High power light emitting diodes (LEDs) are of interest for many lighting applications. Flux improvements can be achieved by scaling conventional chips to larger dimensions. However this scaling results in a decrease in extraction efficiency. These penalties can be offset by modifying the chip geometry such that the number of internal reflections is reduced, thereby increasing the probability of photon escape. LEDs with a truncated-inverted-pyramid (TIP) geometry have been fabricated and packaged. Peak efficiencies exceeding 100 ln/W have been measured (100 mA dc, 300 K) for orange (lambda(p) similar to 610 nm) devices. In the red wavelength regime (lambda(p) similar to 650 nm), peak external quantum efficiencies of 55% (100 mA. de, 300 K) have been achieved. Flux exceeding 65 lumens from a single 594 nm device has also been demonstrated. These characteristics match and/or exceed the performance of many conventional lighting sources.

We have fabricated and studied a violet (λ=403 nm) vertical cavity surface emitting laser structure, composed of an InGaN multiple quantum well active medium and a pair of high reflectivity dielectric mirrors. Lasing under high repetition rate (76 MHz) pulsed optical pumping has been achieved at temperatures up to T=258 K at average pump power of approximately 30 mW.

A truncated-inverted-pyramid (TIP) chip geometry provides substantial improvement in light extraction efficiency over conventional AlGaInP/GaP chips of the same active junction area (∼0.25 mm2). The TIP geometry decreases the mean photon path-length within the crystal, and thus reduces the effects of internal loss mechanisms. By combining this improved device geometry with high-efficiency multiwell active layers, record-level performance for visible-spectrum light-emitting diodes is achieved. Peak efficiencies exceeding 100 lm/W are demonstrated (100 mA dc, 300 K) for orange-emitting (λp∼610 nm) devices, with a peak luminous flux of 60 lumens (350 mA dc, 300 K). In the red wavelength regime (λp∼650 nm), peak external quantum efficiencies of 55% and 60.9% are measured under direct current and pulsed operation, respectively (100 mA, 300 K).

A method is described for fabricating a vertical cavity light emitting structure for nitride semiconductors. The process involves the separation of a InGaN/GaN/AlGaN quantum well heterostructure from its sapphire substrate an its enclosure by a pair of high reflectivity, low loss dielectric mirrors to define the optical resonator. We have demonstrated a cavity Q factor exceeding 600 in initial experiments, suggesting that the approach can be useful for blue and near ultraviolet resonant cavity light emitting diodes and vertical cavity lasers.

A vertical injection, light emitting InGaN quantum well diode has been demonstrated by separating the nitride heterostructure from its sapphire substrate by ultraviolet laser photoablation within a process scheme that allows transferring the devices to a host substrate. The incorporation of a dielectric multilayer stack to the device is shown to be a first practical step towards a resonant cavity light emitting diode.

Lithium gallate (LGO) is an attractive, near lattice matched substrate for the growth of GaN. In addition, LGO substrates provide a convenient route to forming thin films of GaN as used in substrate removal or lift-off processes. We report the wet etching of LGO substrates for the production of GaN thin films. Two face-selective LGO etches have been used for the processing of substrates. The etch rate of the cation face is reported here for the first time and is 0.25 mu m min(-1) at 50 degrees C. The etching solution is safe and benign to most materials including metallic bonding.

Data are presented demonstrating led-orange-yellow spectrum (AlxGa1-x)(0.5)In0.5P/GaP high-power light-emitting diode (LED) lamps which emit 10-20lm of flux while simultaneously maintaining luminous efficiencies of greater than or equal to 201m/W. The flux emitted by these devices represents an improvement of about five times compared to conventional high-brightness transparent-substrate (AlxGa1-x)(0.5)In0.5P/GaP LED lamps.