Defect annealing in 4H-SiC

Transcription

1 Defect annealing in 4H-SiC A. Castaldini 1, A. Cavallini 1, L. Rigutti 1, F. Nava 2 1 INFM and Dipartimento di Fisica, Università di Bologna, Bologna, IT 2 INFN and Dipartimento di Fisica, Università di Modena e Reggio Emilia, Modena, IT

2 Characterization Techniques Detection and characterization of electrically active defects: Deep Level Transient Spectroscopy: concentration, energy level (enthalpy) and capture cross section of electrically active defects. Capacitance-Voltage Characterization: free charge carrier distribution. Electron Beam Induced Current: spatial distribution and recombination strength of extended defects. Characterization of the device: Current-Voltage Characterization: behavior of dark current in presence of defects. Charge Collection Efficiency: effect of the defects on sample performance as a charged particle detector.

3 Applications Defective State analyses to predict trapping effects. Spatial distribution of major recombining centers. Annealing and recovery of free charge carriers at low temperature. Irradiation effects (radiation hardness). Analysis of irradiation-induced compensation effects. CCE analysis as a function of irradiation and annealing temperature.

4 Material n 4H-SiC epilayer grown by CVD: N D =2.2x10 15 cm -3, 30µm thick Au Schottky contact, φ =2mm, 1000Å thick circular Schottky contact Au (1000 Å), Φ = 2 mm n, 4H SiC, 30 µm ND = cm -3 Si-face IRRADIATION: 8.6 MeV electrons at different doses/fluences Dose Fluence (cm -2 ) n +, buffer, 1 µm, ND = cm -3 2 Mrad 4.74 x n +, 4H SiC, 360 µm substrate 10 Mrad 2.37 x ND cm micropipe/cm 2 40 Mrad 9.48 x Ohmic contact - Ti/Pt/Au C-face

5 EBIC micrographs Dislocation density is about 10 5 cm -2 Dislocations appear as dark spots on the surface EBIC contrast up to 40%

6 DLTS analysis Irradiation induced deep levels 0.16 S2 S S0 40 Mrad 9.48 x e/cm 2 40 Mrad 0.12 en=46.5 s S4 S5 C/C S1 as-recived x100 Virgin (X 100) S Temperature (K)

7 DLTS analysis Trap parameters Trap level Deep level enthalpy E T (ev) Concentration N T (cm -3 ) Capture cross section σ inter (cm 2 ) Introduction rate η (cm -1 ) S0 S1 S2 S3 * E c E c E c E c / x x x x x x x x x S4 E 1.3 x x c S5 E 4.6 x x c * S3 undergoes annealing at T~ K; the parameters after annealing are typical of the level known from the literature as Z1/Z2

8 DLTS analysis Arrhenius Plot S5 S4 S3 S2B S2 K SiC I4 virgin SiC G7 2 Mr SiC A4 10 Mr SiC G1 40 Mr SiC G4 40 Mr up down 10 3 S0 S1 T 2 /en (K 2 s) /T (K -1 )

9 DLTS analysis Filling Kinetics G1 306K G1 449K a.u Tp (s) a.u. S4 3.06E-17 S3 σ= 1.4E-17 cm x10-6 2x10-6 3x10-6 4x10-6 5x10-6 Tp (s)

10 DLTS and annealing analysis 1. Run K 2. Run K 3. Run K 4. Run K 5. Run K 1 st annealing stage ( K): 1.1 S S S2B x S1 0.0 S3 C/C (arb.units) very strong decrease of peak S2 slight amplitude gain and temperature shift of S3 S2B and S1 become resolved Temperature (K) S4 S5 2 nd annealing stage ( K) : blue shift of S3 activation energy sharpening of S3 peak

11 C-V analysis Strong compensation of free charge for Φ= 9.48 x cm -2 (~1/10 of the as-grown value). Significant free charge density increase after annealing of peak S2 at 360K-400K as-grown irradiated - after recovery irradiated - before recovery Apparent concentration (cm -3 ) X (µm) Post-recovery free charge increase Possible Possible explanation: explanation: recombination recombination and and annihilation annihilation of of the the defect defect related related to to level level S2 S2

12 CCE characterization CCE vs. irradiation dose In the diffusion regime (Bias<~160V) CCE is degraded by the introduction of traps. In the drift regime (Bias>~160V) CCE saturates to 100% for all irradiation doses. CCE vs. annealing Low T annealing does not change the CCE of the detector G4 Φ= 9.48 x e/cm 2 Pre-recovery Post-recovery CCE (%) REVERSE BIAS (V)

13 Conclusions Electron irradiation Introduction of at least 4 trap levels. Strong compensation of free carrier density. 1 st Annealing stage (360K-400K): Disappearance of level S2 (Ec-0.39 ev). Free carrier density increase (recovery). Rearrangement of peak S3. 2 nd Annealing stage (400K-470K): Blue shift of S3 level energy; S3 parameters are those of Z1/Z2 level. Possible recovery cause: annihilation of the defect related to S2 during 1st annealing stage (360K-400K). Detector performance preserved up to Φ ~ cm CCE saturates to 100% in drift regime and remains unchanged upon annealing.

14 9 MeV electron irradiation on CdZnTe PICTS Gamma Spectroscopy as-grown 4x M rad 0.6 M rad 0.8 M rad 1.2 M rad 3x M rad A A as-grown 0.2 Mrad 0.6 Mrad 0.8 Mrad 1.2 Mrad 1.6 Mrad counts 2x10-2 C X J Z Y W H PICTS/IL0 (a.u.) 1x temperature (K) channels

15 Time recovery of 9 MeV electron irradiated CdZnTe (6 months) PICTS Gamma Spectroscopy 4x10-2 as-grown 1 Mrad after irradiation 1 Mrad after 6 months 3x10-2 2x10-2 1x10-2 A A1 C X D J Y W H PICTS/IL0 (a.u.) 1000 as-grown 1 Mrad after irradiation 1 Mrad after 6 months counts temperature (K) channels