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 the cheap and fast production of ammonothermal GaN.
This approach is based on hybrid Ammono-HVPE GaN seeds.
Ammonothermal GaN is seen as an ideal material for performance driven electronic and optoelectronic 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. Other cases are power transistors and Schottky diodes, where the reliability is related primarily to the device crystalline structure and thus the substrate quality. Last but not least, ultra-high brightness LEDs benefit tremendously from the low substrate dislocation density which, allows the effective dissipation of heat created during 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 such processes produces devices, which in the long term, do not meet the quality targets set by 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 - other technologies are claimed to be at least two orders of magnitude worse.
Ammono and Unipress say they have shown that using hybrid HVPE-Ammontermal approaches allows the manufacture of GaN material, fulfilling the strict requirements of high-end applications.
In the framework of a grant received from the Polish National Centre 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.
Smooth GaN layers up to 2.5 mm thick (crystallised 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 x104 cm-2) have been grown and then sliced from the Ammono-GaN seed wafers. This is illustrated in the figure below..
The structural properties of the free-standing HVPE-GaN do not differ from the structural properties of the Ammono-GaN seeds.
What's more, this is a high purity material. According to the SIMS analysis the oxygen and carbon content is below 1016 cm-3. The only silicon impurity is of the order of 3 x 1016 cm-3. Thus, from the physical properties point of view, this HVPE-GaN is of a much higher quality than 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, 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 in San Francisco).
Threading dislocation densities of 2 x 105 cm-2 and average FWHMs of 19 arcsec define this new ammonothermal material as one of the best compared with other GaN manufacturing approaches.
This new proprietary and patent protected technology allows high volume, high quality GaN seed replication, which will hopefully tremendously accelerate the adoption of Ammonthermal GaN to numerous mass market applications.
It should allow the aggressive driving down of the production cost of Ammono-GaN due to a much faster availability of a vast population of high-quality GaN seeds.