genearlly in metal oxides there will be formation of oxygen vacancies which act as deep donor.some publication suggest to add shallow donor to overcome this issue .? may i know what is the main reason ?
Poshan,
welcome!
Deep and shallow concerns the position of the allowed electronic level in the energy gap of the semiconductor. Deep means that the allowed energy energy level is far from the band edges EC and EV and shallow means that the allowed level lays near the band edges. Donors are electronic states that are normally occupied by an electron and give this electron to the conduction band and therefore are termed donor. Therefore a donor is found in two states, a neutral state and a positive ion state.The energy difference between the the donor sate and the conduction band edge EC is the ionization energy of the donor atom. In case of the shallow donor this energy difference is small and in case of deep donors the difference will be larger and the donor ionization process will be more difficult than the shallow donor.
When the allowed electronic states lays near the mid band, it can act as a trap where it can capture either a hole or electron for long times and release them for short times. There is also electronic states which can act as recombination centers where it can exist in both charge states equally.
I think when you add shallow donor, the deep donor will remain mostly neutral that occupied with an electron.
Best wishes
Poshan,
welcome!
Deep and shallow concerns the position of the allowed electronic level in the energy gap of the semiconductor. Deep means that the allowed energy energy level is far from the band edges EC and EV and shallow means that the allowed level lays near the band edges. Donors are electronic states that are normally occupied by an electron and give this electron to the conduction band and therefore are termed donor. Therefore a donor is found in two states, a neutral state and a positive ion state.The energy difference between the the donor sate and the conduction band edge EC is the ionization energy of the donor atom. In case of the shallow donor this energy difference is small and in case of deep donors the difference will be larger and the donor ionization process will be more difficult than the shallow donor.
When the allowed electronic states lays near the mid band, it can act as a trap where it can capture either a hole or electron for long times and release them for short times. There is also electronic states which can act as recombination centers where it can exist in both charge states equally.
I think when you add shallow donor, the deep donor will remain mostly neutral that occupied with an electron.
Best wishes
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