Deep UV lasers grown on native AlN substrates
The realization of convenient ultrashort-wavelength light emitters that operate in the 100-280 nm range (ultraviolet subtype C, 'UV-C') would benefit many applications, including air and water purification and decontamination, germicidal and biomedical instrumentation systems, ophthalmic surgery tools, non-line-of-sight UV communications, and high-density optical storage. At present, mercury, deuterium, excimer and xenon lamps are used as bulky sources of UV-C light but have several disadvantages. For example, they are constrained by limited output powers, poor lifetimes and instability, are hard to miniaturize and are chemically hazardous.
The cutting edge in semiconductor light sources has moved into the ultraviolet. Developers are pushing the wide-bandgap III-V gallium nitride compounds used in blue and violet lasers to shorter wavelengths by adding aluminum to increase the bandgap. In theory, that family can emit at wavelengths as short as 205 nm if the active layer is aluminum nitride. However, while high performance practical light sources are commercially available for visible and longer wavelength UV lasers, it is still a technical challenge to realize high performance UV lasers at wavelengths shorter than 280 nm (UV-C) due to the material challenges.
AlGaN on native bulk AlN substrates holds great promises
for high performance light sources at deep UV regime
Here, Kalapala and coworkers reported an optically pumped room temperature low threshold lasers based on 21 multiple quantum wells (MQW) grown on native AlN substrate. The growth was carried out in a high-temperature reactor by low pressure organometallic vapor phase epitaxy (LP-OMVPE) process. high quality pseudomorphic growth was achieved, which resulted in high quality AlGaN based heterostructures for low threshold lasing. The team introduced a concept with large number of quantum wells for increasing optical mode confinement factor. Such a confinement factor increase can relax the gain threshold condition for the active region which results in lower threshold current per quantum wells. While further improvement is needed to reduce cavity loss and increase the optical power, the work demonstrated here has shown promising future for AlGaN MQW structures grown on native AlN substrate in realizing practical deep UV-C lasers for practical applications.
About The Group
The research was carried out by a collaborative team. Prof. Weidong Zhou’s group at the University of Texas at Arlington has been working on various semiconductor lasers, including photonic crystal light sources for on-chip integration based on heterogeneous integration of compound semiconductor materials and silicon-based photonic crystal cavities. Prof. Zhenqiang (Jack) Ma’s group at the University of Wisconsin at Madison has been working on various electronic and optoelectronic devices based on semiconductor nanomembranes and heterogeneous integration technics on both rigid and flexible substrates. Prof. John D. Albrecht’s group at Michigan State University has been working on electronic and photonic materials and devices, including fundamental understandings of charge and interface properties based on theoretical simulations and experimental investigations. The work is also in collaborations with Dr. Baxter Moody at HexaTech, Inc., where both bulk AlN substrates and AlGaN MQW heterostructure were grown.
Kalapala A R K, Liu D, Cho S J, Park J P, Zhao D Y et al. Optically pumped room temperature low threshold deep UV lasers grown on native AlN substrates. Opto-Electron Adv 3, 190025 (2020).