Carbon as a Shallow Donor in Transparent Conducting Oxides

Abstract

Carbon is a common unintentional impurity in oxide semiconductors. We use hybrid density functional theory to calculate the electronic and structural properties of carbon impurities in ZnO, In 2 O 3 , and Ga 2 O 3 -materials that are used as transparent conductors. In each of these semiconducting oxides, we find that carbon is most likely to occupy the cation site under most electronic and chemical potential conditions. In ZnO, C Zn acts as a shallow double donor and exhibits large local breathing-mode relaxations. In In 2 O 3 and Ga 2 O 3 , C acts as a shallow donor and moves off the cation site to become threefold oxygen coordinated. In all three oxides, C cation exhibits modest formation energies, indicating that these species will be likely to incorporate. Our results indicate that C impurities are suitable donor dopants in these oxides and will contribute to background n-type conductivity if unintentionally present.

Defect Formation Energies of Interstitial C, Si, and Ge Impurities in β‐Ga2O3

“…As can be seen in Figure , the formation energy of the substitutional defect is lowest for Si and increases moving to Ge and then to Si, following the trend in electronegativety. For C in the q = +1 charge state, one finds the most stable configuration by elongating one C–O bond leading to a planar threefold coordinated C center (C planar ), in agreement with previous calculations . We find that C planar occurs at 0.4 eV lower energy than C tetra .…”

“…DFT calculations have proved invaluable in assessing the atomic structure and the energy levels of point defects in β ‐Ga 2 O 3 . To date, modeling efforts have mainly focused on defects occurring in the mid and lower band gap, leading to tentative assignments to either vacancies or self trapped holes .…”

Doping of Ga2O3 with transition metals

“…This cannot be attributed to oxygen vacancies, which are deep donors with a very large ionization energy. 10 Calculations for various dopant impurities have already been performed; 10,11 Si, Ge, Sn, or C on Ga sites, or Cl and F on O sites have been found to be shallow donors. However, experimental results have shown smaller than expected conductivity upon doping with Si or Sn.…”

Chemical Interpretation of Charged Point Defects in Semiconductors: A Case Study of Mg2Si

“…This can be a valuable guide for applications in which doping is essential for tuning the electrical properties of materials, such as thermoelectrics [34][35][36] and transparent conducting oxides. [37][38][39][40] In fact, the present molecular orbital analyses for Mg 2 Si can directly be applied to compounds with structures having the same atomic positions, such as half-Heusler TiNiSn 41,42 and fluorite CeO 2 . 43…”