Study on the perfection of in situ P-injection synthesis LEC-InP single crystals

Undoped, S-doped and Fe-doped InP crystals with diameter up to 4-inch have been pulled in drop 10 0 drop -direction under P-rich condition by a rapid P-injection in situ synthesis liquid encapsulated Czochralski (LEC) method. High speed photoluminescence mapping, etch-pit density (EPD) mapping and scanning electron microscopy have been used to characterize the samples of the single crystal ingots. Dislocations and electrical homogeneity of these samples are investigated and compared. By controlling the thermal field and the solid-liquid interface shape, 4-inch low-EPD InP single crystals have been successfully grown by the rapid P-injection synthesis LEC method. The EPD across the wafer of the ingots is less than 5 x 10(4) cm(-2). Cluster defects with a pore center are observed in the P-rich LEC grown InP ingots. These defects are distributed irregularly on a wafer and are surrounded by a high concentration of dislocations. The uniformity of the PL intensity across the wafer is influenced by these defects. (C) 2004 Elsevier B.V. All rights reserved.

FexSi grown with mass-analyzed low-energy dual ion beam deposition

Heavily iron-implanted silicon was prepared by mass-analyzed low-energy dual ion beam deposition technique. Auger electron spectroscopy depth profiles indicate that iron ions are shallowly implanted into the single-crystal silicon substrate and formed 35 nm thick FexSi films. X-ray diffraction measurements show that as-implanted sample is amorphous and the structure of crystal is partially restored after as-implanted sample was annealed at 400degreesC. There are no new phases formed. Carrier concentration depth profile of annealed sample was measured by Electrochemical C-V method and indicated that FexSi film shows n-type conductivity while silicon substrate is p-type. The p-n junction is formed between FexSi film and silicon substrate showing rectifying effect. (C) 2003 Elsevier B.V. All rights reserved.

Investigation of Mn-implanted n-Si by low-energy ion beam deposition

Mn ions were implanted to n-type Si(0 0 1) single crystal by low-energy ion beam deposition technique with an energy of 1000 eV and a dose of 7.5 x 10(17) cm(-2). The samples were held at room temperature and at 300degreesC during implantation. Auger electron spectroscopy depth profiles of samples indicate that the Mn ions reach deeper in the sample implanted at 300degreesC than in the sample implanted at room temperature. X-ray diffraction measurements show that the structure of the sample implanted at room temperature is amorphous while that of the sample implanted at 300degreesC is crystallized. There are no new phases found except silicon both in the two samples. Atomic force microscopy images of samples indicate that the sample implanted at 300degreesC has island-like humps that cover the sample surface while there is no such kind of characteristic in the sample implanted at room temperature. The magnetic properties of samples were investigated by alternating gradient magnetometer (AGM). The sample implanted at 300degreesC shows ferromagnetic behavior at room temperature. (C) 2004 Elsevier BN. All rights reserved.

GdxSi grown with mass-analyzed low energy dual ion beam epitaxy technique

Semiconducting gadolinium silicide GdxSi samples were prepared by mass-analyzed low-energy dual ion beam epitaxy technique. Auger electron spectroscopy depth profiles indicate that the gadolinium ions are implanted into the single-crystal silicon substrate and formed 20 nm thick GdxSi film. X-ray double-crystal diffraction measurement shows that there is no new phase formed. The XPS spectra show that one type of silicon peaks whose binding energy is between that of silicide and silicon dioxide, and the gadolinium peak of binding energy is between that of metal Gd and Gd2O3. All of these results indicate that an amorphous semiconductor is formed. (C) 2002 Elsevier Science B.V. All rights reserved.

MnSi similar to 1.73 grown on silicon with mass-analyzed low energy dual ion beam epitaxy technique

Semiconducting manganese silicide, Mn27Si47 and Mn15Si26, were obtained using mass-analyzed low energy dual ion beam epitaxy technique, Auger electron spectroscopy depth profiles showed that some of the Mn ions were deposited on single-crystal silicon substrate and formed a 37.5 nm thick Mn film, and the other Mn ions were successfully implanted into the Si substrate with the implantation depth of 618 nm. Some samples were annealed in the atmosphere of flowing N-2 at 840 degreesC. X-ray diffraction measurements showed that the annealing was beneficial to the formation of Mn27Si47 and Mn15Si26 (C) 2001 Published by Elsevier Science B.V.

A study of the interface of CeO2/Si heterostructure grown by ion beam deposition

Epitaxial cerium dioxide films on single-crystal silicon substrates (CeO2/Si) have been grown by a dual mass-analyzed low-energy ion beam deposition (IBD) system. By double-crystal X-ray diffraction (XRD), Full Width at Half Maximum (FWHM) are 23' and 33' in the rocking curves for (222) and (111) faces of the CeO2 film, respectively, and the lattice-mismatch Delta a/a with the substrate is about - 0.123%. The results show that the CeO2/Si grown by IBD is of high crystalline quality. In this work, the CeO2/Si heterostructure were investigated by X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) measurements. Especially, XPS and AES depth profiling was used to analyze the compositions and structures in the interface regions of the as-grown and post-annealed CeO2/Si. It was found that there was no silicon oxide in the interface region of the as-grown sample but silicon oxide in the post-annealed sample. The reason for obtaining such high quality heterostructure mainly depends on the absence of silicon oxide in the surface at the beginning of the deposition. (C) 1998 Elsevier Science Ltd. All rights reserved.

Theoretical investigation on quantum well lasers with extremely low vertical beam divergence and low threshold current

A specially designed quantum well laser for achieving extremely low vertical beam divergence was reported and theoretically investigated. The laser structure was characterized by two low index layers inserted between the waveguide layers and the cladding layers. The additional layers were intended to achieve wide optical spread in the cladding layers and strong confinement in the active region. This enabled significant reduction of beam divergence with no sacrifice in threshold current density. The numerical results showed that lasers with extremely low vertical beam divergence from 20 degrees down to 11 degrees and threshold current density of less than 131 A/cm(2) can be easily achieved by optimization of the structure parameters. Influences of individual key structure parameters on beam divergence and threshold current density are analyzed. Attention is also paid to the minimum cladding layer thicknesses needed to maintain low threshold current densities and low internal loss. The near and far field patterns are given and discussed. (C) 1998 American Institute of Physics.

Mode analysis of photonic crystal polarization beam splitter and its application in integrated circuits design - art. no. 698437

In this work, the guided modes of a photonic crystal polarization beam splitter (PC-PBS) are studied. We demonstrate that the transmission of a low-loss photonic crystal 120 degrees waveguide bend integrated with the PBS will be influenced if the PBS is multi-moded. We propose a single-moded PC-PBS structure by introducing deformed structures, and it shows twice the enhancement of the transmission. This device with remarkable improvement of performance is promising in the use of photonic crystal integrated circuits design.

Corrugated surfaces formed on GaAs (331)a substrates: The template for laterally ordered InGaAs nanowires

Morphology evolution of high-index (331)A surfaces during molecular beam epitaxy (MBE) growth have been investigated in order to uncover their unique physic properties and fabricate spatially ordered low dimensional nanostructures. Atomic Force Microscope (AFM) measurements have shown that the step height and terrace width of GaAs layers increase monotonically with increasing substrate temperature in conventional MBE. However, this situation is reversed in atomic hydrogen-assisted MBE, indicating that step bunching is partly suppressed. We attribute this to the reduced surface migration length of Ga adatoms with atomic hydrogen. By using the step arrays formed on GaAs (331)A surfaces as the templates, we fabricated laterally ordered InGaAs self-aligned nanowires.

Single-mode holey vertical-cavity surface-emitting laser with ultra-narrow beam divergence

We demonstrated oxide-confined 850-nm vertical-cavity surface-emitting lasers (VCSELs) with a two-dimensional petal-shaped holey structure composed of several annular-sector-shaped holes. Four types of devices with different hole numbers were designed and fabricated. The measured results showed that the larger hole number was beneficial to purifying the lasing mode, and realizing the single-mode operation. The side mode suppression ratio (SMSR) exceeded 30 dB throughout the entire drive current. Mode selective loss mechanism was used to explain the single-mode characteristic. The single-mode devices possessed good beam profiles, and the lowest divergence angle was as narrow as 3.2 degrees (full width at half maximum), attributed to the graded index profile and the shallow etching in the top distributed Bragg reflector (DBR).

High quality CeO2 film grown on Si(111) substrate by using low energy dual ion beam deposition technology

By using the mass-analyzed low energy dual ion beam deposition technique, a high quality epitaxial, insulating cerium dioxide thin film with a thickness of about 2000 Angstrom, has been grown on a silicon (111) substrate. The component species, cerium and oxygen, are homogeneous in depth, and have the correct stoichiometry for CeO2. X-ray double-crystal diffraction shows that the full width at half maximum of the (222) and (111) peaks of the film are less than 23 and 32 s, respectively, confirming that the film is a perfect single crystal. (C) 1995 American Institute of Physics.

Two-Step Spin-Transition Iron(III) Compound with a Wide [High Spin-Low Spin] Plateau

A new iron(III) coordination compound exhibiting a two-step spin-transition behavior with a remarkably wide [HS-LS] plateau of about 45 K has been synthesized from a hydrazino Schiff-base ligand with an N,N,O donor set, namely 2-methoxy-6-(pyridine-2-ylhydrazonomethyl) phenol (Hmph). The single-crystal X-ray structure of the coordination compound {[Fe(mph)(2)](ClO4)(MeOH)(0.5)(H2O)(0.5)}(2) (1) determined at 150 K reveals the presence of two slightly different iron(III) centers in pseudo-octahedral environments generated by two deprotonated tridentate mph ligands. The presence of hydrogen bonding interactions, instigated by the well-designed ligand, may justify the occurrence of the abrupt transitions. 1 has been characterized by temperature-dependent magnetic susceptibility measurements, EPR spectroscopy, differential scanning calorimetry, and Fe-51 Mossbauer spectroscopy, which all confirm the occurrence of a two-step transition. In addition, the iron(III) species in the high-spin state has been trapped and characterized by rapid cooling EPR studies.

Conducting probe atomic force microscopy investigation of anisotropic charge transport in solution cast PBD single crystals induced by an external field

2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxdiazole (PBD) is a good electron-transporting material and can form single crystals from solution. In this work, solution cast PBD single crystals with different crystallographic axes (b, c) perpendicular to the Au/S substrates in large area are achieved by controlling the rate of solvent evaporation in the presence and absence of external electrostatic field, respectively. The orientation of these single crystals on Au/S substrate was characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Conducting probe atomic force microscopy (CP-AFM) was used to measure the charge transport characteristics of PBD single crystals grown on Au/S substrates. Transport was measured perpendicular to the substrate between the CP-AFM tip and the Au/S substrate. The electron mobility of 3 x 10(-3) cm(2)/(V s) for PBD single crystal along crystallographic b-axis is determined. And the electron mobility of PBD single crystal along the c-axis is about 2 orders of magnitude higher than that along the b-axis due to the anisotropic charge transport at the low voltage region.

Fractal roughness characterization of super-ground Mn-Zn ferrite single crystals

The surface of superground Mn-Zn ferrite single crystal may be identified as a self-affine fractal in the stochastic sense. The rms roughness increased as a power of the scale from 10(2) nm to 10(6) nm with the roughness exponent alpha = 0.17 +/- 0.04, and 0.11 +/- 0.06, for grinding feed rate of 15 and 10 mu m/rev, respectively. The scaling behavior coincided with the theory prediction well used for growing self-affine surfaces in the interested region for magnetic heads performance. The rms roughnesses increased with increase in the feed rate, implying that the feed rate is a crucial grinding parameter affecting the supersmooth surface roughness in the machining process.