RD50 Katharina Kaska1 Trento Workshop : Materials and basic measurement problems Katharina Kaska

RD50 Katharina Kaska2 Overview Epitaxial Silicon MCz “High fluence puzzle” Depletion voltage comparison

RD50 Katharina Kaska3 EPI I Why Epi? Thinner device => Smaller current and V fd (but larger capacitance) Less chance for trapping (but less e-h pairs) Material From 25 to 150 μm EPI layers on low resisitvity Cz substrate (O 2 out- diffusion) Overview talk on Epi given by Gregor Kramberger

RD50 Katharina Kaska4 The irradiation with 24 GeV p (200 MeV p, 26 MeV p) introduces positive space charge. SIMS profiling: [O](25µm) > [O](50µm) ; [O](75µm)> [O](100µm)> [O](150µm) Stable Damage: N eff (25µm) > N eff (50µm); g eff = cm -1 > g eff = cm -1 N eff (75µm) > N eff (100µm) > N eff (150µm) g eff = cm -1 > g eff = cm -1 > g eff = cm -1 TSC Defect Spectroscopy: [BD](25µm) > [BD](50µm) >[BD](75µm) G. Lindström et al., NIM A556 (2006) 451. Generation of shallow donors BD (Ec-0.23 eV) strongly related to [O] Possibly caused by O 2i dimers, outdiffused from Cz with larger diffusion constant dimers monitored by IO2 complex t 0 ~8 o C Influence of thickness Additional oxydation g eff [epi-DO]>g eff [epi-ST] The oxygenation increases introduction rate of positive space charge by some 30% at all thicknesses CiS - process J. Lange et al., 13 th RD50 Workshop, CERN, Space charger vs. fluence Gregor Kramberger

RD50 Katharina Kaska5 Protons vs. neutrons V. Khomenkov et al., presented at IEEE-NSS, 2008 Lower damage rates from neutron than proton irradiation type / radiation  cm -1  cm -1 n-Epi / protons p-Epi / protons n-Epi / neutrons p-Epi / neutrons But quite different results for the rates: Gregor Kramberger

RD50 Katharina Kaska6 CCE for different EPI samples The thickness becomes less important as the fluence grows – as expected. The CCE at high fluences is significantly larger than predicted! p-type epi shows better performance after neutron irradiation than the rest G. Kramberger et al., NIM 552 (2005). K. Kaska et al., presented at 11 th RD50 Workshop,2007. V. Khomenkov et al., presented at IEEE-NSS, 2008 Gregor Kramberger

RD50 Katharina Kaska7 MCz I Why Cz now and not before? No demand for high resistivity Cz-Si -> No availability Price for custom specified ingot 25,000 € - 40,000 € (too much for university lab) Now RF-IC industry shows interest on high resistivity Cz-Si (=lower substrate losses of RF-signal)

RD50 Katharina Kaska8 MCz II “p-like” annealing behaviour The most irradiated diode shows an n-like annealing behaviour p-type MCz Nicola Pacifico

RD50 Katharina Kaska9 Charge correction method The corrected charge is constant with voltage if V>V fd

RD50 Katharina Kaska10 MCz III Undepleted (340 V) Peak Ratio: 1.48 Peak ratio: 1 Trapping time from Charge Correction Method: ns Trapping time for equal peak ratio (front/back) constraint: ns Nicola Pacifico

RD50 Katharina Kaska11 High fluence puzzle I Phenomenon: CCE signal is too high and show inexplicable behavior at high fluences. Reasons? –active region (electric field) is different than expected –trapping probability decreases –mobility increases (not likely)

RD50 Katharina Kaska12 Puzzle II: strips detectors β e = 3.2· cm 2 /ns β h = 3.5· cm 2 /ns No trapping, only N eff : Black: measured, Red: simulation SIMULATION FAILS COMPLETELY! Even if trapping is off - the active region assumed by depletion is not enough to reproduce the signal! MICRON RD50 n+-p FZ detectors Gregor Kramberger

RD50 Katharina Kaska13 Puzzle III: pad detectors Trapping probabilities should be the same Electric field in most of the detector also, except close to strips Alpha TCT (25 ns integration) - 100% CCE also observed Vertical bars denote full depletion voltage. The onset of charge saturation is matches the V fd up to 4∙10 15 cm -2. At high fluences and high voltages there are indications rapid increase of charge – indication of charge multiplication? Gregor Kramberger

RD50 Katharina Kaska14 Mixed irradiation MCz-n First proton than neutron irradiation => Vd goes down MCz-p First proton than neutron irradiation => Vd goes up All as expected Gregor Kramberger

RD50 Katharina Kaska15 Annealing Always annealing at elevated temperature to increase speed, but how does it compare to RT annealing? The minimum in V fd : after ~300 days at 20 o C after ~80 min at 80 o C Compatible with acceleration of ~6500 for E a =1.3eV Similar long term annealing for neutron and proton irradiated samples irradiated to the similar fluences! Gregor Kramberger

RD50 Katharina Kaska16 Difference in depletion voltage IV < CV < CCE (β) 24 GeV/c proton irradiated IV < CCE (beta) = CV

RD50 Katharina Kaska17 5∙10 14 cm -2 1∙10 15 cm -2 1∙10 14 cm -2 V fd from C-V is determined for pad detectors ( 60 o C – end of beneficial annealing ) V fd from CV underestimates the onset of saturation in CCE by max V! after V fd the collected charge continues to increase due to shorter drift due to growth of depletion depth from electrode side the offset is smaller than with p-on-n! The correlation holds for all investigated fluences in range of full depletion voltages up to 1000V! Difference in depletion voltage Gregor Kramberger

RD50 Katharina Kaska18 Admittance Spectroscopy I CV measurements strongly dependent on frequency used Admittance Spectroscopy can reveal important properties of deep levels introduced during irradiation, which are responsible for the frequency dependence of the capacitance Hartmut Sadrozinski

RD50 Katharina Kaska19 Admittance Spectroscopy II Frequency dependent filling and emptying of traps Contributes to C Frequency correlated to emission rate I(T) dependent on emission rate Frequency to be used for CV depends on temperature Try to scale f with T doesn’t really work because 10 kHz at RT already doesn’t give the right value (difference CCE and CV curves) Hartmut Sadrozinski

RD50 Katharina Kaska20 Admittance Spectroscopy III How to figure out true capacitance? => Admittance measurements In order to contribute to the admittance, the AC signal has to correspond to the emission time for a particular trap. Equivalent circuit with G(f) and C(f) Take into account deep level traps, free carriers and transition region between space charge and neutral bulk Use C of deep traps as free parameter to fit data Extract concentration, energy, and majority capture cross section for deep levels simulate d(V) and compare to CCE Hartmut Sadrozinski

RD50 Katharina Kaska21 Admittance Spectroscopy IV Comparison of d(V) for CCE and from admitance measurements Only two samples evaluated… Hartmut Sadrozinski