What is GaN?
GaN Chinese name: Nitriding Margin, explained by chemical elements is a Group V compound. The hexagonal lead-zinc type structure is a direct band gap semiconductor. The room temperature band gap is 3.39 eV. The effective inertial masses of electrons and holes are 0.19 and 0.6, respectively. Resistivity: 107 Ω·m, electron mobility (1.25 to 1.50) & TImes; 10-2 m 2 / (V·s). Prepared by chemical vapor deposition. What is GaN? GaN Chinese name: Nitriding Margin, explained by chemical elements is a Group V compound. The hexagonal lead-zinc type structure is a direct band gap semiconductor. The room temperature band gap is 3.39 eV. The effective inertial masses of electrons and holes are 0.19 and 0.6, respectively. The resistivity is greater than 107 Ω·m, the electron mobility (1.25 to 1.50) & TImes; 10-2 m 2 / (V·s). Prepared by chemical vapor deposition. Panasonic has produced a GaN power transistor ("GIT") using a GaN substrate and published it on "IEDM 2016" (speech number: 10.3). Compared with the previous Si substrate products that the company has introduced, the on-resistance (Ron) is reduced to 2/3, and the output charge (Qoss) is reduced to about half. In this way, the product of the on-resistance and the output charge, the "FOM (figure of merit)" for the shutdown switch, can be reduced to about 1/3 to achieve high-speed shutdown. Although the prototype is a HEGaN structure of AlGaN/GaN, a GaN substrate is used, but a horizontal device in which electrons move in the horizontal direction of the device. It can be said that the device structure is basically the same as the original, but the type of the substrate is changed.
Panasonic made a trial of 2.1mm & TImes in the gan substrate product and Si substrate products; 2.0mm test chip was compared. The on-resistance of the Si substrate product was 150 mΩ, and the on-resistance of the GaN substrate product was 100 mΩ. For Qoss, the Si substrate product is 18.3 nC and the GaN substrate product is 9.4 nC. Thus, the GaN substrate product is reduced to 940 mΩ·nC as compared with the FOM of the Si substrate product of 2745 mΩ·nC. Panasonic calculated the speed at turn-off by performing a switching operation. Compared with the conventional Si substrate product of 285V/ns, the speed of the GaN substrate product reached about twice the 140V/ns.
The reason why the on-resistance is reduced after using the gan substrate is that the crystal defects of the GaN-based semiconductor on the substrate are reduced. Thus, the electron mobility is improved and the on-resistance is reduced. The reduction in Qoss is due to the thickening of the buffer layer disposed directly above the GaN substrate. The Si substrate product buffer layer is 5 μm thick, and the GaN substrate product is thickened to 16 μm. Since the Si substrate product grows GaN crystals having different materials from Si, cracks and the like are likely to occur when the buffer layer is excessively thickened. Therefore, the limit is about 5 μm.
In addition, by using a gan substrate, the withstand voltage can be increased and current collapse can be suppressed. In terms of withstand voltage, when the thickness of the buffer layer is 16 μm, the withstand voltage (Lgd) is 10 μm, the withstand voltage is about 1.5 kV, and when the Lgd is 20 μm, the withstand voltage is 2.8 kV. In the Si substrate product, the buffer layer has a thickness of 5 μm, and when the Lgd is 10 μm, the withstand voltage reaches about 1 kV. Moreover, even if Lgd is expanded to 15 μm, the withstand voltage hardly changes.
In the case of current collapse, it has been confirmed that this phenomenon does not occur up to 1 kV. It is equivalent to the Si substrate product that is sold by Matsushita and has an anti-current collapse structure. When this configuration is not provided, current collapse occurs below 1 kV.
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