GaN HEMT on Si for high power applications

Due to the large bandgap and high electron mobility properties, AlGaN/GaN high electron mobility transistor (HEMT) has become one of the most promising candidates for the future generation of power electronic applications. Besides, AlGaN/GaN HEMT grown on Si substrate not only reduces the production cost but also prepares for the possible combination of GaN devices and Si technology. High quality AlGaN/GaN structure on Si substrate (2~6 inches) has been grown by using metal-organic chemical vapour deposition (MOCVD, Veeco D-180 System). From the Hall effect measurements, sheet resistance of 344 ohm/sq, sheet carrier density of 1×10
¹³
cm
^-2
and electron mobility of 1800 cm/V-s are achieved. The HEMT devices are fabricated by using in-house facilities for both high frequency and high power applications. For HEMT device grown on a relatively thinner GaN buffer (1.2μm) with source-drain spacing of 7μm and gate length of 1μm, the device saturated current (Idss) and peak tranconductance (Gm) are 877mA/mm and 120 mS/mm, respectively. For this device, the breakdown voltage is larger than 150V. On the other hand, when a much thicker GaN buffer (5μm) is used, breakdown voltage over 400V is demonstrated. The results indicate that thicker buffer is needed to improve the GaN crystal quality and device endurance for high electrical field. In order to increase the output current, large periphery HEMT devices are also fabricated. The DC characteristics of a 20 mm device with field plate structure show that a total output current of 20A is achieved for AlGaN/GaN HEMT grown on Si. Furthermore, for high frequency applications, device with smaller gate length (0.7 μm) is also fabricated. In such device, a power density of 5 W/mm with 26.2% power added efficiency (PAE) has been measured at 8 GHz and biased at 30V.