Richard P. Schneider

Resonant-cavity InGaN quantum-well blue light-emitting diodes

We describe progress in blue resonant-cavity light-emitting diodes, based on InGaN/GaN quantum-well heterostructures. We have fabricated vertical-microcavity devices in which either one or both mirrors forming the cavity are patterned, high-reflectivity dielectrics Bragg reflectors. The results suggest that a blue vertical-cavity diode laser may be feasible by this approach.

A quasicontinuous wave, optically pumped violet vertical cavity surface emitting laser

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.

Microstructure of laterally oxidized AlxGa1−xAs layers in vertical‐cavity lasers

We have studied the lateral oxidation of AlxGa1−xAs (x=0.98 and 0.92) layers contained in vertical‐cavity lasers using cross‐sectional transmission electron microscopy. We find a fine‐grained (∼4 nm) cubic spinel phase of Al2O3 in both the 2% Ga‐ and 8% Ga‐oxidized layers. The 8% Ga‐oxidized layers contract vertically by 6.7% and not the expected 20% for a fully dense Al2O3 layer, with the 2% Ga‐oxidized layers showing a similar contraction. We observe a ∼17‐nm‐thick amorphous interface between the oxidized and unoxidized AlxGa1−xAs layers, which may account for the excellent electrical properties of these devices. We also observe metastable amorphous cavities associated with the moving reaction front. We infer the reaction proceeds from an initial amorphous phase that then transforms to a porous γ‐Al 2O3 layer.

Dislocation reduction in GaN thin films via lateral overgrowth from trenches

A technology to reduce the dislocation density in GaN thin films by lateral overgrowth from trenches (LOFT) is reported. In LOFT, a GaN thin film was grown on sapphire substrate first, then trenches were formed into the thin film by etching. GaN material was regrown laterally from the trench sidewalls to form a continuous thin film. The average surface density of threading dislocations is reduced from 8×109/cm2 in the first GaN thin film to 6×107/cm2 in the regrown GaN thin film.

Mode control in vertical-cavity surface-emitting lasers by post-processing using focused ion-beam etching

Single-mode emission is achieved in previously multimode gain-guided vertical-cavity surface-emitting lasers (VCSELs) by localized modification of the mirror reflectivity using focused ion-beam etching. Reflectivity engineering is also demonstrated to suppress transverse mode emission in an oxide-confined device, reducing the spectral width from 1.2 nm to less than 0.5 nm.

High-brightness AlGaInN light-emitting diodes

Currently, commercial LEDs based on AlGaInN emit light efficiently from the ultraviolet-blue to the green portion of the visible wavelength spectrum. Data are presented on AlGaInN LEDs grown by organometallic vapor phase epitaxy (OMVPE). Designs for high-power AlGaInN LEDs are presented along with their performance in terms of output power and efficiency. Finally, present and potential applications for high-power AlGaInN LEDs, including traffic signals and contour lighting, are discussed.

Design and performance analysis of deep-etch air/nitride distributed Bragg reflector gratings for AlInGaN laser diodes

The key parameters in the fabrication of deep-etch high-order λ/4 Bragg gratings for short-wavelength nitride-based lasers are investigated. Calculations indicate that, for an air-gap thickness of 1.73 μm and single-spot Gaussian beam profile, the reduction in grating reflectivity due to light diffraction in the air gaps is only 17% with respect to a first-order structure with 0.1 μm air gaps. Scanning electron microscopy and microphotoluminescence characterizations confirm the validity of the numerical predictions and show that the 28%–38% reflectivity obtained from prototype focused-ion-beam-etched air/nitride gratings is mainly limited by imperfections and material disorder due to etching. Improving the etching technique would, therefore, allow standard lithographic fabrication of reduced-threshold GaN lasers.

Ultralow timing jitter picosecond pulse generation from electrically gain-switched oxidized vertical-cavity surface-emitting lasers

Ultralow timing jitter picosecond optical pulses are generated by electrically gain switching oxide-confined vertical-cavity surface-emitting lasers (VCSELs) at repetition rates of up to 10.0 GHz. Timing jitter as low as 1.2 ps is measured, which is at least four times lower than that measured for implanted VCSELs. The ultralow timing jitter is attributed to the high level of spontaneous coupling in the oxide-confined VCSEL due to multimode operation resulting from the index guiding properties of the oxide layer.

InP-Based Monolithic Integration Technology

Low FIT monolithically integrated components with device counts exceeding 50 discrete components are in commercial use. We will present results showing that device counts exceeding 240 discrete components for an individual integrated chip are practical.

GaN-based tunnel junction in optical devices

We have demonstrated hole injection through a tunnel junction embedded in the GaN-based light emitting diode structure. The tunnel junction consists of 30 nm GaN:Si++ and 15 nm InGaN:Mg++ grown on a GaN-InGaN quantum well heterostructure. The forward voltage of the light emitting diode, included the voltage drop across the reverse-biased tunnel junction, is 4.1 V at 50 Z/cm