Hydrogen interaction kinetics of Ge dangling bonds at the Si0.25Ge0.75/SiO2 interface

The hydrogen interaction kinetics of the GePb1 defect, previously identified by electron spin resonance (ESR) as an interfacial Ge dangling bond (DB) defect occurring in densities similar to 7 x 10(12) cm(-2) at the SiGe/SiO2 interfaces of condensation grown (100) Si/a-SiO2/Ge0.75Si0.25/a-SiO2 structures, has been studied as function of temperature. This has been carried out, both in the isothermal and isochronal mode, through defect monitoring by capacitance-voltage measurements in conjunction with ESR probing, where it has previously been demonstrated the defects to operate as negative charge traps. The work entails a full interaction cycle study, comprised of analysis of both defect passivation (pictured as GePb1-H formation) in molecular hydrogen (similar to 1 atm) and reactivation (GePb1-H dissociation) in vacuum. It is found that both processes can be suitably described separately by the generalized simple thermal (GST) model, embodying a first order interaction kinetics description based on the basic chemical reactions GePb1 + H-2 -> GePb1H + H and GePb1H -> GePb1 + H, which are found to be characterized by the average activation energies E-f = 1.44 +/- 0.04 eV and E-d = 2.23 +/- 0.04 eV, and attendant, assumedly Gaussian, spreads sigma E-f = 0.20 +/- 0.02 eV and sigma E-d = 0.15 +/- 0.02 eV, respectively. The substantial spreads refer to enhanced interfacial disorder. Combination of the separately inferred kinetic parameters for passivation and dissociation results in the unified realistic GST description that incorporates the simultaneous competing action of passivation and dissociation, and which is found to excellently account for the full cycle data. For process times t(a) similar to 35 min, it is found that even for the optimum treatment temperature similar to 380 degrees C, only similar to 60% of the GePb1 system can be electrically silenced, still far remote from device grade level. This ineffectiveness is concluded, for the major part, to be a direct consequence of the excessive spreads in the activation energies, similar to 2-3 times larger than for the Si DB P-b defects at the standard thermal (111) Si/SiO2 interface which may be easily passivated to device grade levels, strengthened by the reduced difference between the average Ef and Ed values. Exploring the guidelines of the GST model indicates that passivation can be improved by decreasing T-an and attendant enlarging of t(a), however, at best still leaving similar to 2% defects unpassivated even for unrealistically extended anneal times. The average dissociation energy E-d similar to 2.23 eV, concluded as representing the GePb1-H bond strength, is found to be smaller than the SiPb-H one, characterized by E-d similar to 2.83 eV. An energy deficiency is encountered regarding the energy sum rule inherent to the GST-model, the origin of which is substantiated to lie with a more complex nature of the forward passivation process than basically depicted in the GST model. The results are discussed within the context of theoretical considerations on the passivation of interfacial Ge DBs by hydrogen.status: publishe