| 1. |
- Lin, Yen-Ku, et al.
(author)
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A versatile low-resistance ohmic contact process with ohmic recess and low-temperature annealing for GaN HEMTs
- 2018
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In: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 33:9
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Journal article (peer-reviewed)abstract
- Deeply recessed ohmic contacts for GaN-based high electron mobility transistors (HEMTs) are demonstrated. It is shown that low-resistance ohmic contacts can be achieved with recessing beyond the AlGaN Schottky barrier where the ohmic contacts are formed on the sidewall of the recess. This makes the process versatile and relatively insensitive to the exact recess depth. The ohmic contact is based on a gold-free metallization scheme consisting of a Ta/Al/Ta metal stack requiring a low-temperature annealing. Important parameters for this type of ohmic contact process include the metal coverage, slope of the etched sidewall, bottom Ta-layer thickness, as well as annealing temperature and duration. The optimized contact resistance is as low as 0.24 Omega mm after annealing at 575 degrees C. Moreover, this sidewall contact approach was successfully implemented on different epitaxial heterostructures with different AlGaN barrier thickness as well as with and without AlN exclusion layer. All the samples exhibited excellent contact resistances in a wide range of recess depths. The Ta-based, sidewall ohmic contact process is a promising method for forming an ohmic contact on a wide range of GaN HEMT epitaxial designs.
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| 2. |
- Desieres, Yohan, et al.
(author)
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Strong light extraction enhancement using TiO2 nanoparticles-based microcone arrays embossed on III-Nitride light emitting diodes
- 2018
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 112:23
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Journal article (peer-reviewed)abstract
- Colloidal TiO2 nanoparticles were used for embossing of composite microcone arrays on III-Nitride vertical-thin-film blue light emitting diodes (LEDs) as well as on silicon, glass, gallium arsenide, and gallium nitride surfaces. Ray tracing simulations were performed to optimize the design of microcones for light extraction and to explain the experimental results. An optical power enhancement of ∼2.08 was measured on III-Nitride blue LEDs embossed with a hexagonal array of TiO2 microcones of ∼1.35 μm in height and ∼2.6 μm in base width, without epoxy encapsulation. A voltage increase in ∼70 mV at an operating current density of ∼35 A/cm2 was measured for the embossed LEDs. The TiO2 microcone arrays were embossed on functioning LEDs, using low pressures (∼100 g/cm2) and temperatures ≤100 °C.
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