Evidence for a New Class of Defects in Highlyn-Doped Si: Donor-Pair-Vacancy-Interstitial Complexes

Abstract

Electron channeling experiments performed on individually scanned, single columns of atoms show that in highly n-type Si grown at low temperatures the primary electrically deactivating defect cannot belong to either the widely accepted class of donor-vacancy clusters or a recently proposed class of donor pairs. First-principles calculations suggest a new class of defects consisting of two dopant donor atoms near a displaced Si atom, which forms a vacancy-interstitial pair. These complexes are consistent with the present experimental results, the measured open volume of the defects, the observed electrical activity as a function of dopant concentration, and the enhanced diffusion of impurities in the presence of deactivated dopants.

Segregation of nearest-neighbor donor-pair defects to Si∕SiO2 interfaces

“…In heavily n-type Si, the saturation of free carriers is attributed to the formation of electrically deactivating defects, especially donor-pair defects. [7][8][9] Similarly, it is expected that segregated dopants to the interface are electrically deactivated via the formation of donor pairs.…”

“…However, since dopant concentrations are very high near the interface, dopant segregation may occur in form of donorpair defects, which were suggested to be deactivating centers responsible for the saturation of free carrier concentrations in heavily n-type Si. [7][8][9] To explain the carrier saturation, theoretical calculations suggested donor-pair defects, denoted DP2 and DP4, which consist of two threefold coordinated dopant atoms separated at the second and fourth neighbor distances, respectively, along a ͗110͘ chain. 7 Other classes of deactivating defects are nearest-neighbor donor pairs, denoted d 1 and DP1, in which dopant atoms are either fourfold coordinated at the nearest-neighbor distance or threefold coordinated through bond-breaking relaxations.…”

“…8 Very recently, a different class of deactivating defects, which comprise a pair of donor atoms near a displaced Si atom, was proposed. 9 In this letter, we perform a first-principles theoretical study of the energetics of various deactivating donor-pair defects near Si/ SiO 2 interfaces, and provide an atomic model for dopant segregation to interfaces. For P dopants, we find that the formation energy of a single dopant is significantly reduced as going from bulk Si to the interface region.…”

The role of rough surfaces in quantitative ADF imaging of gallium nitride-based materials

“…Unlike its phase-contrast imaging counterpart, scanning TEM annular dark field imaging enjoys good agreement between simulations and experiments [1,2]. Nowhere is this quantitative assessment more important than for measuring the extent of atomic ordering where the brighter (or darker) contrast of the sample can be interpreted as precipitates, chemical ordering and point defects [2].…”

“…Nowhere is this quantitative assessment more important than for measuring the extent of atomic ordering where the brighter (or darker) contrast of the sample can be interpreted as precipitates, chemical ordering and point defects [2]. However, the preparation of a thin TEM specimen is a grievous process and the sample surface can be left with surface strains, rough surfaces, as well an accompanying amorphous layer, all of which introduce varying levels of point-to-point contrast that may obscure the features of interest.…”