Passivation of copper in silicon by hydrogen

The structures and energies of model defects consisting of copper and hydrogen in silicon are calculated using the AIMPRO local-spin-density functional method. For isolated copper atoms, the lowest energy location is at the interstitial site with $T_d$ symmetry. Substitutional copper atoms are found to adopt a configuration with $D_{2d}$ symmetry. We conclude that the symmetry is lowered from $T_d$ due to the Jahn-Teller effect. Interstitial hydrogen atoms are found to bind strongly to substitutional copper atoms with an energy that is more than the difference in formation energy over the interstitial site for Cu. The resulting complex has $C_{2v}$ symmetry in the $-2$ charge state where the H atom is situated about 1.54 Å away from the Cu atom in a [100] direction. In other charge states the symmetry of the defect is lowered to $C_s$ or $C_1$. A second hydrogen atom can bind to this complex with nearly the same energy as the first. Two structures are found for copper dihydride complexes that have nearly equal energies; one with $C_2$ symmetry, and the other with $C_s$ symmetry. The binding energy for a third hydrogen atom is slightly more than for the first. Calculated electronic levels for the model defects relative to one another are found to be in fair to good agreement with experimental data, except for the copper-dihydride complex. The copper trihydride complex has no deep levels in the bandgap, according to our calculations.

Figure 1

(Color online) Two views of the $C_{2v}$ symmetry copper monohydride complex in Si. The unique, large atom near the center is Cu; the small atom directly below it is H; all the others are Si.

Figure 2

(Color online) Two views of the $C_s$ symmetry copper monohydride complex in Si. The atom identities follow a similar pattern to Fig. 1.

Figure 3

(Color online) Two views of the $C_1$ symmetry copper monohydride complex in Si. The atom identities follow a similar pattern to Fig. 1.

Figure 4

(Color online) Two views of the $C_2$ symmetry copper dihydride complex in Si. The atom identities follow a similar pattern to Fig. 1 with the largest size atom near the center being Cu, surrounded by Si atoms, except there are now two H atoms attached left and right of the Cu in the left-hand view.

Figure 5

(Color online) Two views of the $C_s$ symmetry copper dihydride complex in Si. The atom identities are again in a similar pattern to those in the previous pictures where the Cu atom is at the center with two small-sized H atoms attached to it.

Figure 6

(Color online) Two views of the copper trihydride complex in Si with $C_1$ symmetry. As in the previous pictures, the large atom at the center is Cu, now with three H attoms attached to it.

Figure 7

(Color online) Two views of the copper trihydride complex in Si with approximately $C_s$ symmetry. The atom identities are as described previously.