both the growth direction and also the composition of the interface layer play an important role in determining the band line-up.

Abstract:

Cyclotron resonance measurements on a GaAs heterojunction in the extreme quantum limit are presented. It has been reported recently that a new splitting appears for filling factors less than 1/6. We have applied hydrostatic pressure in order to investigate the dependence on electron g-factor, since a pressure of similar to 8 kbar halves the g-factor, yet changes the effective mass by only similar to 5%. The critical filling factor, defined as the point where the two split resonances have equal intensity, is found to be strongly reduced with pressure. A general relationship is presented for the dependence of the critical filling factor on the Zeeman splitting.

Abstract:

InAs/GaSb strained layer superlattices (SLSs) have been grown by metalorganic vapour phase epitaxy (MOVPE) at atmospheric pressure. Initially the interfaces of the SLS have been biased towards pairs of GaAs or InSb using three different gas switching sequences. Room temperature Raman optical modes show that growing the interfaces using an ALE (atomic layer epitaxy) like switching sequence gives interfaces of very high quality probably near the optimum, which is a monolayer. Growing with other switching sequences leads to one of the interfaces being non-uniform. By growing samples with alternating (InSb,GaAs or GaAs,InSb) pairs of interfaces it is possible to unambiguously assign this non-uniformity to one of the two possible interfaces for the first time. Furthermore, the influence of the band overlap on interface type has been studied using optimised SLSs in the semimetallic regime.