ESR of paramagnetic point defects in pure, 17 O and 13 C doped SiFZ irradiated with 3.5 and 27MeV electrons. Correlation with TSC data. Sergiu V. NISTOR and Alexandra C. JOITA Roxana RADU and Ioana PINTILIE National Institute of Materials Physics Magurele, Romania Presented at the 28 th RD50 workshop, Torino, June 6-8, 2016

ContentContent I. Objective of investigation. II. Electron Spin Resonance (ESR) of irradiation paramagnetic point defects (IPPDs) in pure and doped SiFZ. A. ESR method and equipment. IPPDs identification methodology. B. The investigated SiFZ samples. III. Experimental ESR results. IPPDs in 3.5 MeV and 27MeV e - - irradiated STFZ (undoped), SiFZ-13C and SiFZ-17O samples. IV. Analysis of ESR data. V. Comparison of ESR and TSC production and annealing data. VI. Conclusions.

I. Objective of investigation Main objective: To study in crystalline Si used in tracking detectors at LHC the formation, stability and structure of the IPPDs, expected to influence their radiation induced performance degradation (according to previous TSC studies). How ? Determining by ESR the presence and properties (structure + production and thermal stability) of IPPDs in pure, 17O and 13C doped SiFZ under 3.5 and 27 MeV e - - irradiation. Correlating the ESR and TSC observed production properties to determine the structure of the IPPDs observed by TSC.

A. The method. Principle of ESR. II. ESR of IPPDs in pure and doped SiFZ. A. The method. Principle of ESR.  ESR is the best method-technique to determine (I)PPDs structure in semiconductors (Si, diam., GaAs, ZnS, BN, …)  ESR = Zeeman (B  0) spectroscopy of defects with S  0 (S = 1/2, 1, …) electron states.  The condition of resonance:  E = h   9.5 – 34 GHz, ….250 GHz B  0

II. ESR of IPPDs in pure and doped SiFZ. A. The method. Spectra description with the spin Hamiltonian  L  0 !!  SO + CF interactions H SH =  B S·g·B + S·A·I Particular local symmetry cases (S =1/2, 1; I  0) : Rhombic: H SH =  B [g x B x S x + g y B y S y + g z B z S z ] + A x S x I x + A y S y I y + A z S z I z Axial: H SH = g   B (B x S x + H y S y ) + g   B B z S z + A  (S x I x + S y I y ) + A  S z I z Cubic: H SH = g  B (B x S x + B y S y + B z S z )+ A(S x I x + S y I y + S z I z ) + the specific set of local axes

II. ESR of IPPDs in pure and doped SiFZ. A. Method. The ESR spectra characteristics.  ESR spectra observation  presence and concentration of paramagnetic defects  Sensitive: 2 x spins/Gauss (~ 1 ppb)  High resolution ( ~  W freq.)  high separation of the overlapping spectra from different centers (No deconvolution req.). I vs.  W power and I vs. T meas to identify the spectra lines of the different centers.  Spectra anisotropy  reflects local structure !  Hyperfine structure  atomic structure (ENDOR). The 29 Si (I=1/2) isotope of 4.685% nat. abundance, requires intense spectra (s/n > 50). 17 O (I=5/2; 0.038%) and 13 C(I=1/2; 1.07%) requires doping with enriched isotopes.  Spin Hamiltonian (SH) parameters  Each center is fully characterized by its SH parameters and local symmetry !  The resulting info.  Defect atomic structure = Structural model.

II. ESR of IPPDs in pure and doped SiFZ. A. The equipment. The ESR spectrometer. Q(34 GHz)-band ESR spectrometer ELEXSYS 500Q with optical cryostat and probe head for variable 300 to 3.8 K measurements and goniometer for sample rotation.  - Sensitivity: 2 x spins/Gauss - Magnetic field: 0.01 T < B < 1.8 T. - Stability/accuracy: better that Maximum sample size: 2 mm diam. x 5 mm length

II. ESR of IPPDs in pure and doped SiFZ. II. ESR of IPPDs in pure and doped SiFZ. A. The equipment. In-situ illumination - Frontal window (UV/VIS lamps, lasers, LEDs) - not efficient  - From above, with an optical fiber vacuum tight inserted through the sample holder using laser diodes (637nm P < 80mW; 1060nm P< 60mW)

II. ESR of IPPDs in pure and doped SiFZ.. II. ESR of IPPDs in pure and doped SiFZ. A. Method. The IPPDs identification methodology. Preparing the samples for Q-band ESR measurements. Recording the EPR spectra in the as-irradiated and annealed samples, at 296 K > T >10 K, with B in (110), for low / high  W powers, without/with bandgap (1.05  m) illumination. Identify the spectra of different IPPDs from differences in the specific I vs. T meas, I vs. P(  W) and the angular dependence. Local symmetry and SH parameters with ESR lines simulation- fitting software. Compare with published data  Struct. of IPPDs. Correlate the ESR and TSC data from IPPDs production properties vs. E irrad, dopant type and T ann = 150, 200, 250, C

II. ESR of IPPDs in pure and doped SiFZ. II. ESR of IPPDs in pure and doped SiFZ. A. Method. Identification of the IPPDs structure. Several hundredths of IPPDs in Si were reported in the literature. Their characteristic (SH) parameters [Landolt & Bornstein, vol. III/22b- 41A.2a] were used it to identify the known IPPSs observed in our ESR spectra. Accurate determination of defect structure requests, besides the symmetry and SH parameter values, mapping the hf interactions with nuclei of the involved atoms (ESR/ENDOR). Not too many cases ! The absence of hf data explains the presence of reported IPPDs in Si with proposed different structures/ but very close SH parameters.

II. ESR of IPPDs in pure and doped SiFZ. B. The investigated SiFZ samples - ESR samples of 0.3x0.18x4 mm 3 = 2.16 mm 3, long axis||  B in (110) were cut from 0.3 mm thick (100) Si-FZ platelets (Wacker, n-type, 5 kOhm.cm). - Estimated IPPDs sensitivity threshold in the samples: ~ 5 E12 cm -3 - e - - irrad. with 3.5 MeV (fluence 1E17cm -2 ) / 27MeV (fluence 2E16 cm -2 ). - Impurity concentration in the ESR samples: Standard SiFZ (STFZ) : 16 O ~1E16 cm -3 ; 12 C ~ 1E15 cm -3 ; P ~1E12 cm -3 SiFZ-17O ( 17 O 70%doped by diffusion, c(O) =1.2E17cm -3 – from SIMS) SiFZ-13C (3MeV implanted 13 C; dose 5E13 cm -2 ; non-uniform concentr. )

III. Experimental results. ESR in 3.5MeV e - - irradiated STFZ samples CenterSg 1 [1-10]+  g 2 [110] g 3 [001]+  ºº D (GHz) kAnnealing temp. (K) Fe + (I) (a) 3/2g ┴ = 4.175± ± ±0.5-> 700 Fe + (II) (a) 1/2g ┴ = 5.211± ± < 250 Fe + (IIa) (b) 1/25.144± ± ± ± < 250 Fe + (III) (c) 1/25.823± ± ± ± > 300 Fe + (IIIa) (c) 1/25.635± ± ± ± < 290 CenterSg 1 [1-10]+  g 2 [110] g 3 [001]+  ºº D (GHz) kAnnealing temp. (K) Fe + (I) (a) 3/2g ┴ = 4.175± ± ±0.5-> 700 Fe + (II) (a) 1/2g ┴ = 5.211± ± < 250 Fe + (IIa) (b) 1/25.144± ± ± ± < 250 Fe + (III) (c) 1/25.823± ± ± ± > 300 Fe + (IIIa) (c) 1/25.635± ± ± ± < 290 CenterSg 1 [1-10]+  g 2 [110] g 3 [001]+  ºº D (GHz) kAnnealing temp. (K) Fe + (I) (a) 3/2g ┴ = 4.175± ± ±0.5-> 700 Fe + (II) (a) 1/2g ┴ = 5.211± ± < 250 Fe + (IIa) (b) 1/25.144± ± ± ± < 250 Fe + (III) (c) 1/25.823± ± ± ± > 300 Fe + (IIIa) (c) 1/25.635± ± ± ± < G7[V2] and A38[V3] stable up to C. - PK1[Vn] stable up to C, at least. - H9 [V2]+ observed at T < 120 K. - No [V-O] - or [V2-O] IPPDs were found. Photoinduced ESR spectra in irradiated and annealed samples.

III. Experimental results. ESR of 3.5 MeV and 27MeV e - irradiated SiFZ 13C IPPDs production under 3.5 MeV and 27 MeV e- irradiation. -G7 [V2] - – not affected. -PK1 [Vn] – not seen at 27 MeV e - -irradiation. - A4* [V3] - replaced by A3 [V4] - Photoinduced ESR spectra in irradiated and annealed samples.

III. Experimental results. ESR of 3.5 MeV and 27MeV e - -irradiated SiFZ 17O Photoinduced ESR spectra at 120K and 50K in irradiated samples. E = 3.5 MeV; T meas = 120K and 50K. E = 27 MeV; T meas = 120K and 50K.

III. ESR spectra from unidentified IPPDs in 27MeV e - - irradiated SiFZ-17O. New, unknown paramagnetic centers observed at higher annealing temperatures. T ann =300 o C; T meas = 100K Absorption mode. T ann =250 o C; T meas = 50K Dispersive mode.

IV. Analysis of ESR data. Production of IPPDs in STFZ and SiFZ-13C - Similar IPPDs production properties of the STFZ and SiFZ-13C under 3.5 MeV irradiation. - Under 27 MeV irradiation A4[V3] transforms into A3[V4]. PK1 [Vn] is gone?

IV. Analysis of ESR data. Production of IPPDs in STFZ and SiFZ-17O - V type IPPDs observed in STFZ of lower oxygen content. - V-O type IPPDs observed in SiFZ-17O due to higher oxygen content. - Differences in the nature of IPPDs observed in SiFZ-17O at T ann > 200C at 3.5 MeV and 27MeV. Comparing with Lee and Corbett [PRB 13, 2653, 1976], one finds: 1. Expected absence of A14[V2-O] in STFZ, and: 2. Unexpected absence of A14[V2-O]  P  [V3-O]  P2[V2-O2] … sequence in SiFZ-17O Conclussion: The V aggregation sequence is very sensitive to the O conc. levels !

V. Comparison of ESR and TSC production data. The TSC annealing data TSC on samples e - -irrad. with < 1E15 cm -2 fluence show linear conc. vs. fluence increase. As expected, the most intense ones: [V2] - (stable at T< 200C) and [V-O] - (stable T< 250C) centers are also found by ESR. E30K ~ G15(V-O-C1) / [C i -O i ] ? – stable for 3.5 MeV; decays at T> 200K for 27 MeV. Lower concentrations ? To detect other TSC centers one needs e - fluences of 1E18 cm -2 (3.5MeV) and 1E17cm -2 (27MeV) !

V. Conclusions  Several types of IPPDs were observed at T< 150 K, for low and high uW powers, mainly in samples subjected to across the gap in-situ illumination.  The nature and thermal stability of IPPDs varied with the oxygen concentration and irradiation energy. Lower O conc. (STFZ, SiFZ-13C) favored V aggregation; higher O conc. (SiFZ-17O) favored V-O aggregation. Although the O conc. in SiFZ-13C and STFZ is similar, the IPPDs are thermally more stabile in the SiFZ-13C samples ( C effect ?). The V aggregation is higher in the 27 MeV e - - irradiated samples. Actual models of PK1, A16[V3-O3] and G16[V-O-C2] are questionable. In comparing the ESR and TSC data one needs ESR experiments on samples irradiated with e- fluences of 1E18 cm -2 (3.5MeV) and 1E17 cm -2 (27MeV), as well as with 1E16 cm -2 protons !

Thank you for your attention.