The effect of AlN growth time on the electrical properties of Al0.38Ga0.62N/AlN/GaN HEMT structures

Al0.38Ga0.62N/AlN/GaN HEMT structures have been grown by metal–organic chemical vapor deposition (MOCVD) on 2-inch sapphire substrates. Samples with AlN growth time of 0 s (without AlN interlayer), 12, 15, 18 and 24 s are characterized and compared. The electrical properties of two-dimensional electron gas (2DEG) are improved by introducing AlN interlayers. The AlN growth time in the range of 12–18 s, corresponding to the AlN thickness of 1–1.5 nm, is appropriate for the design of Al0.38Ga0.62N/AlN/GaN HEMT structures. The lowest sheet resistance of 277 Ω sq−1 and highest room temperature 2DEG mobility of 1460 cm2 V−1 s−1 are obtained on structure with AlN growth time of 12 s. The structure with AlN growth time of 15 s exhibits the highest 2DEG concentration of 1.59×1013 cm−2 and the smallest RMS surface roughness of 0.2 nm.