TY - JOUR
T1 - Hydrogen-induced crystallization of amorphous Si thin films. II. Mechanisms and energetics of hydrogen insertion into Si-Si bonds
AU - Valipa, Mayur S.
AU - Sriraman, Saravanapriyan
AU - Aydil, Eray S.
AU - Maroudas, Dimitrios
N1 - Funding Information:
This work was supported by the NSF/DOE Partnership for Basic Plasma Science and Engineering (Award Nos. ECS-0078711, ECS-0317345, and ECS-0317459), an NSF/ITR grant (Award No. CTS-0205584), and Camille Dreyfus Teacher-Scholar Awards to two of the authors (E.S.A. and D.M.). Fruitful discussions with S. Agarwal are gratefully acknowledged.
PY - 2006
Y1 - 2006
N2 - We report a detailed study of the mechanisms and energetics of hydrogen (H) insertion into strained Si-Si bonds during H-induced crystallization of hydrogenated amorphous Si (a-Si:H) thin films. Our analysis is based on molecular-dynamics (MD) simulations of exposure of a-Si:H films to H atoms from a H 2 plasma through repeated impingement of H atoms. Hydrogen atoms insert into Si-Si bonds as they diffuse through the a-Si:H film. Detailed analyses of the evolution of Si-Si and Si-H bond lengths from the MD trajectories show that diffusing H atoms bond to one of the Si atoms of the strained Si-Si bond prior to insertion; upon insertion, a bridging configuration is formed with the H atom bonded to both Si atoms, which remain bonded to each other. After the H atom leaves the bridging configuration, the Si-Si bond is either further strained, or broken, or relaxed, restoring the Si-Si bond length closer to the equilibrium bond length in crystalline Si. In some cases, during its diffusion in the a-Si:H film, the H atom occupies a bond-center position between two Si atoms that are not bonded to each other; after the H diffuses away from this bond-center position, a Si-Si bond is formed between these previously nonbonded Si atoms. The activation energy barrier for the H insertion reaction depends linearly on both the initial strain in the corresponding Si-Si bond and a strain factor that takes into account the additional stretching of the Si-Si bond in the transition-state configuration. The role of the H insertion reactions in the structural relaxation of the a-Si:H network that results in disorder-to-order transitions is discussed.
AB - We report a detailed study of the mechanisms and energetics of hydrogen (H) insertion into strained Si-Si bonds during H-induced crystallization of hydrogenated amorphous Si (a-Si:H) thin films. Our analysis is based on molecular-dynamics (MD) simulations of exposure of a-Si:H films to H atoms from a H 2 plasma through repeated impingement of H atoms. Hydrogen atoms insert into Si-Si bonds as they diffuse through the a-Si:H film. Detailed analyses of the evolution of Si-Si and Si-H bond lengths from the MD trajectories show that diffusing H atoms bond to one of the Si atoms of the strained Si-Si bond prior to insertion; upon insertion, a bridging configuration is formed with the H atom bonded to both Si atoms, which remain bonded to each other. After the H atom leaves the bridging configuration, the Si-Si bond is either further strained, or broken, or relaxed, restoring the Si-Si bond length closer to the equilibrium bond length in crystalline Si. In some cases, during its diffusion in the a-Si:H film, the H atom occupies a bond-center position between two Si atoms that are not bonded to each other; after the H diffuses away from this bond-center position, a Si-Si bond is formed between these previously nonbonded Si atoms. The activation energy barrier for the H insertion reaction depends linearly on both the initial strain in the corresponding Si-Si bond and a strain factor that takes into account the additional stretching of the Si-Si bond in the transition-state configuration. The role of the H insertion reactions in the structural relaxation of the a-Si:H network that results in disorder-to-order transitions is discussed.
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U2 - 10.1063/1.2229429
DO - 10.1063/1.2229429
M3 - Article
AN - SCOPUS:33748910275
SN - 0021-8979
VL - 100
JO - Journal of Applied Physics
JF - Journal of Applied Physics
IS - 5
M1 - 053515
ER -