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P-n junction is a fundamental structure of semiconductor devices, such as the light emitting diodes (LED) and the solar cells. The joint of p-doped and n-doped semiconductors generates the band bending in its boundary surface which is the key for determining the device character. It has been difficult, however, to calculate the electronic structure of such a system because it must contain a large number of atoms in a unit cell. To solve the problem, we have developed a new computational code of the screened KKR method which implements the coherent potential approximation (CPA) and the Kubo-Greenwood formula. This code enables us to calculate the electronic structures and the transport properties of p-n junctions which still have importance for modern electronics. The screened KKR can solve the one-body Schroedinger equations efficiently especially for the multilayered systems by performing the electronic structure calculation within an O(N) computational cost, where N is the number of layers in a unit cell. Thanks to the CPA, we can handle p-n junctions with an arbitrary doping concentration without using any super-cell techniques, which need much larger unit cell when the doping concentration being low. By implementing the Kubo-Greenwood formula into the screened KKR, we can calculate the conductivities of the junction systems. We have calculated the electronic structure and the transport properties of the periodically multilayered systems of p-doped and n-doped GaAs. The band bending in the boundary surface can be obtained clearly from the analysis of the layer-projected density of states. The thickness of depletion layer can also be discussed depending on the carrier concentration. Finally, we show the electric conductivities of biased p-n junctions by introducing a model for the external potentials. |
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