Carrier-Density Fluctuation Noise and the Interface Trap Density in GaN/AlGaN HFETs
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Carrier-Density Fluctuation Noise and the Interface Trap Density in GaN/AlGaN HFETs Dmitri Kotchetkov and Alexander A. Balandin Department of Electrical Engineering University of California at Riverside Riverside, California 92521 U.S.A.
ABSTRACT The interface trap density NT is extracted from the experimental low-frequency noise data for GaN/AlGaN heterostructure field-effect transistors (HFETs). The trap density is determined based on the carrier-density fluctuation formalism. We show that the value of NT approximately defines the noise response of different GaN/AlGaN HFETs fabricated on the same wafer and it weakly depends on the gate bias. The dependence is due to the non-uniformity of the trap distribution. A model for computer simulation of the lowfrequency noise in GaN devices is proposed. INTRODUCTION Wide band-gap semiconductors such as GaN, InN, AlN and their ternary alloys have been extensively investigated in recent years because of their potential microwave and optoelectronic applications. Devices based on these material systems can be used for high-temperature, high-power density, high frequency, and radiation-hard applications [1]. Advances in GaN-related compound materials have already led to a demonstration of the high frequency and high-power-density operation of GaN/GaAlN heterojunction field-effect transistors (HFETs). At the same time, the absence of native substrates for epitaxial growth of III- nitrides, and significant mismatch in the lattice constants and coefficients of thermal expansion for nitrides and sapphire substrates usually lead to large defect concentrations. This results in a high level of the low-frequency noise spectral density in GaN layers and AlGaN/GaN devices [2-5]. The value of the low-frequency noise is a good indicator of material quality for semiconductor structures and an important figure-of-merit for many electronic devices. It has been shown that the value of the low-frequency noise is highly sensitive to the presence of interface traps [6]. The high level of the low-frequency noise in GaN transistors [5] translates into unacceptable phase noise that limits performance of oscillators, mixers, and other electronic systems. This type of noise imposes the lower limit on a signal level in the broadband circuits. In order to model noise behavior of the communication circuit, among other things one needs to know noise response of the constituent devices. In this paper we analyze experimental noise data for GaN/AlGaN HFETs with different gate length fabricated on the same wafer in order to extract the interface trap density NT and γ parameter. These data is then used to build a simple model that describes the noise spectral density in GaN/AlGaN HFETs for different bias conditions. The model can be incorporated into the commercial device and circuit simulation tools. The E9.13.1 Downloaded from https://www.cambridge.org/core. Iowa State University Library, on 21 Mar 2019 at 17:21:14, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/term
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