Last week at the ICNS scientific conference in Strasbourg, France, ALLOS’ co-founder and CTO Dr. Atsushi Nishikawa presented experimental evidence that challenged the validity of three common belief about GaN-on-Si.
Common GaN-on-Si Beliefs Disputed
First, these widespread beliefs included the assertion that the use of carbon doping would be unavoidable. Secondly among these beliefs was the position that employing interlayers in the buffer would be a source of leakage. And the Third of these common ideas that Allos disputed was that the choice of the right reactor hardware would be decisive to achieving good results.
The crystal impurities from the growth process of GaN-on-Si epiwafers cause the isolation of GaN to be far below its theoretically possible values. Carbon doping is usually used to achieve the required isolation. Regrettably, standard methods of carbon and other doping have negative side-effects.
However, ALLOS says its results prove that by focusing on superior crystal quality and thick GaN layers the required low leakage currents can be achieved without any intentional carbon or other doping. Dr. Nishikawa also showed experimental evidence that carefully controlling the interlayer growth conditions and positioning the interlayers can improve isolation by more than one order of magnitude.
Combined, these techniques allowed ALLOS to achieve a very low vertical and lateral leakage current of just 0.07 µA/mm2 and 0.005 µA/mm respectively at 600 V using 7 µm thick GaN with extremely high crystal quality of 316 arcsec for (002) and 413 arcsec for (002) XRD. ALLOS designed this technology for manufacturing with standard silicon production lines, and it is available with both 150 mm and 200 mm epiwafer diameters. The GaN features controlled minimum bow and no cracks.
While good hardware matters, Allos claims it is not by far the dominant factor. ALLOS demonstrated that it can apply its structure and growth methods on several hardware platforms because two leading multi-wafer MOCVD reactor models achieved similar material and electrical properties.