The Influence of AlGaN Spacer Thickness on the Electrical Properties of InAlN/AlGaN/AlN/GaN Heterostructure

InAlN is particularly suitable for applications in high-power electronic devices because it has a higher polarization than traditional barrier layer materials and can achieve no lattice constant mismatch between GaN and InAlN. However, the InAlN epitaxial layer alloy disorder is difficult to improve, which will seriously affect the mobility of two-dimensional electron gas (2DEG) formed by InAlN/GaN heterostructures. In this paper, two groups of GaN-based heterostructures have been fabricated to study the influence of InAlN thickness and AlGaN thickness on the In_0.17Al_0.83N/Al_0.23Ga_0.77N/AlN/GaN heterostructure electrical properties. A wide range of 2DEG sheet density from 1.12 × 10¹³ to 1.92 × 10¹³ cm⁻² was achieved while the mobility varied from 1064 to 1945 cm²/V s. Both the 2DEG mobility and the surface flatness improved a lot with the increase of the Al_0.23Ga_0.77N thickness. The heterostructure with 16 nm InAlN shows a higher electron mobility and 2DEG sheet density compared with that with 8 nm InAlN. In addition, there exists a proper thickness of AlGaN spacer to strike a balance between the 2DEG mobility and sheet density to achieve the lowest sheet resistance. The proper thickness is around 2–4 nm which will keep the sheet resistance in a low level.