H-ion Irradiation-induced Annealing in He-ion Implanted 4H-SiC

Radiation-induced defect annealing in He~+ ion-implanted 4 H-SiC via H~+ ion irradiation is investigated by Raman spectroscopy. There are 4 H-SiC wafers irradiated with 230 keV He~+ ions with fluences ranging from 5.0×10~(15) cm~(-2)to 2.0×10~(16) cm~(-2) at room temperature. The post-implantation samples are irradiated by 260 keV H~+ ions at a fluence of 5.0×10~(15) cm~(-2) at room temperature. The intensities of Raman lines decrease after He implantation,while they increase after H irradiation. The experimental results present that the magnitude of Raman line increment is related to the concentration of pre-existing defects formed by He implantation. A strong new peak located near 966 cm~(-1), which is assigned to 3 C-SiC LO(Γ) phonon, is found in the He-implanted sample with a fluence of 5.0×10~(15) cm~(-2) followed by H irradiation. However, for the He-implanted sample with a fluence of2.0×10~(16) cm~(-2) followed by H irradiation, no 3 C-SiC phonon vibrations are found. The detailed reason for H irradiation-induced phase transformation in the He-implanted 4 H-SiC is discussed.     

Aligned Elongation of Ag Nanoparticles Embedded in Silica Irradiated with High Energy Ni Ions

Metallic nanoparticle(NP) shapes have a significant influence on the property of composite embedded with metallic NPs. Swift heavy ion irradiation is an effective way to modify shapes of metallic NPs embedded in an amorphous matrix. We investigate the shape deformation of AgNPs with irradiation fluence, and 357 MeV Ni ions are used to irradiate the silica containing AgNPs, which are prepared by ion implantation and vacuum annealing. The UV-vis results show that the surface plasmon resonance(SPR) peak from AgNPs shifts from 400 to 377 nm. The SPR peak has a significant shift at fluence lower than 1 × 10~(14) ions/cm2 and shows less shift at fluence higher than 1 × 10~(14) ions/cm~2. The TEM results reveal that the shapes of AgNPs also show significant deformation at fluence lower than 1 × 10~(14) ions/cm~2 and show less deformation at fluence higher than1 × 10~(14) ions/cm~2. The blue shift of the SPR peak is considered to be the consequence of defect production and AgNP shape deformation. Based on the thermal spike model calculation, the temperature of the silica surrounding Ag particles first increases rapidly, then the region of AgNPs close to the interface of Ag/silica is gradually heated. Therefore, the driven force of AgNPs deformation is considered as the volume expansion of the first heated silica layer surrounding AgNPs.     

Investigation of low-temperature cathodoluminescence mechanism of Er-doped Ga N thick films by ion implantation

Er ions are implanted into the Ga N thick films grown by hydride vapor phase epitaxy. The implantation energy is 200 ke V and the implantation doses are 1×10~(13),1 × 10~(14),1 × 10~(15),and 5×10~(15) atom∕cm~2,respectively. The effects of the implantation dose and annealing temperature on the Ga N band-edge luminescence are investigated. The cathodoluminescence spectra from 82 to 323 K are measured for 1×10~(15) atom∕cm~2-implanted Ga N annealed at 1100°C. Luminescence peaks at 356,362,376,390,and 414 nm are observed on the 82 K cathodoluminescence spectrum. When the temperature is increased to 150 K,the intensities of the 356 and 414 nm peaks are nearly unchanged and the 362,376,and 390 nm peaks disappear. The intensity ratio of 538 nm(~2H_(11∕2)→ ~4I/_(15∕2)) and 559 nm(~4S_(3∕2)→ ~4I_(15∕2)) is increased with the increase in temperature. We try to shed light on the above interesting phenomena.     

Structural Distortion and Defects in Ti_3AlC_2 irradiated by Fe and He Ions

Ti_3AlC_2 samples are irradiated in advance by 3.5 MeV Fe-ion to the fluence of 1.0×10~(16) ion/cm~2,and then are implanted by 500 keV He-ion with the fluence of 1.0×10~(17) ion/cm~2 at room temperature.The irradiated samples are investigated by grazing incidence x-ray diffraction(GIXRD) and transmission electron microscopy(TEM).GIXRD results show serious structural distortion,but without amorphization in the irradiated samples.Fe-ion irradiation and He-ion implantation create much more serious structural distortion than single Fe-ion irradiation.TEM results reveal that there are a large number of defect clusters in the damage region,and dense spherical He bubbles appear in the He depositional region.It seems that the pre-damage does not influence the growth of He bubbles,but He-ion implantation influences the pre-created defect configurations.     

Design and simulation of AlN-based vertical Schottky barrier diodes

The key parameters of vertical AlN Schottky barrier diodes(SBDs) with variable drift layer thickness(DLT) and drift layer concentration(DLC) are investigated. The specific on-resistance(R_(on,sp)) decreased to 0.5 m? · cm~2 and the breakdown voltage(V_(BR)) decreased from 3.4 kV to 1.1 kV by changing the DLC from 10~(15) cm~(-3) to 3×10~(16) cm~(-3). The VBRincreases from 1.5 kV to 3.4 kV and the Ron,sp also increases to 12.64 m? · cm~2 by increasing DLT from 4-μm to 11-μm. The VBRenhancement results from the increase of depletion region extension. The Baliga's figure of merit(BFOM) of3.8 GW/cm~2 was obtained in the structure of 11-μm DLT and 10~(16) cm~(-3) DLC without FP. When DLT or DLC is variable,the consideration of the value of BFOM is essential. In this paper, we also present the vertical AlN SBD with a field plate(FP), which decreases the crowding of electric field in electrode edge. All the key parameters were optimized by simulating based on Silvaco-ATLAS.     

Effects of annealing temperature on shape transformation and optical properties of germanium quantum dots

The influences of thermal annealing on the structural and optical features of radio frequency(rf) magnetron sputtered self-assembled Ge quantum dots(QDs) on Si(100) are investigated.Preferentially oriented structures of Ge along the(220) and(111) directions together with peak shift and reduced strain(4.9%to 2.7%) due to post-annealing at 650 ℃ are discerned from x-ray differaction(XRD) measurement.Atomic force microscopy(AFM) images for both pre-annealed and post-annealed(650 ℃) samples reveal pyramidal-shaped QDs(density ~ 0.26×10~(11) cm~(-2)) and dome-shape morphologies with relatively high density ~ 0.92×10~(11) cm~(-2),respectively.This shape transformation is attributed to the mechanism of inter-diffusion of Si in Ge interfacial intermixing and strain non-uniformity.The annealing temperature assisted QDs structural evolution is explained using the theory of nucleation and growth kinetics where free energy minimization plays a pivotal role.The observed red-shift ~ 0.05 eV in addition to the narrowing of the photoluminescence peaks results from thermal annealing,and is related to the effect of quantum confinement.Furthermore,the appearance of a blue-violet emission peak is ascribed to the recombination of the localized electrons in the Ge-QDs/SiO_2 or GeO_x and holes in the ground state of Ge dots.Raman spectra of both samples exhibit an intense Ge-Ge optical phonon mode which shifts towards higher frequency compared with those of the bulk counterpart.An experimental Raman profile is fitted to the models of phonon confinement and size distribution combined with phonon confinement to estimate the mean dot sizes.A correlation between thermal annealing and modifications of the structural and optical behavior of Ge QDs is established.Tunable growth of Ge QDs with superior properties suitable for optoelectronic applications is demonstrated.     

Evaluation of threading dislocation density of strained Ge epitaxial layer by high resolution x-ray diffraction

The analysis of threading dislocation density(TDD)in Ge-on-Si layer is critical for developing lasers,light emitting diodes(LEDs),photodetectors(PDs),modulators,waveguides,metal oxide semiconductor field effect transistors(MOS-FETs),and also the integration of Si-based monolithic photonics.The TDD of Ge epitaxial layer is analyzed by etching or transmission electron microscope(TEM).However,high-resolution x-ray diffraction(HR-XRD)rocking curve provides an optional method to analyze the TDD in Ge layer.The theory model of TDD measurement from rocking curves was first used in zinc-blende semiconductors.In this paper,this method is extended to the case of strained Ge-on-Si layers.The HR-XRD 2θ/ωscan is measured and Ge(004)single crystal rocking curve is utilized to calculate the TDD in strained Ge epitaxial layer.The rocking curve full width at half maximum(FWHM)broadening by incident beam divergence of the instrument,crystal size,and curvature of the crystal specimen is subtracted.The TDDs of samples A and B are calculated to be 1.41×10~8cm~(-2)and 6.47×10~8cm~(-2),respectively.In addition,we believe the TDDs calculated by this method to be the averaged dislocation density in the Ge epitaxial layer.     

Improved Semipolar(11(2|-)2) GaN Quality Grown on m-Plane Sapphire Substrates by Metal Organic Chemical Vapor Deposition Using Self-Organized SiN_x Interlayer

The effect of a self-organized SiN_x interlayer on the defect density of(11(2|-)2) semipolar GaN grown on m-plane sapphire is studied by transmission electron microscopy,atomic force microscopy and high resolution x-ray diffraction.The SiN_x interlayer reduces the c-type dislocation density from 2.5 × 10~(10) cm~(-2) to 5 × 10~8 cm~(-2).The SiN_x interlayer produces regions that are free from basal plane stacking faults(BSFs) and dislocations.The overall BSF density is reduced from 2.1 × 10~5 cm~(-1) to 1.3 × 10~4 cm~(-1).The large dislocations and BSF reduction in semipolar(11(2|-)2) GaN with the SiN_x interlayer result from two primary mechanisms.The first mechanism is the direct dislocation blocking by the SiN_x interlayer,and the second mechanism is associated with the unique structure character of(11(2|-)2) semipolar GaN.     

Study on irradiation-induced defects in GaAs/AlGaAs core–shell nanowires via photoluminescence technique

To gain a physical insight into the radiation effect on nanowires(NWs), the time resolved photoluminescence(TRPL)technique is used to investigate the carrier dynamic behaviors in GaAs/AlGaAs core–shell NWs before and after 1-MeV proton irradiation with fluences ranging from 1.0 × 10~(12) cm~(-2) to 3.0 × 10~(13) cm~(-2). It is found that the degradations of spectral peak intensity and minority carrier lifetime show similar trends against irradiation fluence, which is closely related to the displacement defects induced by irradiation. We also find that the proton irradiation-induced defects behave as Shockley–Read–Hall(SRH) recombination center trapping free carriers. Finally, the defect concentration could be estimated through measuring the minority carrier lifetime.     

Proton radiation effect on GaAs/AlGaAs core–shell ensemble nanowires photo-detector

We demonstrate that the GaAs/AlGaAs nanowires(NWs) ensemble is fabricated into photo-detectors. Current–voltage(I–V) characteristics are measured on Ga As/Al Ga As core–shell ensemble NW photo-detectors at room-temperature before and after 1-MeV proton irradiation with fluences from 1.0 × 10~(13) cm~(-2) to 5.0 × 10~(14) cm~(-2). The degradation of photocurrent suggests that the point defects induced by proton radiation could cause both carrier lifetime and carrier mobility to decrease synchronously. Comparing with a GaAs quantum well, the degradations of light and dark current for the irradiated NWs photo-detector indicate that NWs material is a preferable potential candidate for space applications.     

Terahertz transmission properties of Cr ion implantation glass

<正>Cr ion implantations in glass with the different doses of D=1.493×10~(17) and 4.976×10~(17) ion/cm~2 are obtained by metal vapor vacuum arc(MEVVA).The effects of the different Cr ion implanted doses on terahertz(THz) transmission property are analyzed from THz time-domain spectroscopy.The results show that the more the Cr ion implanted dose in the micro-area implantation glasses,the larger the THz transmission except the larger absorption at 0.24 THz.This is an effect attributed to the coupling of plasmas on both the implantation and the implantation affected zones of the Cr ion implantation glass.     

The structural,magnetic,and optical properties of ZnO (0001) wafers implanted with Co ions

The ion implantation technique was employed to study the structural,magnetic,and optical properties of Co-doped crystalline ZnO.The photoluminescence measurements indicated that the center of green emission of implanted samples shifts gradually from 510 nm to 531 nm with an increase of Co concentrations.All implanted samples are ferromagnetic at room temperature with a saturation magnetization from 6.89×10-5 to 2.31×10-4 emu.The possible mechanisms on the observed ferromagnetism were discussed.     

Crystallization of amorphous silicon beyond the crystallized polycrystalline silicon region induced by metal nickel

Crystallization of amorphous silicon(a-Si) which starts from the middle of the a-Si region separating two adjacent metal-induced crystallization(MIC) polycrystalline silicon(poly-Si) regions is observed. The crystallization is found to be related to the distance between the neighboring nickel-introducing MIC windows. Trace nickel that diffuses from the MIC window into the a-Si matrix during the MIC heat-treatment is experimentally discovered, which is responsible for the crystallization of the a-Si beyond the MIC front. A minimum diffusion coefficient of 1.84×10~(-9)cm~2/s at 550℃ is estimated for the trace nickel diffusion in a-Si.     

Novel infrared differential optical absorption spectroscopy remote sensing system to measure carbon dioxide emission

A CO_2 infrared remote sensing system based on the algorithm of weighting function modified differential optical absorption spectroscopy(WFM-DOAS) is developed for measuring CO_2 emissions from pollution sources. The system is composed of a spectrometer with band from 900 nm to 1700 nm, a telescope with a field of view of 1.12?, a silica optical fiber, an automatic position adjuster, and the data acquisition and processing module. The performance is discussed,including the electronic noise of the charge-coupled device(CCD), the spectral shift, and detection limits. The resolution of the spectrometer is 0.4 nm, the detection limit is 8.5 × 10~(20)molecules·cm~(-2), and the relative retrieval error is 1.5%.On May 26, 2018, a field experiment was performed to measure CO_2 emissions from the Feng-tai power plant, and a twodimensional distribution of CO_2 from the plume was obtained. The retrieved differential slant column densities(dSCDs)of CO_2 are around 2 × 10~(21) molecules·cm~(-2) in the unpolluted areas, 5.5 × 10~(21)molecules·cm~(-2) in the plume locations most strongly affected by local CO_2 emissions, and the fitting error is less than 2 × 10~(20)molecules·cm~(-2), which proves that the infrared remote sensing system has the characteristics of fast response and high precision, suitable for measuring CO_2 emission from the sources.     

Signal photon flux generated by high-frequency relic gravitational waves

The power spectrum of primordial tensor perturbations Vt increases rapidly in the high frequency region if the spectral index n_t 0.It is shown that the amplitude of relic gravitational waves ht(5×10~9 Hz) varies from 10~(-36)to 10~(-25) while n_t varies from-6.25×10~(-3) to 0.87.A high frequency gravitational wave detector proposed by F.-Y.Li detects gravitational waves through observing the perturbed photon flux that is generated by interaction between relic gravitational waves and electromagnetic field.It is shown that the perturbative photon flux N_x~1(5×10~9 Hz)varies from 1.40×10~(-4) s~(-1) to 2.85×10~7 s~(-1) while n_t varies from-6.25×10~(-3) to 0.87.Correspondingly,the ratio of the transverse perturbative photon flux N_x~1 to the background photon flux varies from 10~(-28) to 10~(-16).     

Evaluation of both composition and strain distributions in InGaN epitaxial film using x-ray diffraction techniques

The composition and stain distributions in the InGaN epitaxial films are jointly measured by employing various x-ray diffraction (XRD) techniques, including out-of-plane XRD at special planes, in-plane grazing incidence XRD, and reciprocal space mapping (RSM). It is confirmed that the measurement of (204) reflection allows a rapid access to estimate the composition without considering the influence of biaxial strain. The two-dimensional RSM checks composition and degree of strain relaxation jointly, revealing an inhomogeneous strain distribution profile along the growth direction. As the film thickness increases from 100 nm to 450 nm, the strain status of InGaN films gradually transfers from almost fully strained to fully relaxed state and then more In atoms incorporate into the film, while the near-interface region of InGaN films remains pseudomorphic to GaN.     

The cross sections and their temperature dependence of collisional energy transfer from high vibrationally excited ethylene molecules to electronic ground state Rubidium atoms

The cross sections and their temperature dependence of collisional energy transfer from the high vibrationally excited C_2H_4 to the electronic ground sate of Rb (V-E) have been studied by the method of IR laser pump combined with fluorescence probe. The fluorescence of rudidium atoms due to V-E energy transfer was detected. The measured rate constants of this V-E energy transfer is about 10~(-10)cm~2molec~(-1)s~(-1) and the corresponding cross section varies from 60 (?)~2 to 90 (?)~2. The cross sections decrease with increasing temperature over the temperature range of 393-683 K.     

Polarization effect on critical power and luminescence in an air filament

We demonstrate that the filamentation process is strongly influenced by the polarization state of the driver laser. When the laser polarization changes from linear to circular, the critical power for the self-focusing of a Ti:Sapphire laser(800 nm, 40 fs) in air increases from about 9.6±1.0 to 14.9±1.5 GW, while the second nonlinear refractive index n_2 of air decreases from 9.9 × 10~(-20) to 6.4 × 10~(-20) cm~2∕W. We also demonstrate that the luminescence from the neutral nitrogen molecules at 337 nm is dependent on both the laser intensity and plasma density inside the filament.     

Hydrogen isotopic replacement and microstructure evolution in zirconium deuteride implanted by 150 keV protons

Zirconium tritiated(ZrT_x) is an alternative target material for deuteron–triton(D-T) reaction neutron generator. The isotopic replacement and microstructure evolution induced by hydrogen isotope implantation could significantly affect the performance of the target film. In this work, the zirconium deuteride film deposited on Mo/Si substrate was implanted by 150 ke V protons with fluence from 1×10~(16) to 1×10~(18) protons/cm~2. After implantation, the depth profiles of retained hydrogen(H) and deuterium(D) in these target films were analyzed by elastic recoil detection analysis(ERDA), and time of flight-secondary ion mass spectrometry(To F-SIMS). Additionally, the microstructure evolution was also observed by x-ray diffraction(XRD) and scanning electron microscope(SEM). The D concentration in the Zr Dx film decreased versus the proton implantation fluence. An analytical model was proposed to describe the hydrogen isotopic trapping and exchange as functions of incident protons fluence. Additionally, the XRD analysis revealed that no new phase was formed after proton implantation. Furthermore, circular flakings were observed on the ZrD_x surface from SEM images at fluence up to 1×10~(18) protons/cm~2, and this surface morphology was considered to associate with the hydrogen atoms congregation in Mo/Si boundary.     

Copper Ion Beam Irradiation-Induced Effects on Structural,Morphological and Optical Properties of Tin Dioxide Nanowires

The 0.8 MeV copper(Cu) ion beam irradiation-induced effects on structural,morphological and optical properties of tin dioxide nanowires(SnO_2 NWs) are investigated.The samples are irradiated at three different doses5 × 10~(12) ions/cm~2,1 × 10~(13) ions/cm~2 and 5 × 10~(13) ions/cm~2 at room temperature.The XRD analysis shows that the tetragonal phase of SnO_2 NWs remains stable after Cu ion irradiation,but with increasing irradiation dose level the crystal size increases due to ion beam induced coalescence of NWs.The FTIR spectra of pristine SnO_2NWs exhibit the chemical composition of SnO_2 while the Cu-O bond is also observed in the FTIR spectra after Cu ion beam irradiation.The presence of Cu impurity in SnO_2 is further confirmed by calculating the stopping range of Cu ions by using TRM/SRIM code.Optical properties of SnO_2 NWs are studied before and after Cu ion irradiation.Band gap analysis reveals that the band gap of irradiated samples is found to decrease compared with the pristine sample.Therefore,ion beam irradiation is a promising technology for nanoengineering and band gap tailoring.