Conditioning nano-LEDs in arrays by laser-micro-annealing: The key to their performance improvement
M. Mikulics, P. Kordoš, D. Gregušová, Zdeněk Sofer, A. Winden, St. Trellenkamp, J. Moers, Joachim Mayer, H. Hardtdegen
Abstract
A local so-called laser-micro-annealing (LMA) conditioning technology, which is suitable for the fabrication of a large range of hybrid nano-optoelectronic devices, was applied to III-nitride-based nano-light emitting diodes (LEDs). The LEDs with a diameter of ∼100 nm were fabricated in large area arrays and designed for hybrid optoelectronic applications. The LMA process was developed for the precise local conditioning of LED nano-structures. Photoluminescence measurements reveal the enhancement of nano-LED properties, which is in very good agreement with a simple model introduced based on the reduction of the defect layer depth by the LMA process. The experimental data confirm the reduction of the defect layer depth from ∼17 nm to ∼5 nm determined. In consequence, an increase in work currents up to 40 nA at 5 V bias after the LMA procedure as well as high electroluminescence (EL) and output optical power up to 150 nW in the ∼440–445 nm emission wavelength range corresponding to ∼75% wall-plug efficiency were achieved. Additionally, the LEDs' electroluminescence intensities reach the desired values by conditioning the contact/annealed regions of individual LEDs accordingly. Furthermore, the LMA process affects the long-term stability of the electroluminescence (EL) intensity of single nano-LED devices. A study of the EL during 5000 h in the continuous wave operation testing mode revealed a moderate ∼15% decrease in the intensity in comparison to ∼50% for their non-LMA counterparts. Finally, Raman measurements indicate that the “work” temperature for nano-LED conditioned structures decreases.