P-GaN/AlGaN/GaN high electron mobility transistors

Despite the considerable improvement in GaN-technology and material quality, RF-dispersion is still one of the main issues hampering device progress. RF-dispersion affects device output power and device power added efficiency (PAE) due to a reduction in saturation current and an increase in knee voltage at high frequencies and high biases. Surface passivation, using silicon nitride, has been found to mitigate RF-dispersion and microwave power degradation (B.M. Green et al, IEEE Electron Dev. Lett., vol. 21, pp. 268-270, 2000; S.C. Binari et al, IEEE Trans Electron. Dev., vol. 48, pp. 465-471, 2001; R. Vetury et al, ibid., vol. 48, pp. 560-566, 2001). This paper discusses a novel AlGaN/GaN high electron mobility transistor (HEMT) device structure which has been developed to reduce RF-dispersion prior to silicon nitride passivation. The device structure uses a p-doped GaN cap layer to screen surface potential changes (regardless of origin) from affecting the gate-drain access region resistance, reducing the amount of RF-dispersion in the device. The epilayers of AlGaN/GaN devices were grown by metal organic chemical vapor deposition (MOCVD) on a c-plane sapphire substrate. Sheet electron concentration and electron Hall mobility of the as-grown wafer were /spl sim/1.35/spl times/10/sup 13/ cm/sup 2/ and 1,475 cm/sup 2//V-s at room temperature.