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Extrinsic doping in group IV hexagonal-diamond-type crystals

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Over the past few years, group IV hexagonal-diamond-type crystals have acquired a lot of attention in semiconductor physics thanks to the appearance of novel and very effective growth methods. However, many questions remain unaddressed on their extrinsic doping capability and on how it compares to those of diamond-like structures. This point is here investigated through numerical simulations conducted in the framework of the density functional theory (DFT). The comparative analysis for group III and V dopant atoms shows that (i) in diamond-type crystals the bulk site symmetry (Td) is preserved by doping, while in hexagonal crystals, the impurity site moves toward a higher (Td) or lower (C3v) symmetry configuration dependent on the valence of the dopant atoms; (ii) for Si and Ge, group III impurities can be more easily introduced in the hexagonal-diamond phase—whose local C3v symmetry better accommodates the 3-fold coordination of the impurity—while n-type impurities do not reveal any marked phase preference; and (iii) for C, both n and p dopants are more stable in the hexagonal-diamond structure than in the cubic one, but this tendency is much more pronounced for n-type impurities.