Optically detected microwave-induced impact ionization of excitons and shallow donors is studied in Yb-doped InP grown by metalorganic chemical vapor deposition. The experimental results directly confirm that Yb3+ intrashell emission is induced by nonradiative recombination of Yb bound excitons due to an impurity Auger effect. Yb3+ ions in InP are found to bind excitons with the electron being localized first, followed by subsequent hole capture.

The effects of hydrostatic pressure on the InP:Yb luminescence were explored using a gasketed diamond anvil cell (DAC). The pressure dependence of the Yb3+ luminescence shows a small positive shift (0.96 meV/GPa) at low pressures (< 4 GPa) and a negative one (-0.04 meV/GPa) above 4 GPa. The spectra of the Yb3+ emission differ markedly in these two pressure ranges. It was concluded that intra-4f-shell transitions of the Yb3+ on indium substitutional (T(d)) site dominate in the spectrum above 4 GPa, whereas at lower pressures the emission has a different nature.

The excitation and decay mechanisms of the Yb3+ intra-4f-shell emission are studied in n-type MOVPE-grown and p-type LPE grown InP:Yb layers by photoconductivity measurements, time-resolved photoluminescence, photoluminescence excitation and emission spectroscopy. Assuming a pseudo-donor or pseudo-acceptor-like character of the isoelectronic Yb3+ Td centre the temperature dependences of the 4f-shell transition intensity and lifetime can be consistently explained. Models for the excitation and decay processes of the Yb3+ photoluminescence are proposed.

For the MOVPE growth of Er-doped InP layers we have synthesized tris(methylcyclopentadienyl)erbium, (Er(MeCp)3), and tris(isopropylcyclopentadienyl)erbium, (Er(IpCp)3) and used these compounds as solid and liquid precursors, respectively. The InP:Er layers were grown to study the incorporation behavior and the optical excitation and decay mechanisms of this rare earth element in a III–V compound semiconductor host crystal. Secondary ion mass spectrometry (SIMS) revealed Er concentrations up to 2×1019 cm-3 with a homogeneous Er distribution in the layer. Samples with these high doping concentrations have a semi-insulating character, probably a sign of a deep level correlated to the Er incorporation. A strong Er3+-related signal at 1.54 μm could be detected in low temperature photoluminescence experiments for the highly doped InP:Er samples. Codoping of the InP:Er samples with S or Zn has little influence on the shape and intensity of the Er emission.

For the Yb-doping of MOVPE grown InP, we have synthesized and used for the first time tris(isopropylcyclopentadienyl)-Yb, Yb(IpCp)3. This compound with its melting point at 47°C can be used as a liquid doping source, thus improving the reproducibility of the evaporation compared to the commonly used solid precursors. The grown InP:Yb layers revealed high photoluminescence intensities of the Yb 4f lines, although the Yb concentrations measured by SIMS were only in the range of 1017 cm-3. This indicates the high crystal quality of our samples. Additionally, we have grown InP:Yb:S layers and InP:Yb/InP:S multilayer structures with thicknesses between 10 and 100 nm for each layer to study the dependence of the excitation and decay processes on carrier and impurity concentration. The photoluminescence intensity of the 4f emission decreases for high S concentration in InP:Yb:S samples, whereas in the multilayer structures the intensity is the same as in InP:Yb samples. Based on the assumption of a homogeneous carrier concentration throughout the whole multilayer structure, we believe that a direct interaction between Yb and S atoms is responsible for the decrease in the double-doped single layers. The lifetime of the excited 4f state of Yb3+ is 13 μs, regardless of carrier or Yb concentration. For the InP:Yb samples co-doped with S, a fast nonexponential decay was observed, a further indication of some Yb-S pair interaction.

The occurrence of Yb ions in two charge states (trivalent and divalent) in ZnS is proved with use of the photostimulated electron-paramagnetic-resonance technique. ${\mathrm{Yb}}^{2+}$ is found to form a deep hole-trap center with energy level located at 1.65\ifmmode\pm\else\textpm\fi{}0.05 eV below the bottom of the ZnS conduction band. Efficient ${\mathrm{Yb}}^{3+}$ intrashell luminescence is observed under excitation in the region of the valence band to ${\mathrm{Yb}}^{2+}$ photoionization transition. Indirect recombination of a deep Yb-bound exciton with energy transfer to the 4f shell of ${\mathrm{Yb}}^{3+}$ is proposed to explain the photoluminescence excitation spectrum. Tentative assignment of the observed broad emission band with the maximum at 10 800 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ to direct Yb-bound excitation recombination is suggested.

Dimethyl (3-dimethylaminopropyl) indium was synthesized and used for the first time as an indium source for the growth of InP layers by metalorganic vapor phase epitaxy at atmospheric pressure. This compound is liquid at room temperature with a vapor pressure of 30–40 Pa at 30 °C, which enables its use at low source temperatures. The layers were grown at a bubbler temperature of 30 °C. The growth temperature was varied between 580 and 660 °C. Hall measurements revealed good electrical data with carrier mobilities up to 49 900 cm2 /V s at 77 K. Temperature-dependent photoluminescence experiments confirmed these results and indicated that zinc was the main residual acceptor impurity.

Time-resolved spectroscopy measurements show that the excitation of terbium photoluminescence in thin film ZnS:Tb electroluminescent devices, due to energy transfer from donor-acceptor pairs, is independent of temperature. The differences in the decay kinetics of terbium ions excited in various ways demonstrate that terbium ions in different crystal sites have different excitation mechanisms.

Highly doped InP:Yb layers have been grown by adduct metalorganic vapor phase epitaxy at atmospheric pressure. Yb(MeCp)3, where Me=CH3 and Cp=n5-C5H5, was synthesized as Yb source material because of its relatively high vapor pressure at acceptable source temperatures. The layers were grown in a wide range of growth temperatures (560–670 °C) and Yb mole fractions (10−9–10−7). In photoluminescence experiments they showed strong Yb3+-4f emission. The layers were further characterized by Hall measurements and secondary-ion mass spectroscopy. In order to obtain n-type InP:Yb samples with high carrier concentrations we have grown InP layers double doped with S and Yb.

A novel, highly efficient excitation mechanism of RE3+ emission, proceeding via the RE3+ photoneutral transition is reported on the example of Yb in ZnS single crystals.

Optical and electrical measurements of GaAs layers grown by liquid phase epitaxy with different amounts of Yb metal (0–1000 ppm) added to the Ga solution are reported. The presence of Yb during growth causes strong suppression of all donor-related optical transitions due to the effective removal of donors, as judged from Hall effect data. We have not found any appreciable increase of the background acceptor concentration during conductivity conversion from n-type to p-type, and thus conclude that dominant donor gettering occurs already in the Ga solution. No Yb3+ (4f 13)-related emission was detected in the as-grown GaAs layers.

La premiere mise en evidence experimentale de l'existence de Yb 2+ dans ZnS est presentee par mesures de photoluminescence et de photo-RPE. Le niveau d'energie de Yb 2+ est situe a 1,65±0,05 eV en dessous du bas de la bande de conduction

ZnS bulk crystals grown by the chemical transport method and doped with rare earth impurities have been studied. As will be shown, the most critical point of the whole sample preparation is the starting powder firing in a CS2 stream. The latter influences not only the RE3+ doping level in ZnS but also the incorporation of the RE3+ impurities on an active luminescence site. The special role of europium due to its 2+ charge state has been interpreted on the basis of photosensitive ESR measurements.