Optical third-harmonic investigations of gallium nitride nucleation layers on sapphire

The magnitude of the χ _xxxx ⁽³⁾ element of the third-order optical susceptibility was measured in a series of wurtzite phase GaN nucleation layers (～450Å) deposited on (00.1) sapphire at 540°C and annealed to various temperatures up to 1050°C. The nonlinear optical response exhibited a significant increase in films that were annealed to temperatures in the range of 1015 to 1050°C. In addition, the correlation between the magnitude of χ _xxxx ⁽³⁾ with both the maximum value of the linear absorbance gradient and the residual homogeneous strain in the overlayer suggests that variations in the crystalline content of the film and the bonding distance between the Ga and N atoms are primary factors in determining the third-order nonlinearity in GaN.     

Effects of “fast” rapid thermal anneals on sub-keV boron and BF2 ion implants

The effects of “fast” ramp-rates (up to 425°C/s) and spike anneals are investigated for 0.25 keV, 0.5 keV, and 1.0 keV ¹¹B+ and for 1.1 and 2.2 keV BF₂ at a dose of 1e 15/cm². Below an implant energy threshold where no extended defects form, fast ramp-rates become important in minimizing the thermal diffusion component and reducing the junction depth. Above this implant energy threshold, TED minimizes the advantages of these fast ramp-rates. Annealing in a low and controlled O₂ ppm in N₂ ambient further reduces diffusion by minimizing/eliminating oxygen related enhanced diffusion effects, while simultaneously optimizing anneal reproducibility and across-the-wafer uniformity.     

Study of the spectrum of CH3 35C1 between 4250 and 4600 CM−1: thev 2+v 4 andv 4+v 5 rovibrational bands

About 2500 lines of CH₃ ³⁵Cl have been assigned. The strong xy Coriolis resonance between thev ₂ andv ₅ modes is quite visible between thev ₄+v ₄ ^±1 perpendicular band, centered around 4383 cm^?1, and thev ₄ ^±1 +v ₅ ^±1 perpendicular component, centered around 4475 cm^?1, with a crossing of upper energy levels allowing the observation of lines which are normally forbidden. Although not yet observed with certainty, because of the great density of lines of the spectrum, thev ₄ ^?1 +v ₅ ^±1 parallel component is nevertheless detectable by its effects onv ₂+v ₄ ^±1 which is linked by Coriolis resonance to both components ofv ₄+v ₅. Moreover the spectrum is much complicated by many other resonances with weak bands which occur at level crossings: it is the case ofv ₂+3v ₆ ^±1 , connected tov ₂+v ₄ ^±1 by the well known Darling Dennison resonance which couplesv ₄ ^±1 and 3v ₆ ^±1 , and also ofv ₅ ^±1 +3v ₆ ^±1 connected tov ₄ ^±1 +v ₅ ^±1 by the same resonance; but this last case is complicated by an anharmonic resonance betweenv ₅ ^±1 +3v ₆ ^±1 and 2v ₃+3v ₆ ^?1 . Two more perturbations occur on the ΔK=?1 side ofv ₂+v ₄: a weak Coriolis resonance gives rise to one subband ofv ₁+v ₂ at a level crossing withv ₂+v ₄, and thev ₁+v ₅ band (linked of course tov ₁+v ₂ by the Coriolis resonance between thev ₂ andv ₅ modes) is quite visible and perturbs several subbands ofv ₂+v ₄ of high values of K through an anharmonic resonance. Moreover, the complex (3v ₅ ^±1 ,v+2v ₅ ⁰ , 2v ₂+v ₅ ^±1 , 3v ₂,v ₂+2v ₅ ^±2 , 3v ₅ ^±3 ) system of Coriolis-connected bands is linked to the bands studied in the present work by two Fermi resonances: one betweenv ₂+2v ₅ ⁰ andv ₁+v ₂, and the other one betweenv ₁+v ₅ and 3v ₅ ^±1 , whose several subbands have been observed on the low part of the spectrum. The values of all the band centres and of the different coupling constants have been estimated, but all these interactions make the line assignments and the interpretation of the spectrum very difficult.     

Electrical characteristics of CdTe:Pb single crystals at high temperatures

The electrical properties of CdTe:Pb single crystals at high temperatures (400–900°C) and under controlled Cd vapor pressure (0.001–3 atm) were investigated for the first time. The temperature and baric dependences of the conductivity and Hall coefficient were measured. Low (in comparison with undoped CdTe) electron concentration indicates an increase in the number of impurity point defects related to the Pb impurity. The results obtained are explained within the Kröger theory of quasi-chemical reactions of defect formation on the assumption that lead may exist in the isolated state (Pb _Cd ⁺ ) and as a component of (Pb _Cd ⁺ V _Cd ^2? )^? associates.     

Correlation between chemical and electrical profiles in Si+, Se+ and S+ implanted bulk and epitaxial GaAs

We compare the chemical profiles of Cr, Mn, Si and Se with the electron concentration profiles in Si, Se and S implanted semi-insulating Cr-O doped bulk GaAs substrates and undoped VPE buffer layers annealed with and without a SiO₂ encapsulant in a H₂-As₄ atmosphere. A higher activation efficiency in the net electron concentration and the gateless saturated channel current is measured for SiO₂ encapsulated wafers annealed under arsine overpressure than for capless annealed ones using Cr-O doped bulk GaAs substrates. On the other hand, the net donor concentration peak is higher for implanted buffer epi layers capless annealed under arsine overpressure than for SiO₂ encapsulated ones. Secondary ion mass spectrometry (SIMS) studies of the Cr decoration of the implant damage indicate that the damage from the 100 keV Si implant anneals out at 840°C while a temperature of 900°C is required to anneal out the 260 keV Se implant damage. An explanation of these differences is provided using an impurity redistribution model and charge neutrality considerations. Excellent Hall electron mobilities at liquid nitrogen temperature of 5400–9200 cm²/V-sec are measured for Si-implanted buffer epi substrates.     

Molecular — impurity absorption in KC1 for infrared laser windows

Residual impurity absorption in the 10μm region severely limits the usefulness of KCl as a high-power CO₂ laser window. In order to investigate possible origins for this absorption, KCl was doped with carbonate and hydroxyl impurities, and grown in various atmospheres. Characteristic absorption bands in the infrared and ultraviolet were used to determine relative dopant concentrations. Growth conditions introducing CO/ ₃ ⁼ exclusively, led to relatively low and featureless absorption spectra in the 10.6μm region, while conditions introducing both CO/ ₃ ⁼ and OH⁻ led to enhanced absorption. (Additionally, a correlation is indicated between the strength of absorption at 10.6μm and that of the oxygen band at 0.26μm in samples grown in atmospheres in which oxygen was present). Our observations suggest the possibility of absorption due to CO/ ₃ ^≽ complexes, NO ₃ ⁻ , HCO ₃ ⁻ and/or ClO ₃ ⁻ in the 10μm region. While the effects of ultralow concentration of these impurities remain uncertain, the present results suggest that their presence may well contribute to extrinsic absorption in the 10μm region. Rsch supported by AFCRL(AFSC) - Contr F19628-72-C-0286     

OPTICAL EFFECTS AND MICROSTRUCTURE OF BURIED INSULATOR LAYER FORMED BY O+ AND N+ CO-IMPLANTATION

 The microstructure and optical properties of a buried layer formed by O~+(200 keV,1.8×10~(18)/cm~2)and N~+(180 keV,4×10~(17)/cm~2)co-implantation and annealed at 1200℃ for 2 h have been investigated by Auger electron,IR absorption and reflection spectroscopic measurements.The results show that the buried layer consists of silicon dioxide and SiO_x(x< 2) and the nitrogen segregates to the wings of the buried layer where it forms an oxynitride.By detail theoretical analysis and computer simulation of the IR reflection interference spectrum,the refractive index profiles of the buried layer were obtained.     

Effect of annealing temperature on 1.5 μm photoluminescence from Er-lmplanted 6H-SiC

The effect of post-implantation anneal on erbium-doped 6H-SiC has been investigated. 6H-SiC has been implanted with 330 keV Er⁺ at a dose of 1 × 1013 /cm2. Er depth profiles were obtained by secondary ion mass spectrometry (SIMS). The as-implanted Er-profile had a peak concentration of∼1.3 × 10¹⁸/cm³ at a depth of 770Å. The samples were annealed in Ar at temperatures from 1200 to 1900°C. The photoluminescence intensity integrated over the 1.5 to 1.6 μm region is essentially independent of annealing temperature from 1400 to 1900°C. Reduced, but still significant PL intensity, was measured from the sample annealed at 1200°C. The approximate diffusivity of Er in 6H SiC was calculated from the SIMS profiles, yielding values from 4.5 × 10⁻¹⁶ cm²/s at 1200°C to 5.5 × 10⁻¹⁵ cm²/s at 1900°C.     

The nature of point defects in CdTe

High temperature in-situ Hall effect measurements in CdTe single crystals grown by different techniques at 500–1,200 K under well-defined Cd and Te vapor pressure were made. It was established that native point defects (PD) Cd _i ²⁺ and V _Te ²⁺ are dominant at T>770 K in Cd-rich CdTe. Their formation enthalpies were determined (ΔH _VTe ²⁺ =1.3 eV; ΔH _Cdi ²⁺ =2.5 eV). It was shown that V _Te ²⁺ dominate at low temperatures and Cd _i ²⁺ begin to prevail at T>930 K. In Te-saturated CdTe at heating up to ～800 K, the hole density was Te vapor pressure independent. At higher temperatures (HT), the conductivity changed to intrinsic type, turning then into n-type. The results were explained in the framework of Kröger’s quasichemical formalism assuming the presence of an electrically active foreign point defect, the oxygen acceptor. The PD structure modeling demonstrated satisfactory agreement with experimental results both for temperature and component vapor pressure dependencies.     

Effect of MWNTs on the Electrochemical Reduction Processes of Bi3+, HTeO 2 + , and Their Mixtures

The effect of multiwalled carbon nanotubes (MWNTs) on the electrochemical behaviors of the Bi and Te unitary systems and the Bi–Te binary system was investigated by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Energy-dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD) analyses of the deposits were also conducted to confirm the analysis of the reduction processes. The results show that, when MWNTs were added into each solution, the shape and number of peaks on each voltammogram remained unchanged, but the reduction peaks all shifted positively, and the peak current of each reduction peak increased slightly. The variation trends of the Nyquist plots in each system did not change with the addition of MWNTs. However, the same process occurred at more positive potentials, and the radius of the semicircle decreased at the same potentials compared with blank solutions. All these results indicate that addition of MWNTs into these electrolytes did not change the electrochemical reduction mechanisms of Bi³⁺, HTeO ₂ ⁺ , and their mixtures, but let the reduction processes of Bi³⁺, HTeO ₂ ⁺ , and their mixtures become easier. The results reveal that the presence of MWNTs can promote electrodeposition of Bi _x Te _y compound.     

Simulation of low-temperature arsenic diffusion from a heavily doped silicon layer

Low-temperature (500–800°C) diffusion of As from a heavily doped Si layer was simulated on the basis of a dual pair mechanism. The anomalously high diffusion rate is attributed to excess self-interstitials accumulated in the layer during the preceding high-temperature diffusion stage. The shift of the concentration profile in the region of intermediate values of concentrations is caused by the presence of a maximum in the concentration dependence of the diffusivity. This shift is attributed to the considerable role that negatively charged self-interstitials play in the arsenic diffusion process (f _I ^? ≈0.4).     

Crystal damage and the properties of implanted p-n junctions in silicon

The influence of crystal damage on the properties of implanted p-n junctions has been studied by variation of the amount of initial damage, variation of the recovery process, and variation of the residual damage. This was done by carrying out implantations at - 196, 25 and 700°C with 10¹⁵ B⁺/cm² at an energy of 50 keV, and at 25°C with 10¹⁵ BF₂⁺ at an energy of 250 keV and 10¹⁵ Ga⁺/cm² at an energy of 70 keV. Substrate orientations of both 〈111〉 and 〈100〉 were used, and annealing was done in a temperature range between 400 and 1100°C. Gettered as well as non-gettered slices were used for 〈111〉 oriented substrates. The diode properties were analyzed with the aid of Shockley-Read-Hall recombination statistics. Depending upon crystal history and processing, different traps are found to dominate the reverse current. Traps caused by the gettering of contamination as well as those caused by the damage itself play a role. The number of traps is found to be smaller than 10¹²/cm³ for well annealed diodes, resulting in a reverse current density of 0.2 nA/cm² at 1 V reverse bias.     

Epitaxial growth of (11\bar 20) ZnO on (01\bar 12) Al2O3 by metalorganic chemical vapor deposition2) Al2O3 by metalorganic chemical vapor deposition

There has been increased interest in high quality ZnO films for use in a diverse range of applications such as in high frequency surface acoustic wave filters, buffer layers for GaN growth, transparent and conductive electrodes, and solid state lasers. In the present paper, ZnO films were epitaxially grown on R-plane sapphire substrates by metalorganic chemical vapor deposition at temperatures in the range 350–450°C. X-ray diffraction and electron microscopy results indicate that the ZnO films are epitaxially grown on ( $01\bar 12$ ) Al₂O₃ surface with the ( $11\bar 20$ ) plane parallel to the surface. Cross-sectional high resolution-transmission electron microscopy imaging of the as-grown film shows that the interface is semi-coherent and atomically sharp, with misfit dislocations relieving the misfit strain between ZnO and sapphire. In order to check the thermal stability of the as-grown ZnO films, annealing in an O₂+N₂ ambience at 850°C for 30 min was performed. The annealed films showed improved crystallinity. At the same time, limited reaction between ZnO and sapphire occurred, resulting in the formation of a 15–20 nm thick spinel layer at the interface.     

I–V characteristics and the spectrum width during electron tunneling through nanosandwiches W-WO2-(Au 147 ? )-Al2O3-Al and Nd-Nd2O3-(Au 55 ? )-Nd2O3-Nd. Part I: Quantum-chemical calculation of energies of orbitals for anions of nanoclusters Au55 and Au147

This work is devoted to the investigation of electron tunneling through ??magical?? nanoclusters Au₅₅ and Au₁₄₇. Using the quantum-chemical calculation, it is shown that the energy of the highest occupied molecular orbital (HOMO) level is ${E_{HOMOAu5{5^ - }}} = - 3.2eV$ and E _HOMOAu147 = ?4.4 eV, respectively. It is established that the difference between energy E _LUMO ^? of the lowest unoccupied level LUMO and energy E _LUMO ^? for the anions of clusters (Au ₅₅ ^? and Au ₁₄₇ ^? ) is 0.86 and 0.24 eV, respectively. Based on the results of the calculations, it is assumed that nanosandwiches W-WO₂-(Au ₁₄₇ ^? )-Al₂O₃-Al can be promising structures for implementation of metal nanodiodes based on them, while nanosandwiches Nd-Nd₂O₃-(Au ₅₅ ^? )-Nd₂O₃-Nd can be promising for implementation of energy filters not producing hot electrons and allowing the fabrication of the ring Aharonov-Bohm interferometers based on normal metals at liquid-helium temperatures.     

Quantitative calibration and germanium SIMS depth profiling in Ge x Si1 − x /Si heterostructures

Methods for minimizing nonlinear matrix effects in the quantitative determination of germanium concentrations in Ge _x Si_{1 ? x} layers by secondary ion mass spectrometry are discussed. The analysis conditions with positive SiCs⁺, GeCs⁺ and negative Ge^?, Si^? secondary ions produced during sputtering by cesium ions are used in the TOF.SIMS-5 setup with a time-of-flight mass analyzer. In contrast to published works for TOF.SIMS setups, the linear dependence of the ion-concentration ratio Ge^?/Si^? on x/(1 ? x) is shown. Two new linear calibrations for the germanium concentration as a function of the cluster Ge ₂ ^? secondary ion yield are proposed. The calibration factors are determined for all linear calibrations at various energies of sputtered cesium ions and Bi⁺ and probe Bi ₃ ⁺ ions. It is shown for the first time that the best depth resolution among the possible conditions of quantitative germanium depth profiling in Ge _x Si_{1 ? x} /Si multilayer heterostructures is provided by the calibration mode using elemental Ge^? and Si^? negative secondary ions.     

Pit formations at AL/(100)Si contact windows

The kinetics of etch-pit formation at Al/(100)Si contact windows have been investigated by scanning electron microscopy. Pit growth, which is controlled by the diffusion of Si into the overlying Al, exhibits an activation energy of 0.8 eV. After a 450°C, H₂ anneal, the median pit size is related to the Al/Si contact areaw (μm2) by an equation of the form ∝(w)^-0.4. This relationship is valid for both induction-source and electron-beam evaporated Al, of 0.8 μm and 4.0 μm grain sizes, respectively.     

TE On o -to- mode transducer designmode transducer design

This paper gives a structure on the mode converter from TE _0n ^O mode of gyrotron output to the main mode of the circular groove guide. The design consists of two parts: the first part is to convert TE _0n ^O to TE ₀₁ ^O using an advanced periodic wall perturbation technology, the second part is to convert TE ₀₁ ^O to mode basing on the method of gradually changing the wave guide cross section. An example at 37.5Ghz is given. For the first part, the efficiency is 94.71%, the length is 1.868m. For the second part, the theoretic figure of reflectance coefficient vs. frequency is given.     

Investigation of vacancy-type complexes in GaN and AlN using positron annihilation

The momentum distribution of electron-positron pairs in GaN and AlN has been investigated for the first time by measuring the one-dimensional angular correlation of the annihilation radiation (1D-ACAR). The characteristic parameter of the electron density r _s ^′ (the radius of the sphere occupied by an electron) estimated from the experimental data differs noticeably from r _s calculated in terms of a standard model of noninteracting particles: r _s ^′ (AlN)≈1.28r _s, and r _s ^′ (GaN)≈1.66r _s, where r _s(AlN)≈1.6091 au, and r _s(GaN)≈1.6568 au. The chemical nature of atoms in the environment of the annihilating positron in AlN and GaN was identified from the electron-positron ionic radius of Al³⁺, Ga³⁺, and N⁵⁺ cores, which were determined from the characteristics of the high-momentum component of 1D-ACAR curves. The analysis was based on a comparison of the electron-positron ionic radii with those considered standard for Al and Ga metals and the related compounds GaP, GaAs, and GaSb. A conclusion is made that positron annihilation dominates in the regions of vacancy-type “nitrogen antisite”-“vacancy” complexes, [N _Ga ⁺ V _Ga] and [N _Al ⁺ V _Al], in GaN and AlN, respectively.     

On measuring the permittivity of “living” wood for microwave remote sensing

A procedure for measuring the permittivity of “living” wood is proposed. The permittivity of the trunk of a growing tree ε ₁ ^* has been measured by this procedure. Simultaneously, samples of wood of the same tree have been taken and their permittivities ε ₀ ^* determined under laboratory conditions. The obtained values has been compared, and considerable disagreement between measured ε ₁ ^* and ε ₀ ^* has been revealed. The study has been performed to model the reflection of microwaves from the forest.     

Comparison of p–n junction formed by BF2 and B implantation in silicon microstrip detector with low and high thermal budget: impact of fluorine on electrical characteristics

The influence of crystal damage on the electrical properties and the doping profile of the implanted p⁺–n junction has been studied at different annealing temperatures using process simulator TMA-SUPREM4. This was done by carrying out two different implantations; one with implantation dose of 10¹⁵ BF₂⁺ ions/cm² at an energy of 80 keV and other with 10¹⁵ B⁺ ions/cm² at 17.93 keV. Substrate orientation 1 1 1 of phosphorus-doped n-type Si wafers of resistivity 4 kΩ cm and tilt 7° was used, and isochronally annealing was performed in N₂ ambient for 180 min in temperature range between 400°C and 1350°C. The diode properties were analysed in terms of junction depth, sheet resistance. It has been found that for low thermal budget annealing, boron diffusion depth is insensitive to the variation in annealing temperature for BF₂⁺-implanted devices, whereas, boron diffusion depth increases continuously for B⁺-implanted devices. In BF₂⁺-implanted devices, fluorine diffusion improves the breakdown voltage of the silicon microstrip detector for annealing temperature upto 900°C.For high thermal budget annealing, it has been shown that the electrical characteristics of BF₂⁺-implanted devices is similar to that obtained in B⁺-implanted devices.