Type-<i>n</i> electrical activations of unintentionally auto-doped N atoms in the CVD diamond films grown on the HPHT Ib substrates, after 4-MeV Si2+ irradiations

This article describes observation of n-type conductivity for chemical vapor deposition (CVD) diamond films annealed by using 4-MeV Si2+ ion-beam irradiation at a low temperature of 660 °C. Although CVD diamond films grown on the High-Pressure High-Temperature (HPHT) Ib-substrates showed excellent crystallinity, these films were unintentionally auto-doped with highly concentrated N atoms. At first, n-type conductivity had not been judged for the as-grown state. However, after irradiation by 4-MeV Si2+ ions at 660 °C, the grown diamond film exhibited clear and stable n-type conductivity at a relatively low temperature of 250 °C. This fact was ascertained by measuring the electrical conductivity with a Hall effect apparatus. The as-purchased HPHT Ib-substrate after a normal RCA cleaning processes exhibited evident n-type conductivity at above 300 °C due to intrinsically contained dopant N atoms in the substrate. On the other hand, the as-grown CVD film deposited on the Ib-substrate exhibited evident n-type conductivity at a thoroughly lower temperature of 250 °C after 4-MeV Si2+ irradiation. 250 °C temperature is lower than 300 °C for the as-purchased HPHT Ib-substrate. Theoretical simulations were performed to fit Hall-measured data of sheet resistivity and sheet carrier concentration. The simulation results were based on the charge neutrality principles. The author also proposed novel activation energy of N atoms in diamond semiconductors to be 2.5 eV, which is much larger than formerly reported values of 1.4–1.7 eV. Lastly, the author discussed the possibility of MeV-ion irradiations being as novel and useful annealing technology for heavy type-n-dopants ion implantations into diamond semiconductors.