We present an investigation of the effects of uniaxial stress on the conduction band alignment of type II GaAs/AlAs short period superlattices using photoluminescence (PL) spectroscopy. In the absence of pressure, the conduction band ground state derives from the longitudinal X states in the AlAs layers, whereas at higher pressures the transverse X states shift to a lower energy. This crossing is clearly visible in the PL, and the shift in the transition energies is used to determine a value for the tetragonal shear deformation potential of the X point of AlAs, ΞX1, of 6.9 ± 0.6 eV. This is compared with existing estimates, and is used to confirm a value of 23 meV as the ambient pressure strain dependent splitting between the longitudinal and transverse X states. The ambient pressure confinement splitting is then investigated by using a linear extrapolation of the pressure shift in the transverse X features. This leads to the first estimation of the zero pressure state alignment from samples having a conduction band ground state of longitudinal X character, along with large confinement energies. Comparisons with the Kronig-Penney model suggest that the current value of the transverse effective mass of AlAs may need to be reassessed.
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Acknowledgements-This work was supported by the Engineering and Physical Sciences Research Council of the U.K., and by the Human Capital and Mobility Programme of the European Community.
- A. quantum wells
- A. semiconductors
- C. high pressure
- D. electronic structure