Photoluminescence Comparison of Different Substrates on AlN: Cr Thin Films for Optoelectronic Devices

Abstract

Chromium doped aluminum nitride (AlN: Cr) thin films were grown on silicon, glass and copper substrates by DC and RF magnetron sputtering co-deposition. After growth, thin films on silicon substrates were annealed at 1373 K for 30 min in N2 atmosphere. The AlN: Cr thin films were characterized by x-ray diffraction for structural analysis, by FS5 spectrofluorometer for the study of photoluminescence, absorption, transmission, and chromaticity. As-deposited and annealed silicon substrate and as-deposited glass substrate thin films of AlN: Cr exhibited intense photoluminescence emission in the range of 400 to 679.5 nm. Spectral evidence demonstrated conclusively that the AlN: Cr thin films on as-deposited glass substrate and annealed silicon substrate have excellent photoluminescence emission which is due to both AlN (host) and Cr3+ ions. The reasons of photoluminescence of AlN in the visible region are surface defects and impurities. Impurities become the cause to produce different types of defects and vacancies just like oxygen point defects (O+N), nitrogen vacancies (VN) and various defect complexes (V3-Al – 3 O+N). It may also be due to the recombination of photogenerated hole with the electron occupied by the nitrogen vacancies and due to the transition between deep level of (V3-Al – 3 O+N) defect complexes and shallow level of VN and the reason behind the photoluminescence of Cr3+ ions is due to vibrational energy levels 4T1 and 4T2 and due to 4T1→4A2 and 4T2→4A2 transitions. AlN: Cr thin films can give better results in the applications like light emitting diodes (LEDs), laser diodes (LDs), field emission displays, microelectromechanical system (MEMS), optical MEMS and biomedical applications. Key words: III-V Semiconductor Material, Thin films, Photoluminescence Mechanism