Two-dimensional high-index-contrast dielectric gratings exhibit unconventional transmission and reflection due to their morphologies. For light-emitting devices, these characteristics help guided modes defeat total internal reflections, thereby enhancing the outcoupling efficiency into an ambient medium. However, the outcoupling ability is typically impeded by the limited index contrast given by pattern media. Here, we report strong-diffraction, high-index-contrast cavity engineered substrates (CESs) in which hexagonally arranged hemispherical air cavities are covered with a 80 nm thick crystallized alumina shell. Wavelength-resolved diffraction measurements and Fourier analysis on GaN-grown CESs reveal that the high-index-contrast air/alumina core/shell patterns lead to dramatic excitation of the low-order diffraction modes. Large-area (1075 × 750 μm(2)) blue-emitting InGaN/GaN light-emitting diodes (LEDs) fabricated on a 3 μm pitch CES exhibit ∼39% enhancement in the optical power compared to state-of-the-art, patterned-sapphire-substrate LEDs, while preserving all of the electrical metrics that are relevant to LED devices. Full-vectorial simulations quantitatively demonstrate the enhanced optical power of CES LEDs and show a progressive increase in the extraction efficiency as the air cavity volume is expanded. This trend in light extraction is observed for both lateral- and flip-chip-geometry LEDs. Measurements of far-field profiles indicate a substantial beaming effect for CES LEDs, despite their few-micron-pitch pattern. Near-to-far-field transformation simulations and polarization analysis demonstrate that the improved extraction efficiency of CES LEDs is ascribed to the increase in emissions via the top escape route and to the extraction of transverse-magnetic polarized light.

We report highly emissive and radiatively cooled metallic surfaces that sustain multiple and high-amplitude gap plasmon cavity modes within the principal thermal radiation spectrum at room temperature (i.e., 8–13 μm). A square-lattice array of Cu/ZnS/Cu gap plasmon cavities with five different widths was designed to avoid the near-field coupling between adjacent cavities and the anticrossing of a cavity mode and the first diffraction mode. The gap plasmon cavities fabricated on a Si substrate exhibited an effective emissivity of >0.62, up to an incidence of 60°. Outdoor solar heating experiments showed that the Cu/ZnS/Cu multicavity array lowered the Si substrate temperature by 4 °C at a maximum solar irradiance of 800 W/m2, which is equivalent to a near-one-sun intensity, relative to a planar Cu/ZnS/Cu multilayer. Such mid-infrared spectrum management of metals enables heat dissipation via radiation, which will be further utilized for designing electrodes that cool optoelectronic devices with the same metal/dielectric/metal configuration.

A facile synthesis method for the heterostructures of single-walled carbon nanotubes (SWCNTs) and few-layer MoS 2 is reported. The heterostructures are realized by in situ chemical vapor deposition of MoS 2 on individual SWCNTs. Field effect transistors based on the heterostructures display different transfer characteristics depending on the formation of MoS 2 conduction channels along SWCNTs. Under light illumination, negative photoresponse originating from charge transfer from MoS 2 to SWCNT is observed while positive photoresponse is observed in MoS 2 conduction channels, leading to ambipolar photoresponse in devices with both SWCNT and MoS 2 channels. The heterostructure phototransistor, for negative photoresponse, exhibits high responsivity (100-1000 AW −1 ) at low bias voltages (0.1 V) in the visible spectrum (500-700 nm) by combining high mobility conduction channel (SWCNT) with efficient light absorber (MoS 2 ).

Two-dimensional surface texturing is a widespread technology for imparting broadband antireflection, yet its design rules are not completely understood. The dependence of the reflectance spectrum of a periodically patterned glass film on various structural parameters (e.g., pitch, height, shape, and fill factor) has been investigated by means of full-vectorial numerical simulations. An average weighted reflectivity accounting for the AM1.5G solar spectrum (λ=300-1000  nm) was sinusoidally modulated by a rod pattern's height, and was minimized for pitches of 400-600 nm. When a rationally optimized cone pattern was used, the average weighted reflectivity was less than 0.5%, for incident angles of up to 40° off normal. The broadband antireflection of a cone pattern was reproduced well by a graded refractive index film model corresponding to its geometry, with the addition of a diffraction effect resulting from its periodicity. The broadband antireflection ability of optimized cone patterns is not limited to the glass material, but rather is generically applicable to other semiconductor materials, including Si and GaAs. The design rules developed herein represent a key step in the development of light-absorbing devices, such as solar cells.

Breaking the total internal reflection far above a critical angle (i.e., outcoupling deep-trap guided modes) can dramatically improve existing light-emitting devices. Here, we report a deep-trap guided modes outcoupler using densely arranged microstructured hollow cavities. Measurements of the leaky mode dispersions of hollow-cavity gratings accurately quantify the wavelength-dependent outcoupling strength above a critical angle, which is progressively improved over the full visible spectrum by increasing the packing density. Comparing hollow- and filled-cavity gratings, which have identical morphologies except for their inner materials (void vs. solid sapphire), reveals the effectiveness of using the hollow-cavity grating to outcouple deep-trap guided modes, which results from its enhanced transmittance at near-horizontal incidence. Scattering analysis shows that the outcoupling characteristics of a cavity array are dictated by the forward scattering characteristics of their individual cavities, suggesting the importance of a rationally designed single cavity. We believe that a hollow-cavity array tailored for different structures and spectra will lead to a technological breakthrough in any type of light-emitting device.