Optical absorption of electron inter-band transitions in asymmetric Mg x Zn1-x O/ZnO/Mg y Zn1-y O quantum wells with mixed phases

The inter-band optical absorption of electron transitions in asymmetric MgxZn1-xO/ZnO/MgyZn1-yO quantum wells (QWs), which are the prime functional units of multi-color ultraviolet photodetectors (UVPDs), is investigated with the consideration of mixed phases (0.37 < x(y) < 0.62) by using the density matrix method combined with a weight model. Our results show that the intensity and number of absorption peaks can be modulated by controlling the Mg composition x in single or mixed phases with a given y in mixed phases. The single peak or dual absorption peaks will appear for x being in a single phase. While x is in the mixed phases, at most three observable peaks can be observed to instruct the designation of multi-color UVPDs. Meanwhile, the size dependence of the left barrier and well in the QWs is also discussed. It is shown that relative wider left barrier and narrower well is more beneficial to obtain multi-detectable absorption peaks for photodetectors.