E. Makarona

Stress engineering during metalorganic chemical vapor deposition of AlGaN/GaN distributed Bragg reflectors

In situ stress monitoring has been employed during metalorganic chemical vapor deposition of AlGaN/GaN distributed Bragg reflectors (DBRs). It was found that the insertion of multiple AlN interlayers is effective in converting the tensile growth stress typically observed in this system into compression, thus alleviating the problem of crack generation. Crack-free growth of a 60 pair Al0.20Ga0.80N/GaN quarter-wavelength DBR was obtained over the entire 2 in. wafer; an accompanying reflectivity of at least 99% was observed near the peak wavelength around 380 nm.

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++ InGaN/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.

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.

Ultraviolet light-emitting diodes operating in the 340nm wavelength range and application to time-resolved fluorescence spectroscopy

We report on the development of UV light-emitting diodes in the 340nm wavelength range, based on quaternary AlGaInN quantum-well active media. Output powers up to 1mW from small area devices (<100μm diameter) directly off a planar chip have been achieved. The devices have been operated as subnanosecond pulsed sources to demonstrate their applicability to compact time-resolved fluorescence spectroscopy.

Coherent generation of 100 GHz acoustic phonons by dynamic screening of piezoelectric fields in AlGaN/GaN multilayers

Ultrashort pulse laser techniques have been used to observe and characterize the generation of coherent phonons by rapid screening of strain-induced piezoelectric polarization fields in AlGaN/GaN multilayers. The results are compared with those where coherent phonons are launched by optical techniques without the carrier injections process to show consistency with the anticipated longitudinal phonon dispersion in the nitride semiconductor samples.

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.

Performance and application of high power ultraviolet AlGaInN light emitting diodes

We report on high output power from the quaternary AlGaInN multiple quantum well (MQW) ultraviolet light emitting diodes (UV LEDs) in the 340 nm and 280 nm wavelength range. The output power up to 1.5 mW from a 100 μm diameter device with bare-chip configuration was measured under room temperature cw operation. The internal quantum efficiency was estimated to be between 7 and 10%. In addition, the output power and external quantum efficiency for fully packaged 1x1mm2 large area device were as high as 54.6 mW and 1.45%, respectively, at the injection current of 200 A/cm2 under pulsed operation. The devices were incorporated into prototype system for fluorescence based bio-sensing. We also report the performance of 285 nm UV LEDs.

Toward III-N /spl lambda/-cavity vertical emitters: heteroepitaxy of GaN and AlN

We study the initial nucleation and evolution of strain relaxation during the alternating growth of AlN on GaN and GaN on AlN by MOCVD. Emphasis is given to the evolution of strained nucleation from a few monolayers up to a quarter of wavelength for DBR application. It is found that the AFM morphology of AlN (/spl sim/300 A) depends sensitively on V/III ratios, ranging from large 3D island/platelets (under a high V/III ratio), to two-dimensional step flow mode (V/III ratio) with distinct macroscopic cracks, to the occurence of microscopic cracks (under a very low V/III ratio) accompanied by a reduction of the macroscopic cracks. GaN on AlN exhibited a strong tendency for 3D islanding.

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

Optical switching in an organic semiconductor microcavity in the polariton regime

_2), while that of a standard light emitting diode with a conventional contact structure is 3.5 V. The light output of the diode with the tunnel junction is comparable to that of the standard device. We then employed the tunnel junction in vertical cavity surface emitting laser structures and dual-wavelength light emitters. In the vertical cavity structure, a good lateral current spreading was accomplished, resulting in uniform emission pattern. The dual-wavelength light emitter has been operated as a three- terminal device with independent electrical control of each LEDs to a nsec time scale.