A light emitting device with a μ-cavity including a first spacer of single crystal dielectric material and an active area including single crystal erbium dielectric material positioned on the first spacer. The erbium dielectric material and the single crystal dielectric material of the first spacer are substantially crystal lattice matched at their juncture. A second spacer of single crystal dielectric material is positioned on the active area. The erbium dielectric material and the single crystal dielectric material of the second spacer are substantially crystal lattice matched at the second surface. The high-κ erbium dielectric provides a high gain κ-cavity that emits increased amounts of light in either spontaneous or stimulated modes of operation.