Synthesis and electrical properties study of Ib type diamond single crystal co-doped with boron and hydrogen under HPHT conditions

Abstract

Diamond is well known for its excellent properties, such as its hardness, high thermal conductivity, high electron and hole mobility, high breakdown field strength and large band gap (5.4 eV), which has been extensively used in many fields. However, its application in semiconductor area needs to be further understood, because it is irreplaceable by conventional semiconductor materials, especially in the extreme working conditions. In order to obtain diamond semiconductor with excellent electrical performances, diamond crystals co-doped with boron (B) and hydrogen (H) are synthesized in an FeNi-C system by temperature gradient growth (TGG) at pressure 6.0 GPa and temperature 1600 K. Fourier infrared spectra (FTIR) measurements displayed that H is the formation of sp3 CH2-antisymmetric and sp3 -CH2-symmetric vibrations in the obtained diamond. Furthermore, the corresponding absorption peaks of H element are located at 2920 cm-1 and 2850 cm-1, respectively. Hall effects measurements demonstrated that the co-doped diamond exhibited that p- type material semiconductor performance, and the conductivity of the co-doped diamond is significantly enhanced comparing tocompared with the conductivity of the B-doping diamond. The results indicated that the Hall mobility mobilities is nearly equivalent between B-doped and co-doped diamond crystals are nearly equivalent, while the concentrations of the carriers and conductivity of the co-doped diamonds are higher than those of the B-doped diamond crystals. It is also noticed that the nitrogen concentration of the co-doped diamond decreases obviously, when the H and B are introduced into the diamond structure. Additionally, the change of the conductivity is investigated by first-principles calculation. In the B-doping diamond, two impurity levels are located in the forbidden band with small gaps. These impurity states above the Fermi level couldcan trap the photo-excited electrons, while those below Fermi level can trap the photo-excited vacancies, improving the transfer of the photo-excited carriers to the reactive sites. With the H co-doped diamond, the two impurity states moved to the valance band maximum and merged into each other, which extends the valance band and improves the charge transfer efficiency. From the perspective of energy band, for the co-doped of B and N atoms co-doped diamond, the impurity states are contributed by N/B-2p states while the overlop and splitting of N/B-2p in the band gap appeared. For the H co-doped diamond, the splitting of the N/B-2p states vanishes and shifts to the lower energy level, which was due to the fact that the excess charge transferred from N to H. The calculation results above are in qualitatively agreement with experimental results. We hope that this investigation would be meaningful for the application of diamond in semiconductor field.