Calcium as a nonradiative recombination center in InGaN

Abstract

Calcium can be unintentionally incorporated during the growth of semiconductor devices. Using hybrid functional first-principles calculations, we assess the role of Ca impurities in GaN. Ca substituted on the cation site acts as a deep acceptor with a level ∼1 eV above the GaN valence-band maximum. We find that for Ca concentrations of 1017 cm−3, the Shockley–Read–Hall recombination coefficient, A, of InGaN exceeds 106 s−1 for band gaps less than 2.5 eV. A values of this magnitude can lead to significant reductions in the efficiency of light-emitting diodes.

Deep‐Level Defects and Impurities in InGaN Alloys

“…In this study, we will demonstrate that the previously observed upward shift in the charge‐state transition levels with respect to the InGaN VBM is not ubiquitous. We will examine native point defects ( V Ga , V N ), impurities (Ca Ga , Fe Ga , C N ), and complexes between native point defects and impurities ( V Ga –3H and V Ga –O N –2H).…”

“…In each of these studies, we found the charge‐state transition levels of the defects to shift up with respect to the InGaN valence‐band maximum (VBM) with increasing indium content. A pertinent question is whether this upward shift in the charge‐state transition level is a common feature of all defects in InGaN as a function of indium content.…”

“…We have previously investigated the properties of gallium vacancy complexes and calcium impurities in InGaN as a function of indium content . In these studies, we assumed that the main effect of alloying was the lattice expansion and accounted for the change in the InGaN bandgap as a function of indium content by expanding the lattice parameters of the GaN defect supercell in accordance with Vegard's law.…”

“…We will examine native point defects ( V Ga , V N ), impurities (Ca Ga , Fe Ga , C N ), and complexes between native point defects and impurities ( V Ga –3H and V Ga –O N –2H). We have previously presented results on the defect levels of the V Ga complexes and Ca Ga as a function of indium content using the expanded GaN supercell approach; they are included here with the intention of presenting a comprehensive picture of the properties of defects in InGaN and to contrast with defect levels that do not shift up with respect to the InGaN VBM. Our examination of the atomic states that comprise each of these defects allows us to elucidate why the magnitude and direction of the shift of these defect levels with respect to the InGaN band edges differ so significantly.…”

Luminescent N-polar (In,Ga)N/GaN quantum wells achieved by plasma-assisted molecular beam epitaxy at temperatures exceeding 700 °C

“…Even more intriguing is the fact that the electron capture coefficient of Ca is theoretically predicted to increase by several orders of magnitude when changing the band gap of (In,Ga)N from 2.7 to 2.2 eV. 31 In other words, a certain concentration of Ca may go unnoticed for a blue emitting (In,Ga)N/GaN QW, but may have a devastating effect on the internal quantum efficiency of a green emitting one. This peculiar behavior is consistent with the results of our time-resolved measurements, which indicated a similar density of nonradiative centers for blue emitting Ga-and green emitting N-polar samples, but much larger capture coefficients for the latter ones.…”