Innovations ahead of time

The EXALOS GaAs/GaN material system

EXALOS has a long experience creating industry-leading light sources:

20+ years with InP devices
15+ years with Gallium Arsenid (GaAS) devices
10+ years with Gallium Nitrid (GaN) devices

Thanks to the advanced GaAS/GaN material system, today EXALOS is the only company that provides RGB SLEDs.

2003
Advanced Red SLEDs, including in the highly challenging, lower red spectral range 635 nm.

2007
The world´s first Blue & Violet SLEDs.

2018
The world´s first Green SLED.

Optical + Electrical Long-term Reliability

Long Lifetime.
High-Performance.

EXALOS SLEDs are designed as reliable high-performance light sources with a long life span. Stable electrical characteristics during the whole lifetime are one of the most essential features for the acceptance of demanding products for OCT, Current Sensing or See & Aerospace navigation systems.

Long Lifetime for High Performance RGB SLEDs

In 2016 EXALOS has already demonstrated the reliability of GaN-based SLEDs emitting at 405 nm. A special optimized design reached an estimated lifetime of over 5000 hours under real-life test conditions. Furthermore, the use of optimized p-doped layers allow maximum output powers as high as 350 mW for an injection current of 500 mA have been achieved in continuous-wave operation at room temperature. The test details were scientifically published:

GaN-based superluminescent diodes with long lifetime, A. Castiglia, M. Rossetti, N. Matuschek, R. Rezzonico, M. Duelk, C. Vélez, J-F Carlin, N. Grandjean
(published 26 February 2016 in Proc. SPIE 9748, Gallium Nitride Materials and Devices XI, 97481V)

TEST DETAILS

EXALOS GaAs / GaN-based RGB SLEDs

Revolutionary all-new “low speckle lasers” for Head-Up and Head-mounted displays: LEARN MORE ON OUR DEDICATED VISIIIBLES WEBSITE

VISIIIBLES^RED

635 nm

Hitting the Sweet Spot of higher eye sensitivity and power consumption.

VISIIIBLES^GREEN

510 nm

A visible GaN-based GREEN SLED.
The first of its kind.

VISIIIBLES^BLUE

450 nm

A high-performance
GaN-based BLUE SLED.

GaN-based superluminescent diodes with long lifetime.

A. Castiglia, M. Rossetti, N. Matuschek, R. Rezzonico, M. Duelk, C. Vélez, J-F Carlin, N. Grandjean
Date Published: 26 February 2016, doi: 10.1117/12.2212699, Proc. SPIE 9748, Gallium Nitride Materials and Devices XI, 97481V

Findings:

Modules with standard and optimized p-type layers were tested in terms of lifetime, at a constant output power of 10 mW, in continuous-wave (CW) operation and at a case temperature of 25°C. The results show that the p-dopant concentration affects both IV characteristics and LI laser characteristics. The modules with non-optimized p-type doping showed a fast and remarkable increase in the drive current during the first hundreds of hours, together with an increase of the device series resistance.

The residual drop in output characteristics observed over 2000 hours of device operation was found to be power-dependent and most likely related to the ageing of the mirror facets.

Based on the test results, Hydrogen diffusion is probably responsible for the quick degradation process. During the first hundred hours of the test, hydrogen slowly diffuses towards the p-metal/semiconductor interface, passivating the Mg acceptors in the GaN contact layer, and thus leading to an increase in the device contact resistance. A high Mg-doping level (above 2×1019 cm-3) is likely to lead to the formation of compensating defects (e.g., inversion domains and/or pyramidal defects). The poor p-type quality is responsible for high series resistances and non-uniform current injection into the active region, resulting in lower optical output powers under CW operation. Additionally, complete hydrogen removal could not be achieved with the thermal activation process in such highly-doped layers.

(a) LI characteristics of SLEDs with optimized p-doping profile;
(b) emission spectra for an injected current of 150 mA.

In contrast to these findings, the devices with optimized p-type layers showed no considerable degradation of the electrical characteristics after 2000 hours. The output power drop after this time was limited to 6%. The samples with optimized Mg-doping levels achieved a higher hydrogen removal with the post-growth thermal annealing than highly-doped samples. Under the specific test conditions, the estimated lifetime for those devices was higher than 5000 hours. Furthermore, maximum output powers as high as 350 mW (for an injection current of 500 mA) have been achieved in CW operation at room temperature.

(a) Long-term stress test at a constant power of 10 mW at 25 °C. A lifetime of at about 5000 h can be
extrapolated based on a 35% increase in the injection current end of life criterion;
(b) IV characteristics before and after 2000 h stress test.

Electrical Long-term Reliability

No electrical degradation was observed during lifetime testing over several thousand hours of operation!

Electrical Long-term Reliability

Modules were tested under constant-power mode (Pout = 10 mW ; Tcase = 25 ºC).

Projected lifetime: 5000h
(failure criteria defined as a 35% drive current increase)
Degradation rate ~ 0.005 mA/h after 2000h.

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