Deep levels in semi-insulating InP obtained by annealing under iron phosphide ambiance

Deep levels in semi-insulating (SI) InP obtained by annealing in iron phosphide (IP) ambiance have been characterized by optical transient current spectroscopy (OTCS). Compared with the OTCS result of the SI InP prepared by annealing in pure phosphorus (PP) ambiance, the IP SI InP presents only two traps with activation energies of 0.20 and 0.63 eV, respectively. The results suggest that the diffusion of Fe-atoms suppresses the formation of a few defects in the IP SI InP. The nature of deep levels in the IP and PP SI InP has been discussed on the basis of these results. The relation between material property and defects in those SI InP has also been revealed. (C) 2002 American Institute of Physics.

Photoluminescence assessment of undoped semi-insulating InP wafers obtained by annealing in iron phosphide vapour

We have investigated the photoluminescence mapping characteristics of semi-insulating (SI) InP wafers obtained by annealing in iron phosphide ambience (FeP2-annealed). Compared with as-grown Fe-doped and undoped SI InP wafers prepared by annealing in pure phosphorus vapour (P-annealed), the FeP2-annealed ST InP wafer has been found to exhibit a better photoluminescence uniformity. Radial Hall measurements also show that there is a better resistivity uniformity on the FeP2-annealed Sl InP wafer. When comparing the distribution of deep levels between the annealed wafers measured by optical transient Current spectroscopy, we find that the incorporation of iron atoms into the Sl InP Suppresses the formation of a few defects. The correlation observed in this study implies that annealing in iron phosphorus ambience makes Fe atoms diffuse uniformly and occupy the indium site in the Sl InP lattice. As it stands, we believe that annealing undoped conductive InP in iron phosphide vapour is an effective means to obtain semi-insulating InP wafers with superior uniformity.

Fe-diffusion-induced defects in InP annealed in iron phosphide ambient

Photoluminescence (PL) and photo induced current transient spectroscopy (PICTS) have been used to study deep levels in semi-insulating (SI) InP prepared by annealing undoped InP in pure phosphorus (PP) and iron phosphide (IP) ambient. Defects are much fewer in IP SI-InP than in PP SI-InP. Deep-level-related PL emission could only be detected in IP SI-InP. The results indicate that Fe diffusion inhibits the thermal formation of a number of defects in annealed InP. A complex defect has been formed in the annealing process in the presence of Fe.

Superconductivity in Iron Telluride Thin Films under Tensile Stress

By realizing in thin films a tensile stress state, superconductivity of 13 K was introduced into FeTe, a nonsuperconducting parent compound of the iron pnictides and chalcogenides, with a transition temperature higher than that of its superconducting isostructural counterpart FeSe. For these tensile stressed films, superconductivity is accompanied by a softening of the first-order magnetic and structural phase transition, and also, the in-plane extension and out-of-plane contraction are universal in all FeTe films independent of the sign of the lattice mismatch, either positive or negative. Moreover, the correlations were found to exist between the transition temperatures and the tetrahedra bond angles in these thin films.

富钇稀土-铝合金制取的研究Study on Preparation of Yttrium-Rich RE-Al Alloys

我国江西龙南稀土矿是目前世界上储量最大的富钇稀土矿、研制具有多种用途的钇（Y）-铝（Al）或富钇混合稀土（Ymm）-铝中间合金，对于开拓我国龙南稀土矿的应用领域扩大稀土合金出口具有重要意义。基于这一背景并针对目前氟化物体系制取Ymm-Al合金时存在着电解温度高，腐蚀现象严重，电效偏低等缺点，本文系统开展了在氯化物熔盐体系中电解制取Ymm-Al合金的研究工作。本工作由三部分组成：在第一部分工作中，开展了熔盐电解所需要基本原料-无水稀土氯化物制取的工艺研究。利用化学分析和结构分析手段，弄清了干法氯化过程中YmmCl_3水解的机理，提出了减弱水解的措施，即YmmCl_3先在850-900 ℃灼烧1.5 + 0.2hr，脱掉吸附水并将碱式碳酸盐转化为氧化物，增加稀土氧化物的比表面。通过条件试验得到最佳工艺条件为：采用NH_4 Cl:Ymm_2 O_3 = 14:1（摩尔比）的配料比，每次投入氯化装置的原料量为0.26 - 0.36 kg, 在400-450 ℃氯化反应激烈开始后迅速降温至400 ℃以下，待物料粘结现象消失后，再行升温氯化。出料及后期控制温在475 ± 25 ℃。经过3.8 ± 0.2hr氯化，可制得水不溶物小于1%并符合熔盐电解要求的YmmCl_3原料。此新工艺与原有干法工艺相比，流程短，装置简单，不需密闭抽真空，成本低，适于制取任何量的优质熔盐电解所需氯化稀土原料。在第二部分工作中，利用上述YmmCl_3原料，以液态铝为阴极，在氯化物体系中进行熔盐电解，通过试验得出在小型试验规模制取Ymm-Al合金的最隹工艺条件为：电解质组成（重量比）40%YmmCl_3-1%NaF-59%等摩尔的NaCl-KCl；电解温度为790 ± 5 ℃；阴极电流密为0.7 - 0.02A/cm~2；电解电量为333 ± 5库仑/克铝，制得钇铝合金中Ymm含量为10 ± 2%。添加1%的NaF可消除阴极表面生成枝状物，减少合金中夹渣和熔盐中沉渣。在电解工作中，将方差分析应用于试验数据处理，方差分析结果表明，各种试验因素对电效有明显影响，试验数据可靠，试验误差在允许范围以内。在第三部分工作中，利用线性扫描伏安法测定了在最隹电解工艺条件下Y~（3+）和Ymm在液态铝及钼电极上的析出电位。测定结果表明：Y~（3+）和Ymm~（3+）在液态铝阴极上的析出电位比在钼阴极上偏正0.2 ～ 0.8伏，氟离子的加入要比不加氟时析出电位不有同程度的负移，但考虑到氟离了具有消渣作用，加入少量氟比物添加剂对提高电效有利。

CALCULATED ELECTRONIC AND MAGNETIC-STRUCTURES OF THE NEW TERNARY RARE-EARTH IRON NITRIDE ND2FE17N3

The electronic and magnetic structures of Nd2Fe17 and Nd2Fe17N3 have been calculated using the first-principle, spin-polarized orthogonalized linear combination of atomic orbitals method. Comparative studies of the two materials reveal important effects of the nitrogen atoms (at 9e site) on the electronic and magnetic structures. Results are presented for the total density of states, site-projected partial density of states and the spin magnetic moments on four nonequivalent Fe sites. The highest magnetic moments are found to be located on the 6c site for Nd2Fe17 and on the 9d site for Nd2Fe17N3, in agreement with the neutron and Mossbauer experiments. The variation trends of the magnetic moments on different Fe sites are discussed in terms of the separation between Fe and N atoms. Compared with Nd2Fe17, an increase in the exchange splitting of the Fe d band is found in Nd2Fe17N3, which accounts for its higher Curie temperature as observed in experiments. The calculated results show that the nitrogen atoms are charge acceptors in these compounds.

THE STUDY OF MICROSTRUCTURE IN IRON-DOPED AND SULFUR-DOPED INP CRYSTALS BY MEANS OF HREM AND COMPUTER-SIMULATION

The microstructures in iron- and sulphur-doped InP crystals were studied using both electron microscopy and electron diffraction. A modulated structure has been found in S-doped InP crystal, where the commensurate modulations corresponded to periodicities of 0.68 nm and 0.7 nm in real space and were related to the reflections of the cubic lattice in [111] and [113BAR] directions; they were indexed as q111* = 1/2(a* + b* + c*) and q113BAR* = 1/4(-a* - b* + 3c*), respectively. Single atomic layers of iron precipitate were observed, with preferred orientations along which precipitates are formed. Simulated calculations by means of the dynamical theory of electron diffraction using models for the precipitate structure were in good agreement with our experimental results. The relation between the modulated structure and the precipitates is also discussed.

PHOTOINDUCED CHANGES OF HYDROGEN-BONDING IN SEMIINSULATING IRON-DOPED INDIUM-PHOSPHIDE

After illumination with 1-1.3 eV photons during cooling-down, metastable PH modes are observed by IR absorption at 5 K in semi-insulating InP:Fe. They correlate with the photo-injection of holes, but not with a change of the charge state of the K-related centres present at equilibrium. They are explained by a change of the bonding of H, induced by hole trapping, from IR-inactive centres to PH-containing centres, stable only below 80 K. One metastable centre has well-defined geometrical parameters and the other one could be located in a region near from the interface with (Fe,P) precipitates.

Iron related emission spectra in InP

This paper presents a detailed PL study of Fe2+ related four zero-phonon(ZP) lines and their related phonon sidebands. Four zero-phonon transitions at approximate to 2800 cm(-1) along with the accompanying phonon sidebands extending down to 2400 cm(-1). There are ta two prominent regions in the phonon sidebands. One is ascribed to coupling to acoustic-type phonons (2700 cm(-1) region), the other is due to coupling to optic-type phonons (2500 cm(-1) region). Beside broad coupling with lattice modes, there are several groups of lines. They are ascribed to resonant modes, impurities induced gap modes and local modes.

On the nature of iron in InP: A FTIR study

Fe is still the commonly used dopant to fabricate semi-insulating(SI) InP, a key material for high-speed electronic and optoelectronic devices. High resolved absorption spectra of the internal d-d shell transitions at Fe2+ in InP and the related phonon sidebands and a series of iron related absorption Lines are presented. Detailed infrared absorption study of the characteristic spectra of four zero-phonon lines(ZPLs), which are attributed to transitions within the 5D ground state of Fe2+ (3d(6)) on the indium site in a tetrahedral crystal field of phosphorus atoms and their temperature effects are given.