GaP:(Bi,N)晶体中束缚激子的辐射复合及能量转移

本文研究了在4.2K—147K温度范围内GaP:(Bi,N)晶体的光致发光光谱的精细结构,积分强度及其随温度的变化,并将它们与GaP:Bi,GaP:N光谱进行比较。首次发现在GaP:(Bi,N)晶体中激发能量从孤立N中心和NNi对(i≥3)中心到Bi中心的转移,增大了Bi束缚激子态的浓度,使Bi发射带增强。     

Oxidation and annealing of GaP and GaAs (111)-faces studied by AES and UPS

The annealing behaviour after argon sputtering and the first steps of oxidation of the polar GaP and GaAs (111)-faces are studied by AES and UPS. The Auger spectrum of GaP is briefly discussed. In contrast to GaAs, the GaP surfaces show a gallium accumulation after argon sputtering, but they become stoichiometric by annealing. The photoemission spectra show an additional emission due to oxygen with its maximum at about 5 eV below the valence band edge. The decrease of the emission near the valence band edge by oxidation shows the existence of surface sensitive states. Comparing the results of the two polar faces and for different surface compositions, it is concluded that these states are mainly As- and P-derived, respectively. A linear relationship is found between the UPS and Auger signal of oxygen.     

Quantum action-angle variables for harmonic oscillators

The well-known difficulties of defining a phase operator of an oscillator, caused by the lower bound on the number operator, is overcome by enlarging the physical Hilbert space by means of a spin-like, two-valued quantum number. On the enlarged space a phase representation exists on which trigonometric functions of the phase are numbers, and the “number of quanta” is a differential operator. Physical results are recovered by projection on the “upper components.” Coherent states, indeterminacy relations, as well as generalizations to other Hamiltonians, including the quantum analog of the quasi-periodic case, are discussed.     

Deep defect levels in diode structures based on gallium phosphide

We have studied the characteristic features of defect formation and generation of deep levels that control degradation processes in GaP diodes. We have shown that degradation of GaP diodes is mainly connected with the presence of defects in the space charge region of the p-n junction which are V_Ga-donor complexes, antistructural P_Ga defects, and also intrinsic V_P structural defects with high density of localized states. We have established an interconnection between the degradation rate and the features of the energy spectrum of deep levels in GaP diodes, allowing us to use analysis of tunneling spectra for diagnostics of p-n junction quality and prediction of GaP diode degradation. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 78–81, January–February, 2006.     

The effects of core structure on radiative and non-radiative recombinations at metal ion substituents in semiconductors and phosphors

Carrier binding and recombination processes at transition metal (TM) and post-transition metal impurities in solids are reviewed. The presence of low-lying empty core orbitals in these impurities introduces novel binding and recombination phenomena and leads naturally to a classification of impurity centres as ‘simple’ or ‘structured’. ‘Simple’ impurities, generally the main group elements, introduce only effective-mass-like states into the forbidden gap of the host lattice, whereas ‘structured’ impurities show localized atomic-like transitions below the lattice absorption edge. The fact that donor or acceptor centres generated by TM ions in semiconductors are usually deep is discussed with reference to a simple oxidationstate correlation diagram based on the variable chemical valency characteristic of these ions. Many metal ion impurities in solids generate iso-electronic centres however, and evidence is assembled to show how the normally accepted range of iso-electronic centres can be extended to include such impurities. It is emphasized that the formation of bound states at these ‘structured’ cationic iso-electronic centres is fairly common, in contrast to the situation normally found for anionic substituents in semiconductors. A possible explanation for this general property of structured iso-electronic centres is given in terms of the low-lying core levels which they may introduce in the band gap and their enhanced polarizability. Simple arguments then suggest that those centres showing electron ionization thresholds or atomic inter-configurational transitions just below E _g should be hole-attractive, whereas those showing charge transfer transitions should be electron-attractive. It is shown that two kinds of defect Auger recombination (DAR) may be significant for excitons localized at structured impurities. The first involves hole ionization at a deep neutral acceptor, and the conditions which must be met to make this process significant at room temperature are reviewed. The second DAR process involves the transfer of carrier recombination energy to the core electrons of the structured impurity. A simple model developed for this energy transfer process predicts that the coupling between exciton and core states will be larger if the impurity shows strong, broad dipole-allowed transitions quasi-resonant with the lattice absorption edge. Throughout the paper we stress the importance of recombination processes at structured impurities to the problems of phosphor activation and of shunt recombination mechanisms in semiconductor LEDs. In the final sections this general framework of ideas is used to explain the relative cathodoluminescence efficiencies of different rare-earth activators in crystals of Y₃Al₅O₁₂, with good agreement between the theoretical predictions and the experimental observations. Possible evidence for the occurrence of bound exciton states at structured TM impurities is found in the appearance of anomalously weak zero-phonon lines in the near-edge luminescence of GaP crystals prepared under special conditions.     

纳米GaP粉体对结晶紫的光催化降解及其振动光谱分析

对纳米 Ga P粉体 -结晶紫水溶液光催化降解进行了研究。纳米 Ga P粉体在紫外光照射条件下对结晶紫具有光催化降解作用 ;随平均颗粒度的降低 ,纳米 Ga P粉体的光催化活性增加。红外光谱测试结果表明 :进行光催化过程以后 ,纳米 Ga P表面存在的几种主要振动模式变化较小或不变 ;拉曼光谱测试结果表明 :纳米 Ga P粉体的横向光学声子模与纵向光学声子模 ,以及表面主要振动模式几乎没有发生变化     

Luminescence of Pr,Nd and Yb ions implanted in GaAs and GaP

New experimental data on luminescence spectra of Pr and Nd ions implanted into GaAs and GaP crystals and the results on luminescence kinetics of Nd doped GaP are presented. The results show that RE ions form different complexes in measured samples.     

Deep levels of intrinsic point defects and the nature of “anomalous” optical absorption in ZnGeP2

Deep levels of single vacancies and antisite defects in the structure of the ZnGeP₂ compound are investigated using the pseudopotential method and an extended unit cell. The data obtained are compared with those for the GaP isoelectronic analog. It is demonstrated that, in the case of the ZnGeP₂ crystal, deep levels (degenerate in the GaP structure) are substantially split as a result of lowering the lattice symmetry and anisotropy of the chemical bonding. In particular, the splitting of the V _P ⁰ (t ₂) level is equal to 1.58 eV. The averaged levels of defects in the ZnGeP₂ compound are in close agreement with the levels of defects in the GaP compound. The absorption coefficients for polarized light are calculated with allowance made for the neutral and charged states of the defects. The optical transitions responsible for the absorption peaks in the IR range of the spectrum of the ZnGeP₂ compound are revealed. It is shown that the first peaks are associated with the transitions of electrons from the valence band states located deep in the Brillouin zone to the V _Zn ^?1 and V _P ⁰ deep levels. This leads to a considerable shift (by ～0.3 eV) of these peaks toward the high-energy range as compared to the energy positions of the deep levels in the band gap with respect to the top of the valence band. The experimental data on the photoinduced EPR spectra of postgrowth and electron-irradiated ZnGeP₂ crystals are consistently interpreted by analyzing the electron density.     

Electron Spin Polarization of Photo-Excited Copper Coproporphyrin I: From Monomers to Dimers

The results of the electron paramagnetic resonance (EPR) and transient EPR (TREPR) of copper complexes of coproporphyrin I in different solvents before and after the laser pulse photo-excitation have been presented. Continuous-wave EPR spectra of the CuCPP-1 complex in o-terphenyl indicate the presence of only monomer fragments, while in the solution of the chloroform and isopropanol mixture, the complexes dimerize and the amount of dimers is five times larger than that of monomer complexes. Parameters describing EPR spectra of monomer and dimer CuCPP-1 complexes have been determined. It was established that the fine structure tensor of the dimer complex is rotated with respect to the g-tensor, which coincides with the tensor of monomer complexes. TREPR spectra of CuCPP-1 complexes in o-terphenyl and in the chloroform and isopropanol mixture after the laser photo-excitation are mainly due to spin-polarized ground states of monomer and dimer complexes, respectively. The TREPR spectra of the monomer CuCPP-1 show the emissive spin-polarized signal of the ground state. For dimer fragments, the net polarization is observed in the form of absorption and there is a small contribution from the multiplet polarization, which decays fast in time. The time dependence of TREPR of CuCPP-1 complexes in the chloroform and isopropanol mixture is described with allowance for these contributions from the ground state of the dimer and the contribution from the ground state of the monomer, which is manifested at larger times. Differences in the spin polarization of ground states and their possible origin are discussed.     

Localized vibrational modes of interstitial oxygen and oxygen complexes in GaP

The i.r. absorption spectrum of GaP in the range 500–1500 cm^?1 is found to contain several sharp impurity modes. Doping and annealing experiments show some of these modes to be connected with the presence of oxygen. Such modes are found to be present in all samples of nominally undoped LEC grown GaP. From the unusually high frequency of the modes and correlations with other semiconductors it is concluded that the oxygen is situated in interstitual sites. A linear chain model is developed to explain the frequency of the mode using force constants similar to those in oxygen doped silicon. The model is then used to predict the vibrational frequencies and the absorption strengths of several types of complex involving the oxygen interstitial. These calculations together with the absorption spectra suggest that oxygen-carbon and oxygen-boron complexes are also present in LEC grown GaP.     

Optical properties of the filled tetrahedral semiconductors LiZnX (X=N, P, and As)

We present first principles calculations of the electronic and the optical properties of the filled tetrahedral compounds LiZnN, LiZnP, and LiZnAs performed with the full potential linearized augmented plane wave method within the local density approximation. The origin of the small gap of LiZnN is attributed to the strong p-d coupling in this compound. The assignments of the structures in the optical spectra and band structure transitions are discussed in detail. The predicted values of the dielectric constants for LiZnP and LiZnAs are close to those of the binary compounds GaP and GaAs, respectively.     

The optical properties of Be,Mg and Zn-diffused gallium phosphide

Interest in the Ga-site acceptors Be and Mg was stimulated by the possibility that they might produce efficient luminescence on association with O, analogous to the well-known red Zn-O luminescence in GaP but at higher transition energy. Attention was directed to diffusion doping by Be and Mg of GaP O-doped during growth because the reactivity of Be and Mg with O renders double doping during crystal growth very difficult. Structured green donor-acceptor pair spectra were observed at 1.6°K from many Be-diffused crystals, yielding an accurate measure of (E_A)_BE, 50 ± 1 meV. Moderately efficient orange-red luminescence was also observed below ∼ 100 °K from these crystals, but the intensity of this luminescence decreased rapidly to negligible levels by ∼ 200°K. This luminescence also contains sharp structure at 1.6°K, of a form characteristic of the decay of excitons bound to complex centres. Many sharp phonon replicas occur, involving local modes as well as characteristic GaP modes. One set of no-phonon lines, at least, near 2.19 eV, shows zero-field splitting, luminescence decay times and behaviour in magnetic and external strain fields characteristic of exciton decay at a centre with <100>; or <111>-type symmetry axes, containing no extra electronic particles. The exciton state is split by 2.4 meV by J-J coupling, and the axial field of the centre splits the hole states by ∼ 1.0 meV. These bound excitons are specifically characteristics of diffused GaP and appear analogous to bound excitons observed below 2.12 eV in Zn-diffused GaP. It is probable that the relevant centres contain diffusion components such as Be or Zn interstitials and improbable that O_P is involved. By contrast, weak orange bound exciton luminescence observed in Mg-diffused GaP does involve O, presumably as O_P. No analysis of the magneto-optical behaviour of this Mg-related bound exciton was possible in our crystals, so its symmetry axis was not established. It is possible that this is the Mg_Ga-O_P bound exciton. If so, the two-fold reductions in the exciton localisation energy from ∼ 0.32 eV to ∼ 0.15 eV and in the mass of the Ga-site substituent has produced dramatic changes in the form of the phonon cooperation between the Zn-O and “Mg-O” excitons. The “Mg-O” exciton luminescence is not dominant in our crystals, even at low temperature. The exciton state is again split by a local crystal field as well as by J-J coupling, but here the former splitting is predominant; 2_∈0 = 3.9 meV, Δ = 0.60 meV.     

Interstitial Mn as a new donor in GaP and GaAs: an EPR study

We report the observation of a new electron paramagnetic resonance centre in neutron-irradiated GaP and a similar new EPR centre in Mn-doped GaAs. Both centres have been identified as interstitial Mn and act as a donor. To our knowledge this is the first observation by EPR of an interstitial transition-metal impurity in a III-V compound. The implication of this new finding on the issue of Mn diffusion is discussed.     

Study of the luminescence of tris(2-thenoyltrifluoroacetonato)lanthanide(III) complexes covalently linked to 1,10-phenanthroline-functionalized hybrid sol-gel glasses

The solubility and uniform distribution of lanthanide complexes in sol-gel glasses can be improved by covalently linking the complexes to the sol-gel matrix. In this study, several lanthanide β-diketonate complexes (Ln=Nd, Sm, Eu, Tb, Er, Yb) were immobilized on a 1,10-phenanthroline functionalized sol-gel glass. For the europium(III) complex, a sol-gel material of diethoxydimethylsilane (DEDMS) with polymer-like properties was derived. For the other lanthanide complexes, the sol-gel glass was prepared by using a matrix of tetramethoxysilane (TMOS) and DEDMS. Both systems were prepared under neutral reaction conditions. High-resolution emission and excitation spectra were recorded. The luminescence lifetimes were measured.     

GaP中N和NNi对等电子陷阱态的压力行为

 半导体中的局域电子态和半导体的能带结构密切相关，揭示局域电子态和能带结构之间的内在关系是当前半导体电子理论的重要方面。而压力光谱实验对研究这种相互关系提供了重要手段。本文对GaP中深、浅两组能级的不同压力行为作了系统的实验研究。实验观察到无论在室温还是在低温，压力小于3.3 GPa时，以N陷阱束缚激子的发光过程为主，大于3.3 GPa时则以自由激子零声子过程为主，并且所有与N有关的陷阱态都具有压力的非线性行为。根据有效质量随压力的变化提出能谷中不同能量态具有不同的压力关系。基于有效质量随压力变化的能带格林函数方法，对N和NNi对的压力系数作了模型计算，其结果和陷阱态的压力行为符合得相当好。证实了带结构，尤其是能谷曲率随压力的变化是决定陷阱态压力行为的主要因素。     

Optical properties of the Ge donor and acceptor in GaP

The observation of discrete pair line emission and the analysis of the spectra from Ge donor - C acceptor and S donor - Ge acceptor pairs in GaP is reported. The Ge donor binding energy is 0.200 ± 0.002 eV and the Ge acceptor binding energy is 0.258 ± 0.002 eV. The bound exciton recombination at neutral Ge donors was observed at 2.265 eV corresponding to an exciton binding energy of 0.063 eV. This is the most tightly donor bound exciton observed in GaP.     

Some optical properties of (ZnS)−(GaP) alloys and their interpretation

Optical measurements on the single crystals of the pseudobinary (ZnS)?(GaP) alloy were carried out. The band gap energy decreased more rapidly with increase in GaP concentration than that reported previously. The analysis of the absorption spectra for the crystals of up to 70 mole % GaP indicated a direct transition characteristic, and that the band gap becomes nearly equal to that of pure GaP at about 30 mole % GaP. The photoluminescence spectra observed at liquid nitrogen temperature could first be resolved into three kinds of emission band with Gaussian distribution. The peak energy of these bands were found to be independent of the band gap variation. Thus the observed peak energy shift with alloy composition was attributed to the variation of the emission intensity of each band. The band gap shrinkage and the origin of the photoluminescence spectra on the basis of a molecular orbital method were discussed.     

Resonant shake-up satellites in photoemission at the Ga 3p photothreshold in GaN

Photoemission spectra recorded near the Ga 3p photothreshold from GaN have been found to contain satellites of the main Ga 3d emission line. The intensity of these satellites resonate at this threshold, and are associated with a 3d⁸ state. The correlation energies and binding energies for the satellite multiplet have been measured for the satellite and related Auger transitions. The satellite multiplet contains additional constant binding energy features not observed in previous studies of other Ga compounds. The present results are compared with those for GaP and GaAs.     

Neutral and positively charged excitons in quantum ring

We study theoretically quantized states of the neutral and positively charged exciton complexes confined within a circular narrow ring in the presence of the magnetic field applied along the symmetry axis. We show that in the structural adiabatic limit, when the width of the pattern of the particles pathways within the ring is much smaller than its radius, the wave equations for both complexes are separable and their exact solutions can be found in a form of the Fourier series of one and two variables, respectively. We present results of calculation of the lower energies of complexes as functions of the ring's radius and the magnetic field strength for different values of the electron-to-hole mass ratio. We found that in the molecular adiabatic limit, when this ratio tends to zero and the model describes the corresponding donor complexes, the physical interpretation of the quantum-size effect and the oscillations of energy levels in threading magnetic field revealed for the excitons spectra becomes more transparent.