Abstract
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 (Rsh) 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 (Nt) 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/ƒ noise behavior with the carrier number fluctuation (CNF) model, which is proved by the curves of both (SId/Id2) versus (gm/Id)2 and (SId/Id2) versus (Vgs–Vth). Although low Al composition is favorable to the reduced noise, it causes some problems like low Rsh and high gate leakage current. Therefore, the optimized Al composition in AlGaN/GaN HEMT is required to improve both noise and DC properties.
Highlights
Alx Ga1−x N/GaN high-electron mobility transistors (HEMTs) are very attractive devices for both high-power and high-temperature operations [1]
When Al composition in the Alx Ga1−x N barrier layer increases, the conduction band discontinuity and the polarization-induced electrons are increased, which results in high sheet carrier concentration in the two-dimensional electron gas (2DEG) located at the Alx Ga1−x N/GaN
The reason for the excellent leakage currents in the device with high Al composition is due to the enhanced Schottky barrier height (SBH) [3,15] caused by the enlargement composition is due to the enhanced Schottky barrier height (SBH) [3,15] caused by the enlargement of of energy band gap (Eg) of the AlGaN barrier layer
Summary
Alx Ga1−x N/GaN high-electron mobility transistors (HEMTs) are very attractive devices for both high-power and high-temperature operations [1]. This is because the wide energy band gap (Eg ) of above 3.4 eV allows for higher supply voltages and reliable device performances at high temperature [2]. When Al composition in the Alx Ga1−x N barrier layer increases, the conduction band discontinuity and the polarization-induced electrons are increased, which results in high sheet carrier concentration in the two-dimensional electron gas (2DEG) located at the Alx Ga1−x N/GaN heterostructure [3]. These dislocations play the roles of trap states and charge scattering centers, which leads to the deterioration of device performance, such as severe current
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