Enhanced Photoluminescence from Erbium-Doped Gap Microdisk Resonator
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"**Departmentof Material Science and Engineering
ABSTRACT The fabrication and optical properties of an erbium-doped gallium phosphide microdisk resonator pumped by a Ti-sapphire laser at 980 nm were investigated. Enhanced Er 3+ intra-4fshell photoluminescence was observed in the microdisk resonator compared to a thin film, and is attributed to a microcavity effect. At low pumping power intensity, the photoluminescence from erbium-doped gallium phosphide microdisks is an order of magnitude more intense than that from a thin film sample.
Introduction
Rare-earth doped semiconductors have attracted much attention due to the observation of sharp and strong intra-4f-shell luminescence from the rare-earth centers', 2 . The erbium-doped (Er-doped) semiconductors are of particular interest for light emitting devices and lasers, because its strong emission at 1.54 pim coincides with the minimum transmission loss of the silica-based optical fibers 3-8 . For most of Er-doped semiconductors, however, the luminescence intensity decreases by more than two orders of magnitude as the temperature increases from 10K to room temperature 3 ,4,5. Recently Wang and Wessels 8 demonstrated that the emission intensity from Er-doped GaP is only weakly temperature dependent and strong emission from Er-centers was observed at room temperature. This observation indicates that Er-doped GaP is potentially promising as a material for light-emitting or lasing devices operating at 1.54 jim at room temperature. To assess the use of Er-doped GaP as a resonator material, microcavity structures were chosen for their promise for realizing low-threshold light-emitting or lasing devices. Among microcavity structures, microdisk resonators in different material systems under optical pumping have been studied extensively 9-"1.The thin disk resonator supports optical modes in the form of a whispering gallery mode where photons skim around the disk circumference being continually totally reflected12. Due to the large difference in refractive indices between the thin semiconductor disk (n=3.4) and the surrounding low index medium, e.g. air (n1l), the optical mode is strongly confined inside the disk and coupled to the active medium' 3 . Because of its enhanced optical confinement and strong coupling with the active material, the microdisk resonator is of particular interest for the study of Er-doped semiconductors as 229
Mat. Res. Soc. Symp. Proc. Vol. 392 0 1995 Materials Research Society
potential lasing materials. In this paper we report on the fabrication of Er-doped GaP microdisk resonators, and compare the photoluminescence from the microdisk resonator and thin film of Er-doped GaP. The cavity effect on the luminescence from Er-doped GaP microdisk resonators was observed. Experimental The structure for the Er-doped GaP microdisk resonator consists of a pedestal layer and a disk layer as shown in Fig. 1(a). The Er-doped GaP disk layer was grown by atmospheric pressure metalorganic vapor phase epitaxy (MOVPE) and the AIGaP pedestal layer was grown by g
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