Intra-4f-transitions from erbium atoms are proposed as a probe to determine absorption edges of the hosts. This idea was firstly applied on erbium-doped porous silicon materials. Intense and sharp 1.54 μm luminescence from erbium triply ionized ions as well as visible emissions from porous silicon were observed up to room temperature. Photoluminescence excitation spectroscopy investigations of the samples indicate identical absorption edges for both the 1.54 μm and the visible emissions. No 1.54 μm luminescence can be observed by directly exciting the erbium triply ionized ions. This fact suggests that the erbium ions are excited by energy transfer process from the excited carriers in the hosts. From this result, we can propose that erbium could behave as a good probe to determine the absorption edge or the bandgap of the host material even it is not luminescent.

Photoluminescence characteristics of porous silicon layers (PSLs) doped with Er or Yb ions are studied. 10μm thick PSLs with a luminescence centered at ∼ 0.8μm are formed by anodic etching of p-type silicon wafers of several Ω-cm resistivity. Rare-earth ions are electrochemically incorporated into PSLs. The Er3+-related luminescence at 1.54μm as well as the Yb3+-related luminescence at 1.0μm is observed at room temperature after annealing at high temperatures (>900°C). The Er-related luminescence is enhanced after annealing in O2, whereas the Yb3+-related luminescence needs oxygen-free atmosphere (H2) for the optical activation. The luminescence decay time of the rare earth ions as well as the host PSLs is measured and the energy transfer mechanism is discussed.

Er-doped semiconductors are considered to be important for optical communication systems since one of the prominent luminescent peaks of Er is in the minimum absorption region of silica based fiber and wavelength of the luminescence is insensitive to the ambient temperature. In this work, OMVPE grown InP samples uniformly and δ-doped with Er were investigated by EXAFS and X-ray CTR measurements. The EXAFS measurement revealed that the uniformly doped Er atoms in InP grown at 580°C formed NaCl-structure ErP, and at 530°C occupied the In-sites. The X-ray CTR measurement revealed that the δ-doped Er atoms in InP at 530'C formed NaCl-structure ErP. In the sample, the total number of Er was analyzed to be about 0.171ML(monolayer), and the FWHM of Er distribution was about 5ML. By comparing the results of PL measurement with those of the EXAFS and the X-ray CTR measurements, it was suggested that the Er atoms on In-sites show high efficiency of luminescence and the Er atoms in the NaCl-structure ErP low efficiency.

Zeeman measurements in magnetic fields up to 16 T have been performed on the no-phonon lines labelled #3, #4, and #8 of the spectrum of ytterbium impurities in indium phosphide. A strong polarization effect and changes in intensities were observed. An energy level diagram is presented that satisfactorily explains the magnetic field effect and the relative intensities of the photoluminescence lines and is consistent with experiments described in the literature.

For GaAs:Er,O the anisotropic photoluminescence (PL) properties of the Er-20 center and its preferential alignment within the GaAs matrix have been revealed by the polarization dependence of host-excited PL when detecting emission polarized along certain crystallographic directions. In the present paper, a polarized intra-4f-shell photoluminescence excitation (PLE) spectroscopic study of Er centers incorporated in GaAs is reported. This technique is not only sensitive to those centers which luminesce under host-excitation, but also to other Er centers incorporated in the host, thus allowing the polarized PL properties of most Er centers to be studied. A comparison of the polarization characterisitcs of host-excited PL and direct intra-4f-shell PLE, due to the difference in the excitation mechanisms, is made and the information which may be gained from such measurements is discussed. For the Er-20 center, we confirm the optical anisotropy and preferential alignment of the center previously observed in host-excited PL. Incorporation mechanisms for the Er-20 center which could result in the observed polarization dependence are discussed.

The results of parallel RBS and photoluminescence studies of erbium implanted GaAs are presented. Low dose implantations do not produce any significant PL signals, and the dose must be in the range le14 to le15 /cm2 in order that Er related emission dominates in the PL spectrum. A comprehensive analysis of the effects of coimplantation with oxygen on the Er luminescence is reported and the data are compared to those of GaAs:Er and AIGaAs:Er samples grown by MBE. The evidence indicates that, at high doses, ErAs precipitates are formed unless oxygen is co-implanted, and that the Er atoms which produce the luminescence occupy substitutional Ga sites.

We analyze the Zeeman effect of the 4/13/2 → 4/15/2 transition of Er3+ in GaAs:Er,O grown by metal-organic vapor-phase epitaxy. The photoluminescence spectrum has been assigned previously to one specific Er-O complex. The dominant optical transition at 1538 nm (6499.5 cm−1), which shows a full width at half maximum of only 0.05 cm−1, has been investigated by high-resolution Zeeman spectroscopy. A highly anisotropic Zeeman pattern is found which indicates the low symmetry of the underlying complex. A detailed analysis shows that the defect has a predominant rhombic symmetry C2v,. Additionally, smaller contributions of a crystal field with a monoclinic symmetry Clh are found. The results provide further arguments that an ErO2 complex is the responsible center observed.

Yb in GaAs is generally believed to be optically inactive due to very low fraction of Yb in substitutional position. In the present work it is demonstrated that Yb can be rendered optically active in GaAs if it is incorporated in three-component complexes (Yb+O+S/Se/Te).

Er-doped AIN epilayers have been grown using metal-organic molecular beam epitaxy (MOMBE) with controlled Er densities. Cell temperatures greater than 1000°C were required for the Er solid source in order to achieve significant Er concentrations in the epilayers. Er densities in the 1019 to 1020 cm−3 range were confirmed using secondary ion mass spectrometry (SIMS), quantified using implanted standards. The epilayers were optically excited using an argon-ion laser and infrared luminescence spectra were measured over the temperature range 13 to 300 K. The spectra are centered at 1.54 μm and display features typical of the Er3+ configuration. These data demonstrate that high densities of Er atoms can be incorporated in AIN films during epitaxial growth and that the Er atoms give rise to the intra-4f transitions of the trivalent Er3+ ion.

A systematic study of photoluminescence (PL) of Er and O ion implanted and annealed n-type GaN grown on R-plane sapphire (A12O3) was performed. The Er implants ranged from 2 × 1013 to 1 × 1015 Er++/cm2, and the O co-implants ranged from 1014 to 1016 O+/cm2. The resulting nine different combinations of GaN:Er,O were annealed at 600 °C (4 hrs. in N2), 700 °C (1.5 hrs. in N2), 800 °C (0.75 hr. in NH3), and 900 °C (0.5 hr. in NH3) Following each annealing step, the Er3 -related PL at 1.54 μm was measured from each sample at 77K, when pumped directly with 135 mW of power at 980 nm. The three samples with the highest dose of Er (1 × 1015 Er++/ cm 2), regardless of O co-dopant dose, yielded the strongest PL peak intensity at 1.54 μm after all the anneals. The integrated PL from 1.52 to 1.58 μm was reduced by 62 % when going from 77 K to room temperature (RT).

In the paper the existing information on the optical excitation of the erbium ion in crystalline silicon is critically reviewed. The proposed excitation mechanism is compared to the one which is believed to be responsible for the luminescence of ytterbium in indium phosphide. To this end the influence of constant and microwave electric field on the photoluminescence of both systems is inspected. It is shown that, although both systems show some similarities, their analogy is limited.

The particular role of excitons and electrons in both the excitation as well as the de-excitation mechanism is investigated for the Si:Er system. The results of photoluminescence decay studies (T=4.2 K) are presented. It is argued that a nonradiative energy transfer to conduction electrons is responsible for the limitation of the energy transfer to the Er core and for its nonradiative recombination. Also, a prominent role of excitons in the energy transfer mechanism is confirmed. Finally, the origin of the 873 meV photoluminescence band recently reported in Er-implanted Si is discussed in relation to a possible defect-mediated activation of Er.

Temperature quenching of the 1.54 μm photoluminescence intensity and lifetime of Er in crystal Si was investigated between 12 K and 150 K. A p-type Czochralski-grown Si (100) wafer was doped with Er to a peak concentration of 5×1018 cm−3 using 1.5 MeV ion implantation. The Er doped layer was co-implanted with N to a peak concentration of 6×1019 N cm−3 The sample was annealed at 490 °C for 2 hours and at 600 °C for 1 hour. The 1.54 μm photoluminescence intensity shows a weak temperature quenching between 12 and 75 K, characterised by an activation energy of 1–10 meV. For temperatures above 75 K, a strong intensity quenching with an activation energy of 210 ± 10 meV is observed. The luminescence lifetime decreases from 420 μs at 12 K to 1 μs at 170 K, and shows strong quenching behaviour above 75 K, characterised by an activation energy of 135 ± 5 meV. The results are interpreted in terms of an impurity Auger energy transfer model. The lifetime quenching is attributed to a phonon assisted backtransfer process which becomes dominant at high temperatures. Intensity quenching is attributed to both the backtransfer process and a carrier de-trapping process which reduces the Er excitation rate. Spectral response measurements on Er implanted solar cells confirm the presence of a backtransfer process at room temperature.

The Er2O3 quantum dot (cluster) with dimensions about 1.2nm in silicon is discussed as the possible source of the Er related emission in Si:Er,O, excited by photogenerated carriers or in a light-emitting diodes (LED) at forward bias. This quantum dot is represented as a spherical quantum well 0.9eV in depth. The electron level with energy about 0.15eV below the bottom of the silicon conduction band plays role of an electron trap. The trapped electron interacts with a hole in valence band of silicon forming “indirect” exciton bonded to quantum well. The energy is transferred to f - shell of erbium by the Auger electron - hole recombination.

Hydrogenated amorphous silicon thin films, co-doped with oxygen, are made using lowpressure chemical vapor deposition (LPCVD) or plasma-enhanced chemical vapor deposition (PECVD). The films are implanted with Er to a peak concentration of 0.2 at.%. Roomtemperature photoluminescence at 1.54 μm is observed in both amorphous materials, after thermal annealing at 300–400 °C. The PECVD films with low 0 content (0.3, 1.3 at.%) show a luminescence intensity quenching by a factor 7–15 as the temperature is raised from 10 K to room temperature. The quenching is well correlated with a decrease in luminescence lifetime, indicating that non-radiative decay of excited Er3+ is the dominant quenching mechanism as the temperature is increased. In the LPCVD films, with 31 at.% 0, the quenching is only a factor 3, and no lifetime quenching is observed. The results are interpreted in the context of an impurity Auger excitation model, taking into account the fact that oxygen modifies the Si bandgap and the Er-related defect levels in the gap.

The optical properties of rare-earth impurities in InGaP and the factors which influence their luminescence efficency are presented. Basic energy transfer processes are described. Practical devices that utilize characteristic rare-earth luminescence are reported.

An efficient transfer of excitonic energy to rare earth (RE) ions is crucial for possible optoelectronic applications of RE doped semiconductors. In order to investigate the energy transfer mechanism to RE ions after optical above bandgap excitation we studied the intensity of the 4I13/2 →4 4I15/2-transition of Er3+ (1.54μm) and the one of the 2F5/2 →2F7/2 -transition of Yb3+ (lμm) (loped into InGaAsP-layers lattice matched to InP. By varying the composition of the quaternary compoun ds, the bandgap energy together with the RE bound exciton energy were tuned relative to the RE excitation energy, and the effect on the RE luminescence intensity was observed. The results can be interpreted by stating a) that the energy transfer to the RE proceeds via the RE bound exciton, and b) that the intensity of the RE luminescence is essentially determined by the rate of back transfer of the RE excitation energy ERE to the bound exciton (with excitation energy Ebe). In this back transfer the energy of the excited RE ion plus the energy of 0, 1, 2 ... L0-phonons (energy Elo) is used to reexcite the bound exciton, instead of being emitted as an RE luminescence photon. For compositions where Ebe = ERE + n. Elo (n = 0, 1, 2...) we have a maximum of back transfer and correspondingly a, minimum in RE luminescence. In between the intensity has a, maximum.

GaAs grown by metalorganic chemical vapor deposition and codoped with Er and oxygen shows a simple spectrum with sharp luminescence lines due predominantly to one type of Er center. This center is identified as an Er atom substituting a Ga site, coupled with two oxygen atoms. Photoluminescence measurements under host excitation and photoluminescence excitation measurements that directly excite the 4f-shell of the Er3+ ion indicate that this center is excited much more efficiently than other Er centers simultaneously present in the same sample. A possible energy-transfer mechanism and its implications are discussed.

The photoluminescence properties of MOCVD GaP:Er were investigated as a function of temperature, applied hydrostatic pressure, and excitation wavelength. Four sharp peaks are observed on the high energy side of the 1.54 μm Er3+ emission. These peaks are selectively excited by below-gap energies and have a significantly shorter lifetime than the main Er3+ emission, suggesting that at least two distinct Er3+ centers contribute to the luminescence. The low temperature photoluminescence excitation (PLE) spectrum of the 1.54 μm emission was also measured. Strong broad excitation of the Er3+ centers occurs with energies well below the indirect bandgap energy. In fact, the Er3+ emission intensity is significantly stronger when excited with below-gap wavelengths than with above-gap wavelengths. This result has been explained in terms of competition between Er3+ excitation and nonradiative deep level recombination for free carriers under above-gap excitation. With below-gap excitation, carriers are promoted directly into the Er3+ excitation pathway via absorption at an erbium-related trap. At 42 kbar, below-gap excitation is no longer more efficient than above-gap excitation, suggesting that competitive capture of free carriers by deep levels has been reduced.

In this work we have developed a model for the kinetics of the energy transfer from the host lattice to the core states of rare earth (RE) centers. We have derived a set of kinetics differential equations of RE luminescence in p-type semiconductor. Numerically computed rise and decay time of RE luminescence as a function of excitation power shows good agreement with the experimental data obtained for p-type GaAs:Nd.

Rare Earth (RE) doped II–VI semiconductors are currently used for production of thin film light emitting electroluminescence devices. The excitation and recombination processes in RE activated wide band gap II–VI semiconductors (ZnS, ZnSe, SrS and CaS) are reviewed. Mechanisms relevant for obtaining bright photoluminescence (energy transfer processes, RE ionisation and exciton binding), electroluminescence (impact excitation and impact ionisation) and cathodoluminescence are described based on the recent experimental results. Efficiency of the light emission from RE doped II–VI materials is limited by several processes of nonradiative recombination. The Auger-type energy transfer processes and electric field- or thermally-activated processes responsible for 4f-4f nonradiative recombination of RE ions are discussed.