Dynamic properties of interstitial carbon and carbon-carbon pair defects in silicon

Abstract

Interstitial carbon, C i , defects in Si exhibit a number of unexplained features. The C i defect in the neutral charge state gives rise to two almost degenerate vibrational modes at 920 and 931 cm Ϫ1 whose 2:1 absorption intensity ratio naturally suggests a trigonal defect in conflict with uniaxial stress measurements. The dicarbon, C s -C i , defect is bistable, and the energy difference between its A and B forms is surprisingly small even though the bonding is very different. In the B form appropriate to the neutral charge state, a silicon interstitial is believed to be located near a bond-centered site between two C s atoms. This must give rise to vibrational modes which involve the motion of both C atoms in apparent conflict with the results of photoluminescence experiments. We use an ab initio local density functional cluster method, AIMPRO, to calculate the structure and vibrational modes of these defects and find that the ratio of the absorption intensities of the local modes of C i is in reasonable agreement with experiment even though the structure of the defect is not trigonal. We also show that modes in the vicinity of those detected by photoluminescence for the B form of the dicarbon center involve independent movements of the two C atoms. Finally, the trends in the relative energies of the A and B forms in three charge states are investigated. ͓S0163-1829͑96͒05848-1͔

G-centers in irradiated silicon revisited: A screened hybrid density functional theory approach

“…The results obtained by the PBEsol functional only agree with the experimental value in the energetic order for the charge neutral state, while the value is substantially larger. Our HSE calculations yield results that agree with the experiment better than previous theoretical studies, [32][33][34] except for the À1 charge state for which the total energy difference is 0.07 eV, while the experimental value is À0.04 eV. The total energy difference for the charge neutral state is found to be 0.04 eV, which is very close to the experimental value of 0.02 eV, and for the þ1 charge state the value of À0.09 eV is also qualitatively comparable to the experimental result of À0.02 eV.…”

Density-functional calculations of carbon diffusion in GaAs

“…[30][31][32] Using the AIMPRO method, Leary et al estimated the activation energy to be 1.10 eV. 33 Since a smaller cluster ͑87 atoms͒ and a smaller basis was used than in the present work, it is reasonable to expect that the results given here for C i in GaAs are more reliable than previously obtained for C i in Si. A less sophisticated procedure was also employed to determine the migration path, which tends to overestimate the barrier.…”

Controlling A-center concentration in silicon through isovalent doping: mass action analysis

“…[17][18][19] These defects in turn introduce states within the Si band gap, which can impact devices [20][21][22] and therefore their structure and properties have been thoroughly investigated. [23][24][25][26][27] Finally, during irradiation Ci, CiOi, and CiCs defects are nucleation centres for more extended defects such as CiOiSiI. [28][29][30] The experimental studies of Watkins 31,32 and Kimerling et al 33 demonstrated that isovalent impurities [carbon (C), germanium (Ge) and tin (Sn)] can impact the formation processes of VO pairs in Si.…”