MOCVD grown AlGaN/AlN/GaN HEMT structure with compositionally step-graded AlGaN barrier layer

摘要

Unintentionally doped AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures with compositionally step-graded AlGaN barrier layer were grown on sapphire substrates by metalorganic chemical vapor deposition (MOCVD). The HEMT structure exhibited typical two-dimensional electron gas (2DEG) mobility of 1600cm~2/Vs at room temperature and 6412cm~2/Vs at 79K with almost equal 2DEG concentration of 1.0 × 10~(13)/cm~2. The 50mm HEMT wafer exhibited an average sheet resistance of 318.0Ω/square, with a good resistance uniformity of 0.89%. Atomic force microscopy (AFM) measurements revealed a smooth AlGaN surface with root-mean-square roughness (RMS) of 0.199nm and 0.295nm for scan area of 2μm × 2um and 5μm × 5μm, respectively. A combined using of compositionally step-graded AlGaN barrier structure and A1N interlayer results in the high electrical performance and smooth surface of this heterostructure.