In this paper we present a novel single-step RIE process for InP membrane optical waveguide etching. The optimization of the process is focused on the sidewall verticality and surface roughness of the etched profile. Significant improvement on the etched profile is achieved for the first time in a single-step RIE process. Loss measurement on fabricated membrane waveguides etched with the proposed RIE process results in a record low waveguide propagation loss (2.5 dB/cm).
Herein, AlN growth by metalorganic vapor‐phase epitaxy on hole‐type nanopatterned sapphire substrates is investigated. Cracking occurs for an unexpectedly thin‐layer thickness, which is associated to altered nucleation conditions caused by the sapphire pattern. To overcome the obstacle of cracking and at the same time to decrease the threading dislocation density by an order of magnitude, high‐temperature annealing (HTA) of a 300 nm‐thick AlN starting layer is successfully introduced. By this method, 800 nm‐thick, fully coalesced and crack‐free AlN is grown on 2 in. nanopatterned sapphire wafers. The usability of such templates as basis for UVC light‐emitting diodes (LEDs) is furthermore proved by subsequent growth of an UVC‐LED heterostructure with single peak emission at 265 nm. Prerequisites for the enhancement of the light extraction efficiency by hole‐type nanopatterned sapphire substrates are discussed.
In order to understand the electrical properties of V/Al/Ni/Au metal contacts to Si-doped Al0.75Ga0.25N layers, X-ray photoelectron spectroscopy analysis was performed on differently treated AlGaN:Si surfaces before metal deposition, and transmission electron microscopy was used to study the semiconductor-metal interface after contact annealing at 900 °C. Cl2 plasma etching of AlGaN increases the aluminum/nitrogen ratio at the surface, and Al oxide or oxynitride is always formed by any surface treatment applied after etching. After contact annealing, a complex interface structure including amorphous AlOx and different metal phases such as Al-Au-Ni, V-Al, and V2N were found. The electrical properties of the contacts were determined by thermionic emission and/or thermionic field emission in the low voltage regime. Nearly ohmic contacts on AlGaN surfaces exposed to a Cl2 plasma were only obtained by annealing the sample at a temperature of 815 °C under N2/NH3 prior to metallization. By this treatment, the oxygen contamination on the surface could be minimized, resulting in a larger semiconductor area to be in direct contact with metal phases such as Al-rich Al-Au-Ni or V-Al and leading to a contact resistivity of 2.5 × 10−2 Ω cm2. This treatment can be used to significantly reduce the operating voltage of current deep ultraviolet light emitting diodes which will increase their wall plug efficiency and lower the thermal stress during their operation.
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