Erbium doped materials are of great interest in thin film integrated optoelectronic technology, due to their Er3+ intra-4f emission at 1.54 μm, a standard telecommunication wavelength. Er-doped dielectric thin films can be used to fabricate planar optical amplifiers or lasers that can be integrated with other devices on the same chip. Semiconductors, such as silicon, can also be doped with erbium. In this case the Er may be excited through optically or electrically generated charge carriers. Er-doped Si light-emitting diodes may find applications in Si-based optoelectronic circuits. In this article, the synthesis, characterization, and application of several different Er-doped thin film photonic materials is described. It focuses on oxide glasses (pure SiO2, phosphosilicate, borosilicate, and soda-lime glasses), ceramic thin films (Al2O3, Y2O3, LiNbO3), and amorphous and crystalline silicon, all doped with Er by ion implantation. MeV ion implantation is a technique that is ideally suited to dope these materials with Er as the ion range corresponds to the typical micron dimensions of these optical materials. The role of implantation defects, the effect of annealing, concentration dependent effects, and optical activation are discussed and compared for the various materials.

Erbium implanted thin film photonic materials

We present a new electro‐chemical method for incorporating high concentration Er ions deep into porous silicon layers and its intense photoluminescence at ∼1.54 μm at room temperature. Porous silicon layers prepared by anodic etching of p‐type silicon substrates in HF/H2O are immersed in ErCl3/ethanol solution. Then the negative bias relative to a counter platinum electrode is applied to the samples. Er3+ ions are drawn into fine pores of the porous silicon layers by the electric field. After thermal annealing at ∼1300 °C in an O2/Ar atmosphere, the samples show sharp and intense Er3+‐related photoluminescence at ∼1.54 μm at room temperature upon excitation with an Ar ion laser.

Electrochemical Er doping of porous silicon and its room‐temperature luminescence at ∼1.54 μm

The composition dependence of room temperature 1.54 μm Er3+ photoluminescence of erbium-doped silicon:oxygen thin films produced by electron cyclotron resonance plasma enhanced chemical vapor deposition of SiH4 and O2 with concurrent sputtering of erbium is investigated. The Si:O ratio was varied from 3:1 to 1:2 and the annealing temperature was varied from 500 to 900 °C. The most intense Er3+ luminescence is observed from the sample with a Si:O ratio of 1:1.2 after a 900 °C anneal and the formation of silicon nanoclusters embedded in the SiO2 matrix. The high active erbium fraction, efficient excitation via carriers, and high luminescence efficiency due to the high quality SiO2 matrix are identified as key factors in producing the intense Er3+ luminescence.

Composition dependence of room temperature 1.54 μm Er3+ luminescence from erbium-doped silicon:oxygen thin films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition

The photoluminescence of erbium‐doped semi‐insulating polycrystalline and amorphous silicon containing 30 at. % oxygen is studied. The films were deposited on single‐crystal Si substrates by chemical vapor deposition, implanted with 500 keV Er to fluences ranging from 0.05 to 6×1015 ions/cm2, and annealed at 300–1000 °C. Upon optical pumping near 500 nm, the samples show room‐temperature luminescence around 1.54 μm due to intra‐4f transitions in Er3+, excited by photogenerated carriers. The strongest luminescence is obtained after 400 °C annealing. Two classes of Er3+ can be distinguished, characterized by luminescence lifetimes of 170 and 800 μs. The classes are attributed to Er3+ in Si‐rich and in O‐rich environments. Photoluminescence excitation spectroscopy on a sample with 1×1015 Er/cm2 shows that ∼2% of the implanted Er is optically active. No quenching of the Er luminescence efficiency is observed between 77 K and room temperature in this Si‐based semiconductor. The internal quantum efficiency for the excitation of Er3+ via photogenerated carriers is 10−3 at room temperature. A model is presented which explains the luminescence data in terms of trapping of electrical carriers at localized Er‐related defects, and subsequent energy transfer to Er3+ ions, which can then decay by emission of 1.5 μm photons.

Erbium in oxygen-doped silicon: Optical excitation

We have observed intense line spectra in the neighborhood of 154 μm from erbium‐implanted samples of 4H, 6H, 15R, and 3C SiC Samples were implanted to a fluence of about 1013 erbium ions/cm2 using four implant energies An anneal at 1700 °C in a SiC cavity was used The temperature dependence of the integrated luminescence intensity from 149 to 164 μm varies very little from 2 to 400 K No major differences are found for the spectra of the hexagonal and rhombohedral polytypes but there is a difference for cubic SiC (3C SiC)

Intense erbium‐1.54‐μm photoluminescence from 2 to 525 K in ion‐implanted 4H, 6H, 15R, and 3C SiC

A review of the main results concerning the ion implantation of the rare-earth elements is given. To obtain the best optical activation of rare-earths, we attempt to optimize the implantation (energy, dose) and annealing (temperature, duration) conditions. The studied materials are Si, II-VI binaries (ZnTe, CdS), III-V binaries (GaAs, InP), III-V ternaries (GaAlAs, GalnAs) and III-V quaternaries (GaInAsP).

Optical Activation of Ion Implanted Rare-Earths

The influence of the hydrogen content and the oxygen content on the luminescence from erbium-implanted hydrogenated amorphous silicon (a-Si: H) is presented. The Er3+ -related emission is correlated to the efficiency of Er3+ optical centres with the bandgap variation and was found to depend strongly on the hydrogen content in the films. A direct correlation between the optical gap energy of the semiconductor and the hydrogen film content was observed. Moreover. the direct role played by oxygen impurities in the erbium optical activation was clearly evidenced. This effect is due to the higher oxygen content (1-2 at.%) and to the oxygen incorporation into a-Si: H during low-temperature annealing under an oxygen flow. Thus oxygen incorporation into a-Si: H films considerably enhances the photoluminescence intensity at room temperature and produces an increase in the value of the optical gap up to 2.1 eV.

Oxygen enhancement of 1-54 μm Er3+ luminescence in hydrogenated amorphous silicon

The luminescence of erbium implanted in hydrogenated amorphous silicon (a-Si: H) is presented. For the first time an intense and relatively sharp luminescence at 1.54 mm is observed in a-Si: H, using implanted erbium. The Er+ emission intensity strongly depends on the hydrogen film content and on the measurement temperature. A direct correlation between the optical gap energy of the semiconductor and the hydrogen film content is observed.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400467990

M. Salvi

Papers

Optical Activation of Ion Implanted Rare-Earths

Oxygen enhancement of 1-54 μm Er3+ luminescence in hydrogenated amorphous silicon

1.54 μm Photoluminescence of Erbium Implanted Hydrogenated Amorphous Silicon