Effect of uniaxial stress on the electronic state of a platinum-dihydrogen complex in silicon and charge-state-dependent motion of hydrogen during stress-induced reorientation

We have combined isothermal deep-level transient spectroscopy (IT-DLTS) technique with the application of uniaxial compressive stress along ⟨111⟩ direction to study the effect of stress on the electronic state of a platinum-dihydrogen complex in Si and the kinetics of charge-state-dependent motion of hydrogen around the Pt atom during stress-induced reorientation. We have found that the application of stress splits the IT-DLTS peak into two components and the electronic energy of the short-time component increases linearly with ⟨111⟩ compressive stress as 35±4meV/GPa, indicating antibonding character. We have also studied the reorientation kinetics of the complex under the applied stress, and have found that the defect aligned at 78-88 K in the configuration with the smallest activation energy of the level only when the level was not occupied by an electron. This indicates a clear charge-state effect on the local motion of hydrogen around the Pt atom, that is, hydrogen is mobile only in the singly negative charge state of the complex. We have estimated an activation energy 0.27 eV for the hydrogen motion around the Pt atom under a stress of 0.6 GPa. We have examined three structural models, among which a model where the two hydrogen atoms are directly bonded to the platinum atom may be the most plausible candidate. In this structure, defect reorientation needs no bond switching but only the rotation of the whole Pt−H₂ entity. A possible mechanism of the charge-state-dependent reorientation observed may be that if the electronic state with antibonding character is occupied by an electron, the two hydrogen atoms may be displaced outward, probably retarding their motion for the reorientation.