Different III-V compound semiconductors have been doped with the rare earth (RE) elements Yb, Er, and Tm using atmospheric pressure metalorganic vapor phase epitaxy. Best results have been obtained using the novel metalorganic compounds tris-isopropyl-cyclopentadienyl-RE as precursors which have an acceptable vapor pressure and can be used as liquids at bubbler temperatures of 60°-90°C. Only Yb has been found to occupy a regular lattice site in InP, whereas the other RE show complex optical spectra because of their incorporation in form of different centers and clusters.

Erbium doped GaAs was grown by metalorganic chemical vapor deposition using a novel liquid precursor: Tris(n-butylcyclopentadienyl)erbium, Er(C4H9C5H4)3. Growth parameter, i.e. temperature, V/III ratio, Er-vapor flow, were investigated. The maximum erbium incorporation in layers with excellent morphology was 1.2× 1019cm−3. The erbium-related photoluminescence intensity and the incorporated concentrations, as measured by secondary ion mass spectrometry, were correlated. Based on a simple model for, the excitation dependence of the emission, the non-radiative Auger-type process was estimated to be nearly five times that of the energy transfer process from bound excitons to the Er3+ ions, which subsequently resulted in the Er-related light emission. Temperature induced quenching of the emission was found to be dominated by transitions with an activation energy of 74meV.

The overall objective of this research is to develop source materials for doping AIGaAs. We compared Er(C5H5)3 to Er{N[Si(CH3)3]2)3 for purity, decomposition kinetics and doping of germanium films deposited from Ge(CH3)4 in a hydrogen atmosphere. Cyclopentadienyl erbium left large amounts of carbon both in pure metal films, and in the germanium film, at low pressure and temperatures to 850°C. Bis-(tri-methylsilyl) erbium amide decomposed cleanly without carbon, nitrogen or silicon in the deposited film.

Praseodymium dioxide (PrO2) -doped In0.69Ga0.31As0.67P0.33 layers are grown on semiinsulating In P substrates with liquid-phase epitaxy. The PrO2 doping of the growth solution varies from 0 to 0.32 wt %. The quaternary In0.69Ga0.31As0.67P0.33 layer composition determined with two-crystal X-ray diffraction and photoreflectance is found to be independent of the PrO2 concentration in the melt. The photoluminescence spectra measured at 12 K show both exciton and donor-acceptor peaks, the magnitudes of which depend on the PrO2 doping. The carrier concentration of the n-type quaternary layer decreases and the mobility increases with increasing PrO2 concentration and reaches the values of 8.3.1015 cm−3 and 7300 cm2/Vs, respectively, at about 0.1 wt% at 77 K. The experiments show that PrO2 has an impurity gettering effect in the growth process.

The problem of manufacturing high purity semiconductor materials with super high electron mobility is among important, though technologically difficult ones.

Traditional with regard to III-V compounds this problem has been solved using the following technique

- the choice of alternative crucible material

- the application of high purity initial materials

- oxygen doping for shallow donors removal

- isoelectronic doping (e.g. bismuth)

We can also mention other attractive directions in this sphere of activity, such as secondary methods of influence upon the crystals grown - heat treatment and purification by radiation methods, the latter ones still wanting being explored.

From the late 70's we have been carrying out the investigations of the rare-earths (RE) influence upon the electrical characteristics of InP, and later - of GaAs.

In this work submitted are the results of comprehensive investigation of RE applications in bulk III-V crystal growth technology with the aim of purification and heavy doping of the crystals.

Some metal plasma techniques have been developed that provide a convenient means for the doping of semiconductor hosts with rare-earths. These plasma and ion beam tools are based on the application of vacuum arc discharges for the formation of dense rare-earth plasmas which then can be used in a number of ways for doping and otherwise introducing the rare-earths into substrate materials. At the low energy end of the spectrum, the streaming metal plasma can be used for the deposition of thin films, and if more than one plasma source is used then of multilayer structures also. Or by building the vacuum-arc rare-earth plasma generator into an ion source configuration, high current ion beams can be produced for doing high energy ion implantation; alternatively the substrate can be immersed in the streaming rare-earth plasma and by using appropriately phased high voltage substrate pulsing and pulsed plasma generation, plasma immersion ion implantation can be done. Between these two limiting techniques – low energy plasma deposition and high energy ion implantation – a spectrum of hybrid methods can be utilized for rare earth doping. We've made a number of plasma and ion sources of this kind, and we've doped a wide range of substrates with a wide range of rare-earths. For example we've implanted species including Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er and Yb into host materials including Si, GaAs, InP and more. The implantation dose can range from a low of about 1013 cm−2 up to as high as about 1017 cm−2, and the ion energy can be varied from a few tens of eV up to about 200 keV. Here we review these vacuum-arc-based plasma methods for rare-earth doping, describing both the tools and techniques that are available and the applications to which we've put the methods in our laboratory.

Thin Si films doped with Er have been grown at low temperature by plasma enhanced chemical vapor deposition. The Er gas source is a sublimed organo-metallic compound fed into the process chamber. High doping concentrations without precipitation are possible because of the low deposition temperatures. The process relies on the beneficial effects of low energy ion bombardment to reduce the growth temperature. The ions as well as reactive chemical species are produced by an electron cyclotron resonance (ECR) plasma stream source. A hydrogen plasma stream is used to perform an in-situ pre-deposition clean to remove oxide from the Si surface. Film crystallinity and impurity concentration are determined by Rutherford backscattering spectrometry.

Highly Er-doped (∼ 1020 atoms/cm3) silicon and silica films were deposited by RF magnetron sputtering. Erbium was doped into the host material by co-sputtering technique. Deposited films (0.5 - 1.2 µm thick) were characterized by photoluminescence (PL), secondary ion mass spectroscopy (SIMS), and fluorescence decay measurements. Er-doped silica glass films show a strong, room-temperature luminescence at 1.54 µm wavelength. In contrast, Er-doped silicon films show a weak luminescence at room temperature. However, a big enhancement in the Er3+ luminescence was observed after a proper annealing, for example, 900 °C for 30 to 120 min in air ambient, resulting in the luminescence intensities comparable with that of the Er-doped silica films. This enhancement is attributed to the oxygen incorporation into the Si host film during the annealing, thus forming an Er-doped oxide layer on top of the film. The result suggests that Er-O bonding plays important role in forming optically active erbium ions. Erdoped, three-component silicate glass (SiO2 + A12O3 + MgO) films were also sputter deposited to investigate the dependence of Er3+ luminescence on the host material's composition. Even stronger luminescence was observed from the Er-doped, three component silicate glass films compared with the Er-doped SiO2 films.

Erbium ions were successfully doped in silicon by pulsed laser irradiation above the threshold laser energy density. Photoluminescence peaks at 1.54, 1.59 and 1.64 µm from Er-optical centers were observed after annealing of Er-doped samples. The intensity of the 1.54 µm Er-emission band increased upon increase in the laser energy density, and then gradually decreased after reaching the maximum, due to the laser sputtering of the silicon substrate. Oxygen atoms, which were unintentionally codoped with Er-ions, were found to be distributed in the same region as in Er-ions, and were suggested to play roles to activate Er-optical centers. The maximum concentration of Er-ions doped in the solid state regime were estimated to be the order of 1018 cm−3 by the Rutherford backscattering measurements.

We have carried out an investigation of the laser doping of Si with rare-earth ions. In this technique a silicon surface coated with a thin layer of the rare-earth metal is melted with a pulsed laser, the dopant is mixed in the molten layer, and incorporated in the crystal during regrowth. Er was chosen for the main part of our work as it is the best characterized of the rare-earth ions in Si. Luminescence is observed around 1.54µm and is assigned to optical transitions on Er3+ ions. This preliminary study shows that this new technique is viable for the production of optically active Er3+ in Si.

The properties of Si grown from the melt having impurities of germanium and gadolinium have been studied by IR-absorption and Hall effect methods.It was stated that Ge and Gd are effective getters for technological impurities of oxygen and carbon in silicon melt. It has been shown that the combined doping by rare earth and isovalent impurities allows to increase the thermostability of dislocationless monocrystals of silicon.

Epitaxial layers (EL) Si:Sn doped with Yb in the process of liquid phase epitaxy were studied by optical microscopy and photoluminescence (PL) methods.At low concentration of lanthanoid (0,01 < Nyb < 0,1 weight %) the good planarity of the interface and high quality of the surface are detected. At NYb > 0,1 weight % microirregularities are presented.

In EL Si:(Sn, Yb) irradiated by 4,5 MeV-electrons the suppression of the generation of radiaton defects, responsible for G- and C-lines of PL, has been found. This effect has been explainedwithin the score of the model takeng into the consideration gettering propering ofYb in reference to the impurities of 0 and 0 as deformation fields, attributed to the presence of Sn atoms.

We have fabricated the first Si:Er LED, operating at 300 K, based on an understanding of the Si-Er-O materials system. Er-doped Si (Si:Er) provides an exciting opportunity for the monolithic integration of Si based opto-electronics. In this paper, Er-Si reactivity, and Er diffusivity and solubility have been studied to establish Si:Er process compatibility with a silicon IC fabline. Er3 Si5 is the most stable silicid formed; and it can be oxidized into Er2O3 at high temperature under any oxidizing conditions. Among Er compounds, Er2O3 luminesces and Er3Si5 and ErN do not. The diffusivity of Er in Si is low and SIMS analysis yields a diffusivity D(Er) ∼ 10−12cm2/s at 1300 C and ∼ 10−15cm2/s at 900 C, and a migration enthalpy of δHm(Er) ∼ 4.6 eV. The equilibrium solubility of Er in Si is in the range of 1016 cm−3 at 1300 C. The Si:Er LED performance is compared with GaAs LEDs to demonstrate its feasibility.

Favennec et al. (Jap. J. Appl. Phys. 29, L524, 1990) reported that the 1.54µm photoluminescence of Si implanted with Er+3 is activated by oxygen impurities. We observe a significant enhancement in the luminescence in Er-doped silicon epitaxial layers MBE-grown with intentional oxygen contamination. The PL is shown to be a bulk property of the material as it persisted after a partial layer removal by wet etching.

Solid phase epitaxy and ion-beam-induced epitaxial crystallization of Er-doped amorphous Si are used to incorporate high concentrations of Er in crystal Si. During solid phase epitaxy, substantial segregation and trapping of Er is observed, with maximum Er concentrations trapped in single crystal Si of up to 2 × 1020 /cm3. Ion-beam-induced regrowth results in very little segregation, with Er concentrations of more than 5 × 1020 /cm3 achievable. Photoluminescence from the incorporated Er is observed.

Optical direct and indirect excitation of erbium (Er) ions in silicon substrates was performed in order to investigate the high efficiency of Er3+− related 1.54µm emission (4I13/2→4I15/2) for direct excitation that is not concerned with the indirect band gap and low quantum efficiency of a Si host. The samples were prepared by ion-implantation or thermal diffusion methods. In each sample, photoluminescence (PL) showed the peaks originating from 4I13/2→4I15/2 of Er3+ ions.

In Er thermally diffused samples, optical excitation for energy level 4I11/2 of Er3+ ions was successfully effected by photoluminescence excitation spectroscopy (PLE). The PLE spectra consisted six peaks (963. lnm, 965.Onm, 976.lnm, 978.9nm and 980.9nm) which were caused by direct excitation (4I15/2→4I11/2) of Er3+ ions. The emission directly excited is about 2 times more intense than the indirectly excited emission. The six peaks originating from the splitting of the 4I11/2 levels meant that Er3+ ions were in the sites of noncubic symmetry. The samples prepared by Er ion-implantation did not show the effect.

Ca1−xErxF2+x thin films, with a substitution rate, x, varying from 1 to 20%, were deposited on Si(100) substrates by sublimation of high purity solid solution powders under ultra-high-vacuum. Rutherford backscattering studies have shown that the films have the composition of the initial solid solution powders, are quite homogeneous and are epitaxially grown on the substrates.

The optical properties of these films were studied by means of cathodoluminescence and photoluminescence. At room temperature, the emissions due to the de-excitations from the 4S3/2, 4F9/2, 4I11/2 and 4I13/2 excited levels to the 4I15/2 ground state of Er 3+ (4f11) ions are easily detected (λ = 0.548, 0.66, 0.98 and 1.53 µm)

The strong 1.53 µm infrared luminescence, which presents evident potential applications for optical communications, is maximum for an erbium substitution rate included between 15 and 17%. These Er concentrations are three or four orders of magnitude greater than the optimum ones in the case of Er-doped semiconductors, which are close to 1018 cm−3.In the visible range, the luminescences are also important.They allow us to detect high energy ion or electron beams. However their maximum efficiencies were observed for a relatively low erbium concentration, close to 1%. These different behaviours are explained by the cross relaxation phenomena, which depopulate the higher levels to the benefit of the 4I13/2→ 4I15/2 transition. The energy distribution of the Stark sublevels of the 4I15/2 state, which results from crystal field splitting, was deduced from a photoluminescence study at 2K. The obtained results show that the environment of the luminescent centres does not change with the erbium concentration.

At last, it must be noted that the refractive index of the layers increases with the erbium concentration, leading to the realization of optical guides. Consequently opto-electronic components could be developed from such erbium doped heterostructures.

An understanding of the electrical, structural, and optical properites of Er in Si is necessary to evaluate this system as an opto-electronic material. Extended x-ray absorption fine structure, EXAFS, measurements of Er-implanted Si show that the optically active impurity complex is Er surrounded by an O cage of 6 atoms. The Er photoluminescence intensity is a square root function of excitation power, while the free exciton intensity increases linearly. The square root dependence of the 1.54μm-intensity is independent of measurement temperature and independent of co-implanted species. Ion-implantation of Er in Si introduces donor activity, but spreading resistance carrier concentration profiles indicate that these donors do not effect the optical activity of the Er.

The several processes required to achieve Er luminescence in Si are investigated. In particular, the role of Er - O interactions to obtain the incorporation of high Er concentrations, electrically and optically active, in crystalline Si is investigated. It is found that a large enhancement in the electrical activation of Er (up to three orders of magnitude) is obtained by co-implanting Er with O at 573 K or at 77 K. However, the introduction of high concentrations of active Er in Si is not sufficient to obtain a large enhancement in the luminescence since an efficient pumping of the optically active sites is also required. The optical efficiency of this sample has been studied by photoluminescence. It is seen that an enhancement by a factor of ∼ 5 with respect to literature data is obtained. Moreover studies on the luminescence intensity as a function of the pump power gave important information on the mechanisms underlying Er luminescence in Si and its competing phenomena. These data are presented and discussed.

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.