Effect of gate leakage current on noise properties of AlGaN/GaN field effect transistors

The effect of the gate leakage current fluctuations on noise properties of AlGaN/GaN heterostructure field effect transistors (HFETs) has been studied in conventional HFET structures and in AlGaN/GaN metal-oxide-semiconductor heterostructure field effect transistors (MOS-HFETs). The comparison of the noise properties of conventional AlGaN/GaN HFETs and AIGaN/GaN MOS-HFETs fabricated on the same wafer, allowed us to estimate the contribution of the gate current noise to the HFET's output noise. The effect of the gate current fluctuations on output noise properties of HFETs depends on the level of noise in the AIGaN/GaN HFETs. For the transistors with a relatively high magnitude of the Hooge parameter alpha similar to 10(-3) even a relatively large leakage current I-g (I-g/I(d)similar to 10(-3)-10(-2), where I-d is the drain current) does not contribute much to the output noise. In HFETs with a relatively small values of alpha (alpha similar to 10(-5)-10(-4)), the contribution of the leakage current to output noise can be significant even at I-g/I(d)similar to 10(-4)-10(-3). For such transistors, a very rapid increase of the 1/f noise with gate bias was observed. The differences in the noise behavior can be linked to the material quality of the AlGaN and GaN layers in different types of HFETs. (C) 2000 American Institute of Physics. [S0021-8979(00)08823-X].