Preliminary measurements of charge collection and DLTS analysis of p + /n junction SiC detectors and simulations of Schottky diodes F.Moscatelli, A.Scorzoni, A.Poggi, R.Nipoti DIEI and INFN Perugia and CNR-IMM Bologna (Italy) D.Menichelli, M.Scaringella, S.Sciortino, M.Bruzzi INFN Firenze (Italy) 1
The research team University of Perugia (Italy) Device design and simulation Electrical measurements (IV, CV, contact resistance) INFN-Italy (SiCPOS project) CCE and DLTS measurements Partner (SiC technology) CNR-IMM Bologna (Italy) Collaborations Cegely Lyon (France) 2
Motivations Realization and characterization of a particle detector based on SiC Use of a planar technology (no Mesa) ion implanted p + /n junctions 3
Outline Fine tuning of the simulator with Schottky diodes p + /n SiC junctions Highlights on p + /n SiC process Available diodes CCE experimental results Defects and impurities study by DLTS and TSC. Conclusions 4
Simulation Results presented during last RD50 Workshop: Collected charge was overestimated due to negligible recombination in the n + substrate 5
Model parameters Electron mobility (cm 2 /Vs) 380 Hole mobility (cm 2 /Vs) 70 Relative dielectric constant 9.66 Intrinsic concentration n i @300K (cm 3 ) 1.6 10 6 Saturation velocity (cm/s) 2 10 7 Electron lifetime (ns) 100 Hole lifetime (ns) 20 Diffusion length 2µm @300K 6
New calibration of the model Simulation tool: DESSIS ISE-TCAD Heavy Ion Ionizing track Parameter w t was modified l max w l 7
New calibration of the model (2) epi Hole density 1.9 10 14 cm -3 1.3 10 14 cm -3 W t = 0.05 µm W t = 0.07 µm 8
Simulation of CC of Schottky diodes Schottky contact: qφ B =1.6 ev 50 µm nepi5 10 13 cm -3 n + substrate 38 µm L (µm) Collection length ( 90 Sr source, β particles ) 40 35 30 25 20 no. coll. charges L = 55 pairs/ µ m simulations measurements * 15 0 20 40 60 80 100 Voltage [V] With default w t : no saturation Ohmic contact * Measurements from: S. Sciortino et al., SiC detectors for α and β spectroscopy in a wide temperature range 3rd Italian Workshop, March 28, 2003 Chivasso (TO). 9
SiC Process: p + /n Al (350 nm) / Ti (80 nm) deposition n 4H SiC Epi (40 µm) N doping: N D = 1.1 10 15 cm n -3 + From CREE Annealing 1000 C in vacuum 2 min Not suitable for detectors! p + p - Ion implantation Al + @ 300 C Annealing 1650 C 30 min p + doping (0.4 µm) = 4 10 19 cm -3 Optional p - extensions 10
Diodes (INSA-Cegely design) 3 big diodes (1000 µm) 8 medium diodes (400 µm) 6 small diodes (300 µm) 1 big diode (1000 µm) 6 medium diodes (400 µm) 10 small diodes (300 µm) 11
Number of collected charges CCE experimental results Measurements on p + /n diodes ( big ): epi 1.1 10 15 cm -3 40 µm, Max. applied voltage: 900V (30 µm depleted). V dep (from theory) = 1600V 90 Sr source, β particles (energy = 2.2 MeV), generation of 55 pairs/µm 1600 1200 800 p+/n 200 400 600 800 Reverse voltage [V] no. coll. charge L = 55 pairs/ µ m L 2 ε s ( ψ B0 + V qn 100% collection efficiency in the 30 µm deep depleted region using estimated lengths of depleted region (assumption: epi doping N D is uniform CV measurements only in some microns) D R 12
Thermal Spectroscopy Techniques C1-C2 13
C-DLTS? H1 Hole trap 1 (Shallow B?) E=0.3 ev σ~1x10-15 cm 2 N ~ 5-10x10 13 cm -3 Nitrogen E=0.1 ev σ~5x10-14 cm 2 N=1.1x10 15 cm -3 N 20 40 60 80 100 120 Kimoto et al., Appl. Phys. Lett. 67 (1995) 2833. Zhang J., J. Appl. Phys. 93 (2003) 4708. 14
capacitance [pf] 0.1 0.05 0-0.05-0.1-0.15-0.2-0.25-0.3 t 1 =5 ms t 2 =45 ms V rev =10 V 15 20 25 30 35 Temperature [K]...Shallower than N This feature is likely to be due to a superposition of a hole and of an electron trap. 15
I-DLTS confirms C-DLTS results idlts signal [a.u.] 0.12 0.08 0.04 t 1 =1 ms t 2 =9 ms V rev =10 V N Shallow B? 0 0 50 100 150 200 250 300 350 Temperature [K] 16
HIGH Temperature TSC Current (µa) 1.1 0.7 0.3 E =1.7-1.8 ev σ ~10-15 cm 2 N ~10 13 cm -3 fit meas. S.A. Reshanov et al. Presented at ICSCRM03 0 400 450 500 550 600 650 Temperature (K) 17
Conclusions Parameters of the simulation model adjusted to obtain good agreement with CC measurements on Schottky diodes First CCE experimental results: 100% collection efficiency in 30 µm using estimated lengths of depleted region DLTS, TSC: in addition to N peak, dominant deep levels near 0.3 ev and 1.8 ev. Concentrations <[N]/10. 18
Future developments Verification of uniformity of epi doping with high voltage CV measurements Radiation hardness will be verified New p + /n SiC detectors with p - JTE will be realized on a wafer from IKZ (N epi = 2 10 14 cm 3 ) taking into account the simulation results 19
Appendix 20
p - I-V measurements on p + /n diodes Ti-Al p + n n + Ni J (A/cm 2 ) 1x10 3 1x10 1 1x10-1 1x10-3 1x10-5 1x10-7 Forward I-V 1x10-9 0 1 2 3 4 5 V (V) 75% of diodes have good I-V curves V BD is about 4 kv Theoretical limit for this device: 5 kv n [1.5,1.6] n = 2 A few diodes now available for testing as particle detectors J (A/cm 2 ) 1x10 0 1x10-1 1x10-2 1x10-3 1x10-4 1x10-5 1x10-6 V BD Reverse I-V 1x10-7 -4000-3000 -2000-1000 0 V (V) Diode diameter: [0.3,1] mm Power diode layout design by INSA-CEGELY, Lyon France 21