III-Nitride grating grown on freestanding HfO2 gratings
© Wang et al; licensee Springer. 2011
Received: 31 March 2011
Accepted: 18 August 2011
Published: 18 August 2011
We report here the epitaxial growth of III-nitride material on freestanding HfO2 gratings by molecular beam epitaxy. Freestanding HfO2 gratings are fabricated by combining film evaporation, electron beam lithography, and fast atom beam etching of an HfO2 film by a front-side silicon process. The 60-μm long HfO2 grating beam can sustain the stress change during the epitaxial growth of a III-nitride material. Grating structures locally change the growth condition and vary indium composition in the InGaN/GaN quantum wells and thus, the photoluminescence spectra of epitaxial III-nitride grating are tuned. Guided mode resonances are experimentally demonstrated in fabricated III-nitride gratings, opening the possibility to achieve the interaction between the excited light and the grating structure through guided mode resonance.
PACS: 78.55.Cr; 81.65.Cf; 81.15.Hi.
KeywordsInGaN/GaN QWs fast atom beam etching molecular beam epitaxy
Freestanding III-nitride structures can take advantage of the large refractive index contrast between III-nitride and air [1–7]. In such structure, the excited light has a potential to interact with freestanding structure through guided modes. Among the approaches towards creating suspended III-nitride structures, growth of III-nitride on freestanding structured template is an emerging technology. During growth process, nanoscale structures locally change the growth conditions and thus, the selective growth can be achieved to generate epitaxial III-nitride structures with smooth facets [8–11]. Meanwhile, freestanding III-nitride structures are formed by growth method and free of the etching damage. Moreover, the as-grown III-nitride structures can provide a natural optical cavity to support guided mode resonances, opening the possibility to achieve the interaction between the excited light and the epitaxial structures.
From the growth point of view, small material lattice mismatch between HfN and GaN crystals makes HfN film a superior buffer layer for the growth of GaN [12, 13]. During molecular beam epitaxy (MBE) growth, HfN surface can be formed by nitrifying HfO2 substrate. Hence, structured HfO2 film can be used as a template for growing III-nitride materials . On the other hand, HfO2 film is an excellent optical material with high laser damage threshold, thermal, and chemical stability [15–17]. Recently, we have fabricated freestanding HfO2 gratings and experimentally demonstrated their guided mode resonances . It is of great interest to implement the growth of III-nitride materials on freestanding HfO2 gratings.
Here, we demonstrate the freestanding III-nitride gratings grown on suspended HfO2 gratings. The epitaxial growth of InGaN/GaN quantum wells (QWs) are performed on freestanding HfO2 gratings by MBE technique. The optical performances of the resultant epitaxial structures are characterized in photoluminescence (PL) and reflectance measurements.
Experimental results and discussion
The epitaxial growth of III-nitride material is performed on the suspended HfO2 grating. The 60-μm long freestanding HfO2 grating beam can sustain the stress change during MBE growth. The PL spectra and reflectance of epitaxial III-nitride gratings are experimentally characterized. Epitaxial III-nitride grating can function as an optical cavity to support resonance mode, which is demonstrated and compared to the resonances of original HfO2 grating. These results indicate that resonant III-nitride gratings are promising for the development of resonant optical devices and the realization of the resonant emission. This work also opens the possibility for fabricating novel III-nitride optic devices by a combination of freestanding HfO2 nanostructures with epitaxial growth of III-nitride materials.
This work was partially supported by the JSPS Research Project (19106007 and P09070) and the NJUPT Research Project (NY211001).
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