Impurity State-Dangling Bond Pairs in Hydrogenated Amorphous Silicon
- PDF / 306,955 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 76 Downloads / 212 Views
IMPURITY STATE-DANGLING BOND PAIRS IN HYDROGENATED AMORPHOUS SILICON L. H. YANG*, C. Y. FONG* AND C. S. NICHOLS** *Department of Physics, University of California, Davis, CA 95616 **IBM Research Division, T. J. Watson Research Center, Yorktown Heights, NY 10598
ABSTRACT We use the self-consistent pseudopotential method with a supercell model of a-Si:H to study the electronic structures of substitutional fourfold-coordinated P and fourfold-coordinated B at the second neighbor of a Partial transfer of charge from the impurity state to the dangling bond. The influence of passivating the dandangling bond state is examined. gling bond by a single H atom on the impurity state is also discussed. INTRODUCTION The modified 8-N rule proposed by Street[l] suggests that there is an intimate relation between the db and the dopant in a-Si:H. More recently, Kocka[2] and Kocka et al.[3] have suggested that intimate pairs of P4 + - Dand B 4 - D+ are the dominant defects in n-type and p-type hydrogenated amorphous silicon( a-Si:H). In their results, which are derived from the subgap optical absorption coefficient determined by the constant creates prephotocurrent measurement(CPM), they found that doping dominantly intimate pairs of db's with dopants, and the db state exhibits more binding in comparison with the energy of an isolated Si-related db state. In addition, due to the long range of Coulomb attraction the pair need not be in the nearest neighbor configuration. These results suggest that dopants of valences III and V can occupy a substitutional fourfold coordinated site (or ) in conjunction with the presence of dangling bond(db) defects. These complexes provide the low energy acceptor or donor center. Therefore, the study of relationship between db's and dopants is consequently of importance in understanding the doping mechanism in a-Si:H. We have carried out a series of self-consistent pseudopotential calculations based on a realistic supercell model of a-Si:H. Two kinds of intimate pairs(i.e., db with P and with B atoms) are considered to Partial charge transfer between the db study their electronic structures. and the impurity atom is examined by calculating the charge difference around the db site and the impurity site. Effects on the impurity state by passivating the db with a single H atom are also discussed.
Mat. Res. Soc. Symp. Proc. Vol. 118. ' 1988 Materials Research Society
514
CALCULATIONS We have used a computer generated model of a-Si:H of Guttman[4], in conjunction with the self-consistent pseudopotential method and local density approximation, to calculate the electronic properties of the db paired with a dopant at a second neighbor. The model contains 54 Si atoms and 6 H atoms, in which no more than one H atom is bonded to any Si atom and no two H atoms are closer than the fourth neighbors. Nelson et al.[5] have used a similarly constructed model to calculate properties of the H-related states and the dangling bond state. Nichols and Fong[6] used the same model to study the effects of coordination and lo
Data Loading...
