Strain-Enhanced Doping in Semiconductors: Effects of Dopant Size and Charge State

Abstract

When a semiconductor host is doped by a foreign element, it is inevitable that a volume change will occur in the doped system. This volume change depends on both the size and charge state difference between the dopant and the host element. Unlike the "common expectation" that if the host is deformed to the same size as the dopant, then the formation energy of the dopant would reach a minimum, our first-principles calculations discovered that when an external hydrostatic strain is applied, the change of the impurity formation energy is monotonic: it decreases if the external hydrostatic strain is applied in the same direction as the volume change. This effect also exists when a biaxial strain is applied. A simple strain model is proposed to explain this unusual behavior, and we suggest that strain could be used to significantly improve the doping solubility in semiconductor systems.

Anisotropic Strain Enhanced Hydrogen Solubility in bcc Metals: The Independence on the Sign of Strain

“…The accumulation of H in metals leads to formation of voids, bubbles, and blisters [10]. In this regard, our finding suggests a cascading 3 effect of H bubble formation in bcc metals, which has significant implications in using bcc metals as PFM.…”

“…Strain engineering has been recognized to provide an effective way to enhance the solubility of impurity in solids, such as doping of impurity in semiconductors. In general, the impurity formation energy is a linear monotonic function of strain following elasticity theory, no matter a hydrostatic or biaxial strain [2,3]. Thus, one can expect when a "large" impurity induces a compressive lattice stress, tending to expand the lattice, its solubility can only be enhanced by applying a tensile strain but decreased by a compressive strain; and the reverse is true for a "small" impurity.…”

“…The H behavior under strain is then dictated by the H-induced lattice stress tensor, i.e., force dipole tensor as demonstrated before [2,3]. The defect induced lattice stress generally has two contributions [2,3,20]: the atomic size effect (bond deformation) and electronic band effect (Fermi level shift) termed as quantum electronic stress [20].…”

“…The defect induced lattice stress generally has two contributions [2,3,20]: the atomic size effect (bond deformation) and electronic band effect (Fermi level shift) termed as quantum electronic stress [20].…”

Bowing of the defect formation energy in semiconductor alloys

“…Due to the large lattice mismatch between CdS and CdTe, as S atoms are incorporated into the system (x increases), the lattice constant of the alloy decreases. Therefore, the strain induced by the defect is released, so the formation energy decreases [23]. In each alloy, sites surrounded by more S atoms have shorter bond lengths, so the strain effect is small; sites surrounded by more Te atoms have longer bond lengths, so the strain effect is large and the formation energies change more significantly.…”