ESR study on hydrogen passivation of intrinsic defects in p-type andsemi-insulating 4H-SiC
K. Murakami1), S. Tanai1), T. Okuda2), J. Suda2), T. Kimoto2), T. Umeda1)
1)
Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8573, Japan2)
Department of Electronics Science and Engineering, Kyoto University, Kyoto
615-8510, Japan
E-mail: s1520374@u.tsukuba.ac.jp
Hydrogen is an important element in the manufacturing process of semiconductor devices. For
instance, hydrogen atoms can combine with defects and impurities in semiconductors, enabling us tocontrol electronic properties of semiconductors. In silicon and diamond, hydrogen-vacancy
complexes were found by electron-spin-resonance (ESR) spectroscopy [1,2]. In SiC, however, thesame types of defects have not been found, despite vacancy defects are also present in SiC. Recently,
it was found that a high-temperature annealing in H2 ambience drastically increases a carrier lifetimeof p-type 4H-SiC [3]. Furthermore, the enhanced carrier lifetime was reversibly decreased to its
original value by high-temperature annealing in Ar ambience [3]. These results indicate thathydrogen atoms passivate or de-passivate lifetime killing defects in p-type 4H-SiC [3]. However, themicroscopic entity of the lifetime killing defect is not clear yet.
In this work, we study the hydrogen passivation of intrinsic defects in p-type or semi-insulating
4H-SiC substrates by means of ESR. In p-type 4H-SiC, dominant intrinsic defects are alreadyknown: positively-charged carbon vacancy (VC(+), the EI5/6 centers) [4] and positively-charged
carbon antisite-carbon vacancy pair (CSiVC(+), the HEI9/10 centers) [5]. These defects are expected
to become a lifetime killing defect of p-type 4H-SiC. We therefore examined the hydrogenpassivation and de-passivation of these defects by observing their ESR signals.
The samples used in this study were semi-insulating 4H-SiC substrates which included the EI5/6
centers and the HEI9/10 centers, as similarly to p-type substrates. Their defect densities are in theorder of 1014 cm-3. The substrates were thinned to 180 μm by chemical mechanical polishing, tointroduce hydrogen atoms into the whole substrate. The Si face of the substrate was subjected tohigh-temperature annealing at H2 ambience at 500 to 1000ºC for 20 min. This hydrogen-annealing
procedure is the same as that used for passivating the lifetime killing defects in p-epitaxial layers [3].
ESR spectra of the substrates before and after H2 annealing were measured at 4.2 K to room
temperature under an optimum microwave excitation.
Figure 1 shows ESR spectra of the base substrate (before H2 annealing) for magnetic field // [0001].
The substrate shows the EI5/6 signal of VC(+), the HEI9/10 signals of CSiVC(+), and unidentifiedsignals (we name them “HEI7/8”), as shown in the figure. These signals have different
microwave-saturation behaviors and different temperature dependences.
Thus, we could
experimentally separate ESR signals into two components (EI5/6 and HEI7/8 + HEI9/10) by changing
a microwave power and temperature. Further lower temperatures (< 50 K) and with photo excitation,neutral divacancies (VSiVC(0), the P6/7 centers [6]) were also detected in our substrates. Accordingly,
we could examine the hydrogen passivation of four types of intrinsic defects (EI5/6, HEI7/8, HEI9/10,and P6/7).
Figure 2 shows hydrogen-induced changes in the ESR spectra. The signal intensities greatly
decreased after H2 annealing at 600ºC, indicating the hydrogen passivation of the intrinsic defects.
We found that the EI5/6 signal is reduced by about 10%, while the HEI7/8 + HEI9/10 component issignificantly reduced by about 90%. The relative changes in the ESR signals after H2 annealing areplotted in Fig. 3, as a function of annealing temperature. Obviously, the hydrogen passivationdifferently affects each defect. For EI5/6, it is less effective and does not work above 700°C. On
the contrary, for HEI7/8 + HEI9/10, it works much more drastic and is maximized above 700°C.
This striking difference will be attributed to the different passivation form (either Si-H or C-H) of eachdefect. We will interpret details of the hydrogen-passivation effect of each defect as well as arelationship to the lifetime killing defect, based on more detailed data.

[1] B. B. Nielsen et al., Phys. Rev. Lett. 79, 1570 (1997).
[2] C. Glover et al., Phys. Rev. Lett. 92, 135502 (2004).
[3] T. Okuda et al., Appl. Phys. Express 6, 121301 (2013).
[4] T. Umeda et al., Phys. Rev. B 69, 121201(R) (2004).
[5] T. Umeda et al., Phys. Rev. B 75, 245202 (2007).
[6] N. T. Son, et al., Phys. Rev. Lett. 96, 055501 (2006).

FIG. 1. ESR signals of the base substrate
at different microwave powers andtemperatures.

FIG. 2. Hydrogen passivation of ESR
centers by H2 annealing.
Both ESR spectra were measured atroom temperature.

FIG. 3. Hydrogen passivation of the intrinsic defects as a function of H2 annealing
temperature.
“100%” represents ESR signals equal to those in the base substrate.