M.G. Ganchenkova 1, V.A. Borodin 2, R. Nieminen 1 1 COMP/Laboratory of Physics, Helsinki University of Technology, Espoo, Finland 2 RRC Kurchatov Institute, Moscow, Russia Annealing of vacancy complexes in P-doped silicon COSIRES th International Conference on Computer Simulation of Radiation Effects in Solids June 2004, Helsinki, Finland

PV and V 2 : Experimental data P.Pellegrino et al., Phys.Rev.B, 64 (2001), The defects are annealed out PV V2V2 150  C 250  C Recombination with highly mobile interstitial type defect NONO PV – NO V 2 - NO Possible reasons: Thermal dissociation YES ?NO ? PV – YES ? V 2 – NO ? Long-range diffusion to sinks NO ?YES ? PV – NO ? V 2 – YES ? DLTS spectra of n-type Si samples after isochronal annealing (30min) between 150 and 300 DLTS spectra of n-type Si samples after isochronal annealing (30min) between 150 and 300 C June 2004, Helsinki, Finland

Schematic representation of E-center Ps acts as a trap for vacancies … Formation and binding energies for PV complex a. C.S.Nichols, C.G.Van de Walle and S.T.Pantelides, Phys.Rev.B 40, 8 (1989) 5484 b. X.Y.Liu, W.Windle, K.M. Beardmore and M.P.Masqueller, Appl.Phys.Lett 82, 12 (2003), 1839 c. R.Virkunnen and R.M.Nieminen, Comp.Mat.Science 1 (1993) 351 d. R.Car, P.J.Kelly, A.Oshyama, amd S.T.Pantelides, Phys.Rev.Lett. 54, 4 (1985) 360 e. O.Sugino and A.Oshyama, Phys.Rev.B 46 (1992)12335 f. P.M.Fahley, P.B.Griffin, and J.D.Plummer, Rev.Mod.Phys. 61 (1989) 1049 P-V complex June 2004, Helsinki, Finland

Binding energy vs. constituent separation : PV PV 0, PV - binding energy decreases monotonically with increasing separation …with a big vacancy capture radius PV is a bound system for P - V separations extending to at least three intermediate chemical bonds

Thermal dissociation or … ??? Experiment : … PV centers anneal already at 150  C … Possible reason: thermal dissociation June 2004, Helsinki, Finland Dissociation of PV complex - vacancy jumps outside the "three-bond layer" Dissociation of PV complex - multistage process Vacancy jumps : 1 NN + 2 NN 3 NN + 4 NN +… 5 NN + …

Thermal dissociation or … ??? The vacancy return jump is more than 10 times more probable than the jump in the outward direction. at 150 o C : favorable conditions for P atom mobility … annealing on sinks ??? Activation energy sequence for PV complex dissociation

Migration energies for PV complex possible diffusion jumps L.C.Kimerling: ring mechanism is responsible for annealing of PV centers at 150  C Limiting reaction of the ring mechanism – direct exchange jump a. C.S.Nichols, C.G.Van de Walle and S.T.Pantelides, Phys.Rev.B 40, 8 (1989) 5484 b. X.Y.Liu, W.Windle, K.M. Beardmore and M.P.Masqueller, Appl.Phys.Lett 82, 12 (2003), 1839 … annealing on sinks ??? June 2004, Helsinki, Finland

Thermal dissociation or … annealing on sinks ??? June 2004, Helsinki, Finland dissociation times are quite small as compared to typical experiment durations : 30 min ! Main reason – Thermal dissociation P atom displacement is rather small, except as a part of PV 2-

The relative decrease of PV complex concentration as a function of time and annealing temperature PV + PV 0 PV - PV 2-

The relative decrease of PV complex concentration as a function of time and annealing temperature PV 2- up to 100 sPV 2- up to 1000 s June 2004, Helsinki, Finland

2 3, 216 SCГ, 216 SCExperiment (0/+) d (-/0) ~0.55 f 0.78 e (2-/-) d E f (V 2 0 ) , 216 SCГ, 216 SCExperiment (+/2+ ) a 0.13 b (0/+) a 0.05 b (-/0) a - (2-/-) a - V 2 + V 2 0 V 2 - V 2 2- V + V 0 V - V 2- V 2+ Some words about mono- and divacancy in Si M.J.Puska et al. Phys. Rev. B 58 (1998) 1318; b) G. D. Watkins, in Deep Centers in Semiconductors, edited by S.T. Pantelides (Gordon and Breach, New York, 1986 ), p.147; c)M.Pesola et al. Phys.Rev. 58 (1998) 1106 ; d)G. D. Watkins, J. W. Corbett, Phys. Rev. 138 (1965) A543; f) P.Hauttojärvi et al., Defect Diffus.Forum (1998) 97; e) E.V. Monakhov, A.Yu. Kuznetsov and B.G. Svensson, Phys. Rev. B 63 (2001)

June 2004, Helsinki, Finland Binding energy vs. constituent separation : V 2 Two vacancies are strongly bound in the first NN configuration the second NN configuration is unstable The trend of binding energy change with increase of coordination sphere number that defines the mutual arrangement of vacancies in V 2 complex

… vacancy jumps directly to the third or fifth NN position much higher stability of a divacancy as compared to PV June 2004, Helsinki, Finland

The relative decrease of V 2 complex concentration as a function of time and annealing temperature V2+V2+ V20V20 V2-V2- V 2 2-

Conclusions 1. Both PV complex and a divacancy are strongly bound complexes in silicon, but their kinetic behaviour is completely different. 2. Experimentally observed disappearance of PV signal at temperatures ≈ 150 o C can be explained in terms of thermal dissociation of PV complex, but only provided this complex is in the doubly negatively charged state. 3. The divacancy in all investigated charge states is found to be very stable against thermal dissociation at experimentally reported temperatures. 4. Specific features of vacancy interaction at small separations completely exclude any reasonable possibility for divacancy migration in the bound state. June 2004, Helsinki, Finland