Deactivation of nitrogen donors in silicon carbide

Hexagonal SiC is either co-implanted with silicon $\left({\mathrm{Si}}^{+}\right)$, carbon $\left({\mathrm{C}}^{+}\right)$, or neon $\left({\mathrm{Ne}}^{+}\right)$ ions along with nitrogen $\left({\mathrm{N}}^{+}\right)$ ions or irradiated with electrons $\left({\mathrm{e}}^{-}\right)$ of $200\mathrm{keV}$ energy. During the subsequent annealing step at temperatures above $1450°\mathrm{C}$ a deactivation of N donors and a reduction of the compensation are observed in the case of the ${\mathrm{Si}}^{+}∕{\mathrm{N}}^{+}$ co-implantation and ${\mathrm{e}}^{-}$ irradiation. The N donor deactivation is investigated as a function of the concentration of the co-implanted species and the annealing temperature. The formation of energetically deep defects is analyzed with deep level transient spectroscopy. A detailed theoretical analysis based on the density functional theory is conducted; it takes into account the kinetic mechanisms for the formation of N interstitial clusters and (N-vacancy) complexes. In accordance with all the experimental results, this analysis distinctly indicates that the ${\left({\mathrm{N}}_{\mathrm{C}}\right)}_4\text{−}{V}_{\mathrm{Si}}$ complex, which is thermally stable at high temperatures and which has no level in the band gap of 4H-SiC, is responsible for the N donor deactivation.

Figure 1

Free electron concentration versus reciprocal temperature determined by Hall effect in ${\mathrm{N}}^{+}$-implanted as well as in ${\mathrm{C}}^{+}∕{\mathrm{N}}^{+}$ and ${\mathrm{Si}}^{+}∕{\mathrm{N}}^{+}$ co-implanted 4H-SiC layers. The implantation parameters are listed in Table . The symbols are measurement points and the solid lines correspond to least-squares-fits of neutrality Eq. (2) to the experimental points.

Figure 2

Concentration of N donors (full symbols) and of the compensation (open symbols) as a function of the co-implanted Ne, Si or C concentration. The horizontal dashed straight line indicates the N donor concentration of the reference sample N(1).

Figure 3

Concentration of N donors and of the compensation as a function of the annealing temperature determined by Hall effect in ${\mathrm{Si}}^{+}\text{−}∕{\mathrm{N}}^{+}$ co-implanted 4H-SiC samples (see series B samples).

Figure 4

DLTS spectra taken on (a) $n$-type and (b) $p$-type 4H-SiC samples, which are annealed at different temperatures as indicated in the figures (see series C and D samples).

Figure 5

Concentration of the $Z_1∕Z_2$ and of the $P_1$ center as a function of the annealing temperature determined by DLTS in series C and D samples (see Table ).

Figure 6

Concentration of N donors and of the compensation as a function of the annealing temperature determined by Hall effect in ${\mathrm{e}}^{-}$-irradiated samples (see series E in Table ). The horizontal dashed straight lines correspond to the not-irradiated reference sample e(ref).

Figure 7

Concentration of the $Z_1∕Z_2$ and of the $P_1$ center as a function of the annealing temperature determined by DLTS in the ${\mathrm{e}}^{-}$-irradiated samples of series F and G (see Table ).

Figure 8

N concentration per defect group as a function of the chemical potential $\Delta {\mu }_{\mathrm{Si}}$ calculated for the thermal equilibrium.

Figure 9

(Color online) Vacancy aggregates in 3C-SiC: divacancy $V_{\mathrm{C}}\text{−}{V}_{\mathrm{Si}}$ (left side) and vacancy cluster ${\left(V_{\mathrm{C}}\right)}_4\text{−}{V}_{\mathrm{Si}}$ (right side).

Figure 10

(Color online) Nitrogen-vacancy complex ${\left({\mathrm{N}}_{\mathrm{C}}\right)}_4\text{−}{V}_{\mathrm{Si}}$.