Layer interdependence of transport in an undoped electron-hole bilayer

The layer interdependence of transport in an undoped electron-hole bilayer (UEHBL) device was studied as a function of carrier density, interlayer electric field, and temperature. The UEHBL device consisted of a density tunable, independently contacted two-dimensional electron gas (2DEG) and two-dimensional hole gas (2DHG) in distinct (100) GaAs quantum wells separated by a 30 nm Al0.9Ga0.1As barrier. The 2DEG and 2DHG are induced via field effect by top and bottom gates, respectively. Transport measurements were made simultaneously on each layer using the van der Pauw method. An increase in 2DHG mobility with increasing 2DEG density was observed, while the 2DEG mobility showed minimal dependence on the 2DHG density. Changes in both surface-gate voltages for the mobility-density measurements were observed. Decreasing the interlayer electric field and thereby increasing interlayer separation also increased the 2DHG mobility with negligible effects on the 2DEG mobility. The change in interlayer separation as interlayer electric field changed was estimated using 2DHG Coulomb drag measurements. A general discussion of the results is given in which the possible sources for the apparent interlayer dependence of the hole transport are examined.