Preliminary measurements of charge collection and DLTS analysis of p + /n junction SiC detectors and simulations of Schottky diodes

Transcription

1 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

2 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

3 Motivations Realization and characterization of a particle detector based on SiC Use of a planar technology (no Mesa) ion implanted p + /n junctions 3

4 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

5 Simulation Results presented during last RD50 Workshop: Collected charge was overestimated due to negligible recombination in the n + substrate 5

6 Model parameters Electron mobility (cm 2 /Vs) 380 Hole mobility (cm 2 /Vs) 70 Relative dielectric constant 9.66 Intrinsic concentration n (cm 3 ) Saturation velocity (cm/s) Electron lifetime (ns) 100 Hole lifetime (ns) 20 Diffusion length 6

7 New calibration of the model Simulation tool: DESSIS ISE-TCAD Heavy Ion Ionizing track Parameter w t was modified l max w l 7

8 New calibration of the model (2) epi Hole density cm cm -3 W t = 0.05 µm W t = 0.07 µm 8

9 Simulation of CC of Schottky diodes Schottky contact: qφ B =1.6 ev 50 µm nepi cm -3 n + substrate 38 µm L (µm) Collection length ( 90 Sr source, β particles ) no. coll. charges L = 55 pairs/ µ m simulations measurements * 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

10 SiC Process: p + /n Al (350 nm) / Ti (80 nm) deposition n 4H SiC Epi (40 µm) N doping: N D = 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) = cm -3 Optional p - extensions 10

11 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

12 Number of collected charges CCE experimental results Measurements on p + /n diodes ( big ): epi cm 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 p+/n 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

13 Thermal Spectroscopy Techniques C1-C2 13

14 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 Kimoto et al., Appl. Phys. Lett. 67 (1995) Zhang J., J. Appl. Phys. 93 (2003)

15 capacitance [pf] t 1 =5 ms t 2 =45 ms V rev =10 V Temperature [K]...Shallower than N This feature is likely to be due to a superposition of a hole and of an electron trap. 15

16 I-DLTS confirms C-DLTS results idlts signal [a.u.] t 1 =1 ms t 2 =9 ms V rev =10 V N Shallow B? Temperature [K] 16

17 HIGH Temperature TSC Current (µa) E = ev σ ~10-15 cm 2 N ~10 13 cm -3 fit meas. S.A. Reshanov et al. Presented at ICSCRM Temperature (K) 17

18 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

19 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 = cm 3 ) taking into account the simulation results 19

20 Appendix 20

21 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 1x 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 1x V (V) Diode diameter: [0.3,1] mm Power diode layout design by INSA-CEGELY, Lyon France 21