CPM Seminar

AlGaN-based technology for deep UV emitters

Zlatko Sitar

Department of Materials Science and Engineering
North Carolina State University

Despite the rapid progress in III-nitride-based laser diodes, sub-300 nm UV semiconductors lasers have not been realized. UV optoelectronic devices have a variety of applications such as sterilization, water purification, spectroscopy, high density optical data storage, and biological sensing. Technical and scientific barriers arise from the lack of proper crystalline substrates and a poor understanding of defect control in the wide bandgap semiconductors. AlGaN-based technology developed on single crystalline AlN substrates and impurity control in the active region offers a pathway to address all these challenges.

In addition to low dislocation density, reduction in non-radiative centers and compensating point defects in the active region are required to achieve high IQE. In order to understand the influence of point defects on radiative lifetime and ultimately achieve high IQE, we have carried out an extensive study of vacancy and carbon control via Fermi level and supersaturation management for various MQW structures grown on bulk AlN substrates. The use of bulk AlN substrates enabled us to undoubtedly distinguish the effect of growth condition, such as V/III ratio, on optical quality from the influence of dislocation density. At a high V/III ratio, a record high IQE of ~80% at a carrier density of 10¹⁸ cm^-3 was achieved at ~258 nm.

Using this technology, we achieved lasing at room temperature in AlGaN-based MQW structures with a threshold below 60 kW/cm² and lasing wavelength from 237 to 281 nm. All samples had a lasing FWHM less than 0.8 nm, which is the narrowest reported so far.