Record-breaking lasing performance demonstrated in optically pumped, 264 and 280 nm lasers fabricated on HexaTech AlN substrates.
MORRISVILLE, N.C. – In a parallel effort to its development of UV-C light emitting diodes (LEDs), HexaTech recently demonstrated optically pumped, AlGaN-based lasers grown on highest-quality, single crystalline AlN substrates. Laser structures fabricated at HexaTech and tested in collaboration with North Carolina State University (NCSU) featured lasing thresholds as low as 85 kW/cm2 at wavelengths of 264 and 280 nm. This not only represents record-breaking laser performance, but also further validates the value proposition of HexaTech's AlN substrate platform for UV-C opto-electronic applications.
“Our recent results show convincing evidence of the feasibility of a solid-state UV-C laser”, commented Dr. Andy Xie. "The tests not only demonstrate lasing at low pump intensities, but we also observed emission peak line widths as narrow as 0.02 nm, and further telltale signs of a properly operating laser, including spectrally resolved cavity modes, TE-mode polarization, and elliptically-shaped far-field patterns."
The observed lasing at low pump intensities is an important milestone toward the development of semiconductor lasers operating at short wavelengths in the UV-C range. Enabled by HexaTech’s industry-leading, low dislocation density bulk aluminum nitride (AlN) substrates, these results add to the record-breaking UV-C LED and laser performance reported by other groups. The use of high-quality, native AlN substrates that are lattice-matched to the overgrown III-nitride device layers allow for fabrication of opto-electronic devices of superior structural quality, and, thus, previously unachievable performance.
There is a growing market opportunity for UV-C lasers used for chemical, biological, and explosive material detection. “HexaTech's core expertise in AlN crystal growth and wafer fabrication has already led to the development of world-class UV-C LEDs with previously unachievable device lifetimes”, noted Joe Grzyb, HexaTech CEO. “Our AlN substrate platform, again, advances UV-C opto-electronics to new levels of performance.”
Further technical details will be published in the scientific literature in the near future.
HexaTech, Inc. will develop Aluminum Nitride technology for power devices to more efficiently control the flow of electricity across high-voltage electrical lines. The future “Smart Grid” requires new high efficiency, high frequency power conversion electronics to decrease the cost of electricity transmission while increasing overall grid security and reliability. This development is the first step to establish the epitaxial growth techniques and demonstrate the superior high-voltage performance capability for AlN-based 20 kV power devices.
MORRISVILLE, N.C. – HexaTech has received a $2.2 M award from the U.S. Department of Energy Advanced Research Projects Agency – Energy (ARPA-E) that will enable the development of a new power semiconductor technology for the modernization of our electrical power grid. HexaTech’s high-quality Aluminum Nitride (AlN) technology was identified by the Department of Energy as a transformational, breakthrough technology with significant technical promise.
Using very low dislocation density single crystal AlN substrates, HexaTech will develop novel doping schemes and contact metals for AlN/AlGaN with high Al content. Dr. Baxter Moody, Director of Engineering said “This contract marks the beginning of a technological leap in device performance and efficiency for power semiconductors. The development will enable a significant step toward producing 20 kV AlN-based Schottky diodes (SBD, JBSD) and transistors (JFET, MOSFET). The ARPA-E contract has opened the door for the material development and research to demonstrate AlN high-voltage, high-efficiency power conversion capability.” For power systems and grid-scale power conversion applications, high efficiency AlN-based power devices will offer a significant reduction in size, weight, and cooling.
Power semiconductor devices at this level are not currently available on the market. Experimental devices based on Silicon Carbide (SiC) technology are currently being developed. Compared to SiC technology, it is expected that Aluminum Nitride will enable power electronics with a 10X improvement in performance. Based on the wide bandgap material properties of AlN, the critical field is 6X larger, the on resistance will be lower, and the resulting power device area will be smaller for a comparable power level. This is a transformational technology that will revolutionize the power distribution grid.
Industry Leaders Demonstrate Dramatic Improvements in Power and Efficiency for UV-C LEDs Used for Water and Surface Disinfection Applications
MORRISVILLE, N.C. and TOKYO, JAPAN – The rapidly accelerating interest in light emitting diodes (LEDs) for disinfection applications operating at UV-C wavelengths requires a solution with high output power, high efficiency and long lifetimes. HexaTech, Inc. today announced the results of an ongoing collaboration with development partner Tokuyama Corporation of Tokyo, Japan, which has demonstrated exceptional output power and dramatic internal quantum efficiency (IQE) improvements. These results raise the bar to what is possible with the technology, and enable commercially available high performance, high reliability UV-C LEDs.
By coupling HexaTech’s industry-leading low dislocation density bulk aluminum nitride (AlN) substrates, with Tokuyama’s hydride vapor phase epitaxy (HVPE) and device fabrication, Tokuyama was able to produce UV-C LEDs with over 25 mW of output power at 265 nm, and internal quantum efficiencies greater than 70%.
“This collaboration demonstrates that when combining HexaTech’s market-leading bulk substrate quality, with Tokuyama’s high quality HVPE and excellent device fabrication, breakthrough, record-setting results are possible”, noted Joe Grzyb, HexaTech CEO. “It further highlights our commitment to working with our customers to bring the best in aluminum nitride technology to market.”
“Working together with HexaTech and their substrates, Tokuyama has made great improvements in the performance of our UV-C LEDs, accelerating the process for their commercial availability “, stated Mr. Toru Kinoshita, Chief Research Engineer at Tokuyama Corporation.
Since their inception, UV-C LEDs have held the promise of a compact, highly efficient, long-life light source for sterilization and purification applications. However, most commercially available products currently struggle with limited output power, efficiency and device lifetimes. A key requirement for improving these limitations is to drive the device defect density down, for which IQE is a key measure and is critically related to the underlying bulk material quality.
“As HexaTech’s own device development has shown, using our high quality, low dislocation material, we are able to produce UV-C LEDs with record-setting reliability and lifetimes, exceeding more than 600 hours of accelerated testing, with virtually no degradation”, commented Dr. Baxter Moody, HexaTech Director of Device Development.
For further technical information see our recent publication in Applied Physics Express.
Morrisville, NC - HexaTech, Inc. today announced the commercial availability of a new class of high transparency single crystal Aluminum Nitride (AlN) material. This improved capability provides a significant reduction in optical absorption in the UV-C wavelengths, resulting in dramatic improvements in the processing and performance of UV-C optoelectronic components.
This enhanced material will offer an improvement of lifetime and power output for UV-C light emitting diodes (LEDs). For the rapidly growing water purification market, the requirement for extended lifetime and improved efficiency are critical market enabling parameters. This new high transparency bulk AlN substrate material has demonstrated improved output performance for UV-C LEDs, by increasing short wavelength transparency, and limiting the amount of substrate thinning required for optimal UV-C emission.
“This new substrate will provide our customers with the bulk AlN material required to develop industry leading UV-C LEDs which will enable improved EQE, lifetime and reliability” stated Joe Grzyb, HexaTech CEO. “The improved transparency, coupled with industry leading bulk quality, once again demonstrates HexaTech’s commitment to quality and technology leadership.”
The improved material performance, after correction for reflection losses, exhibits absorption coefficient values of < 100 cm-1 (50 cm-1 typical) @ 265 nm, and is measurably superior to previous generations of single crystal AlN.
Morrisville, NC May 22, 2012 - HexaTech collaborates with three leading research teams to accelerate the technology advancement in bulk Aluminum Nitride (AlN) substrate materials that enable UV-C LED technology. HexaTech’s single crystal AlN substrates are a critical requirement for the fabrication of UV-C LEDs with high output power and long lifetime. These parameters are key technology enablers for the rapidly expanding disinfection markets.
“The successful collaboration of research scientists from HexaTech, North Carolina State University, Tokuyama Corporation, and Tokyo University of Agriculture and Technology is another important step in the advancement of bulk AlN materials” says Dr. Baxter Moody. “We are excited to work with these leading semiconductor research and manufacturing groups to realize major improvements in substrate transparency and LED performance.”
Details of the collaboration were announced on May 14, 2012 by North Carolina State University in their press release titled “Research Opens Doors To UV Disinfection Using LED Technology”. The complete article can be found here.
Additional scientific details have been published online in Applied Physics Letters in an article entitled On the origin of the 265 nm absorption band in AlN bulk crystals.
On Thursday, December 1, 2011, Dr Jinqiao Xie presented a paper entitled "Fermi Level Effect on Strain in n-type GaN"
Even after two decades of intense research and development, GaN-based optoelectronic and electronic devices are still mainly fabricated on foreign substrates. As a consequence, most heteroepitaxial GaN thin films exhibit relatively high dislocation density and some remnant strain due to varied reasons, such as thermal mismatch, lattice mismatch, growth procedure, buffer layer choice and doping. Among them, the strain introduced by Si doping is the most interesting phenomena since Si is not expected to have a "size" effect. In some cases, the remnant compressive strain changed to tensile strain, as doping and film thickness were increased, eventually leading to cracks. Therefore, strain management in Si-doped GaN became an important factor for fabricating GaN based devices with high reliability and performance.
Strain caused by Si doping is widely observed in heteroepitaxial GaN, AlGaN, and AlN, independent of the growth method. In contrast, there was no measurable shift of the AlN bandedge for Si up to 1x1019 cm-3 for homoepitaxial growth on single crystalline substrates, implying that the strain is a consequence of doping and high dislocation density. Based on TEM studies, an effective dislocation-climbing model was proposed to explain the strain. However, the driving force for the dislocation inclination was still under debate :(1) a mask effect in which SiNx formation at the dislocation core blocks the dislocation; (2) dislocation climbing to relax the remnant strain, in which case the strain is the cause for dislocation climbing instead of the result; and (3) surface mediated dislocation climbing.
By using co-doping, it was found that the tensile strain in Si-doped GaN is only related with the free carrier concentration. The strain became immeasurable as co-doped C electronically compensated the donor Si. Therefore, the dislocation inclination in n-type GaN is a result of dislocation climbing as governed by Ga vacancies during the extension of the dislocation during growth. Ga vacancy formation becomes favorable as the Fermi energy increases due to the increase in the free carrier concentration. This, in turn, will increase the climbing rate, causing a large inclination angle and strain. Such an effect is similar to the well known Fermi level effect in other III-V semiconductor.
On Tuesday, May 3, 2011, Dr Ramon Collazo presented a paper entitled: "265 nm Light Emitting Diodes on AlN Single Crystal Substrates: Growth and Characterization."
High crystalline quality AlN and pseudomorphic AlGaN films were deposited by metalorganic chemical vapor deposition on single crystal AlN substrates for the fabrication of a 265 nm light emitting diode with estimated IQE above 40%.