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Communication Dans Un Congrès Année : 2021

AlGaN Nanostructures for Electron Beam Pumped UV Emitters

Résumé

UV disinfection is receiving renewed attention due to the global pandemic, as an immediately deployable and cost-effective option. The common sources used for this application are low-pressure arc lamps, emitting at 254 nm and containing toxic mercury, which Europe is trying to phase out. Furthermore, this radiation is highly carcinogenic and cataractogenic, which represents a health hazard. Recently different replacements for mercury lamps have been proposed, e.g. excimer lamps that emit at 222 nm, supposedly harmless. However, most of the focus is now on AlGaN-based UV LEDs, with numerous advantages (fast on/off switching, longer lifetime, reduced ozone generation, wider wavelength selection). Yet the wall plug efficiency of commercial LEDs at  260 nm is WPE < 1%, far below that of mercury lamps, and drops dramatically at shorter wavelengths. Therefore, there is still a need and opportunity for alternative UV sources. This work proposes electron-beam pumped UV lamps as an alternative to LEDs to overcome issues related to doping, transport and contacting. This approach obviates the need for p-type doping and efficient and homogeneous carrier injection is achieved without an electron blocking layer. Furthermore, the WPE should not vary much over 210−350 nm. Here, we study the performance of AlGaN/AlN dots-in-a-wire [1] and Stranski-Krastanov quantum dot superlattices [2], whose UV emission can be tailored in the 230-330 nm range. The three-dimensional (3D) carrier confinement in such nanostructures results in high internal quantum efficiency (IQE = 50% on average) and promising external quantum efficiency (EQE up to 5% for as-grown structures). Studies conducted under operation conditions (high injection) show no degradation of the IQE for excitation power densities up to 1 MW/cm2, obtained by pumping with a pulsed Nd-YAG laser. With e-beam excitation, the emission efficiency remains stable up to 10 kV of acceleration voltage and 0.5 mA of injected current (current limit of our setup). E-beam pumping offers also an interesting alternative for the fabrication of UV lasers, highly demanded in the fields of medicine and biotechnology, as well as in 3D printing and non-line-of-sight communication. Today, this spectral range is covered by gas lasers (ArF, KrF, XeF) or lasers based on frequency conversion (Nd:YAG). III-nitride semiconductor laser diodes are promising candidates to provide an efficient semiconductor-based alternative, but current injection is a major problem for wavelengths shorter than 360 nm. For this application, advantages of the e-beam pumping include higher flexibility in the choice of materials for the active medium due to the absence of doping or electrical contacts, as well as higher radiative recombination efficiency since the electrons and holes generated by impact ionization share the same distribution in the active medium. This technology has enabled the fabrication of ZnSe-based pulsed lasers that emit up to 600 W at 535 nm. There are some studies of e-beam pumped UV lasers using AlGaN/GaN separate confinement heterostructures (SCH), but they are limited to pulsed electron beam excitation at cryogenic temperatures [3,4]. New device architectures are required with the prospect of achieving room temperature lasers. Here, we present a study of undoped AlGaN/GaN SCHs designed to operate under e-beam injection with an acceleration voltage  10 kV. We discuss the effect of spontaneous and piezoelectric polarization on the carrier diffusion and demonstrate that the performance is improved using an asymmetric graded-index separate-confinement heterostructure (GRINSCH). [1] H. Arkumar et al., Nanotechnology 31 505205 (2020). [2] I. Dimkou et al., Nanotechnology 31 204001 (2020). [3] T. Wunderer et al., IEEE Photonics Technology Letters 29 1344 (2017). [4] T. Hayashi et al., Scientific Reports 7 2944 (2017).
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Dates et versions

hal-03995673 , version 1 (18-02-2023)

Identifiants

  • HAL Id : hal-03995673 , version 1

Citer

Anjali Harikumar, Sergi Cuesta, Ioanna Dimkou, Quang Minh Thai, Fabrice Donatini, et al.. AlGaN Nanostructures for Electron Beam Pumped UV Emitters. UKNC Winter Meeting, UK Nitrides Consortium, Jan 2021, Cambridge, United Kingdom. ⟨hal-03995673⟩
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