Hydrostatic pressure control of the carrier density in GaAs/GaAlAs heterostructures; Role of the metastable deep levels

Abstract

Hydrostatic pressure up to 18 kbar has been used to characterize GaAs/GaAlAs heterostructures manufactured using MOCVD and MBE techniques. The pressure dependence of the carrier concentration n s has been deduced from Hall measurements between 4.2 and 300 K and Shubnikov-De Haas experiments have been performed at helium temperature. The main result we have observed is a linear decrease of the carrier concentration as the pressure increases. We explain this behaviour taking into account the deep character of the impurity level in GaAlAs connected with the X minimum whose variation is found to be 11 meV kbar . When the Fermi energy is large enough compared to the difference of affinities Δ E c, a transition between a metallic to an insulating behaviour of the heterojunction is induced. Moreover, the metastable character of this impurity level, clearly pointed out by changing the cooling conditions must be taken into account. In conclusion, this kind of experiment, in which the carrier concentration may be varied, appears as a powerful tool to investigate the properties of the heterostructures. In the particular case of GaAs/GaAlAs the role of the metastable state is predominant in all the investigations.