Scientists from Ammono and the Institute of High Pressure Physics of the Polish Academy of Sciences (Unipress) have conceived a new proprietary breakthrough technology, which allows cheap and fast production of ammonothermal GaN on the basis of hybrid Ammono-HVPE GaN seeds.
Ammonothermal gallium nitride is seen today as a perfect material for performance driven electronic and opto-electronic applications, which require very good crystal quality. An example of such applications are laser diodes, where the output power and lifetime depend strongly on the GaN substrate quality. Another case are power transistors and Schottky diodes, where the reliability is related primarily with the device crystalline structure and thus the substrate quality. Last but not least, the ultra-high brightness LEDs benefit tremendously from the substrate low dislocation density which, allows to dissipate effectively the heat created during the device operation.
Competing GaN production technologies such as HVPE or LPE use foreign (not GaN) seeds and the quality of the GaN material obtained in this way allows to manufacture devices, which on a long term do not verify the quality targets set by the device makers. This lower quality is reflected in many parameters. The most important is the dislocation density, which in the case of the Ammonthermal GaN is of the order of 104 cm-2 and where other technologies perform at least two orders of magnitude worse.
Ammono and Unipress have shown that using hybrid HVPE-Ammontermal approaches allows to manufacture GaN material fulfilling the strict requirements from the high-end applications. In the framework of a grant received from the Polish National Center for Research and Development (PBS1/B5/7/2012) it was shown that using ammonothermally grown GaN (as a seed) one can obtain high quality free-standing HVPE-GaN (for details see Appl. Phys. Expri 6, 075504 (2013)).
Smooth GaN layers up to 2.5 mm thick (crystallized with a stable growth rate of 240 μm h-1) and of an excellent crystalline quality, without cracks, and with low threading dislocation density (5×104 cm-2) have been grown and then sliced from the Ammono-GaN seed wafers (see Figure below). The structural properties of the free-standing HVPE-GaN do not differ from the structural properties of the Ammono-GaN seeds. Additionally, this is a high purity material. According to the SIMS analysis the oxygen and carbon content is below 1016 cm-3. The only Si impurity is of the order of 3×1016 cm-3. Thus, from the physical properties point of view this HVPE-GaN is of a much higher quality than the one obtained using MOCVD-GaN/sapphire templates or GaAs crystals as seeds.
Subsequently, the new material was used again as a seed for the ammonthermal process. As a result a new kind of GaN crystals were grown (Ammono-HVPE-Ammono). Their characteristics were presented for the first time during the 2014 Photnics West (SPIE Gallium Nitride Materials and Devices IX conference 2014, San Francisco). Threading dislocation density of 2×105 cm-2 and average FWHMs of 19 arcsec define this new ammonothermal material as top of the class compared with other today's GaN manufacturing approaches.
This new proprietary and patent protected technology allows high volume, high quality GaN seed replication, which will accelerate tremendously the spread of the Ammonthermal GaN to numerous mass market applications. It will allow to drive the production cost of Ammono-GaN down in an aggressive way due to a much faster availability of a vast population of high-quality GaN seeds.