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

Seyed Ehsan Hashemi (Institutionen för mikroteknologi och nanovetenskap, Fotonik) ; Jörgen Bengtsson (Institutionen för mikroteknologi och nanovetenskap, Fotonik) ; Johan S. Gustavsson (Institutionen för mikroteknologi och nanovetenskap, Fotonik) ; Stefan Carlsson (Institutionen för mikroteknologi och nanovetenskap, Fotonik) ; G. Rossbach ; Åsa Haglund (Institutionen för mikroteknologi och nanovetenskap, Fotonik)
Proceedings of SPIE: High Contrast Metastructures IV. Conference on High Contrast Metastructures IV, San Francisco, CA, FEB 11-12, 2015 (0277-786X). Vol. 9372 (2015), p. Art. no. 93720D.
[Konferensbidrag, övrigt]

For GaN-based microcavity light emitters, such as vertical-cavity surface-emitting lasers (VCSELs) and resonant cavity 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 TiO2 grating with the help of a SiO2 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 TiO2/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.

Nyckelord: dielectric materials , gallium nitride , high-contrast grating , TiO2 , vertical-cavity surface-emitting laser



Denna post skapades 2015-05-12. Senast ändrad 2015-12-07.
CPL Pubid: 217039

 

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Institutioner (Chalmers)

Institutionen för mikroteknologi och nanovetenskap, Fotonik

Ämnesområden

Ytbehandlingsteknik
Nanoteknik

Chalmers infrastruktur