We report single layer resistivities of 2-dimensional electron and hole gases in an electron-hole bilayer with a 10nm barrier. In a regime where the interlayer interaction is stronger than the intralayer interaction, we find that an insulating state
($drho/dT < 0$) emerges at $Tsim1.5{rm K}$ or lower, when both the layers are simultaneously present. This happens deep in the $$metallic regime, even in layers with $k_{F}l>500$, thus making conventional mechanisms of localisation due to disorder improbable. We suggest that this insulating state may be due to a charge density wave phase, as has been expected in electron-hole bilayers from the Singwi-Tosi-Land-Sjolander approximation based calculations of L. Liu {it et al} [{em Phys. Rev. B}, {bf 53}, 7923 (1996)]. Our results are also in qualitative agreement with recent Path-Integral-Monte-Carlo simulations of a two component plasma in the low temperature regime [ P. Ludwig {it et al}. {em Contrib. Plasma Physics} {bf 47}, No. 4-5, 335 (2007)]
We report Coulomb drag measurements on GaAs-AlGaAs electron-hole bilayers. The two layers are separated by a 10 or 25nm barrier. Below T$approx$1K we find two features that a Fermi-liquid picture cannot explain. First, the drag on the hole layer show
s an upturn, which may be followed by a downturn. Second, the effect is either absent or much weaker in the electron layer, even though the measurements are within the linear response regime. Correlated phases have been anticipated in these, but surprisingly, the experimental results appear to contradict Onsagers reciprocity theorem.
We report our work on fabricating lithographically aligned patterned backgates on thin (50-60$mu$m) Roman{roman3}-Roman{roman5} semiconductor samples using {it single sided mask aligners only}. Along with this we also present a way to photograph both
sides of a thin patterned chip using inexpensive infra-red light emitting diodes (LED) and an inexpensive (consumer) digital camera. A robust method of contacting both sides of a sample using an ultrasonic bonder is described. In addition we present a mathematical model to analyse the variation of the electrochemical potential through the doped layers and heterojunctions that are normally present in most GaAs based devices. We utilise the technique and the estimates from our model to fabricate an electron-hole bilayer device in which each layer is separately contacted and has tunable densities. The electron and hole layers are separated by barriers either 25 or 15nm wide. In both cases, the densities can be matched by using appropriate bias voltages.
