Electrical properties of thick boron and nitrogen contained CVD diamond films

Abstract

The acceptor and donor defects of thick (approx. 0.4 mm) free-standing boron and nitrogen containing microwave plasma CVD polycrystalline diamond films were investigated. Charge-based deep level transient spectroscopy (Q-DLTS) was applied to study impurity-induced defects, their density and energy distribution in the energy range of 0.01 eV≤E−Ev≤1.1 eV above the valence band. It was shown, that differential capacitance–voltage, and Hall effect measurements combined with DLTS data can be used to determine the degree of compensation, and the concentration of compensating donors (mostly the positively charged single-substitutional nitrogen (N+)) in p-type CVD polycrystalline diamond films. It was found, that incorporated boron atoms induce three levels of electrically active defects. Two of them with concentration (2–3)×1016 cm−3 each have activation energies of 0.36 and 0.25 eV with capture cross-sections of 1.3×10−13 and 4.5×10−19 cm2, respectively. The third type of defect has an activation energy of 0.02 eV, capture cross-section 3×10−20 cm2 and concentration 1015 cm−3, this shallow trap being a probable general caterer of holes in low-doped films. The total concentration of electrically active uncompensated acceptors in all p-type diamond samples was approximately 2×1017 cm−3 with hole concentration of approximately 1.5×1014 cm−3 and hole mobility in the range of 30–40 cm2 V−1 s−1 at room temperature. If assumed that compensating donors are mostly nitrogen, the films contained no less than 3×1016 cm−3 of N+.