Research Challenge 4: Defect-Carrier Interactions
- Measured density of an InGaN QW deep level defect located 0.15 eV above the valence band edge. Note that the density is much higher in the rightmost QW1 closest to the n-type GaN region.
This Research Challenge aims to develop an in-depth understanding of the electrical, optical and structural properties of defects in InGaN materials and heterostructures. With such understanding, routes to circumventing a key contributor to non-radiative carrier recombination might be realized, helping to overcome the blue-efficiency, RYG-gap, and functional-light technology challenges.
Our study of defects involves unique experimental and theoretical capabilities. We are using deep-level optical spectroscopy to quantify defect energy levels and densities. Advanced density functional theory is being used to predict the atomic structure and carrier-capture mechanisms of defects.
This Research Challenge focuses on non-radiative processes that are mediated by point defects and the deep levels in the semiconductor band gap that they create. Our goal is to develop an in-depth understanding of these defects in InGaN, from their atomistic structure and carrier capture cross-sections and dynamics to learning how their spatial distribution depends on the growth environment.
- Calculation of the relaxed configuration of the -2 and -3 charge states of the gallium vacancy in GaN. Future work will accurately determine the crossing of the two levels, which dictates carrier capture and recombination processes.
We focus on the role of defects because, until recently, developing such an understanding was not possible in wide-bandgap semiconductor multi-heterostructures such as InGaN/GaN MQWs – there were no quantitative defect spectroscopies applicable to levels deeper than ~1 eV from a carrier band edge with nanoscale depth resolution. In the past several years, however, due to work at Sandia and elsewhere, depth-selected deep-level optical spectroscopy (DS-DLOS) has emerged as just such a spectroscopy.
In combination with growth of tailored heterostructures and the parallel development of advanced density functional theory, we are building an unprecedented level of understanding of deep-level defects in InGaN, and along the way we are developing methodologies broadly applicable to virtually all wide-bandgap semiconductors and insulators.
- Dr. Andrew Armstrong (SNL) – Principal Investigator, deep level optical spectroscopy (DLOS) investigation of (In)GaN films and InGaN/GaN LEDs.
- Dr. Tania Henry (SNL post-doctoral researcher) –DLOS studies of InGaN films and InGaN/GaN LEDs.
- Dr. Daniel Koleske (SNL) – MOVPE growth of c-plane InGaN films and InGaN/GaN LEDs.
- Dr. Normand Modine (SNL/CINT) – Advanced density function theory calculations.
- Prof. James Speck and Kathryn Kelchner (Ph. D. student) (UCSB) – MOVPE growth of m-plane (In)GaN films and LEDs.
This Research Challenge brings together expertise and capabilities at SNL (particularly the powerful and rapidly evolving technique of deep-level optical spectroscopy), CINT (transition-state-surface mapping through density functional calculations), and the CEEM EFRC at UCSB (synthesis of heterostructures with novel orientations and defect distributions). In addition, we are studying questions that intersect other parts of our EFRC, including the implications of defect-induced recombination on efficiency droop (Research Challenge 3), and point defect distributions and their influence on nanowire properties (Research Challenge 1).
Research Challenge Publications
Armstrong, Andrew; Crawford, Mary H.; and Koleske, Daniel D. Quantitative and Depth-Resolved Investigation of Deep-Level Defects in InGaN/GaN Heterostructures, Journal of Electronic Materials, 40, 369 (2011). [10.1007/s11664-010-1453-4]