Reduction in Majority-Carrier Concentration in N-Doped or Al-Doped 4H-SiC Epilayer by Electron Irradiation

Reduction in Majority-Carrier Concentration in -Doped or Al-Doped 4H-SiC Epilayer by Electron Irradiation Hideharu Matsuura, Hideki Yanagisawa, Kozo ishino, Takunori ojiri Shinobu Onoda, Takeshi Ohshima Japan Atomic Energy Agency The 9 th International Workshop on Radiation Effects on Semiconductor Devices for Space Applications (RASEDA-9) 27 October, 20, Takasaki, Japan Matsuura Laboratory

Background of our study Silicon carbide (SiC) is a promising wide bandgap semiconductor for fabricating high-power and high-frequency electronic devices capable of operating at elevated temperature under radiation environment. In order to understand the radiation-degradation of SiC electronic devices, changes of properties in SiC by radiation should be investigated. Matsuura Laboratory

Comparison of radiation resistance of Si and SiC 16 Al-doped Si Hole Concentration [cm -3 ] 13 12 : unirradiated : 0.5x 16 cm -2 of 0.5 MeV electrons Al-doped Si : unirradiated : 1x 16 cm -2 of 1 MeV electrons 1 2 3 4 5 6 7 8 9 00/T [K -1 ]

Hole Concentration [cm -3 ] Comparison of radiation resistance of Si and SiC 16 Al-doped Si Irradiation conditions 13 12 : unirradiated : 0.5x 16 cm -2 of 0.5 MeV electrons Al-doped Si : unirradiated : 1x 16 cm -2 of 1 MeV electrons 1 2 3 4 5 6 7 8 9 00/T [K -1 ] 1 MeV electrons 1x 16 cm -2 fluence p(t) decreased slightly.

To understand the origin of the decrease in p(t) in by electron irradiation, the densities and energy levels of acceptors and defects should be determined from p(t). How to accurately determine the densities and energy levels of acceptors and defects from p(t) Matsuura Laboratory

Free Carrier Concentration Spectroscopy H ( T, E ref ) º (FCCS) p( T ) ( kt) 5 / 2 2 exp æ ç è E ref kt The FCCS signal has a peak corresponding to each acceptor level or defect level. DE @ kt + E i peak i ref i @ kt H ( T, E ) exp( -1) peaki peak i ref ö ø Matsuura Laboratory

FCCS: H ( T, E ref ) º p( T ) ( kt) 2 5 / 2 exp æ ç è E ref kt ö ø Hole Concentration [cm -3 ] 16 Sample number SiC(0001) : #2 2 3 4 5 00/T [K -1 ] 348.7 mev 4.15x cm -3 H(T, 0.0085) [x 35 cm -6 ev -2.5 ] 2 1.5 1 0.5 0 Sample number #2 Peak 507.8 K 1.70x 35 cm -6 ev -2.5 200 300 400 500 600 Temperature [K]

FCCS signal of H2(T, E ref ), in which the influence of the previously determined acceptor is removed, is calculated H2(T, 0.12) [x 36 cm -6 ev -2.5 ] 4 3 2 1 0 Peak Sample number #2 323.1 K 3.89x 36 cm -6 ev -2.5 200 300 400 500 600 Temperature [K] 225.8 mev 6.49x cm -3 Hole Comcentration [cm -3 ] 16 To verify the results determined by FCCS : Experimental data : Simulation A1 = 6.49 cm -3 DE A1 = 225.8 mev A2 = 4.15 cm -3 DE A2 = 348.7 mev comp = 1.45 13 cm -3 Sample number #2 2 3 4 5 00/T [K]

Relationship between Al and DA in unirradiated epilayer Unirradiated p-type 4H-SiC epilayers DA = 0.6 x Al 16 DA = 0.6 Al DA [cm -3 ] 16 Al [cm -3 ] The unknown deep acceptor is most likely related to Al Matsuura Laboratory

Hole Concentration [cm -3 ] Reduction in p(t) in Al-doped p-type 4H-SiC by 200 kev electron irradiation Fluence of 200 kev electrons [x 16 cm -2 ] : 0 : 1 : 3 : 5 : 7 : 9 16 Fluence [cm -2 ] 13 12 1 2 3 4 5 6 7 8 9 00/T [K -1 ] 0

Fluence Dependence of Al and DA in 4H-SiC 16 Al or DA [x cm -3 ] : Al : DA 0 1 2 3 4 5 6 7 8 9 Fluence of 200 kev Electrons [x 16 cm -2 ] Matsuura Laboratory

Al or DA [x cm -3 ] 16 Fluence Dependence of Al in 4H-SiC : Al : DA d Al( F) df k Al = = -k Al 4.4-17 Al ( F) cm 2 0 1 2 3 4 5 6 7 8 9 Fluence of 200 kev Electrons [x 16 cm -2 ] Matsuura Laboratory

Al or DA [x cm -3 ] 16 Fluence Dependence of DA in 4H-SiC : Al : DA 0 1 2 3 4 5 6 7 8 9 Fluence of 200 kev Electrons [x 16 cm -2 ] d Al( F) df k Al = = -k dda( F) = - df - k k DA Al 4.4 Al ( F) dal( F) df ( F) DA = 1.0-17 DA -17 cm cm Matsuura Laboratory 2 2

Motivation of our study 1. To investigate changes of p(t) in Al-doped 4H-SiC by electron irradiation with lower energies (0 or 150 kev) 2. To investigate decreases of n(t) in -doped 4H-SiC by 200 kev electron irradiation Matsuura Laboratory

Sample Configuration Investigation of acceptors in from p(t) obtained by Hall-effect measurements p-type epilayer Thickness: um Ohmic contact Ti/Al Substrate n + -type 4H-SiC wafer Size: 1x1 cm 2 Matsuura Laboratory

16 Change in p(t) in Al-doped p-type 4H-SiC by 0 kev electron irradiation Fluence [cm -2 ] Hole Concentration [cm -3 ] Fluence of 0 kev electrons [cm -2 ] : 0 : 5x 16 2 3 4 5 00/T [K -1 ] 0

16 Change in p(t) in Al-doped p-type 4H-SiC by 0 kev electron irradiation Fluence [cm -2 ] Hole Concentration [cm -3 ] Fluence of 0 kev electrons [cm -2 ] : 0 : 5x 16 2 3 4 5 00/T [K -1 ] 16 5 0 kev electron irradiation could not reduce p(t).

16 Reduction in p(t) in Al-doped p-type 4H-SiC by 150 kev electron irradiation Fluence [cm -2 ] Hole Concentration [cm -3 ] Fluence of 150 kev electons [cm -2 ] : 0 : 3x 16 : 5x 16 1 2 3 4 5 00/T [ K -1 ] E E Al Al DA DA 0 Simulation Result comp 15 = 6.3 cm = E + 0.22 ev = V V 2.7 14-3 15 = 4.9 cm = E + 0.38eV -3 cm -3

16 Reduction in p(t) in Al-doped p-type 4H-SiC by 150 kev electron irradiation Fluence [cm -2 ] Hole Concentration [cm -3 ] Fluence of 150 kev electons [cm -2 ] : 0 : 3x 16 : 5x 16 1 2 3 4 5 00/T [ K -1 ] 16 3 Simulation Result E E Al Al DA DA comp = 5.5 = = E = V V + + 15 = 5.1 E 0.21eV 15 0.36 6.9 cm cm 14-3 -3 ev cm -3

16 Reduction in p(t) in Al-doped p-type 4H-SiC by 150 kev electron irradiation Fluence [cm -2 ] Hole Concentration [cm -3 ] Fluence of 150 kev electons [cm -2 ] : 0 : 3x 16 : 5x 16 1 2 3 4 5 00/T [ K -1 ] 16 5 Simulation Result E E Al Al DA DA = = comp = = 6.0 E V V + 15 0.20 7.4 E + 15 0.35 = 1.7 cm cm 15-3 ev cm -3 ev -3

7 Fluence Dependence of Al in 4H-SiC Acceptor Density [x cm -3 ] 6 5 4 3 2 1 Experimental data : Al : DA Simulation results : Al : DA 0 1 2 3 4 5 6 Fluence of 150 kev electrons [x 16 cm -2 ] Matsuura Laboratory

Acceptor Density [x cm -3 ] 7 6 5 4 3 2 1 Fluence Dependence of Al in 4H-SiC Experimental data : Al : DA Simulation results : Al : DA 0 1 2 3 4 5 6 Fluence of 150 kev electrons [x 16 cm -2 ] d Al( F) df k Al = = -k Al 4.8-18 Al ( F) cm Matsuura Laboratory 2

Acceptor Density [x cm -3 ] 7 6 5 4 3 2 1 Fluence Dependence of DA in 4H-SiC Experimental data : Al : DA Simulation results : Al : DA 0 1 2 3 4 5 6 Fluence of 150 kev electrons [x 16 cm -2 ] d Al( F) df k Al = = -k Al 4.4-17 Al ( F) cm Matsuura Laboratory 2

Comparison of removal cross sections for Al-doped 4H-SiC by 150 and 200 kev electron irradiation 150 kev 200 kev k Al k DA [cm 2 ] [cm 2 ] 4.8 1.0-18 -18 4.4 1.0-17 -17 kal kda and for 150 kev electron irradiation is lower by one order than that for 200 kev electron irradiation Matsuura Laboratory

Sample Configuration Investigation of donors in -doped 4H-SiC from n(t) obtained by Hall-effect measurements n-type -doped 4H-SiC epilayer Thickness: um Ohmic contact i Substrate p + -type 4H-SiC wafer Size: 3x3 mm 2 Matsuura Laboratory

Reduction in n(t) in -doped n-type 4H-SiC by 200 kev electron irradiation -doped 4H-SiC Fluence [cm -2 ] Electron Concentration [cm -3 ] 13 12 Fluence of 200 kev electrons [cm -2 ] : 0 : 1x 16 : 2x 16 3 4 5 6 7 8 9 11 12 00/T [K -1 ] 0

Electron Concentration [cm -3 ] 13 12 Reduction in n(t) in -doped n-type 4H-SiC by 200 kev electron irradiation Fluence of 200 kev electrons [cm -2 ] : 0 : 1x 16 : 2x 16 -doped 4H-SiC 3 4 5 6 7 8 9 11 12 00/T [K -1 ] Fluence [cm -2 ] 16 1 Simulation Result E E H H K K = 1.6 = = = E C 4.0 E C - - 14 0.09 ev 14 0.12 cm cm -3 ev -3

Electron Concentration [cm -3 ] 13 12 Reduction in n(t) in -doped n-type 4H-SiC by 200 kev electron irradiation Fluence of 200 kev electrons [cm -2 ] : 0 : 1x 16 : 2x 16 -doped 4H-SiC 3 4 5 6 7 8 9 11 12 00/T [K -1 ] Fluence [cm -2 ] 16 2 Simulation Result E E H H K K < 1 = = = E C 0.09 4.1 E C - - 13 cm 14 0.12-3 ev cm -3 ev

Donor Density [x cm -3 ] 6 5 4 3 2 1 Fluence Dependence of H in 4H-SiC Experimental data : H : K Simulation results : H : K -doped 4H-SiC 0 1 2 Fluence of 200 kev electrons [x 16 cm -2 ] Matsuura Laboratory

Donor Density [x cm -3 ] 6 5 4 3 2 1 Fluence Dependence of H in 4H-SiC Experimental data : H : K Simulation results : H : K -doped 4H-SiC 0 1 2 Fluence of 200 kev electrons [x 16 cm -2 ] d H( F) df k H = -k H = 1.2 H -16 ( F) cm Matsuura Laboratory 2

Donor Density [x cm -3 ] 6 5 4 3 2 1 Fluence Dependence of K in 4H-SiC Experimental data : H : K Simulation results : H : K -doped 4H-SiC 0 1 2 Fluence of 200 kev electrons [x 16 cm -2 ] d H( F) df k H = -k H = 1.2 H -16 ( F) cm Matsuura Laboratory 2

Donor Density [x cm -3 ] 6 5 4 3 2 1 Fluence Dependence of H and K in 4H-SiC Experimental data : H : K Simulation results : H : K -doped 4H-SiC 0 1 2 Fluence of 200 kev electrons [x 16 cm -2 ] d H( F) df k d K( F) df k H K = = -k = -k H = 1.2 K 6.0 H -16-18 K ( F) cm ( F) cm Matsuura Laboratory 2 2

Comparison of removal cross sections for 200 kev electron irradiation of donors located at hexagonal and cubic C-sublattice sites 200 kev k H k K [cm 2 ] [cm 2 ] 1.2 6.0-16 -18 donors at hexagonal C-sublattice sites are less radiation-resistant than donors at cubic C- sublattice sites. Matsuura Laboratory

Conclusion In Al-doped p-type 4H-SiC 1. p(t) was unchanged by 0 kev electron irradiation. 2. 150 kev electron irradiation may transform Al acceptors into deep acceptors. In -doped n-type 4H-SiC 3. donors at hexagonal sites are less radiation-resistant than donors at cubic sites.