Doping of Diamond by Combining Ion-implantation and High-pressure and High-temperature Annealing
Kenji Ueda and Makoto Kasu
Materials Science Laboratory
Ion implantation is a widely used doping technique for semiconductors such as Si and GaAs. However, ion implantation severely damages the crystal. In Si and GaAs, the damage can be easily recovered by thermal annealing in a vacuum or in an inert gas. However, it is extremely difficult to recover the damage in diamond by thermal annealing. One possible reason is that the annealing condition is not located in diamond's stable region but rather in graphite's stable region. Therefore, we propose high-pressure and high-temperature (HPHT) annealing as a new activation method for ion-implanted dopants in diamond. The concept is to recover from implantation-induced damage by annealing under high pressure, that is, under diamond's stable condition (Fig. 1) [1, 2]. Here, we show that HPHT annealing is highly effective for damage recovery in ion-implanted diamond.
Homoepitaxial diamond films were grown on Ib-type diamond (100) single crystals by microwave plasma CVD. Boron (B) ions were implanted at an acceleration voltage of 60 keV with a dose of 1×1015 cm-2. The HPHT annealing of the B-implanted films was performed using a cubic-anvil-type high-pressure apparatus. The pressure was fixed at 〜7 GPa and the annealing temperature was changed from 1200 to 1400 ℃. Thermal annealing of the B-implanted films was also performed in a vacuum for comparison.
Figure 2 compares the annealing temperature (Ta) dependence of doping efficiency of the B-implanted films after HPHT annealing and conventional thermal annealing evaluated from Hall measurements. The doping efficiency of HPHT-annealed films increased exponentially as Ta increased and reached 7.1 % at 1400 ℃. In contrast, the doping efficiency for conventional thermal annealing increased linearly and reached 0.73 % at 1400 ℃. At the same Ta of 1400 ℃, the doping efficiency for HPHT-annealed films is 10 times higher than that for conventional thermal annealing. These results indicate HPHT annealing is much more effective for activation of ion-implanted dopants than conventional thermal annealing.
This work was partly supported by the SCOPE project of the Ministry of Internal Affairs and Communications, Japan.
 K. Ueda, M. Kasu, A. Tallaire, and T. Makimoto, Diamond Relat. Mater. 15 (2006) 1789.
 K. Ueda, M. Kasu, and T. Makimoto, Appl. Phys. Lett. 90 (2007) 122102.
Fig. 1. Phase diagram of carbon, which shows conditions for HPHT annealing and conventional thermal annealing.
Fig. 2. Doping efficiency of the B-implanted films after HPHT annealing and conventional thermal annealing.
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