Different physics for edge and centre delta-doping into a QW

This study measured the absorption spectra of a centre and an edge delta-doped boron into the quantum wells (QWs). The samples used were MBE grown Si/Si_0.88/Ge_0.12 MQWs. Absorption spectra were taken in the spectral range 100-550 cm^-1 using Fourier infrared spectrometer in the temperature interval 10-77 K. The experiments showed that absorption spectra in the case of the edge doped samples were approximately 1.5 times broader than for the centre doped ones. The change of absorption is connected with the dependence of a binding energy of impurity states on a position of acceptors in the QW, and also with lowering of symmetry of the structure. With d-doping made to the edge the QW becomes asymmetric in comparison with the centre doped ones. It leads to a change in symmetry for wave functions and consequently to a change in selection rules for optical transitions both for optical transitions between impurity end space quantization levels and interlevel transitions as well.