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      Effects of P, As, and Sb heavy doping on band gap narrowing of germanium as light-emitting materials

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          Abstract

          The n-type tensile-strained Ge can be used as high-efficient light-emitting materials. To reveal the influence of n-type doping on the electronic structure of Ge, we have computed the electronic structure of P, As and Sb doped Ge using first-principles calculation and band unfolding technique. We find that these n-type doping can induce both indirect and direct band gap narrowing, which well reproduce experimental observation that red-shifts occur in photoluminescence spectra of Ge with n-type doping. We reveal that the indirect band gap narrowing is mainly caused by impurity state, while the direct band gap narrowing is a result of lattice distortion induced by the dopant atom. Moreover, we find that it can use E_g^{\Gamma}-E_g^L to explain the voltage increase was needed to reach the same current densities of light emission through the different samples with increasing doping concentrations.

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          Tensile-strained, n-type Ge as a gain medium for monolithic laser integration on Si.

          We analyze the optical gain of tensile-strained, n-type Ge material for Si-compatible laser applications. The band structure of unstrained Ge exhibits indirect conduction band valleys (L) lower than the direct valley (Gamma) by 136 meV. Adequate strain and n-type doping engineering can effectively provide population inversion in the direct bandgap of Ge. The tensile strain decreases the difference between the L valleys and the Gamma valley, while the extrinsic electrons from n-type doping fill the L valleys to the level of the Gamma valley to compensate for the remaining energy difference. Our modeling shows that with a combination of 0.25% tensile strain and an extrinsic electron density of 7.6x10(19)/cm(3) by n-type doping, a net material gain of ~400 cm(-1) can be obtained from the direct gap transition of Ge despite of the free carrier absorption loss. The threshold current density for lasing is estimated to be ~6kA cm(-2) for a typical edgeemitting double heterojunction structure. These results indicate that tensile strained n-type Ge is a good candidate for Si integrated lasers.
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            Effects of extrinsic and intrinsic perturbations on the electronic structure of graphene: Retaining an effective primitive cell band structure by band unfolding

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              Strain-induced band gap shrinkage in Ge grown on Si substrate

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                Author and article information

                Journal
                2017-06-13
                Article
                1706.04050
                fae9721f-4f83-41bc-ba40-e1bceffa2f72

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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                Custom metadata
                7 pages
                cond-mat.mtrl-sci

                Condensed matter
                Condensed matter

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