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Register a new userPlasmonically-Enhanced Emission from an Inverted GaN Light Emitting Diode
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Silver nanoparticles dispersed on the surface of an inverted GaN LED were found to plasmonically enhance the near-bandedge emission. The resonant surface plasmon coupling led to a significant enhancement in the exciton decay rate and the ensemble of nanoparticles provided a mechanism to scatter the coupled energy as free space radiation. The inverted LED structure employed a tunnel junction to avoid the standard thick p+ GaN current spreading contact layer. In contrast to a standard design, the top contact was a thin n++ AlGaN layer, which brought the quantum well into the fringing field of the silver nanoparticles. This proximity allowed the excitons induced within the quantum well to couple to the surface plasmons, which in turn led to the enhanced band edge emission from the LED.
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We report direct evidence of enhanced spontaneous emission in a photonic crystal (PhC) light-emitting diode. The device consists of p-i-n heterojunction embedded in a suspended membrane, comprising a layer of self-assembled quantum dots. Current is injected laterally from the periphery to the center of the PhC. A well-isolated emission peak at 1300nm from the PhC cavity mode is observed, and the enhancement of the spontaneous emission rate is clearly evidenced by time-resolved electroluminescence measurements, showing that our diode switches off in a time shorter than the bulk radiative and nonradiative lifetimes
Single-photon sources are essential building blocks in quantum photonic networks, where quantum-mechanical properties of photons are utilised to achieve quantum technologies such as quantum cryptography and quantum computing. Most conventional solid-state single-photon sources are based on single emitters such as self-assembled quantum dots, which are created at random locations and require spectral filtering. These issues hinder the integration of a single-photon source into a scaleable photonic quantum network for applications such as on-chip photonic quantum processors. In this work, using only regular lithography techniques on a conventional GaAs quantum well, we realise an electrically triggered single-photon source with a GHz repetition rate and without the need for spectral filtering. In this device, a single electron is carried in the potential minimum of a surface acoustic wave (SAW) and is transported to a region of holes to form an exciton. The exciton then decays and creates a single photon in a lifetime of ~ 100ps. This SAW-driven electroluminescence (EL) yields photon antibunching with $g^{(2)}(0) = 0.39 pm 0.05$, which satisfies the common criterion for a single-photon source $g^{(2)}(0) < 0.5$. Furthermore, we estimate that if a photon detector receives a SAW-driven EL signal within one SAW period, this signal has a 79%-90% chance of being a single photon. This work shows that a single-photon source can be made by combining single-electron transport and a lateral n-i-p junction. This approach makes it possible to create multiple synchronised single-photon sources at chosen positions with photon energy determined by quantum-well thickness. Compared with conventional quantum-dot-based single-photon sources, this device may be more suitable for an on-chip integrated photonic quantum network.
A two-dimensional (2D) ZnS photonic crystal was deposited on the surface of a one-dimensional (1D) III-nitride micro cavity light-emitting diode (LED), to intermix the light extraction features of both structures (1D+2D). The deposition of an ideal micro-cavity optical thickness of lambda/2 is impractical for III-nitride LEDs, and in realistic multi-mode devices a large fraction of the light is lost to internal refraction as guided light. Therefore, a 2D photonic crystal on the surface of the LED was used to diffract and thus redirect this guided light out of the semiconductor over several hundred microns. Additionally, the employment of a post-epitaxy ZnS 2D photonic crystal avoided the typical etching into the GaN:Mg contact layer, a procedure which can cause damage to the near surface.
Artificial lighting is a widespread technology which consumes large amounts of energy. Triplet-triplet annihilation photochemical upconversion is a method of converting light to a higher frequency. Here, we show theoretically that photochemical upconversion can be applied to Watt-scale lighting, with performance closely approaching the 50% quantum yield upper limit. We describe the dynamic equilibrium of an efficient device consisting of an LED, an upconverting material, and an optical cavity from optical and thermal perspectives.
Recently, the use of bottom-TJ geometry in LEDs, which achieves N-polar-like alignment of polarization fields in conventional metal-polar orientations, has enabled enhancements in LED performance due to improved injection efficiency. Here, we elucidate the root causes behind the enhanced injection efficiency by employing mature laser diode structures with optimized heterojunction GaN/In$_{0.17}$Ga$_{0.83}$N/GaN TJs and UID GaN spacers to separate the optical mode from the heavily doped absorbing p-cladding regions. In such laser structures, polarization offsets at the electron blocking layer, spacer, and quantum barrier interfaces play discernable roles in carrier transport. By comparing a top-TJ structure to a bottom-TJ structure, and correlating features in the electroluminescence, capacitance-voltage, and current-voltage characteristics to unique signatures of the N- and Ga-polar polarization heterointerfaces in energy band diagram simulations, we identify that improved hole injection at low currents, and improved electron blocking at high currents, leads to higher injection efficiency and higher output power for the bottom-TJ device throughout 5 orders of current density (0.015 - 1000 A/cm$^2$). Moreover, even with the addition of a UID GaN spacer, differential resistances are state-of-the-art, below 7x10-4 $Omega$cm$^2$. These results highlight the virtues of the bottom-TJ geometry for use in high-efficiency laser diodes.
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