Deep level transient spectroscopy (DLTS) study of defects introduced in antimony doped Ge by 2 MeV proton irradiation

Deep level transient spectroscopy (DLTS) and Laplace-DLTS have been used to investigate the defects created in Sb doped Ge after irradiation with 2 MeV protons having a fluence of 1×10¹³ protons/cm². The results show that proton irradiation resulted in primary hole traps at E_V +0.15 and E_V +0.30 eV and electron traps at E_C ?0.38, E_C ?0.32, E_C ?0.31, E_C ?0.22, E_C ?0.20, E_C ?0.17, E_C ?0.15 and E_C ?0.04 eV. Defects observed in this study are compared with those introduced in similar samples after MeV electron irradiation reported earlier. E_C ?0.31, E_C ?0.17 and E_C ?0.04, and E_V +0.15 eV were not observed previously in similar samples after high energy irradiation. Results from this study suggest that although similar defects are introduced by electron and proton irradiation, traps introduced by the latter are dose dependent.     

Characterization of defects introduced in Sb doped Ge by 3 keV Ar sputtering using deep level transient spectroscopy (DLTS) and Laplace-DLTS (LDLTS)

We have used deep level transient spectroscopy (DLTS), and Laplace-DLTS to investigate the defects created in antimony doped germanium (Ge) by sputtering with 3 keV Ar ions. Hole traps at E_V+0.09 eV and E_V+0.31 eV and an electron trap at E_C−0.38 eV (E-center) were observed soon after the sputtering process. Room temperature annealing of the irradiated samples over a period of a month revealed a hole trap at E_V+0.26 eV. Above room temperature annealing studies revealed new hole traps at E_V+0.27 eV, E_V+0.30 eV and E_V+0.40 eV.     

Electrical characterization of deep levels in n-type GaAs after hydrogen plasma treatment

Deep level transient spectroscopy (DLTS) and Laplace-DLTS (L-DLTS) have been used to investigate defects in an n-type GaAs before and after exposure to a dc hydrogen plasma (hydrogenation). DLTS revealed the presence of three prominent electron traps in the material in the temperature range 20-300 K. However, L-DLTS with its higher resolution enabled the splitting of two narrowly spaced emission rates. Consequently four electron traps at, E_C—0.33 eV, E_C—0.36 eV, E_C—0.38 eV and E_C—0.56 eV were observed in the control sample. Following hydrogenation, all these traps were passivated with a new complex (presumably the M3), emerging at E_C—0.58 eV. Isochronal annealing of the passivated material between 50 and 300 °C, revealed the emergence of a secondary defect, not previously observed, at E_C—0.37 eV. Finally, the effect of hydrogen passivation is completely reversed upon annealing at 300 °C, as all the defects originally observed in the reference sample were recovered.     

Electronic properties of dislocations introduced mechanically at room temperature on a single crystal silicon surface

This paper focuses on the effects of temperature and environment on the electronic properties of dislocations in n-type single crystal silicon near the surface. Deep level transient spectroscopy (DLTS) analyses were carried out with Schottky electrodes and p⁺–n junctions. The trap level, originally found at E_C−0.50 eV (as commonly reported), shifted to a shallower level at E_C−0.23 eV after a heat treatment at 350 K in an inert environment. The same heat treatment in lab air, however, did not cause any shift. The trap level shifted by the heat treatment in an inert environment was found to revert back to the original level when the specimens were exposed to lab air again. Therefore, the intrinsic trap level is expected to occur at E_C−0.23 eV and shift sensitively with gas adsorption in air.     

Reinvestigation of microwave spectrum, molecular structure, dipole moment, and theoretical calculation of s-trans (E)- and s-trans (Z)-acrylaldehyde oxime

The spectroscopic constants of s-trans (E)-acrylaldehyde oxime of normal, CH₂CHCHNOH, and deuterated, CH₂CHCHNOD, species were refined by adding a-type R-branch transitions observed in the frequency range of 34-40 GHz in the ground vibrational state. For s-trans (Z) form, the spectroscopic constants of normal species were refined by refitting the reported frequencies with four b-type Q-branch transitions and those of deuterated species were determined by the least-squares fitting of the observed a-type R-branch transitions in the ground vibrational state. The spectroscopic constants of two isomers of normal species were also determined in the vibrationally excited states. The inertial defects (ΔI=I_c−I_a−I_b) of normal and deuterated species were determined to be −0.042(24) and −0.064(17) u Å² for s-trans (E)-1 form, and −0.0536(8) and −0.063(11) u Å² for s-trans (Z)-1 form, respectively. From the r_s coordinates of the hydroxyl hydrogen atom determined for s-trans (Z)-1 form, its OH bond was concluded to be at the trans position with respect to the CN double bond. The dipole moments of deuterated species of s-trans (E)-1 form and those of normal and deuterated species of s-trans (Z)-1 form were determined. The structural parameters of r(C₂C₃), ∠C₁C₂C₃, ∠C₂C₃N, and ∠C₃NO for s-trans (E)-1 and s-trans (Z)-1 forms were adjusted separately using to their rotational constants observed. It was found that the bond angle of ∠C₂C₃N in s-trans (Z)-1 form are much wider than that in s-trans (E)-1 form by about 10°. The difference between the observed and calculated (using MP2/6-311++G (d,p) level) rotational constants of s-trans (Z)-1 form was larger than that of s-trans (E)-1 form.     

Deep levels in low‐energy electron‐irradiated 4H‐SiC

Deep levels introduced by low‐energy (200 keV) electron irradiation in n‐type 4H‐SiC epitaxial layers grown by chemical vapour deposition were studied by deep level transient spectroscopy (DLTS) and photoexcitation electron paramagnetic resonance (photo‐EPR). After irradiation, several DLTS levels, EH1, EH3, Z_1/2, EH5 and EH6/7, often reported in irradiated 4H‐SiC, were observed. In irradiated freestanding films from the same wafer, the EPR signals of the carbon vacancy in the positive and negative charge states, V_C⁺ and V_C^‐, respectively, can be observed simultaneously under illumination with light of certain photon energies. Comparing the ionization energies obtained from DLTS and photo‐EPR, we suggest that the EH6/7 (at ～E_C – 1.6 eV) and EH5 (at ～E_C – 1.0 eV) electron traps may be related to the single donor (+ | 0) and the double acceptor (1– | 2–) level of V_C, respectively. Judging from the relative intensity of the DLTS signals, the EH6/7 level may also be contributed to by other unidentified defects. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical characterization of rare-earth implanted GaN

Deep-level transient spectroscopy (DLTS) measurements were used to characterize the electrical properties of MOCVD grown, europium- (Eu) and xenon- (Xe) implanted GaN films on sapphire substrates. Implantation energy was 80 keV with a fluence of 1×10¹⁴ cm⁻² along a channeled crystallographic direction. Defect levels were observed at E_C−0.19 eV for both Eu- and Xe-implantation which were predicted to be a rare-earth related donor level by theoretical calculations. Other defect levels are observed with energy levels located at 0.22, 0.68, 0.49, 0.60, 0.77 eV and 0.48, 0.64, 0.45, 0.72 eV below the conduction band for Eu and Xe implantation, respectively. Some of these levels have similar defect signatures and can be related to other implantation related defects introduced in erbium, praseodymium and helium implantations.     

Study of E3 trap annealing in GaAs by DDLTS technique

Double correlation deep level transient spectroscopy (DDLTS) has been used to determine the profile of the electron trap E3 (E_C?0.33 eV) introduced in n-type GaAs after proton irradiation at 300 K and annealing at 190°C. We show that E3 anneals without long range migration by close pair recombination mechanism.     

The effect of gamma irradiation on electrical and dielectric properties of Al-TiW-Pd2Si/n-Si Schottky diode at room temperature

The effects of ⁶⁰Co (γ-ray) irradiation on the electrical and dielectric properties of Al-TiW-Pd₂Si/n-Si Schottky diodes (SDs) have been investigated by using capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements at room temperature and 500 KHz. The corrected capacitance and conductance values were obtained by eliminating the effect of series resistance (R_s) on the measured capacitance (C_m) and conductance (G_m) values. The high-low frequency capacitance (CHF-CLF) method given in [12] as N_ss = (1/qA) [((1/C_LF) − (1/C_ox))⁻¹ −  ((1/C_HF) − (1/C_ox))⁻¹] was successfully adapted to the before-after irradiation capacitance given in this report as N_ss = (1/qA) [((1/C_bef) − (1/C_ox))⁻¹ − ((1/C_after) − (1/C_ox))⁻¹] for the analyzing the density of interface states. The N_ss-V plots give a distinct peak corresponding to localized interface states regions at metal and semiconductor interface. The experimental values of the ac electrical conductivity (σ_ac), the real (M′) and imaginary (M″) parts of the electrical modulus were found to be strong functions of radiation and applied bias voltage, especially in the depletion and accumulation regions. The changes in the dielectric properties in the depletion and accumulation regions stem especially from the restructuring and reordering of the charges at interface states and surface polarization whereas those in the accumulation region are caused by series resistance effect.     

Electrical characterization of defects introduced in n-GaAs by alpha and beta irradiation from radionuclides

We investigated defect production in n-type GaAs with two different free-carrier densities (4×10¹⁴ and 1×10¹⁶/cm³) by using particles liberated from radionuclides. ⁹⁰Sr and ²⁴¹Am were employed as beta and alpha sources, respectively. The results obtained for electron irradiation showed that the same set of primary defects can be produced by beta irradiation from the Sr source as by electrons produced in an accelerator. Similarly, the defects produced by alpha irradiation from the Am source closely resemble those introduced by alpha irradiation in a Van de Graaff accelerator. It was found that the relative concentrations of the primary defects in electron-irradiated GaAs are different to those in alpha-particle irradiated GaAs. Further, for the first time, an alpha irradiation induced defect which seems to be related to the doping concentration was observed in the 10¹⁶/cm³ Si doped GaAs. It is concluded that the use of radionuclides is an inexpensive and convenient method to introduce and to study radiation induced defects in semiconductors.     

Fabrication of nanostructured CuInS2 thin films by ion layer gas reaction method

CuInS₂ thin films were prepared by a two-stage ion layer gas reaction (ILGAR) process in which the Cu and In precursors were deposited on glass substrate by using a simple and low-cost dip coating technique and annealed in H₂S atmosphere at different temperatures. The influence of the annealing temperature (250-450 °C) on the particle size, crystal structure and optical properties of the CuInS₂ thin films was studied. Transmission electron microscopy revealed that the particle radii varied in the range 6-21 nm with annealing. XRD and SAED patterns indicated polycrystalline nature of the nanoparticles. The optical band gap (E_g) varied from 1.48 to 1.56 eV with variation of particle size. The variation of Urbach tail with temperature indicated higher density of the defects for the films annealed at lower temperature. From the Raman study, it was observed that the FWHM of the A₁ mode at ∼292 cm⁻¹ corresponding to the chalcopyrite phase of CuInS₂ decreased with increasing annealing temperature.     

高温电子辐照硅中缺陷的研究

本文对高温电子辐照硅中产生的缺陷进行了研究,发现缺陷的引进率随电子辐照温度的增加而增加,在达到极值温度T_m后,缺陷的引进率将随之而下降,T_m值与缺陷的退火激活能有关。E₃缺陷(E_c—0.36eV)浓度在高温电子辐照中显著增加,在330℃高温电子辐照时,E₃缺陷浓度为室温电子辐照的6倍。研究结果表明,E₃缺陷的可能结构为与多空位和氧有关的复合体。 关键词：     

Positron study of radiation embrittlement of steels used in water cooled, water moderated energy reactors

Positron annihilation spectroscopy (PAS) lifetime study was applied in the evaluation of the microstructure parameters and degradation processes of nuclear reactor pressure vessel (RPV) steel surveillance specimens. Study was oriented to the material investigation of Russian WWER-1000 steels (15Kh2MNFAA and 12Kh2N2MAA) with higher Ni content (1.26 wt.% in base metal and 1.7 wt.% in weld). For comparison, the WWER-440 weld metal (Sv10KhMFT) without Ni was measured too. Specimens were studied in as received stage, after irradiation in LVR-15 experimental reactor to the neutron fluence F_{(E > 0.5 MeV)} = 4 × 10²³ m⁻² s⁻¹ and after annealing in vacuum at 475 °C/2 h. Post-irradiation thermal treatment and annealing of defects was well detected by different PAS techniques. It was observed that the sensitivity of PAS parameters to defined irradiation treatment decreases with Ni-content increase. Results confirm the hypothesis that Ni affects size (decrease) and distribution (more homogeneous) of the Cu- and P-rich clusters and M_xC_x carbides.     

Photoluminescence and electric spectroscopy of dislocation-induced electronic levels in semi-insulated CdTe and CdZnTe

We studied deformation-induced defects in semi-insulating CdTe and CdZnTe by infrared photoluminescence (PL), contact less photoconductivity and resistivity. Plastic deformation increased the concentrations of grown-in defects, namely, those of an important midgap level E_C−0.74 eV in CdTe and Cd_1−xZn_xTe (x<0.1), the materials of choice in today’s X-ray and gamma ray detector technology. We confirmed the direct correlation between Y-emission and the dislocation density in both compounds. The Y-band intensified near an indenter deformation or near a scribing line, but was barely visible in low-dislocation areas (etch pit density <2×10⁵ cm⁻²). Our results correlate with recent findings that dislocation-induced defects and their clusters degrade charge collection in radiation detectors. Photoluminescence of midgap levels can serve as a tool to identify areas of degraded performance in semi insulated CdTe and CdZnTe crystals for radiation detectors.     

Study of deep level defects in doped and semi-insulating n-6H-SiC epilayers grown by sublimation method

Deep level transient spectroscopy (DLTS) is employed to study deep level defects in n-6H-SiC (silicon carbide) epilayers grown by the sublimation method. To study the deep level defects in n-6H-SiC, we used as-grown, nitrogen doped and nitrogen-boron co-doped samples represented as ELS-1, ELS-11 and ELS-131 having net (N_D–N_A) ∼2.0×10¹² cm⁻³, 2×10¹⁶ cm⁻³ and 9×10¹⁵ cm³, respectively. The DLTS measurements performed on ELS-1 and ELS-11 samples revealed three electron trap defects (A, B and C) having activation energies E_c – 0.39 eV, E_c – 0.67 eV and E_c – 0.91 eV, respectively. While DLTS spectra due to sample ELS-131 displayed only A level. This observation indicates that levels B and C in ELS-131 are compensated by boron and/or nitrogen–boron complex. A comparison with the published data revealed A, B and C to be E₁/E₂, Z₁/Z₂ and R levels, respectively.     

Electronic and annealing properties of the E0.31 defect introduced during Ar plasma etching of germanium

Low energy (±80 eV) Ar plasma etching has been successfully used to etch several semiconductors, including GaAs, GaP, and InP. We have studied the only prominent defect, E_0.31, introduced in n-type Sb-doped Ge during this process by deep level transient spectroscopy (DLTS). The E_0.31 defect has an energy level at 0.31 eV below the conduction band and an apparent capture cross-section of 1.4×10⁻¹⁴ cm². The fact that no V-Sb defects and no interstitial-related defects were observed implies that the etch process did not introduce single vacancies or single interstitials. Instead it appears that higher order vacancy or interstitial clusters are introduced due to the large amount of energy deposited per unit length along the path of the Ar ions in the Ge. The E_0.31 defect may therefore be related to one of these defects. DLTS depth profiling revealed the E_0.31 concentration had a maximum (6×10¹³ cm⁻³) close to the Ge surface and then it decreased more or less exponentially into the Ge. Finally, annealing at 250 °C reduced the E_0.31 concentration to below the DLTS detection limit.     

A comparison of the M3/M4 metastable defect detected in hydrogen and ICP Ar plasma treated n-GaAs

Defects created by a dc hydrogen plasma have been compared to those observed in n-GaAs exposed to an inductively coupled (ICP) Ar plasma. The reference sample (in the case of H-plasma treated material) contained two prominent native deep level electron traps, possibly M4 and E_C−0.56 eV, which were both passivated by hydrogen. Plasma treatment also resulted in the formation of a defect observed at 0.58 eV (M3) below the conduction band. This defect transforms back into what is believed to be M4 when annealed at 350 K for 3 h under reverse bias. These two defects compare well with two similar defects observed in the Ar ICP treated samples also showing metastable behavior. Additionally, the electrical characterization of Schottky barrier diodes on n-GaAs, prior to and after hydrogen passivation shows that, depending on the plasma conditions, the plasma ions significantly damage the surface resulting in poor rectifying contacts. The damage is considerably reversed/repaired upon annealing between the room temperature and 573 K (300 °C).     

Inductively coupled plasma induced deep levels in epitaxial n-GaAs

The electronic properties of defects introduced by low energy inductively coupled Ar plasma etching of n-type (Si doped) GaAs were investigated by deep level transient spectroscopy (DLTS) and Laplace DLTS. Several prominent electron traps (E_c—0.046 eV, E_c—0.186 eV, E_c—0.314 eV. E_c—0.528 eV and E_c—0.605 eV) were detected. The metastable defect E_c—0.046 eV having a trap signature similar to E1 is observed for the first time. E_c—0.314 eV and E_c—0.605 eV are metastable and appear to be similar to the M3 and M4 defects present in dc H-plasma exposed GaAs.     

Effective, fast, and low temperature encapsulation of fullerene derivatives in single wall carbon nanotubes

High filling of single wall nanotubes (SWCNTs) with the typical exohedrally functionalized fullerene derivative of C₆₀N-methyl-3,4-fulleropyrrolidine C₆₀-C₃NH₇ is reported at the temperature of refluxing hexane. The new peapod material is characterized by STM (scanning tunneling microscopy), TEM (transmission electron microscopy) and Raman spectroscopy. Atomically resolved STM scans on SWCNT show no excessive defects or sidewall functionalization as a result of this treatment. The radial breathing mode (RBM) mode of SWCNT at 165 cm⁻¹ becomes weaker and shifted to 169 cm⁻¹ indicating filled nanotubes. TEM studies show bundles of SWCNT are highly filled with derivative C₆₀-C₃NH₇ and form the (C₆₀-C₃NH₇)_n peapods. Individual pyrrolidine-type functional groups attached to the fullerene cages are unambiguously visualized by a lower-dose observation.     

Energy distributions of atomic and molecular ions sputtered by C60 projectiles

In the process of investigating the interaction of fullerene projectiles with adsorbed organic layers, we measured the kinetic energy distributions (KEDs) of fragment and parent ions sputtered from an overlayer of polystyrene (PS) oligomers cast on silver under 15 keV C₆₀⁺ bombardment. These measurements have been conducted using our TRIFT™ spectrometer, recently equipped with the C₆₀⁺ source developed by Ionoptika, Ltd. For atomic ions, the intensity corresponding to the high energy tail decreases in the following order: C⁺(E^−0.4) > H⁺(E^−1.5) > Ag⁺(E^−3.5). In particular, the distribution of Ag⁺ is not broader than those of Ag₂⁺ and Ag₃⁺ clusters, in sharp contrast with 15 keV Ga⁺ bombardment. On the other hand, molecular ions (fragments and parent-like species) exhibit a significantly wider distribution using C₆₀⁺ instead of Ga⁺ as primary ions. For instance, the KED of Ag-cationized PS oligomers resembles that of Ag⁺ and Ag_n⁺ clusters. A specific feature of fullerene projectiles is that they induce the direct desorption of positively charged oligomers, without the need of a cationizing metal atom. The energy spectrum of these PS⁺ ions is significantly narrower then that of Ag-cationized oligomers. For characteristic fragments of PS, such as C₇H₇⁺ and C₁₅H₁₃⁺ and polycyclic fragments, such as C₉H₇⁺ and C₁₄H₁₀⁺, the high energy decay is steep (E⁻⁴ − E⁻⁸). In addition, reorganized ions generally show more pronounced high energy tails than characteristic ions, similar to the case of monoatomic ion bombardment. This observation is consistent with the higher excitation energy needed for their formation. Finally, the fraction of hydrocarbon ions formed in the gas phase via unimolecular dissociation of larger species is slightly larger with gallium than with fullerene projectiles.