The publisher regrets for the below error in typesetting: In the first paragraph in section “Results and discussion” “… We use atomic units(au) such that the unit of energy is the effective Rydberg energy [Formula presented] and the unit of length is the effective Bohr radius [Formula presented]. For GaAs, the material parameters are [Formula presented] and [Formula presented] [9,40]. The effective Rydberg energy and Bohr radius are [Formula presented] and [Formula presented] for GaAs.” The above mentioned error should be corrected as following “… We consider a hydrogenic impurity located at the center of a spherical cavity, and we use the effective Rydberg energy [Formula presented] is equal to Rydberg energy [Formula presented] and effective Bohr radius [Formula presented] is equal to Bohr radius [Formula presented].” The publisher would like to apologise for any inconvenience caused. Ref. [40] which is given below was omitted. It was given here.