Abstract: Electronic excitation energy can be efficiently transferred by dipole-dipole interaction between suitable chromophores over distances of the order of 50 A. As proposed by Forster (6), the transfer rate is proportional to the inverse sixth power of the distance between the donor and acceptor (2, 13, 23). This steep distance-dependence enables fluorescence energy transfer to be used as a spectroscopic ruler in the 20 to 80 A range [for a recent review, see Ref. (22)]. Other transfer mechanisms, such as ex­ change interactions involving electron overlap, become important at shorter distances when the donor and acceptor are nearly in contact (4). In most energy transfer studies carried out thus far, the donor-acceptor distance was essentially constant during the lifetime of the excited donor, which was typically a few nanoseconds. A different and potentially

Abstract: Residence lifetimes of Mg on GaAs surfaces were observed using 10 KV reflection electron diffraction and Auger electron spectroscopy to decrease from ∼120 s at 550 °C to ∼1 s at 600 °C. The electrical incorporation coefficient is ∼0.3 at and below 500 °C decreasing to ∼3×10−4 at 600 °C at the expense of desorption. Hole mobilities of uniformly Mg‐doped samples are as good as those for equivalently Be‐doped GaAs samples. Calcium does not behave as a shallow acceptor in GaAs grown by molecular‐beam epitaxy.

Abstract: Deep levels in iron-dopedp-type silicon are investigated by means of Deep Level Transient Spectroscopy (DLTS) and the Hall effect. Pairs of Fe with the acceptors B, Al, and Ga are observed at 0.1, 0.19, and 0.24 eV above the valence band edgeEv. For interstitial iron, (Fei), a level energy ofEv+0.39+-0.02 eV is obtained with DLTS after correction with a measured temperature dependence of the capture cross section. The Hall effect yieldsEv+0.37 eV for Fei. The annealing behavior of levels related to Fe is investigated up to 160 °C. Iron participates in at least four different types of impurity states: Fei, Fe-acceptor pairs, precipitations (formed above 120 °C) and an additional electrically inactive state, which is formed at room temperature.

Abstract: Silicon‐doped GaAs has been grown simultaneously on (100), (110), and (111)B oriented GaAs substrates by molecular beam epitaxy. For constant Si, Ga, and As4 fluxes the surface morphology of the (110) and (111)B faces degraded with increasing substrate temperature above ∼500 °C. (100) films had an n‐type free‐electron concentration of 5×1016 cm−3 independent of substrate temperature. Films on (110) substrates were p type when grown above ∼550 °C and n type below ∼550 °C whereas (111)B films were highly resisitive under most growth conditions. Low‐temperature (4 K) photoluminescence showed good correlation between the Si acceptor peak heights and the compensation ratios derived from electrical measurements.

Abstract: Acceptors present in undoped p‐type conducting GaAs have been studied with photoluminescence, temperature‐dependent Hall measurements, deep level transient spectroscopy, and spark source mass spectrometry. It is shown that p‐type conduction is due to presence of the shallow acceptor CAs and the cation antisite double acceptor GaAs. The first and second ionization energies determined for GaAs are 77 and 230 meV from the valence‐band edge.

Abstract: A study of the photoluminescence emission band at ∼1.44 eV present in GaAs has been made at temperatures between 2–300 K. Changes in photoluminescence excitation intensity, emission energy, and emission intensity as a function of temperature lead to the identification of a 77±2‐meV deep acceptor. The temperature dependence of the emission‐peak energy follows Eagles’ model for the free electron‐neutral acceptor transition. The origin of the acceptor is discussed on the basis of the presence of a high concentration of arsenic vacancies.

Abstract: Emission quantum yields and lifetimes of the [Ru(bpy)3]2+ ion were measured in various solvents at 25 °C. Nonradiative rate constants (knr) were calculated from these data. A plot of knr vs. the Gutmann’s acceptor number was found to be linear. This result can be explained in terms of the contributions of charge transfer to solvent (CTTS).

Abstract: We observe the infrared absorption spectra associated with a residual 78‐meV acceptor in undoped liquid encapsulated Czochralski GaAs. The acceptor appears to be associated with an intrinsic defect, most likely the antisite GaAs. This acceptor is the dominant level in material grown from heavily Ga‐rich melts. The concentration of the level depends strongly on melt stoichiometry increasing from about 3×1015 cm−3 to 3×1016 cm−3 as the As atom fraction changes from 0.47 to 0.43.

Abstract: Intentionally undoped n -type and high purity Ga 1− x Al x As alloys with compositions in the range 0.19≤ x ≤0.78 are found to show a long life time photoconductivity effect at low temperatures ( T K ) when irradiated with white light filtered through a Ge filter and also when the light source is removed after photoexcitation. For the direct gap materials (0≤ x ≤ 0.43), it is shown that the deep level in the alloys, which controls the electrical properties of the crystals, captures and emits electrons via the first higher energy subsidiary conduction band inima L although the Γ minimum is the lowest in energy. These indirect electron transitions by the deep level, via the L minima, which is found to have an acceptor like nature, provide a natural explanation of the photoconductivity storage at low temperatures. For indirect gap materials ( x > 0.43), when X minima are the lowest energy subsidiary minima, the photoconductivity storage at low temperatures is due to the double acceptor nature of the deep level.

Abstract: Results of a detailed photoluminescence study of deep radiative transitions in InP crystals prepared by the bulk and epitaxial techniques are reported. In order to understand the origin of the photoluminescence (PL) spectra, bulk samples were subjected to isothermal anneals at different partial pressures of phosphorus. Similarly, the liquid phase epitaxy (LPE) wafers were grown with and without phosphorus in the gas stream. The electrical nature of some of the species responsible for the PL emission was inferred by a study of Cd diffused bulk samples. Based on these experiments the following tentative assignments are proposed. The photoluminescence band at 0.99 eV, common to all samples, is due to emission from a donorlike level related to the P vacancy. Bands at 1.21 and 1.14 eV appear to be due to emission to native acceptor levels associated with the In vacancy. The 1.08‐eV band is attributed to emission to a complex of the donor (0.99 eV) and acceptor (1.21 eV) species. The relationship between these bands and residual impurities is discussed.

Abstract: The near-infrared optical-absorption, luminescence, and luminescence-excitation spectra of liquid-encapsulation Czochralski-grown, vanadium- (V) doped GaP and GaAs have been investigated. The behavior of the characteristic V emission has been studied in magnetic fields up to 5.3 T. An analysis of the data within the framework of crystal-field theory indicates that the V-induced optical bands arise from crystal-field transitions within nonassociated ${V}^{2+}{3d}^{3}$ ions in the strong-field (low-spin) case. The electron-spinresonance spectrum of semi-insulating GaAs:V contains a characteristic signal which is identified as isolated ${V}^{3+}{3d}^{2}$. The characteristics of this signal show that V can act as a deep acceptor. The distribution coefficient of V in GaAs is close to that of Cr in GaAs.

Abstract: Mice exposed to contact sensitizing agents such as oxazolone (ox) or picryl (pic) derivatives develop specific immunological suppression to these substances which results from the activation of a circuit of T suppressor cells1–3. However, one of the final immunological events in the T suppressor cell circuit is the release of a nonspecific, H–2 unrestricted inhibitor by I–J+, Lyt-2+ cyclophosphamide-sensitive T acceptor cells (Tacc)3–7'. This nonspecific inhibitor (nsINH) can block the passive transfer of contact sensitivity and depress DNA synthesis by lymphocytes exposed to mitogens and alloantigens but the molecular mechanism is poorly understood. We provide evicence here that the production of interleukin-2 (IL-2)8–15 by stimulated lymphoid cells is suppressed when the cells have been exposed to nsINH.

Abstract: Aus aquimolaren Mischungen von Hexamethylbenzol (I) und dem Salz (II) in-Trifluoressigsaure last sich unter kontrollierten Bedingungen ein 1:1-Elektronendonator-Akzeptor-Komplex (III) in kristalliner Form isolieren.

Abstract: Thin layers of ZnSe were grown on (100) GaAs substrates by organometallic chemical vapor deposition in the presence of ammonia with the intent to incorporate nitrogen as a group V acceptor. Low‐temperature photoluminescence studies confirm that nitrogen is indeed incorporated as a shallow impurity with an activation energy of between ∼110 meV. ZnSe grown in the presence of phosphine gas, on the other hand, exhibits a photoluminescence spectrum characteristic of deep impurity level. A comparison of these results with other published data suggests that both N and P are incorporated as substitutional acceptors replacing Se.

Abstract: We have studied the kinetics of transfer of glucocerebroside between phospholipid bilayers by using pyrene and 3H-labeled glucocerebroside incorporated into dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) bilayers. Pyrene-labeled glucocerebroside (PyrCer) molecules are able to form an excited complex (eximer, E) between a PyrCer in the ground state and an excited monomer (M). When vesicles contained a known amount of PyrCer (donors) are incubated with unlabeled vesicles (acceptors), transfer of PyrCer from donor to acceptor populations is reflected in a decrease of the observed E/M intensity ratio. The results obtained from these studies show that the half-time of transfer from donor DMPC-PyrCer vesicles to acceptor DMPC vesicles is greater than 30 days at 37 degrees C. This very slow transfer of glucocerebroside was confirmed by using tritiated glucocerebroside incorporated into small unilamellar DPPC donor vesicles incubated with large unilamellar DPPC acceptor vesicles above the phase transition. Separation of the two vesicle populations by molecular sieve chromatography at 45 degrees C shows a half-time for transfer of approximately 32 days. We conclude that, in contrast to the results obtained for phosphatidylcholines [Roseman, M., & Thompson, T. E. (1980) Biochemistry 19, 439], glucocerebroside does not rapidly transfer between bilayers under these conditions.

Abstract: Publisher Summary This chapter presents an overview of the experimental investigations of point defects in gallium phosphide (GaP), gallium arsenide (GaAs), and indium phosphide (InP). It divides the experimental methods suitable for defect investigations into destructive, impurity element-specific, nondestructive, and defect-specific techniques. Among the impurity element-specific, mass-spectroscopy, atomic absorption, and nuclear methods like neutron activation analysis are the most important, as they provide information about the total impurity content of a specific element. Defect-specific techniques are grouped into four categories: electrical, optical, magnetic, and nuclear. The chapter outlines some general aspects of these techniques. It mentions that the standard semiconductor assessment techniques, resistivity and Hall-effect measurements, are indispensible tools to establish the electrical properties of shallow donors and acceptors. Special emphasis is given to deep-center identification. The chapter reveals that donors and acceptors are mostly deliberate dopants enabling n- or p-type conductivity of the crystal. Donor states are created by group VI elements on anion (P, As) sites as well as by group IV elements on cation (Ga, In) sites. Correspondingly, acceptor states are formed by electron-deficient dopants— that is, by group II elements on cation sites and by group IV elements on anion sites.

Abstract: The hole and electron capture cross sections of the gold donor and acceptor have been measured directly in n -type silicon. The samples have been grown by the Czochralski technique and have originated from several different suppliers. They have been diffused with gold so that N T ≲ 0.1 ( N D - N A ). Measurements have been made on both Schottky diodes and diffused junctions and similar results obtained from all samples. The electron cross section of the acceptor level was found to be (0.85±0.2) × 10 −16 cm 2 and the hole cross section of the donor (3.5±0.8) × 10 −15 cm 2 , both were essentially temperature independent. The hole cross section of the acceptor was (0.9±0.2) × 10 −14 cm 2 at 300 K and showed a T −1.3 temperature dependence. The electron cross section of the donor was (0.9±0.2) × 10 −15 cm 2 at 180 K with a T −2 dependence.

Abstract: The defect structure of acceptor-doped (Fe, Al, Cr) polycrystalline strontium titanate was investigated by measuring the equilibrium electrical conductivity as a function of oxygen activity (10−21≤ao2≤1) and temperature (85°C≤T≤ 1050°C). The electrical conductivity was n type with ∼−1/4 dependence on a02 for a02 10−8, the observed data for Fe- or Al-doped samples were proportional to ∼1/4.5 power of a02. In this region for Cr-doped samples, the value of m in.σp αa02+1/m varies from ∼4.80 to ∼9.00 as the concentration of Cr is increased from 460 to 10 000 ppm. The onset of p -type conductivity depends on the amount. of acceptor impurity added to the sample. The absolute values of the conductivity in the acceptor-doped samples were lower in the n-type region than those for undoped SrTiO3. The conductivity minima shift toward lower oxygen activity with increasing acceptor concentration. For the entire oxygen activity rangae used in this study, the defect structure of SrTiO3 is dominated by the added acceptor impurities.

Abstract: We provide experimental evidence of electrical activity correlated with residual boron impurities and native point defects in undoped liquid‐encapsulated Czochralski GaAs crystals. In Ga‐rich samples containing ≥1017 cm−3 boron, an 0.073‐eV acceptor level is observed in which the concentration increases with Ga and B content. An approximately quadratic increase in the concentration of the 0.073‐eV defect acceptor is observed with increasing boron concentration, suggesting that a complex involving boron with an intrinsic defect (VAs, Gai, or GaAs ) is responsible for the observed acceptor behavior. No evidence of electrically active boron or boron complexes was found in semi‐insulating GaAs pulled from stoichiometric or As‐rich melts.

Abstract: Annealing of acceptor dominated α‐Al2O3 at Tsat = 1100–1500 °C in atmospheres containing hydrogen leads to dissolution of hydrogen, changing the material from p‐ to n‐type when the concentration of hydrogen donors is larger than that of the acceptor impurities present. If oxygen equilibrium is maintained, the concentration of ionized donors depends on pH2 as well as pO2 (or pH2O). In measurements of dc conductivity in atmospheres not containing hydrogen, a contribution to the conductivity by mobile protons rapidly disappears as a result of polarization. Analysis of the rate of polarization leads to values for the concentration and mobility of mobile protons. In measurements in atmospheres with well‐defined hydrogen and oxygen fugacities, protons, native ions, and electrons and holes contribute continuously to the conductivity. Transference numbers of the various species and the corresponding partial conductivities were determined by emf measurements. The amount of dissolved hydrogen increases with decreas...

Abstract: The passivation of deep acceptor level defects (Ev +0.33 eV, Ev +0.19 eV) associated with copper in single‐crystal germanium by reaction with atomic hydrogen has been observed using deep level transient spectroscopy. The concentration profile of the Ev +0.33 eV center is presented as a function of the duration and temperature of the exposure to atomic hydrogen—when exposed for 3 h at 300 °C, 90% of the acceptor defects were passivated to a depth of ∼80 μm.

Abstract: An analysis employing Poisson's equation is used to determine surface potential and effective carrier concentration as a function of N/sub ss/, the surface acceptor concentration, for a particular set of material parameters in RF- sputtered ZnO thin films. The results are used to obtain a semiquantitative description of gas sensitivity addressing electronic processes of the gas-solid system. The analysis involves numerical solution of Poisson's equation and the charge neutrality equation simultaneously. 8 refs.