Nitride based wide bandgap semiconductors (GaN, AlN, InN and related materials) have been attracting the attention of device researchers since the early 1990's as the promising candidates for high-power high-frequency applications. The value of the low-frequency noise is a good indicator of material quality for semiconductor structures and an important figure-of-merit for electronic and optoelectronic devices. It has been shown that the value of the low-frequency noise is highly sensitive to the presence of crystal imperfections and, under certain conditions, can be used as a diagnostic tool for quality and reliability of devices. At the same time, high level of the low-frequency noise has been one of the factors, which so far restricted application of newly developed devices for communication systems. In most cases, the high low-frequency noise level in GaN transistors translates into unacceptable phase noise that limits performance of oscillators, mixers, and other electronic systems.; In this research, we studied the low frequency noise characteristics in GaN based advanced field effect transistors developed as a part of the study. Measurements and analysis were performed in a systematic way to determine the possible sources and mechanisms of the observed low frequency noise. Our measurements and analysis for SiO2/AlGaN/GaN Metal-Oxide-Semiconductor Heterostructure Field Effect Transistors (MOS-HFETs) and the base-line HFETs showed that in the GaN-based HFETs both generation-recombination noise and 1/f noise contributed to overall output noise. In the devices with very low noise level, contribution of the gate current fluctuations to output noise was also observed. In the devices with a relatively high level of the 1/f noise, the contribution of the gate leakage current was fully masked by other noise mechanisms. Further analysis revealed the contribution to noise from a local level with activation energy Ea ∼ 0.8--1.0 eV. We also concluded that the trap responsible for the observed generation-recombination noise could be located in the AlGaN barrier layer. We developed a model based on tunneling of 2DEG electrons to bulk GaN in Doped Channel HFETs and explained the behavior of noise at low temperatures successfully. The Hooge parameter alpha, was estimated to be alpha = 4 x 10-4 for both HFETs and MOSHFETs.; Similar analyses for GaN Highly Doped thin channel Metal-Semiconductor field Effect Transistors (HD-MESFETs) and HD-MESFETs showed that the noise properties of MESFETs and MESFETs were similar and drain and source contacts did not contribute much to the low frequency noise. The dependence of the noise on gate voltage indicated that the noise originated from the bulk GaN in the channel and in the source-gate and drain-gate regions. The Hooge parameter alpha, was estimated to be alpha = (2--3) x 10-3.
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