Light-emitting diode (LED) materials

Group III nitrides such as InN, GaN, AlN and their alloys have attracted a lot of interest due to their potential in providing high efficiency electronic and optoelectronic devices in a broad spectral regime including UV-C through to the whole visible spectrum. For semipolar InGaN-based LEDs with reduced quantum confined Stark effect, higher radiative recombination rate and improved overall efficiency are expected. However, the quantum efficiency in green is still substantially lower than the blue counterparts due to extended defects such as threading dislocations and basal-plane stacking faults.

Whereas for InGaN-based blue to green LEDs already very high efficiencies have been achieved, AlGaN-based UV devices still suffer from relatively poor external quantum efficiencies. As a potential material allowing to reduce the strain in the AlGaN/AlN quantum well, AlBGaN has been proposed. By adding boron as the lightest and smallest group III element to the currently used AlGaN system, another degree of freedom in band gap and lattice constant tailoring can be utilized. However, the solubility of boron in AlGaN is very low.

The goals of the project are listed as following:

  • Investigate how the boron incorporation can be improved by optimized growth conditions.
  • Clarity which B concentrations help to reduce the strain in Al-containing heterostructures.
  • Retrieve information about many fundamental properties of this quaternary material system.
(a) InGaN/GaN multi quantum wells showing several extended basal-plane stacking faults. (b) HRTEM image of an I2-type BSF with the stacking sequence of …ABABCACA….

References

[1] O. Rettig, J. P. Scholz, N. Steiger, S. Bauer, T. Hubácek, M. Zíková, Y. Li, H. Qi, J. Biskupek, U. Kaiser, K. Thonke, F. Scholz , Investigation of Boron Containing AlN and AlGaN Layers Grown by MOVPE. pysica status solidi (b) 255 (2018) 1700510

[2] Y. Li, H. Qi, T. Meisch, M. Hocker, K. Thonke, F. Scholz, Ute Kaiser, Formation of I2-type basal-plane stacking faults in In0.25Ga0.75N multiple quantum wells grown on a (10-11) semipolar GaN template. Applied Physics Letters 110 (2017) 022105

Collaborations

Prof. Dr. F. Scholz, Ulm University
Apl. Prof. Dr. K. Thonke, Ulm University