The resonant III-nitride grating reflector

Wang, Yongjin; Wu, Tong; Tanae, T.; Zhu, Hongbo; Hane, Kazuhiro

doi:10.1088/0960-1317/21/10/105025

Cited by 7 publications

(5 citation statements)

References 24 publications

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“…There have been a few attempts, such as bandgap-selective photoelectrochemical etching of a sacrificial InGaN superlattice to form an AlGaN HCG membrane 74 however, with a limited airgap height, and focused-ion-beam etching to create an airgap underneath a GaNbased HCG 75 , an impractical process for device integration on a wafer-scale. In addition, GaN membrane gratings have been fabricated from a GaN-on-Si structure [76][77][78] by selective etching of Si, and free-standing hafnium-oxide gratings using the same approach 79 , but applying this concept to fabricate a bottom mirror in a VCSEL is not straightforward, since growth of high-quality GaN on Si for laser applications is very challenging. Due to the difficulties in realizing a III-nitride based HCG structure with an airgap, a grating reflector without an airgap could be used, which previously has been proposed for long-wavelength VCSELs where the mirror fabrication also is complex.…”

Section: Mirrorsmentioning

confidence: 99%

Progress and challenges in electrically pumped GaN-based VCSELs

et al. 2016

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The Vertical-Cavity Surface-Emitting Laser (VCSEL) is an established optical source in short-distance optical communication links, computer mice and tailored infrared power heating systems. Its low power consumption, easy integration into two-dimensional arrays, and low-cost manufacturing also make this type of semiconductor laser suitable for application in areas such as high-resolution printing, medical applications, and general lighting. However, these applications require emission wavelengths in the blue-UV instead of the established infrared regime, which can be achieved by using GaN-based instead of GaAs-based materials. The development of GaN-based VCSELs is challenging, but during recent years several groups have managed to demonstrate electrically pumped GaN-based VCSELs with close to 1 mW of optical output power and threshold current densities between 3-16 kA/cm 2 . The performance is limited by challenges such as achieving high-reflectivity mirrors, vertical and lateral carrier confinement, efficient lateral current spreading, accurate cavity length control and lateral optical mode confinement. This paper summarizes different strategies to solve these issues in electrically pumped GaN-VCSELs together with state-of-the-art results. We will highlight our work on combined transverse current and optical mode confinement, where we show that many structures used for current confinement result in unintentionally optically anti-guided resonators. Such resonators can have a very high optical loss, which easily doubles the threshold gain for lasing. We will also present an alternative to the use of distributed Bragg reflectors as high-reflectivity mirrors, namely TiO2/air high contrast gratings (HCGs). Fabricated HCGs of this type show a high reflectivity (>95%) over a 25 nm wavelength span.

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Section: Mirrorsmentioning

confidence: 99%

Progress and challenges in electrically pumped GaN-based VCSELs

et al. 2016

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“…There have been a few attempts, such as bandgap-selective photoelectrochemical etching of a sacrificial InGaN superlattice to form an AlGaN HCG membrane, 9 however, with a limited airgap height, and focused-ion-beam etching to create an airgap underneath a GaN-based HCG, 10 an impractical process for device integration on a wafer-scale. In addition, GaN membrane gratings have been fabricated from a GaN-on-Si structure by selective etching of Si, [11][12][13] but applying this concept to fabricate a bottom mirror in a VCSEL is not straightforward, since growth of high-quality GaN on Si for laser applications is very challenging. Due to the difficulties in realizing a III-nitride based HCG structure with an airgap, a GaN grating reflector without an airgap has been proposed.…”

Section: Introductionmentioning

confidence: 99%

TiO2 membrane high-contrast grating reflectors for vertical-cavity light-emitters in the visible wavelength regime

Hashemi

Bengtsson

Gustavsson

et al. 2015

Journal of Vacuum Science &Amp; Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phen

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In this work, the authors describe a novel route to achieve a high reflectivity, wide bandwidth feedback mirror for GaN-based vertical-cavity light emitters; using air-suspended high contrast gratings in TiO2, with SiO2 as a sacrificial layer. The TiO2 film deposition and the etching processes are developed to yield grating bars without bending, and with near-ideal rectangular cross-sections. Measured optical reflectivity spectra of the fabricated high contrast gratings show very good agreement with simulations, with a high reflectivity of >95% over a 25 nm wavelength span centered around 435 nm for the transverse-magnetic polarization.

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“…Alternatively, an airgap underneath the GaN grating structure was fabricated by using a focused-ion-beam (FIB) etching process, 11 which is inconvenient for large-scale production despite its proof-of-principle approach. Moreover, in the GaN-on-Si platform, 12 an airgap was obtained by backside Si wafer etching, 13,14 by which the integration to VCSELs will remain difficult until the full epitaxial growth of nitrides on Si with high enough quality is feasible.…”

Section: Introductionmentioning

confidence: 99%

Air-suspended TiO₂-based HCG reflectors for visible spectral range

et al. 2015

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For GaN-based microcavity light emitters, such as vertical-cavity surface-emitting lasers (VCSELs) and resonantcavity light emitting diodes (RCLEDs) in the blue-green wavelength regime, achieving a high reflectivity wide bandwidth feedback mirror is truly challenging. The material properties of the III-nitride alloys are hardly compatible with the conventional distributed Bragg reflectors (DBRs) and the newly proposed high-contrast gratings (HCGs). Alternatively, at least for the top outcoupling mirror, dielectric materials offer more suitable material combinations not only for the DBRs but also for the HCGs. HCGs may offer advantages such as transverse mode and polarization control, a broader reflectivity spectrum than epitaxially grown DBRs, and the possibility to set the resonance wavelength after epitaxial growth by the grating parameters. In this work we have realized an air-suspended TiO 2 grating with the help of a SiO 2 sacrificial layer. The deposition processes for the dielectric layers were fine-tuned to minimize the residual stress. To achieve an accurate control of the grating duty cycle, a newly developed lift-off process, using hydrogen silesquioxan (HSQ) and sacrificial polymethyl-methacrylate (PMMA) resists, was applied to deposit the hard mask, providing sub-10 nm resolution. The finally obtained TiO 2 /air HCGs were characterized in a micro-reflectance measurement setup. A peak power reflectivity in excess of 95% was achieved for TM polarization at the center wavelength of 435 nm, with a reflectivity stopband width of about 80 nm (FWHM). The measured HCG reflectance spectra were compared to corresponding simulations obtained from rigorous coupled-wave analysis and very good agreement was found.

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The resonant III-nitride grating reflector

Cited by 7 publications

References 24 publications

Progress and challenges in electrically pumped GaN-based VCSELs

Progress and challenges in electrically pumped GaN-based VCSELs

TiO2 membrane high-contrast grating reflectors for vertical-cavity light-emitters in the visible wavelength regime

Air-suspended TiO₂-based HCG reflectors for visible spectral range

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The resonant III-nitride grating reflector

Cited by 7 publications

References 24 publications

Progress and challenges in electrically pumped GaN-based VCSELs

Progress and challenges in electrically pumped GaN-based VCSELs

TiO2 membrane high-contrast grating reflectors for vertical-cavity light-emitters in the visible wavelength regime

Air-suspended TiO2-based HCG reflectors for visible spectral range

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Product

Resources

About

Air-suspended TiO₂-based HCG reflectors for visible spectral range