Low-Frequency Noise Behavior of AlGaN/GaN HEMTs with Different Al Compositions

AlxGa1-xN/GaN heterostructures with two kinds of Al composition were grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrates. The Al compositions in the AlGaN barrier layer were confirmed to be 13% and 28% using high resolution X-ray diffraction (HRXRD). AlxGa1-xN/GaN high-electron mobility transistors (HEMTs) with different Al compositions were fabricated, characterized, and compared using the Hall effect, direct current (DC), and low-frequency noise (LFN). The device with high Al composition (28%) showed improved sheet resistance (R-sh) due to enhanced carrier confinement and reduced gate leakage currents caused by increased Schottky barrier height (SBH). On the other hand, the reduced noise level and the low trap density (N-t) for the device of 13% of Al composition were obtained, which is attributed to the mitigated carrier density and decreased dislocation density in the AlxGa1-xN barrier layer according to the declined Al composition. In spite of the Al composition, the fabricated devices exhibited 1/integral noise behavior with the carrier number fluctuation (CNF) model, which is proved by the curves of both (S-Id/I-d(2)) versus (g(m)/I-d)(2) and (S-Id/I-d(2)) versus (V-gs-V-th). Although low Al composition is favorable to the reduced noise, it causes some problems like low R-sh and high gate leakage current. Therefore, the optimized Al composition in AlGaN/GaN HEMT is required to improve both noise and DC properties.