Measurements of the linewidth enhancement factor (also termed the aparameter) for quantum dot semiconductor lasers emitting at 1310 nm in both single and multiple transverse modes are presented. Values between 1.5 and 3.0 were measured depending on the device length. In addition, its spectral dependence within the inhomogeneously broadened ground and excited state is investigated.

Photoluminescence (PL) from GaAs quantum wells with widths from 50 to 300 A and AI,Ga,.,As barriers ( x = 0.3 and 1) was studied under pressure up to 35 kbar at two temperatures (300 K and 77 K). We used (and compared) three types of pressure devices: gas cells, liquid cells and the diamond-anvil cell. Accurate values for the pressure variation of the PL energy were obtained. They reveal the small dependence on the parameters of the well, in agreement with the envelope-function calculation. Pressure shift of the PL lines is the same at 77 K and at 300 K. In several samples we found the change of the pressure coefficient of the direct (r) line at the T-X crossover pressure. We interpret this as the resonance effect due to the mixing of the r state in t h e well with the X continuum in the barriers. This means that the pressure dependence of the quantum-well pressure. From our results we obtain the linear pressure coefficient of the GaAs energy gap equal to 11.6 meV kbar-'. The deformation potential of the gap seems to be almost independent of pressure u p to 15 kbar. shouIci noi be iiiied Wiih a singie Cur".e 'irelow and above ihe r-x CiosBOvei

Lattice constants of GaAs layers grown by molecular beam epitaxy were examined by using the high resolution x-ray diffractometer. For highly doped samples ͑up to 9ϫ10 18 cm Ϫ3 of free-electron concentration͒ we observed an increase of the lattice constant with respect to the undoped layers. Since substitutional silicon atoms decrease the lattice constant of GaAs, the results are explained by the influence of free-electrons via the deformation potential of the ⌫ minimum of the conduction band. The best fit to our diffractometric data was obtained for the band-gap deformation potential equal to Ϫ8.5 eV.

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