Erbium-doped silicon films are grown by ion beam epitaxy (IBE) using an electric-mirror sputtering-type metal ion source in ultrahigh vacuum. In-situ erbium doping with concentrations ranging from 1×1016 to 6×1020 cm−3 is achieved by sputtering the erbium metal pellet with ions extracted from the silicon metal ion source. The oxygen concentration in the films is also controlled in-situ over the range from below 1×1018 to 2×1020 cm−3 by using argon gases containing 1 ppb to 100 ppm of oxygen impurities. The erbium incorporation probability drastically increases (by two or more orders of magnitude) when oxygen is contained in the argon gas during film growth. Erbium is selectively oxidized in the Si host. Erbium segregation and precipitation formation are well suppressed by the oxidation. Sharp and well-split photoluminescence is clearly observed in as-deposited films grown typically at 480°C with oxygen co-doping.

We report on a systematic study of the growth parameters of erbium-oxygen-doped silicon grown by molecular beam epitaxy. The surface quality of the grown layers was measured in situ by RHEED. The samples were characterized by photoluminescence measurements and SIMS. An Er-O-doped Si light emitting diode grown with the optimized parameters is presented.

The incorporation of erbium in silicon is studied during solid phase epitaxy (SPE) of Erimplanted amorphous Si on crystalline Si, and during Si molecular beam epitaxy (MBE). Segregation and trapping of Er is observed on Si(100), both during SPE and MBE. The trapping during SPE shows a discontinuous dependence on Er concentration, attributed to the effect of defect trap sites in the amorphous Si near the interface. Trapping during MBE is described by a continuous kinetic growth model. Above a critical Er density (which is lower for MBE than for SPE), growth instabilities occur, attributed to the formation of silicide precipitates. No segregation occurs during MBE on Si(111), attributed to the epitaxial growth of silicide precipitates.

The growth of epitaxial GaAs doped with the rare earth thulium (Tm) by MBE is reported for the first time. The nature of the incorporation of Tm has been studied using SIMS, RBS, TEM, PL and DCXRD. Sharp doping profiles have been observed by SIMS from samples doped in a staircase structure. Under standard GaAs growth conditions, TEM has revealed a solubility limit of ∼5×1019cm−3, above which Tm precipitates as spherical nano-particles of uniform size (1.3–1.7nm). High resolution TEM has provided no evidence for strain relaxation around these precipitates. Growth at higher substrate temperatures (≥620°C) or at As:Ga ratios close to stoichiometry, results in the formation of precipitate wires and/or bifurcated structures (“quantum trees”) aligned approximately in the direction of growth. Such behaviour is in common with that of Er in GaAs and suggests that the precipitates result from the self-organised growth of TmAs. Mechanisms for the formation of the quantum wires and trees are suggested. Initial photoluminescence spectra from these samples show two groups of narrow Tm3+ intra 4f transition lines corresponding to the 3H5 – 3H6 (∼1.01eV/1.2μm) and 3H4 – 3H6 (∼ 0.71eV/1.7μm) transitions. The spectra exhibit an excellent correlation with those obtained from samples grown by MOVPE and also those implanted with Tm by other groups.

The growth of erbium doped GaAs by molecular beam epitaxy (MBE) can, depending on growth conditions, result in the precipitation of small spherical particles of erbium arsenide. It has been observed that by reducing the V:III (As:Ga) flux ratio to close to stoichiometry wirelike precipitates roughly aligned in the direction of growth are produced. The concentration of erbium incorporated into the GaAs lattice for a constant erbium flux is also affected by the As:Ga flux ratio with an increase in erbium doping being observed with decreasing As:Ga flux ratio.

Electrical measurements have been performed on erbium doped GaAs samples co-doped with selenium, an n-type dopant. Measurements have revealed that when erbium is present, the electron concentration is reduced by an amount approximately equal to 70% of the erbium concentration. DLTS measurements have shown that although large concentrations of deep levels are present in erbium doped material, the measured concentration of these deep levels is not high enough to account for the observed reduction in electron concentration with erbium doping.

We have fabricated Si:Er films by ion implantation and ultra-high vacuum chemical vapor deposition (UHV-CVD). The energy of the ion implantation was varied from 200 keV to 4.5 MeV. Oxygen was co-implanted to overlap the erbium profile. At implant energies of 400 keV, we found that the luminescence was optimized at a lower annealing temperature (800° C, 30 minutes) than that needed for the 4.5 MeV implant (900°C, 30 minutes). The light intensity per erbium atom is critically dependent on the implantation energy. However, spreading resistance measurements show that the donor activity of the implanted erbium is independent of energy. We have correlated the donor activity with quantum efficiency by varying the donor spatial distribution and concentration through post implantation heat treatments.

For the UHV-CVD grown Si:Er films, two erbium metallorganic precursors, Er(TMHD)3 and Er(FOD)3. have been used for growths from 550–620°C. The thickness of the erbium layers are similar to that of implanted devices but the Er concentration of 4 × 1021/cm3 exceeded the implanted material by two orders of magnitude.

Er incorporation into GaN, AIN, MAIN and InGaN can be achieved using either direct ion implantation or by doping during Metal Organic Molecular Beam Epitaxy using metalorganic or elemental sources. When co-implanted with 0 and annealed between 600–800°C, strong luminescence at 1.54pm from optically excited Er3+ is detected in both binary nitrides and there was no measurable diffusion of Er in any of the materials. The low vapor pressures of the gaseous source compounds (erbium 2, 2, 2, 6-tetramethyl-3, 5-heptanedionate for Er + O; erbium bistrimethylsilylamide for Er) makes transport difficult unless high bubbler temperatures are used. Er concentrations up to ∼3×1021cm−3 in AIN have been obtained using a solid Er source. Microdisk laser structures with Er-doped active layers have been fabricated using a novel KOH selective wet etch and Cl2/CH4/H2/Ar dry etching.

Epitaxial growth of Er-doped silicon films has been performed by plasma-enhanced chemical vapor deposition at low temperature (430°C) using an electron cyclotron resonance source. The goal was to incorporate an optically active center, erbium surrounded by nitrogen, through the use of the metal organic compound tris (bis trimethyl silyl amido) erbium. Films were analyzed by Rutherford backscatter spectrometry, secondary ion mass spectroscopy and high resolution x-ray diffraction. The characteristic 1.54 μm emission was observed by photoluminescence spectroscopy. Previous attempts to incorporate the complex (ErO6) using tris (2,2,6,6-tetramethyl-3,5-heptanedionato) erbium (III) indicated that excessive interstitial carbon lowered epitaxial quality and reduced photoluminescent intensity. In this study, much of the carbon was introduced onto substitutional sites maintaining good epitaxial growth. A response surface method was employed to find the plasma growth parameters yielding the highest quality luminescent films. Luminescent intensity increased for anneals up to 600°C but decreased at higher temperatures.

The overall objective of this research is to develop temperature stable 1.54 ptm light sources based upon ionic emitters. LEDs and diode lasers were fabricated in MOCVD grown AIGaAs materials but only weak electroluminescence was observed. The III-V compound semiconductors were doped with erbium amide sources of the form: Er{N[Si(CH 3)3]R}3 where R s an organic unit. These amide sources had reduced carbon and oxygen levels in a GaAs film compared to the use of a cyclopentadienyl erbium source, but did dope the semiconductor with silicon. Silicon doping levels were a function of growth temperature. Erbium photoluminescence was enhanced with oxygen codoping, but diode electrical characteristics were degraded. PLE showed that erbium ions were excited by above bandgap light absorbed by GaAs.

Strong rare earth (RE) emissions from Nd and Er implanted into MOCVD grown GaN were observed through photoluminescence (PL) with below bandgap excitation from an Ar+laser. Three well resolved manifolds of 4f lines from the crystal-field split 4F3/2 → 4I9/2, 4F3/2 → 4I11/2, and 4F3/2 → 4I13/2 transitions of Nd3+ were observed at low temperature at ˜0.98, ˜1.14, and ˜1.46 μm, respectively. The Er implanted GaN showed both the 4I13/2 → 4I15/2 Er3+ transition at ˜1.54 μm and the 4I11/2 → 4I15/2 Er3+ transition at ˜1.00 μm. The Er luminescence at ˜1.54 μm and Nd luminescence at ˜1.1 μm persisted to room temperature. Both Er and Nd implanted samples showed increasing RE3+ signal as annealing temperature increased from 700 to 1000 °C. The growth of new 4f crystal-field split-lines in the ˜1.54 μm 4I13/2 → 4I15/2 manifold as annealing temperature was increased to 1000 °C suggests multiple Er3+ radiative centers.

Excimer laser irradiation has been applied to dope erbium ions in silicon. Er-doping is realized with both processes of the Er-diffusion in the melted region and the subsequent solid solidification. Er atoms at the maximum concentration of 1021 cm3 are doped in the region of 150 nm thickness without significant defect formation and amorphization. Stable Er-optical centers, emitting well known series of luminescence lines near 1.54 jim, are formed after short term heat treatments at a relatively low temperature. Optical centers are distributed in proportional to the total Er concentration in the doped region. Oxygen atoms are found to play critical roles for stabilizing Er-optical centers and for rearranging the surroundings of Er ions. Modified bonding states of O and Er other than those in SiO2 or Er2O3 are formed in the Er doped region during both doping and annealing processes.

Erbium films are evaporated on crystalline silicon substrates and are thermally diffused into silicon in an Ar+02 or H2 flow. Very sharp Er3+-related luminescence peaks are observed around 1.54 μ m.The main peak as well as the fine structures of the luminescence spectra depend on the annealing atmosphere, suggesting different luminescence centers. The full width at half maximum (FWHM) of the main peaks is ≤ 0.5nm at 20K. Thermal diffusion with Al films on top of the Er films is found to increase the intensity of the Er3+-related peaks greatly. The temperature dependence between 20 K and room temperature is relatively small, and a strong luminescence is obtained at room temperature.

Having preliminary confirmed the possibility of erbium doping by thermal diffusion, we have used this process to introduce erbium into a silicon substrate from metallic erbium or erbium oxide sources. Diffusion experiments were carried out at 1050, 1200 and 1250°C. The Er:Si diffused samples were investigated using four probe resistivity and thermopower techniques for the measure of the concentration and type of carriers, SIMS and Auger spectroscopy for chemical analysis of the diffused layers and photoluminescence (PL) measurements at temperatures ranging from 2 to 298 K for the detection of optical activity. None of the samples prepared presented measurable PL at 2 K, except for one single sample on top of which was deposited an erbium doped silica glass. The electrical properties, instead, were deeply influenced by doping, indicating the formation of both donor and acceptors.

It is found that Er could only be deposited on a Si cathode by electrolysis of near neutral ErCl3 electrolyte with a large current density. The deposited Er hydrolytic layer reacts with Si at 1200 °C to form the activated Er centers that emit a 1.533 μm photoluminescence peak at room temperature. By applying this process to porous Si, an apparent doping concentration of Er larger than 1019/cm3 in the whole porous Si layer and a strong PL intensity with little temperature quenching are achieved.

We present a high resolution photoluminescence (PL) study of Si:Er which allows to distinguish a variety of Er centers occurring in Er-implanted Si. The lines belonging to a particular center are identified from the influence of processing parameters, temperature, excitation power, co-doping and hydrostatic pressure. The center-dependent high temperature yield is limited by the competition in efficiency of capturing excitons at Er centers or nearby defects followed by the excitation transfer to the Er-4f shell and by recombination of excitons at other, non-radiative centers. The excitation transfer probability is shown to depend on hydrostatic pressure of a few kbar. This effect indicates a new possibility to improve the efficiency of Si:Er light emitters.

We have investigated the effects of oxygen codoping and thermal annealing on the deep level spectrum and carrier lifetime of Er implanted crystalline Si. It is found that oxygen codoping produces a dramatic modification in the concentration and energetic position of Er-related deep levels in the Si band gap. In particular the formation of Er-O complexes is shown to produce a promotion from deep to shallow levels. This effect is the major responsible of the enhancement of Er donor behaviour in presence of oxygen and also produces a large increase in the minority carrier lifetime

Photoluminescence of silicon implanted with erbium and oxygen was measured in the time domain focussing on the temperature and excitation density dependence of the intra-4f-shell emission from Er3+. The decay of this luminescence is similar for the different optically active crystal field split Er-centres. At low temperatures the luminescence transients consist of a fast initial non-exponential component followed by slower exponential behaviour. An increase in excitation density results in a higher proportion of the luminescence decaying with the faster decay time. Our results indicate a relation of the fast component to nonradiative processes. Auger recombination is proposed as a possible mechanism.

Recent results contributing to our understanding of mechanisms of defect formation and excitation of Er luminescence in Si:Er system are presented. An essential role of non-equilibrium intrinsic point defects in Er-related defects formation for both implanted and in-diffused Si:Er structures is demonstrated.

The data of electroluminescence (EL) measurements evidence that the Er3+ excitation occurs via capture of free excitons on neutral Er-related donor centers with subsequent Augerrecombination of bound excitons.

The optical properties of an Er-implanted SiGe sample have been studied Sharp and temperature-stable Er-related PL peaks were observed at around 1.5pm, which correspond to the Er 4I13/2 to 4I15/2 transition. It was found that the Er ions form more than three noncubic luminescence centers in the SiGe host. Although the PL intensity quenches at high temperatures, the Errelated PL signal can still be observed at room temperature. For a Si0.87Ge0.13:Er sample annealed at 850°C for 20 min, the activation energy is 130 meVwhich is slightly smaller than that of the Er-doped Si.

Results of a photoluminescence excitation (PLE) study of Er-implanted porous Si (Er: PSi) are presented. Erbium was implanted at a dose of 1×1015 Er/cm2 at 380 keV and annealed for 30 minutes at 6507deg;C. We observed a nearly identical PLE intensity behavior from 1.54 μm and visible-emitting Er: PSi. This observation indicates that both visible and infrared photoluminescence (PL) arise from carrier mediated processes, and that the 1.54 μm Er3+ PL is related to the porous Si nanostructures. Measurements of the temperature dependence (15–375K) of Er3+ PL intensity and lifetime are also reported.