Reduction of the threading edge dislocation density in AlGaN epilayers by GaN nucleation for efficient 350 nm light emitting diodes

AbstractLow dislocation density epitaxial layers of AlxGa1-xN can be grown pseudomorphically on c-face AlN substrates prepared from high quality, bulk crystals. Here, we will report on initial characterization results from deep ultraviolet (UV) light emitting diodes (LEDs) which have been fabricated and packaged from these structures. As reported previously, pseudomorphic growth and atomically smooth surfaces can be achieved for a full LED device structure with an emission wavelength between 250 nm and 280 nm.A benefit of pseudomorphic growth is the ability to run the devices at high input powers and current densities. The high aluminum content AlxGa1-xN (x∼70%) epitaxial layer can be doped n-type to obtain sheet resistances < 200 Ohms/sq/μm due to the low dislocation density. Bulk crystal growth allows for the ability to fabricate substrates of both polar and non-polar orientations. Non-polar substrates are of particular interest for nitride growth because they eliminate electric field due to spontaneous polarization and piezoelectric effects which limit device performance. Initial studies of epitaxial growth on non-polar substrates will also be presented.

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Threading dislocation density effect on the electrical and optical properties of InGaN light-emitting diodes

Optik ◽

10.1016/j.ijleo.2017.10.096 ◽

2018 ◽

Vol 155 ◽

pp. 26-30 ◽

Cited By ~ 6

Author(s):

Suihu Dang ◽

Chunxia Li ◽

Mengchun Lu ◽

Hongli Guo ◽

Zelong He

Keyword(s):

Optical Properties ◽

Dislocation Density ◽

Light Emitting Diodes ◽

Density Effect ◽

Threading Dislocation ◽

Electrical And Optical Properties ◽

Light Emitting ◽

Threading Dislocation Density

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Influence of substrate dislocation density and quantum well width on the quantum efficiency of violet-emitting GaInN/GaN light-emitting diodes

physica status solidi (c) ◽

10.1002/pssc.200880789 ◽

2009 ◽

Vol 6 (S2) ◽

pp. S833-S836 ◽

Cited By ~ 1

Author(s):

Thorsten Passow ◽

Markus Maier ◽

Michael Kunzer ◽

Crenguta-Columbina Leancu ◽

Shangjing Liu ◽

...

Keyword(s):

Dislocation Density ◽

Quantum Well ◽

Quantum Efficiency ◽

Light Emitting Diodes ◽

Light Emitting ◽

Quantum Well Width ◽

Influence Of Substrate

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Reliability and Performance of Pseudomorphic Ultraviolet Light Emitting Diodes on Bulk Aluminum Nitride Substrates

MRS Proceedings ◽

10.1557/proc-1195-b03-04 ◽

2009 ◽

Vol 1195 ◽

Author(s):

James Grandusky ◽

Yongjie Cui ◽

Mark C. Mendrick ◽

Shawn R. Gibb ◽

Leo Schowalter

Keyword(s):

Dislocation Density ◽

Ultraviolet Light ◽

Light Emitting Diodes ◽

Light Emitting ◽

Al Content ◽

Future Performance ◽

Low Dislocation Density ◽

And Performance ◽

Initial Power ◽

Ultraviolet Light Emitting Diodes

AbstractReliability and performance of ultraviolet light emitting diodes have suffered due to the high dislocation density of the AlN and high Al-content AlxGa1-xN layers when grown on foreign substrates such as sapphire. The development of pseudomorphic layers on low dislocation density AlN substrates is leading to improvements in reliability and performance of devices operating in the ultraviolet-C (UVC) range. One major improvement is the ability to operate devices at much higher current densities and input powers than devices on sapphire substrates. This is due to the better thermal properties and lower dislocation density of devices on AlN substrates. Devices with active area of 0.001 cm2 emitting at ∼265 nm have been measured for their reliability and change in power output over time at input currents of 20 mA (20 A/cm2), 100 mA (100A/cm2) and 150 mA (150 A/cm2). When operating at currents of 20 mA over 3500 hours of consecutive operation has been demonstrated with typical decay of ∼27% over the 3500 hours. Extrapolating the decay with a linear fit gives a L50 (time to 50% of initial power) of ∼5000 hrs. However it is desirable to be able to model the decay to better understand the kinetics and better understand the mechanisms. In order to do this, the lifetime at 20 mA and 100 mA were modeled using an exponential decay function, square root transformation and a log transformation to both be able to fit the experimental data and predict future performance.

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SEM and TEM investigation of VPE layer structure for Gap light emitting diodes

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100107824 ◽

1978 ◽

Vol 36 (1) ◽

pp. 136-137

Author(s):

D.B. Darby ◽

J. Palolil ◽

G.R. Booker

Keyword(s):

Dislocation Density ◽

Light Emitting Diodes ◽

Basic Problem ◽

Layer Structure ◽

Substrate Surface ◽

High Dislocation Density ◽

Device Performance ◽

Light Emitting ◽

Lattice Strains ◽

Experimental Structure

A basic problem associated with the fabrication of GaP LEDs is the high dislocation density present in GaP VPE layers grown on GaP LEC substrates, which is detrimental to device performance. Most of the layer dislocations originate from loops present in the substrate that intersect the substrate surface when growth commences. This paper is concerned with an experiment designed to reduce the dislocation density in the layer by deliberately introducing lattice strains during the growth.An experimental structure was prepared comprising a substrate cut 10° off the [100] axis, onto which was grown a layer 17μm thick doped with 2 × 1019 cm-3 of N atoms, followed by a layer 30μm thick undoped. The N causes a crystallographic mismatch at the two interfaces, and it was anticipated that some of the dislocations propagating through the first layer would bend around so as to lie along the second interface.

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Yellow-green emission for ETS-LEDs and lasers based on a strained–InGaP quantum well heterostructure grown on a transparent, compositionally graded AlInGaP buffer

MRS Proceedings ◽

10.1557/proc-744-m7.5 ◽

2002 ◽

Vol 744 ◽

Cited By ~ 1

Author(s):

Lisa McGill ◽

Juwell Wu ◽

Eugene Fitzgerald

Keyword(s):

Dislocation Density ◽

Quantum Well ◽

Gallium Phosphide ◽

Light Emitting Diodes ◽

Green Emission ◽

Threading Dislocation ◽

Peak Wavelength ◽

Device Structure ◽

Light Emitting ◽

Threading Dislocation Density

ABSTRACTEpitaxial-transparent-substrate light emitting diodes with a primary emission peak at 590nm and a secondary peak at 560nm have been fabricated in the indium aluminum gallium phosphide (InAlGaP) system. The active layer consists of an undoped, compressively strained indium gallium phosphide (InGaP) quantum well on a transparent In0.22(Al0.2Ga0.8)0.78P/ ∇x[1nx(Al0.2Ga0.8)1-xP] /GaP virtual substrate. Theoretical modeling of this structure predicts an accessible wavelength range of approximately 540nm to 590nm (green to amber). Emission with a peak wavelength of 570nm has been observed via cathodoluminescence studies of undoped structures with a quantum well composition of In0.35Ga0.65P. Light emitting diodes have been fabricated utilizing simple top and bottom contacts. The highest LED power of 0.18μW per facet at 20mA was observed for a quantum well composition of In0.32Ga0.68P and a bulk threading dislocation density on the order of 7×106 cm-2. The spectrum of this device was composed of two peaks: a weak peak at the predicted 560nm wavelength and a stronger peak at 590nm. Based upon superspots present in electron diffraction from the quantum well region, we believe that the observed spectrum is the result of emission from ordered and disordered domains in the active region. The same device structure grown with a bulk threading dislocation density on the order of 5×107 cm-2 exhibited an identical spectral shape with a reduced power of 0.08μW per facet at 20mA. For a quantum well composition of In0.37Ga0.63P and an overall threading dislocation density on the order of 5×107 cm-2, a single peak wavelength of 588nm with a power of 0.06μW per facet at 20mA was observed.

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