Luminescence characteristics of Er-doped GaN semiconductor thin films

Abstract

Semiconductors doped with rare earth atoms have been studied for more than a decade because of the potential of using them to develop compact and efficient electroluminescence (EL) devices. Trivalent erbium ions (Er 3+) are of special interest because they exhibit atomic-like transitions centered at 1540 nm, which corresponds to the low-loss window of silica-based optical fibers. While EL devices, based on Er-doped Si and GaAs materials, have been fabricated, their efficiency remains too low for practical applications. Several years ago an important observation was made that there was less detrimental temperature quenching of Er luminescence intensity for larger bandgap host materials. Therefore, Er-doping of wide gap semiconductors, such as the III–V nitrides, appears to be a promising approach to overcoming the thermal quenching of Er luminescence found in Si and GaAs. In particular, GaN epilayers doped with Er ions have shown a highly reduced thermal quenching of the intensity of the Er luminescence from cryogenic to elevated temperatures. The remarkable thermal stability of the light emission may be due to the large energy bandgap of the material, as well as to the optical inactivity of the material defects in the GaN films. In this paper, recent data concerning the luminescence characteristics of Er-doped GaN thin films are presented. Two different methods have been used for Er-doping of the GaN films: ion implantation and in situ doping during epitaxial growth. Both methods have proven successful for incorporation and optical activation of Er 3+ ions. Infrared photoluminescence spectra, centered at 1540 nm, have been measured for various Er-doped III–N films. Considerably different emission spectra, with different thermal quenching characteristics, have been observed, depending upon the wavelength of the optical pump and the Er-doping method. Defect-related absorption centers permit excitation of the Er ions using below-bandgap optical sources. Elemental impurities, such as O and C, in the thin films have also been shown to influence the emission spectra and to lead to different optical characteristics.