High-density structures
of subsurface phosphorus dopants in silicon
continue to garner interest as a silicon-based quantum computer platform;
however, a much-needed confirmation of their dopant arrangement has
been lacking. In this work, we take advantage of the chemical specificity
of X-ray photoelectron diffraction to obtain the precise structural
configuration of P dopants in subsurface Si:P δ-layers. The
growth of δ-layer systems with different levels of doping is
carefully studied and verified using X-ray photoelectron spectroscopy
and low-energy electron diffraction. Subsequent diffraction measurements
reveal that in all cases, the subsurface dopants primarily substitute
with Si atoms from the host material. Furthermore, no signs of carrier-inhibiting
P–P dimerization can be observed. Our observations not only
settle a nearly decade-long debate about the dopant arrangement but
also demonstrate how X-ray photoelectron diffraction is surprisingly
well suited for studying subsurface dopant structure. This work thus
provides valuable input for an updated understanding of the behavior
of Si:P δ-layers and the modeling of their derived quantum devices.