Transcript Slide 1
Palladium Related Defects in Silicon Rakesh Dogra Punjab Technical University, INDIA A.P. Byrne, D.A. Brett, M.C. Ridgway Australian National University, AUSTRALIA Motivation • Fast Diffusion of Pd in Si • Introduces Deep Levels in band gap • Deep levels act as trap/recombination centres • DLTS: Pd has amphoteric behavior Acceptor in n-type Si Donor in p-type Si Large probability to form Pd-Dopant (P, As, Sb, B) pairs Pd can be gettered Motivation Local Structure of isolated Pd and Pd related defects (Pd-dopant, Pd-V, Pd-I pairs) can be studied with Nuclear Hyperfine Methods Perturbed Angular Correlation Spectroscopy Experimental Details Sample Preparation • Cz-Si (100) were implanted with Phosphorus and Boron • Doses: 5e15 to 1e20 ions cm-3 • Samples annealed at 900oC for 10s using RTA Experimental Details PAC Probe • • • • 100Rh; E = 70 MeV Recoil energy = 8 MeV Implantation Depth = 3 mm deep into Si wafers Isochronal annealing in N2 atmosphere 100Pd 92Zr(12C,4ng)100Pd EC 1+ 84 keV Zr foil 2+ 2.5mm 75 keV 12C Beam Si wafer 1100Rh T1/2=3.6d I = 2 +, t1/2 = 214ns, Q = 0.115b, A22 = 0.1 Experimental Details PAC Measurements • • Slow-Fast coincident using four conical BaF2 scintillator detectors Perturbation spectra formed from coincidence counts C (180, t ) C (90, t ) R(t ) 2 C (180, t ) 2C (90, t ) • Least squares fitted with: i R(t ) A22 G22 (t ) A22 f i G22 (t ) C i Site 1: Damaged Site 2: Unperturbed Site 2: Defect specific From coupling constant nQ, the largest component of electric field gradient, Vzz is extracted nQ eQVzz h Results 0.10 5e17 P cm -3 5e17 P cm-3 0.05 Well defined interaction frequency 4 0.00 1e18 P cm 0 -3 1e18 P cm-3 0.05 4 Fractional Population (%) 0.10 0.10 2e18 P cm -3 2e18 P cm-3 0.05 0.00 0.10 5e18 P cm -3 5e18 P cm-3 0.05 0 4 0 25 0 1E17 4 1E19 1E21 2 Phosphorus concentration (ions/cm ) 0.00 0.10 1e19 P cm 1e19 P 0.05 0 -3 cm-3 4 0.00 0 0.10 -3 1e20 P cm 1e20 P cm-3 0.05 4 0.00 0 200 400 600 Time (ns) 800 0 0.00 0.05 (Grad/s) 0.10 Relative Probe Fraction (%) R(t) Intensity (FFT) 0.00 50 75 50 25 0 0 100 200 300 400 Annealing Temperature (C) 500 Results 6.7x10 P cm -3 <100> 0.08 15 1.9x10 B cm -3 <100> P-Si 0.00 0.00 19 0.08 5.8x10 P cm -3 <100> 0.08 19 8.4x10 B cm -3 <100> 19 0.08 5.8x10 P cm -3 <110> 0.00 19 4.3x10 As cm 0.08 -3 R(t) R(t) 0.00 0.00 0.08 19 8.4x10 B cm -3 Fractional Population (%) 14 0.08 <111> 60 40 20 0 540 600 660 720 Annealing Temperature (C) Thermally unstable <100> 0.00 0.00 0.08 19 0.08 0.7x10 Sb cm -3 19 5.8x10 P cm -3 <100> <100> 0.00 0.00 0 200 400 600 800 Time (ns) 0 200 400 600 800 Time (ns) n-Si EFG Parameters p-Si ► nQ = 13.1(2) MHz ► h= 0 Symmetric EFG ► EFG orientation <111> ► nQ = 35.5(3) MHz ► h= 0 Symmetric EFG ► EFG orientation <111> Discussions Similar EFG parameters in highly doped n-Si -Same defect formation -Ruled out the formation of Pd-dopant pairs -Defect pair dissociate above TA = 500oC -Maximum probe fraction b/w TA = 200-300oC -n+-Si comprises of excess vacancies (negative) -Formation of PdSi-VSi pair, PRB 72 (2005) 193202 -Phosphorus Diffusion Gettering of Pd ! EC Pd Vacancy Ei Si V- EF for n-Si Ev=Ec-0.12(2) EV Unique interaction frequency for P dose ≥ 5e17 ions cm-3 Discussions Strong EFG in highly doped p-Si • Defect pair is observed between TA = 550-750oC • • • Around this temperature Pd diffuses interstitially Axially symmetric EFG Tentatively Pdi-BSi pair supported by theoretical calculations IT2 B IT1 IO Discussions Temperature dependence of EFGs Both pairs show T3/2 dependence 3 n Q (T ) n Q (0) 1 T 2 15.2 40 Pd-B nQ (MHz) 14.4 Pd-B (0)=36.8(2) MHz -3/2 =2e-5 K Pd-V 13.6 35 30 12.8 25 Pd-V nQ 12.0 (0)=13.5(2) MHz Pd-V -3/2 =6.1E-6 K 0 150 300 450 Temperature (K) 600 20 750 nQ (MHz) nQ Pd-B •Different charge states of the defect complexes •Effect is stronger for Pd-B pair Acknowledgements • Organizers for waiving off the registration fee • Dept of Science & Technology, India for financial support