| Popis: |
Strained (InGa)As single and multiple quantum wells, embedded in GaAs and (AlGa)As, have been grown by molecular beam epitaxy. The critical thickness for (InGa)As/GaAs was studied by photoluminescence (PL) and found to follow the theoretical expression proposed by J.W. Matthews and A.E. Blakeslee [J. Cryst. Gr. 2Z (1974) 118]. In the PL spectra of strained QW's the dominating narrow line (at 2 K and 77 K) is associated with the recombination of excitons characterized by the ground state levels of electrons and heavy holes. Photoconductivity spectra at 77 K of QW's in GaAs revealed three peaks which are due to allowed excitonic transitions involving ground states, excited states as well as hole states from the strain split off valence subband. This split off valence subband in (InGa)As is below the band edge of the unstrained GaAs. The transition energies of SOW and MQW:s have been analysed with the conduction band offset, ΔEc, and the energy gap of the strained (InGa)As as adjustable parameters. This has shown that the conduction-to-valence band offset ratio across the GaAs/strained (InGa)As interface is; ΔEc:ΔEv = 0.83(±0.06) : 0.17, and it slightly decreases for the (AlGa)As - strained (InGa)As interface depending on the Al and In concentrations. In addition we found that with reduced In-concentration the offset approached that for the GaAs/(AlGa)As heterojunction. |
