Electrical operation of III-Nitride light emitting diodes (LEDs) with photonic crystal structures is demonstrated. Employing photonic crystal structures in III-Nitride LEDs is a method to increase light extraction efficiency and directionality. The photonic crystal is a triangular lattice formed by dry etching into the III-Nitride LED. A range of lattice constants is considered (a ~ 270 - 340nm). The III-Nitride LED layers include a tunnel junction providing good lateral current spreading without a semi-absorbing metal current spreader as is typically done in conventional III-Nitride LEDs. These photonic crystal III-Nitride LED structures are unique because they allow for carrier recombination and light generation proximal to the photonic crystal (light extraction area) yet displaced from the absorbing metal contact. The photonic crystal Bragg scatters what would have otherwise been guided modes out of the LED, increasing the extraction efficiency. The far-field light radiation patterns are heavily modified compared to the typical III-Nitride LED’s Lambertian output. The photonic crystal affects the light propagation out of the LED surface, and the radiation pattern changes with lattice size. LEDs with photonic crystals are compared to similar III-Nitride LEDs without the photonic crystal in terms of extraction, directionality, and emission spectra.
Aluminum-oxide thermally grown into high Al-concentration AlxGa1-xAs layers has recently been studied extensively. The material shows electrical and optical properties that make it useful in a semiconductor laser fabrication process where it can provide electrical isolation and optical guiding, as well as simplify the fabrication and integration process considerably. We use this thermal oxide to produce GaAs/AlGaAs semiconductor lasers that can be integrated with other devices. The GaAs cap- layer is masked with photoresist and the exposed GaAs areas are etched away, leaving a GaAs oxidation mask on the AlGaAs upper cladding layer. Using N2 carrier gas saturated with H2O vapor, the uncovered Al0.8Ga0.2As material is converted into a stable aluminum-oxide at temperatures around 450 degree(s)C. Due to the near-isotropic oxidation an `ellipsoidal' diffusion front is created, which is in strong contrast to the well-known mesa cross-section in conventional dry-etched ridge-waveguides but is more similar to e.g. wet-etched buried heterostruture lasers.