Structural, optical and electrical properties of undoped and Si-doped Al xGa 1− xN thin films on Si (1 1 1) substrate grown by PA-MBE

Abstract

We have studied the structural properties of undoped and Si-doped Al x Ga 1− x N/GaN/AlN on Si (1 1 1) substrate prepared by plasma-assisted molecular beam epitaxy (PA-MBE) using high-resolution X-ray diffraction (HR-XRD) and atomic force microscopy (AFM). In comparison with undoped AlGaN, the roughness and dislocation density on the surface of the AlGaN layer decrease with Si doping. Full width half maximum (FWHM) of the undoped and Si-doped samples were equal to 0.69° and 0.52°, respectively. This indicates that the Si doping improves the crystalline quality of the Al x Ga 1− x N layer compared with the undoped one. Raman scattering measurement reveals that the optical phonon modes of A 1(LO) and E 2(H) of the AlGaN show a one-mode and two-modes behavior, respectively. The Fourier-transform infrared reflectance (FTIR) investigation confirms the one-mode (two-mode) behavior of the LO (TO) phonon in our samples. This is in good agreement with Raman measurement. Finally, the barrier height ( Φ B ) of undoped and Si-doped Al x Ga 1− x N samples was found to be 0.86 and 0.74 eV, respectively.