Abstract. The astrophysical S(E) factor of14 N(p, γ) 15 O has been measured for effective center-of-mass energies between E ef f = 119 and 367 keV at the LUNA facility using TiN solid targets and Ge detectors. The data are in good agreement with previous and recent work at overlapping energies. R-matrix analysis reveals that due to the complex level structure of 15 O the extrapolated S(0) value is model dependent and calls for additional experimental efforts to reduce the present uncertainty in S(0) to a level of a few percent as required by astrophysical calculations. .KvX -and γ ray spectroscopy -97.10.CvStellar structure and evolution PACS

We report experiments on the impact of 2.5 MeV proton irradiation on self-diffusion and dopant diffusion in germanium (Ge). Self-diffusion under irradiation reveals an unusual depth independent broadening of the Ge isotope multilayer structure. This behavior and the observed enhanced diffusion of B and retarded diffusion of P demonstrates that an interstitial-mediated diffusion process dominates in Ge under irradiation. This fundamental finding opens up unique ways to suppress vacancy-mediated diffusion in Ge and to solve the donor deactivation problem that hinders the fabrication of Ge-based nanoelectronic devices. DOI: 10.1103/PhysRevLett.103.255501 PACS numbers: 61.80.Jh, 61.72.jj, 61.82.Fk, 81.40.Wx Over the past few years the elemental semiconductor Ge has been the subject of many experimental [1-13] and theoretical investigations [14][15][16][17][18][19][20][21][22][23][24][25] to elucidate the electronic and diffusion properties of point defects as well as their interaction. Understanding these properties helps to develop strategies for efficient defect engineering that are crucial for the fabrication of the next generation of nanoelectronic devices. Utilizing Ge instead of silicon (Si) for complementary metal oxide semiconductors (CMOS) technology one can take advantage of the higher electron and hole mobilities in Ge compared to Si [26]. Whereas the p-channel Ge-MOSFET (metal oxide semiconductor fieldeffect transistor) made of heavily B doped source and drain regions was already demonstrated [27], the n-channel MOSFET remains a challenge due to the enhanced diffusion of n-type dopants such as P, As, and Sb under extrinsic doping conditions and the deactivation of the donors for concentrations exceeding 10 19 cm À3 [7,9,27]. The enhanced diffusion is a consequence of the singly negatively charged donor-vacancy ðAVÞ À pair that mediates donor diffusion in Ge according to the reaction [7,9] where A þ s and V 2À are the singly positively charged substitutional donor with A 2 fP; As; Sbg and the doubly negatively charged vacancy (V 2À ), respectively. The deactivation is related to the formation of inactive donorvacancy clusters whose formation is favored due to Coulomb attraction between A þ s and ðAVÞ À via the reaction [9]The formation of A 2 V and even bigger clusters A n V m is consistent with the predictions of density functional theory calculations [23]. Reactions (1) and (2) indicate that the donor-vacancy pair mediates both the diffusion and deactivation of n-type dopants in Ge. Effective defect engineering that aims to suppress the enhanced diffusion and deactivation of donors in Ge should reduce the concentration of the AV pairs. In this letter we demonstrate that defect engineering with Ge interstitials makes it possible to effectively suppress the enhanced diffusion of donor atoms.

We report experiments on proton irradiation enhanced self-and boron (B) diffusion in germanium (Ge) for temperatures between 515 • C and 720 • C. Modeling of the experimental diffusion profiles measured by means of secondary ion mass spectrometry is achieved on the basis of the Frenkel pair reaction and the interstitialcy and dissociative diffusion mechanisms. The numerical simulations ascertain concentrations of Ge interstitials and B-interstitial pairs that deviate by several orders of magnitude from their thermal equilibrium values. The dominance of self-interstitial related defects under irradiation leads to an enhanced self-and B diffusion in Ge. Analysis of the experimental profiles yields data for the diffusion of self-interstitials (I) and the thermal equilibrium concentration of BI pairs in Ge. The temperature dependence of these quantities provides the migration enthalpy of I and formation enthalpy of BI that are compared with recent results of atomistic calculations. The behavior of self-and B diffusion in Ge under concurrent annealing and irradiation is strongly affected by the property of the Ge surface to hinder the annihilation of self-interstitials. The limited annihilation efficiency of the Ge surface can be caused by donor-type surface states favored under vacuum annealing but the physical origin remains unsolved.

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