GaAs-Ga1-xAlxAs heterostructures studied under hydrostatic pressure

The authors report an investigation of transport properties of GaAs-Ga 0.72 Al 0.28 As heterojunctions under hydrostatic pressure up to 1.5 GPa in the temperature range 150>T>300 K. Pressure induces a decrease in both the two-dimensional electron gas (2DEG) concentration and the free-electron concentration in Ga 1-x Al x As. At pressures sufficiently high, the parallel conduction through the Ga 1-x Al x As layer becomes negligible compared to the contribution of the 2DEG. They have used this fact to study the 2DEG alone at high temperature, which showed that its concentration is temperature dependent. Results are analyzed with two different models, one based on a simple triangular-well approximation and the other using a self-consistent description of the structure. The Ga 0.72 Al 0.28 As layer is fully taken into account in both of these models in order to obtain a quantitative description of the parallel conduction. The analysis indicates that the activation energy of the Si donor in Ga 1-x Al x As is temperature dependent. This is corroborated by measurements made on bulk Ga 0.72 Al 0.28 As samples.