Characterization of Deep Level Defects in 4H and 6H SiC Via DLTS, SIMS and MEV E-Beam Irradiation
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1 1 typically performed using six to eight rate windows ranging from (20 ms)- to (3.2 s)- . 4f IMS Cameca a using performed was (SIMS) spectrometry mass ion Secondary microanalyzer utilizing either a cesium or oxygen ion beam. Electron irradiations were 2 2 conducted at 2 MeV with the dose varying from lx1015 e-/cm up to lxl017 e-/cm . The of the samples. being selected according to the doping concentration dose
Results Figure 1 shows a DLTS spectrum for an as-grown n-type SiC-6H sample which displays a number of deep levels which are more clearly observed after electron irradiation as shown in figure 2. In the as-grown case we observe a strong peak at a position 0.41 eV below the conduction band edge (Ec) with evidence of another closely spaced deep level indicated by the slight shoulder on the low temperature side of the peak. 0.016 As-Deposited 0.0 12
Figure 1. DLTS spectra E -0.41 eVRc W of an as-grown layer of Rate Window : (3.2 s) n-type VPE grown SiC6H doped with nitrogen Bias Voltage: V S~Pulse Voltage: -15 15 V to a level of Ix10 15 cm- 3 . i va P
0.008
A nickel Schottky contact eWas for used
w2eV m
0-004
the
Ec-0.51 eV Ec-062/064 eVmeasurement. 0 100
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Temperature (K)
Rate Window:
0.06
(2.56 s)'l
Ec-0.34/0.41 eV
10 micron epilayer
/
Electron Irradiated
Figure 2. Results from electron irradiation of a portion of the sample -, shown in figure 1. A - 0.04 dose of IxI0 15 e- /cm 2 at .0 an energy of 2 MeV. The ) Ec-0.51 eV level is found t, a concentration of M 0.02 to have Ix10 13 cm- 3 .
-0.51 eV Ec-
Ec-1.2 eV Ec -0.62/0.64 eV
,
,
,
0
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60C
Temperature (K)
Additionally, we observe evidence for the Zl/Z 2 center (Ec-0.62/0.64 eV) in the asgrown state which has previously been observed in Lely grown crystals or after electron irradiation of epitaxial films 1,8. With the aid of the electron irradiated sample we have 520
Ec- 1.2 eV and Ec-0. 5 1 eV. also been able to assign positions to levels corresponding to of the Ec-0. 4 1 eV peak can be ascribed to the case in observed shoulder the Additionally, the Ec-0.3 4 eV level. In order to assess the nature of the defect level via electron irradiation, a sample doped to 2 17 a level of IxI0 17 cm-3 was electron irradiated to a dose of IxI0 e- /cm with the 3. in figure shown spectra resulting DLTS 5 Electron
4
Figure 3. N-type SiC-6H sample doped to a level of lx10 17 cm- 3 and irradiated with 2 MeV electrons with a dose of dose of lx1017 e- /cm 2 . The concentration of the Ec-0.34 and Ec-0.51 eV levels is found to 1016 cm-3 . approach The rate window is shorter than in figures 1 and 2 in order to avoid the freezeout of the lower ar carriers temperatures.
Irradiated
10 micron epi-layer
E: -0.51 eV 0.
3
C
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i
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0
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Note that the rate window chosen was three orders of magnitude shorter than the previously discussed samples in order to avoid carrier freezeout at
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