AlInGaN/GaN HEMTs with Different GaN Cap Layer on Low Resistivity Silicon Substrate

We report the fabrication and characterization of 136-nm-gate AlInGaN/GaN high-electron mobility transistors with different thickness GaN cap layer. Using Matlab to simulate the energy band diagram under different cap layer thicknesses, the results show that the thicker cap layer will reduce the two-dimensional electron gas concentration due to the uplift of the conductive band and increase the carrier mobility. The HEMTs with 5 nm cap layer exhibit I
ds,sat
= 1.10 A/mm, gm = 405 mS/mm, and on/off ratio = 4.4×10
⁷
. In small-signal operation, cut-off frequency F
T
/F
MAX
= 106.7/114.7 GHz are achieved, which gives a high value of (F
T
*L
g
) = 14.5 GHz*μm among the reported GaN-on-Si devices.