We discuss the energy transfer mechanism between rare-earth 4f-shells and III-V semiconductor hosts. For Yb-doped InP, we have proposed an excitation and relaxation model, which explains experimental results for the electronic and optical properties. The Yb 4f-shell is excited by a recombination of an electron and a hole at an electron trap formed by Yb, which is located near the bottom of the conduction band of InP. At high temperatures, the relaxation energy of the Yb 4f-shell is back transferred as a host electron-hole pair, resulting in Yb luminescence quenching. We have found that Er-doped GaAs samples grown by metalorganic chemical vapor deposition contain as much C as Er. Rutherford back scattering and electronic property measurement results suggested that most of the Er atoms form complexes with C atoms, and these complexes are not electrically active. Such samples showed complicated Er 4f-shell luminescence spectra. To obtain a simple Er luminescence spectrum with a high peak intensity, O was intentionally doped with Er. Er-O complexes seemed to be formed in GaAs and these are responsible for simple and strong 4f-shell luminescence.

We have investigated the effects of Yb addition to melts used for the growth of InGaAs/InP heterostructures by liquid phase epitaxy. Our results indicate that impurities in the Yb play an important role in determining the changes in electrical properties observed in the epilayers after Yb treatment of the melt. We have examined samples using double-crystal x-ray diffractometry, photoluminescence, Hall/van der Pauw measurements, and secondary-ion mass spectroscopy. After Yb treatment, the residual carrier concentrations of the epilayers were reduced by more than one order of magnitude and the samples luminesced more strongly; while the lattice matching and crystal quality of the epilayers were not measurably affected by the Yb. There was a smaller-thanexpected ncrease in the 77K mobility and a marked increase in the compensation ratio of the epilayers grown after the addition of Yb to the melt. We believe the Yb is both acting as a scavenging agent in the melt, combining with impurities that otherwise would have been incorporated in the epilayers, and introducing deep level impurities of its own, which are incorporated into the grown layers.

In this paper we report results from electrical and optical measurements carried out on GaAs:Yb, Er.

For GaAs:Yb electrical experiments such as photoconductivity (PC) and Photo Induced Current Transient Spectroscopy (PICTS) show that there is a level at 0.65eV related to Yb. This explains why no Yb3+ photoluminescence (PL) emission is detected, the recombination energy of the trapped excitons is too low (≈ 0.6eV) to excite the Yb3+ internal transition(≈ 1.24eV). We also present results on Er doped GaAs materials. From PL experiments we deduce an estimate of 10−19cm2 for the stimulated emission cross section. By PICTS and PC, we have evidenced a trap at 0.67eV related to Er ions in GaAs. And we think that in this case, the rare earth ions are excited via formation of bound excitons.

A systematic photoluminescence study of erbium and oxygen co-implantation into GaAs and AlxGal1−xAs with × = 0.1, 0.2, 0.3, and 0.4 was carried out. The addition of oxygen greatly enhanced the Er emission intensity from AlxGal1−xAs:Er while the O and Er co-doping into GaAs rather made the Er emission intensity decrease from that of the GaAs:Er. The Er emission intensity from AlxGal1−xAs:(Er+O) generally increases with increasing Al mole fraction and O dose up to 1 × 10 15/cm2, but it does not depend much on the substrate conductivity.

Epitaxial Er-doped GaAs and Al0.5Ga0.5As films, 1.6 μm thick, grown by MBE on (100) GaAs substrates at 560°C, with Er concentrations in the range 9 × 1017 to 2 × 1020 cm−3 were studied with RBS/channeling and photoluminescence techniques. Angular scans in the <110> and <111> axial and (111) planar directions indicate that the Er atoms in GaAs are located on interstitial sites. In Al0.5Ga0.5As doped with 5 × 1019 Er cm−3, 70% of the Er atoms are on positions slightly displaced from the interstitial site, the rest presumably substitutional. In Al0.5Ga0.5As doped with 9 × 19 Er cm−3, more than 88% of the Er atoms are on substitutional sites.

Photoluminescence around 1.54 μm is observed at room-temperature in Er-doped Al0.5Ga0.5As. Both the low and highly Er-doped samples show similar luminescence intensities; the luminescence lifetimes are on the order of 1 ms. The Er-doped GaAs does not show any measurable signal at room-temperature. Correlation of the luminescence data to the Er lattice location suggests that only substitutional Er in AlGaAs is in the luminescent trivalent state.

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, GaInAs) and III-V quaternaries (GaInAsP).

We investigate the excitation mechanism of the characteristic 4f luminescence 3H5 →3H6 of Tm3+ in GaAs by photoluminescence excitation spectroscopy. This luminescence transition is also used to study the incorporation of thulium into the GaAs lattice by angular dependent Zeeman spectroscopy.

For the evaluation of an implanted layer, photoluminescence (PL) and photoluminescence excitation (PLE) measurements, which are nondestructive and sensitive methods for identifying impurities and defects, were performed. Yb3+ -related sharp luminescence was observed at a wavelength of 1002nm, due to the transitions which occurred between the spin-orbit levels 2F5/2→2F7/2 of Yb3+ (4f13). Most efficient luminescence of Yb3+ was achieved at an excitation wavelength of around 880nm. The luminescence intensity of this peak (Yb3+) decreased with an increase in annealing temperature. Since the peak has not been observed for good samples in crystallinity, it may indicate that new, efficient energy transfer processes to rare-earth ions occur through the defect energy level. Especially, for the sample annealed at 600°C, Yb-related luminescence intensity excited by the photon energy below the band gap is about 3 times larger than that of excited by the photon energy above the band gap.

GaP single crystals have been grown from 5at.% solution of P in Ga with (0.01-0.1)at.% of La, Sm or Gd as dopants. Electric properties, photoconductivity and luminescence of the crystals have been investigated by standard methods.

Energy levels of impurities, mobility and concentration of current carriers have been determined in wide temperature region. It was shown that nitrogen (N) and other uncontrolled impurities present in the crystals due to some peculiarities of crystal growth. The intrinsic RE impurity luminescent spectra can be seen only together with spectra of excitons bounded on N traps. The evaluation of quantum eficiency for RE impurity made on the base of luminescence decay measurements gives the value close to 1. The interpretation of GaP:RE luminescence spectra is presented as intrashell transitions activated by bound exciton recombination as well as D-A and D-valency band transitions between some contaminating impurity (donor) and RE element (acceptor).

Electron Spin Resonance experiments of several diluted rare-earths (Dy3+, Er3+, Yb3+) in the narrow gap semiconductor PbTe show ground states appropriated with a cubic crystal field splitting of the lowest multiplet (J). The data permits the determination of the sign and ratio of the cubic crystal field parameters A4 <r4>and A6< r6 >. These results suggest that the rare-earths substitute the Pb2+ ions and that the crystal field is mainly associated to an octahedron of Te2− ions. The observed ESR spectra also show lower symmetry sites probably associated with nearest neighbor Pb2+ vacancies.

Rutherford backscattering (RBS) and channeling measurements have been applied to study lattice location of the Yb atoms implanted into III-V compounds. It has been found that the Yb atoms locate in the lattice positions only in InP and its alloys with Ga and As, while in gallium compounds the substitutional fraction of Yb atoms could not be detected. The intra- 4f-shell luminescence of the Yb3+ ions in different crystalline matrices have been studied. It has been shown that the ability of efficient excitation of the atomic-like luminescence of Yb3+ ions is associated with their substitutiontl location in the lattice. The intracentre emission from substitutionally located Yb3+ ions may serve as a probe of the local alloy disorder in GaInP and InPAs crystals.

Doping with the rare earth elements is widely used for the improvement of parameters of the PbTe-based lasers. It has been found that Tm is a donor in PbTe, and the solubility of TmTe in PbTe does not exceed 7 - 8 mol.%. Electron concentration in obtained PbTe(Tm) crystals reaches 4.1020 cm-3 and depends on Tm content and on deviation from stoichiometry. The analysis of the magnetoresistance oscillation picture shows no variation of the energy spectrum parameters for Tm contents less than I at.%. The g-factor does not change as well. This may be due to a rather small exchange interaction between Tm atom, which is magnetic in both +2 and +3 valence states, and band electrons. The experimental data for PbTe(Tm) are compared with the properties of semimagnetic PbTe(Cr) with quite the same electron consentration value.

Te analyses of the processes of radiation defect formation in germanium doped with phosphorus in the presence of rare-earth element neodimium and without it has been carried out.It has been shown that the presence of neodimium in n-Ge results in the change of enthalpy and entropy of the major radiation defect ionization (complex with the level being near EB-0.20 eV). The change of enthalpy by 0.03-0.04 eV as well as more than six fold increase of entropy of the complex ionization in Ge:Nd has been stated to be connected with the local deformation of the lattice around defect formed in the process of irradiation.

The excitation mechanisms of rare-earth dopants in III-V semiconductors are being reviewed. The discussion is focused on ytterbium-doped InP crystals for which a particularly large amount of experimental data has been gathered. Here, the results obtained recently by optically detected microwave-induced impact ionization are being examined in detail. On the basis of the experimental findings it is argued that the intrashell luminescence is excited by an intermediate state involving binding of an exciton. Direct evidence for the existence of such a state, of pseudoacceptor type, will be given. The nonradiative recombination channel responsible for the fast decay of Yb luminescence will also be discussed and, for the first time, evidence for an Auger process will be presented. It will also be shown that the nonradiative channel may be effectively blocked by impact ionization of a participating carrier.

Electrical and optical measurements were performed on p-type GaAs implanted with 1013 Er ions/cm2 at an energy of 1 MeV. The samples were annealed at 650, 750, 850, or 900 °C for 15 seconds using the rapid thermal annealing technique. Although annealing at 650 °C was insufficient to recover measureable electrical conductivity in the implanted region, Er3+ 4f-4f emissions were still observed. Annealing at 750 TC produced a large concentration of hole traps at EV + 360 meV, and the most intense Er-related emissions at 1.54 μm. The two higher annealing temperatures returned the implanted region to the conductivity of the substrate but resulted in weak Er-related emissions. Two distinct Er-related centers were found, and they are believed to be the cause of the intense and weak emissions, an Er-interstitial and Er substituting for Ga, respectively.

Sharp photoluminescence from the intra-4f shell of Er3+ is observed from erbium doped AlxGal-xAs (0 ≤x ≤ 1) grown by molecular beam epitaxy. The intensity of the luminescence from the erbium is strongly dependent on the aluminum composition with a maximum at x ≈ 0.6. We will present a model that explains the variation in intensity based on the energy transfer coupling efficiency between the host semiconductor and the optically active erbium ions. The coupling efficiency is dominated by the alignment or misalignment of the erbium energy levels with the energy bands of the host semiconductor and by the excess carrier lifetime in the host. The data and model, which are presented here for the first time, are consistent with our previous work on the effects of co-doping with Be or Si and with other workers' measurements of thermal quenching in rare earth doped semiconductors.

The photoluminescence, time resolved spectra and kinetics of Yb implanted InP samples are studied under pulsed and CW excitations (above and below band-gap) at different temperatures and excitation intensity. The photoluminescence intensity and decay time as a function of temperature is explained by a proposed new quenching mechanism involving Fe ion. The rise and decay times depend on excitation intensity. The above experimental facts was explained using the kinetics model developed by H.J. Lozykowski [2]. The numerically simulated luminescence rise and decay times show a good quantitative agreement with experiment, over a wide range of generation rates. The electric field InP:Yb photoluminescence quenching was investigated and reported for the first time.

Energy transfer from donor-acceptor pair states is known to be an efficient excitation channel for 4f-4f emission, especially if the rare-earth centers themselves are the relevant donors. Information on this type of mechanism can be obtained in the case when it is possible to observe, parallel to the 4f-4f emission, luminescence arising from radiative deexcitation of the pairs.

We have found these two kinds of emission, under electron-beam excitation, in ZnS:Tm crystals which, according to earlier site-selective studies performed by us, contain predominantly donor-type rare-earth centers. Characteristic differences between the two kinds of emission are found in the dependence of intensities on pumping rate; these arise from partial blocking of the energy transfer due to depopulation of the 4f ground levels. By quantitative studies of the correlation between those intensities we demonstrate that the same types of initial states are involved in the energy transfer and the pair transitions.

The role of the excitonic excitation mechanism of the rare earth (RE) intra-shell emission is discussed. Two cases are analyzed. For Yb ion in InP 4f-4f emission of Yb3+ is induced by energy transfer from bound exciton state to the RE core state. For Eu in CaS and SrS RE emission is induced by carrier trapping directly to the excited state of Eu2+ ion. Also in this case the intermediate excitonic state may participate in RE excitation, as suggested by some experimental results.

The photoluminescence (PL) and time resolved spectra of Nd- and Yb-implanted CdS samples are studied under pulsed and CW excitations using Ar+ ion laser for different excitation intensities and temperature (9 - 300 K). The samples were annealed under different conditions using the thermal-pulse method. For CdS:Nd, the PL spectra was recorded in the range 890-930 nm (transitions 4F3/2→4I9/2) and for CdS:Yb it was recorded in the range 985 - 1010 nm (transitions 2F5/2 →2F7/2). The Rise time and decay time were studied for both CdS:Nd and CdS:Yb at different emission lines as a function of temperature and excitation power.