Abnormal increase of 2DEG density in AlGaN/GaN HEMT grown on free-standing GaN substrate

Abstract

In this study, AlGaN/GaN high-electron-mobility transistors (HEMTs) were grown on a GaN template and GaN substrate under the same growth conditions. It was observed that, in the HEMT structure grown on the GaN substrate, mobility decreased because of an increase in the two-dimensional electron-gas (2DEG) density; the origin of these redundant electrons was studied. The 2DEG density decreased with decreasing temperature, this phenomenon closely related to unintentionally induced shallow donors with ionization energy calculated to be around 67.8 meV. After Ⅴ/Ⅲ ratio regulation, the 2DEG density returned to a normal level; this combined with photoluminescence, confirmed for the first time that the abnormal increase of 2DEG density in HEMT structure grown on the GaN substrate is associated with nitrogen vacancies. Therefore, increasing the Ⅴ/Ⅲ ratio is beneficial for obtaining higher mobility by returning the 2DEG density to a normal level.

Fabrication of AlGaN/GaN heterostructures on halide vapor phase epitaxy AlN/SiC templates for high electron mobility transistor application

“…These values were comparable to those of a thicker GaN film on a SiC substrate or GaN bulk described in previous reports. [18][19][20] An AlGaN/GaN heterostructure comparable to the properties in Table I was fabricated, and the heterointerface quality was investigated under a magnetic field by a PPMS with respect to the carrier transport. Figure 3 shows the temperature dependence of the magnetic resistance (R xx ) and Hall resistance (R xy ).…”

“…The residual carriers in the buffer layer are often compensated by doping impurities of C 3,4) or Fe. 5,6) However, the electrons trapped at the deep-level defects caused by these impurities can be injected into the AlGaN surface at a high operating voltage, which is considered to be one explanation for current collapse. 7) The growth processes for multilayer and the thick GaN buffer layer are time-consuming.…”

Study on the Point‐Contact Gate AlGaN/GaN High Electron Mobility Transistor with 0.1 μm Gate Length

“…In a GaN HEMT, the variation of the 2DEG density almost determines the overall device performance. [ 25–27 ] At the same time, considering that the thickness of the GaN layer under the AlGaN layer in the point‐contact gate structure is 0.2 μm, the GaN layer in all the improved Γ ‐type gate structures is set to 0.2 μm. In addition, considering the novelty of the point‐contact gate structure and the rationality of the comparison with the improved Γ ‐type gate structure, in 5 μm SPL, the gate‐drain spacing and the gate‐source spacing are set according to the ratio of the gate‐drain spacing and the gate‐source spacing in the point‐contact gate structure.…”