T. Takeuchi

A dual-wavelength indium gallium nitride quantum well light emitting diode

We have designed and implemented a monolithic, dual-wavelength blue/green light emitting diode (LED) consisting of two active indium gallium nitride/gallium nitride (InGaN/GaN) multiple-quantum-well segments. The segments are part of a single vertical epitaxial structure in which a p++/n++u2009InGaN/GaN tunnel junction is inserted between the LEDs, emitting in this proof-of-concept device at 470 nm and 535 nm, respectively. The device has been operated as a three-terminal device with independent electrical control of each LEDs to a nanosecond time scale.

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.

Vertical cavity violet light emitting diode incorporating an aluminum gallium nitride distributed Bragg mirror and a tunnel junction

We have designed and implemented a vertical cavity violet light emitting diode which features an optical resonator composed of an in situ grown GaN/AlGaN DBR and a high reflectivity dielectric mirror. The active InGaN MQW medium is grown directly atop the AlGaN DBR and the structure includes an intracavity lateral current spreading layer based on a p++/n++ InGaN/GaN tunnel junction. Electroluminescence shows directional emission, with modal linewidths as narrow as 0.6 nm.

Low threshold 1.2 μm InGaAs quantum well lasers grown under low As/III ratio

We have achieved 160 A/cm2 threshold current density of a 1.21 μm InGaAs/GaAs quantum well (QW) laser grown under a very low As/III ratio. We investigated the As/III ratio dependence on the optical quality of InGaAs QWs grown with arsine and tertiarybutylarsine (TBA). We found that TBA allows us to grow high quality InGaAs QWs under a very low As/III ratio (∼3), while a higher As/III ratio (∼10) with arsine is necessary to obtain the similar quality QWs. This high quality InGaAs QW grown under the low As/III ratio leads to the realization of high quality InGaAsN QW which should be grown under a low As/III ratio and a high N/V ratio.

A Matrix Addressable 1024 Element Blue Light Emitting InGaN QW Diode Array

We have fabricated a 32 x 32 two-dimensional proof-of-concept array of individually matrix addressable blue InGaN MQW LEDs. Each 30 μm diameter element is equipped with its own integrated microlens, making these types programmable arrays potentially useful as sources for proximity microscopy with high parallel throughput such as in spatially resolved fluorescence spectroscopic imaging applications.

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.

Low resistance ohmic contacts to n-GaN and n-AlGaN using NiAl

The intermetallic compound NiAl (50:50 at.u2009%) has been shown to be a low-resistance ohmic contact to n-GaN and n-AlGaN. NiAl contacts on n-GaN (n=2.5×1017u200acm−3) had a specific contact resistance of 9.4×10−6u200aΩu2009cm2 upon annealing at 850u2009°C for 5 min. NiAl contacts annealed at 900u2009°C for 5 min in n-Al0.12Ga0.88Nu200a(n=2.4×1018u200acm−3) and n-Al0.18Ga0.82Nu200a(n=2.7×1018u200acm−3) had specific contact resistances of 2.1×10−5u200aΩu2009cm2 and 4.7×10−5u2009Ωu2009cm2, respectively. Additionally, these contacts were subjected to long-term annealing at 600u2009°C for 100 h. On n-GaN, the contact specific contact resistance degraded from 9.4×10−6u200aΩu2009cm2 to 5.3×10−5u200aΩu2009cm2 after the long-term anneal. Contacts to n-Al0.18Ga0.82N showed only slight degradation with a change in contact resistance, from 4.7×10−5u200aΩu2009cm2 to 9.2×10−5u200aΩu2009cm2. These results demonstrate the NiAl has great promise as a stable, low-resistance contact, particularly to n-AlGaN used in high-temperature applications.

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.

A high injection resonant cavity violet light emitting diode incorporating (Al, Ga)N distributed bragg reflector

A vertical cavity violet LED has been designed and implemented which includes an optical resonator composed of an in-situ grown GaN/AlGaN DBR and a high reflectivity dielectric mirror. The structure incorporates an intracavity lateral current spreading layer based on a p ++ /n ++ InGaN/GaN tunnel junction. Electroluminescence shows directional emission, with modal line-widths as narrow as 0.6 nm.

MOCVD growth of InGaAsN QWs and 1.3 /spl mu/m VCSELs

This paper demonstrates MOCVD growth of InGaAsN quantum wells and fabrication of vertical cavity surface emitting lasers (VCSELs). Results on the modulation and high temperature characteristics of 1.3 /spl mu/m-range InGaAsN vertical cavity surface emitting lasers (VCSELs) are also presented. Over 1 mW of single-mode output power is obtained at 80/spl deg/C. Clear eye opening at 2.5 Gb/s and 10 Gb/s are obtained up to 120/spl deg/C and 90/spl deg/C, respectively.