Restructuring of defects in silicon by action of subthreshold-energy electrons

The influence of irradiation of silicon p⁺-n diodes by 15 to 30 keV electrons on the deep level transient spectroscopy (DLTS) spectra of the diodes was studied. It was discovered that irradiation leads to the transformation of the DLTS spectra in crystals containing defect clusters. A comparison of the depth of the p-n junction in the crystal with the penetration depth of the electrons indicates that the detected rearrangement of defects is due to secondary electrons diffusing into the p-n junction. A recombination-stimulated mechanism of defect rearrangement is proposed. In crystals containing only point defects, transformation of the DLTS spectra is not observed.Deceased.Translated from Izvestia Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 32–37, June, 1990.     

Deep level transient spectroscopy on radioactive impurities: Demonstration for Si:111In*

A defect specific analysis technique is introduced that combines the high concentration sensitivity of deep level transient spectroscopy (DLTS) with the radioactive transmutation of probe atoms; this technique results in the chemical identification of particular atoms which participate in the observed defect centres. The method is demonstrated for n- and p-type silicon samples, which are implanted with radioactive ¹¹¹In* ions. The activity of the indium ions decreases with half-life T _1/2 of 2.83 d by a decay into stable cadmium ions. A series of Cd-related levels whose concentrations increase exponentially with the decay time of ¹¹¹In* are identified in the DLTS spectra. Cd-diffused silicon samples are investigated for comparison; these samples reveal similar DLTS spectra. The analysis method described can be extended to all semiconductors and to a variety of radioactive probe atoms.Dedicated to H.-J. Queisser on the occasion of his 60th birthday     

Si基GaN外延层光致发光光谱与二次离子质谱的研究

报道了在Si基上用简便的真空反应法制备出GaN外延层．光致发光光谱测试结果表明不同的生长温度和退火工艺会对GaN外延层的发光特性产生影响,在1050℃下生长的GaN外延层的发光强度高于其他温度下生长的发光强度,退火可以使GaN外延层的发光强度增强．二次离子质谱(SIMS)测试结果表明外延层中Ga和N分布均匀,在表面处Ga发生了偏聚,同时外延层中还存在Si,O等杂质,这使得外延层中背景电子浓度高达1.7×10¹⁸/cm³. SIMS测试结果还表明,在外延生长前采用 关键词：     

Influence of extended defects on gold diffusion in plastically deformed silicon

The effect of defects formed in dislocation trails behind dislocations on the gold diffusion has been investigated by the deep level transient spectroscopy (DLTS) and electron beam induced current (EBIC) methods. It is found that the gold concentration in the deformed samples is two orders of magnitude higher than that in the defect-free crystal. Estimations show that the concentration of electrically active gold obtained from the DLTS data is at least ten times higher than the value, which might be expected for the dislocations themselves. A strong increase in the recombination activity of dislocation trails after gold diffusion is found from EBIC measurements, which probably is related with gettering properties of defects formed in the dislocation trails.     

Structure,impurity composition,and photoluminescence of mechanically polished layers of single-crystal silicon

The introduction of optically active defects (such as atomic clusters, dislocations, precipitates) into a silicon single crystal using irradiation, plastic deformation, or heat treatment has been considered a possible approach to the design of silicon-based light-emitting structures in the near infrared region. Defects were introduced into silicon plates by traditional mechanical polishing. The changes in the defect structure and the impurity composition of damaged silicon layers during thermal annealing (TA) of a crystal were examined using transmission electronic microscopy and x-ray fluorescence. Optical properties of the defects were studied at 77 K using photoluminescence (PL) in the near infrared region. It has been shown that the defects generated by mechanical polishing transform into dislocations and dislocation loops and that SiO₂ precipitates also form as a result of annealing at temperatures of 850 to 1000°C. Depending on the annealing temperature, either oxide precipitates or dislocations decorated by copper atoms, which are gettered from the crystal bulk, make the predominant contribution to PL spectra.     

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.     

Effect of surface modification by thermally oxidization and HF etching on UV photoluminescence emission of porous silicon

Photoluminescence of porous silicon (PS) is instable due perhaps to the nanostructure modification in air. The controllable structure modification processes on the as-prepared PS were conducted by thermal oxidization and/or HF etching. The PL spectra taken from thermally oxidized PS showed a stable photoluminescence emission of 355 nm. The photoluminescence emission taken from both of PS and oxidized porous silicon (OPS) samples etched with HF were instable, which can be reversibly recovered by the HF etching procedure. The mechanism of UV photoluminescence is discussed and attributed to the transformation of luminescence centers from oxygen deficient defects to the oxygen excess defects in the thermal oxidized PS sample and surface absorbed silanol groups on PS samples during the chemical etched procedure.     

Tellurium-related trap levels in silicon

Tellurium-related defects inn-type silicon have been analysed by deep level transient spectroscopy (DLTS). The tellurium doping of the samples was performed by ion implantation or during epitaxy. In all the samples, a level having a thermal activation energy around 0.37 eV is observed. This activation energy is found to be dependent on the electric field. Taking into account the Poole-Frenkel (FP) effect and a temperature dependence proportional toT ^?2 in the capture cross-section, a value ofE _A=0.41eV is obtained. A second Te-related level having an activation energy ofE _A=0.14eV without correction of the FP effect could only be measured in the implanted samples. The same concentration is observed for the two levels in the implanted samples thus indicating that both peaks in the DLTS spectra are caused by the identical Te-related defect.     

Nd photoluminescence study of Nd-doped Si-rich silica films obtained by reactive magnetron sputtering

Nd³⁺-doped silicon-rich silicon oxide (SRSO) thin films have been fabricated by reactive magnetron sputtering of a pure silica target topped with Nd₂O₃ chips. The concentration of Nd ions in the deposited layers is controlled by the number of Nd₂O₃ chips, whereas the incorporation of silicon excess is monitored by the hydrogen partial pressure, P_H2, introduced in the Ar plasma, owing to the ability of hydrogen to reduce the oxygen released by the sputtering of the silica target. Photoluminescence (PL) experiments were made at room temperature using a nonresonant excitation line from an Ar laser. The influences of Nd³⁺ content and P_H2 have been studied to optimize the Nd³⁺ emission. PL spectra reveal a two order of magnitude enhancement of the Nd³⁺ emission around both 0.9 and 1.1 μm, when Si nanoclusters (Si-nc) are formed in the same Nd³⁺-doped matrix. The dependence of the Nd³⁺ PL with P_H2 and Nd concentration is indicative of the occurrence of an efficient energy transfer from the Si-nc to the rare earth ions. The radiative lifetime is also deduced and commented in the light of Nd³⁺-Si-nc coupling.     

Electrical and optical analyses of Er-doped silicon grown by liquid-phase epitaxy

We have studied the deep levels present in Er-doped silicon epilayers grown by the liquid-phase epitaxy method by deep level transient spectroscopy (DLTS) and optical DLTS, in order to identify the majority and minority carrier traps and a possible correlation between these traps and the observed photoluminescence (PL) and cathodoluminescence (CL) spectra. Capacitance–voltage analyses have been performed to analyze uniformity and depth distribution of the existing traps and marked differences have been observed between the luminescent and non-luminescent materials.The PL and depth resolved CL revealed the presence of dislocation-related emission lines which can possibly be correlated to the broadened peaks observed in DLTS analyses of luminescent material.     

Electron irradiation-induced defects in lithium doped n-type silicon with different oxygen concentrations

Electron irradiation-induced defects and their annealing behaviour in lithium (Li) doped n-type silicon containing different oxygen concentrations have been studied with deep level transient spectroscopy (DLTS) in conjunction with the capacitance-voltage (C-V) method. Two Li-related defects E(0.17) and E(0.50) situated at, respectively, 0.17 and 0.50 eV below the conduction band minimum have been observed on different conditions. It has been shown that oxygen in silicon can restrain the interaction between Li and radiation-induced defects. Only when the concentration of Li is not far less than that of oxygen in silicon can lithium interact effectively with radiation-induced defects.     

Composition of oxygen precipitates in Czochralski silicon wafers investigated by STEM with EDX/EELS and FTIR spectroscopy

In this work, we investigated the stoichiometry of oxygen precipitates in Czochralski silicon wafers. The thickness dependence of the Cliff–Lorimer sensitivity factor for the silicon/oxygen system was determined and applied for the investigation of the stoichiometry of oxygen precipitates by EDX. The results show that both plate‐like oxygen precipitates and a transitional form between plate‐like and octahedral precipi‐ tates consist of SiO₂. This was confirmed by EELS low loss spectra where the typical spectrum for amorphous SiO₂ was observed. Moreover, the absorption band of plate‐like precipitates at 1227 cm^–1 was found in the low temperature FTIR spectrum. It was demonstrated that this band can only be simulated by the dielectric constants of amorphous SiO₂. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Blue photo- and electroluminescence of silicon dioxide layers ion-implanted with group IV elements

The microstructural, optical and electrical properties of Si-, Ge- and Sn-implanted silicon dioxide layers were investigated. It was found, that these layers exhibit strong photoluminescence (PL) around 2.7 eV (Si) and between 3 and 3.2 eV (Ge, Sn) at room temperature (RT), which is accompanied by an UV emission around 4.3 eV. This PL is compared with that of Ar-implanted silicon dioxide and that of Si- and Ge-rich oxide made by rf magnetron sputtering. Based on PL and PL excitation (PLE) spectra we tentatively interpret the blue–violet PL as due to a T₁→S₀ transition of the neutral oxygen vacancy typical for Si-rich SiO₂ and similar Ge- or Sn-related defects in Ge- and Sn-implanted silicon dioxide. The differences between Si, Ge and Sn will be explained by means of the heavy atom effect. For Ge-implanted silicon dioxide layers a strong electroluminescence (EL) well visible with the naked eye and with a power efficiency up to 5×10^-4 was achieved. The EL spectrum correlates very well with the PL one. Whereas the EL intensity shows a linear dependence on the injection current over three orders of magnitude, the shape of the EL spectrum remains unchanged. The I-V dependence exhibiting the typical behavior of Fowler–Nordheim tunneling shows an increase of the breakdown voltage and the tunnel current in comparison to the unimplanted material. Finally, the suitability of Ge-implanted silicon dioxide layers for optoelectronic applications is briefly discussed. Received: 9 March 2000 / Published online: 30 June 2000     

Controlling surface states and photoluminescence of porous silicon by low-energy-ion irradiation

Porous silicon (PS) was irradiated by three kinds of low-energy ions with different chemical activity, namely argon ions, nitrogen ions and oxygen ions. The chemical activity of ions has significant effect on the surface states and photoluminescence (PL) properties of PS, The photoluminescence quenching after argon ions and nitrogen ions irradiation is ascribed to the broken Si-Si bonds, while the PL recovery is attributed to the oxidation of Si-H back bonds. Oxygen ions irradiation leads to the formation of a SiO_x layer with oxygen defects and PS shows different PL evolution than PS irradiated by argon ions and nitrogen ions.     

Nanocrystal and interface defects related photoluminescence in silicon-rich Al2O3 films

In this study, silicon nanocrystal-rich Al₂O₃ film has been prepared by co-sputtering a silicon and alumina composite target and subsequent annealing in N₂ atmosphere. The microstructure of the film has been characterized by infrared (IR) absorption, Raman spectra and UV-absorption spectra. Typical nanocrystal and interface defects related photoluminescence with the photon energy of 1.54 (IR band) and 1.69 eV (R band) has been observed by PL spectrum analysis. A post-annealing process in oxygen atmosphere has been carried out to clarify the emission mechanism. Despite the red shift of the spectra, enhanced emission of the 1.69 eV band together with the weak emission phenomenon of the 1.54 eV band has been found after the post-annealing. The R band is discussed to originate from silicon nanocrystal interface defects. The IR band is concluded to be a coupling effect between electronic and vibrational emissions.     

Effect of the annealing environment on the optical properties of ZnO/GaAs grown by MOCVD

The optical properties of ZnO grown on (1 0 0) GaAs substrate using metalorganic chemical vapor deposition are investigated by photoluminescence (PL) spectroscopy. Postgrowth annealing in nitrogen and oxygen was performed for different times and temperatures in order to incorporate As from the substrate into the ZnO thin films. The PL spectra of the samples annealed in different ambients reveal that the effect of As diffusion into the ZnO thin films is more pronounced when the annealing is performed in oxygen at 550 °C. The 11 K PL spectra show the appearance of a transition at ∼3.35 eV after annealing in oxygen at 550 °C for 1 h. A further increase in the annealing temperature leads to the disappearance of this line, while for annealing times longer than 2 h at 550 °C, it is no longer prominent. The increase in intensity of this new transition is also accompanied by the enhancement of radiative centers related to structural defects, such as the stacking fault-related transition at 3.31 eV and the Y-line. Temperature dependent PL illustrates the excitonic nature of the new transition at ∼3.35 eV, which is therefore assigned to (A⁰, X) transition, where the acceptor is possibly the 2V_Zn-As_Zn complex, with an activation energy E_A in the range of 160-240 meV. Furthermore, the enhancement of the radiative centers related to structural defects is regarded as evidence that As atoms tend to segregate in the vicinity of structural defects to relieve local strain.     

Defect sites in thin films of germanium dioxide irradiated with silicon ions

Optical transmission spectra of GeO₂ films irradiated with silicon ions and subjected to postimplantation annealing in the regime of silicon nanocrystal formation are analyzed. It is shown that point defects form in the films after irradiation with doses D ～ 10²⁰ m^?2: germanium electron centers, neutral oxygen vacancies, and Ge²⁺ centers, which have been annealed at a temperature of 1000°C for an hour. At D ≥ 1 × 10²¹ m^?2, more complex defects arise in the films, which are only partially annealed under the same conditions.     

Optical Analysis of Nanocrystalline ZnO Films Coated on Porous Silicon by Radio Frequency (RF) Magnetron Sputtering

Zinc oxide thin films have been deposited onto porous silicon (PSi) substrates at high growth rates by radio frequency (RF) sputtering using a ZnO target. The advantages of the porous Si template are economical and it provides a rigid structural material. Porous silicon is applied as an intermediate layer between silicon and ZnO films and it contributed a large area composed of an array of voids. The nanoporous silicon samples were adapted by photo electrochemical (PEC) etching technique on n-type silicon wafer with (111) and (100) orientation. Micro-Raman and photoluminescence (PL) spectroscopy are powerful and non-destructive optical tools to study vibrational and optical properties of ZnO nanostructures. Both the Raman and PL measurements were also operated at room temperature. Micro-Raman results showed that the A₁(LO) of hexagonal ZnO/Si(111) and ZnO/Si(100) have been observed at around 522 and 530 cm^–1, re- spectively. PL spectra peaks are distinctly apparent at 366 and 368 cm^–1 for ZnO film grown on porous Si(111) and Si(100) substrates, respectively. The peak luminescence energy in nanocrystalline ZnO on porous silicon is blue-shifted with regard to that in bulk ZnO (381 nm). The Raman and PL spectra pointed to oxygen vacancies or Zn interstitials which are responsible for the green emission in the nanocrystalline ZnO.     

Structure and radiation properties of dislocations arising during oxygen precipitate growth in silicon

The structural and radiation properties of defects formed during oxygen precipitation in Czochralski-grown silicon (Cz-Si) has been investigated by the methods of transmission electron microscopy (TEM) and photoluminescence (PL). It has been shown that the spectral intensity of dislocation-related luminescence (DL) is considerably redistributed as precipitates grow. A comparison of the concentration of different types defects with the DL integral intensity has shown that the secondary defects, namely, dislocations punched out of precipitates, make a main contribution to DL. In this case, the spectral distribution and integral intensity of DL are related to the extension of dislocation loops. The results show the capability of optimization of the dislocation-generation process to increase the intensity of the D1 line for its use in optoelectronics.     

Structural and photoluminescence properties of Si nanoclusters obtained by ion implantation into Si3N4 films

In the present paper we report structural and photoluminescence (PL) results from samples obtained by Si implantation into stoichiometric silicon nitride (Si₃N₄) films. The Si excess was introduced in the matrix by 170 keV Si implantation performed at different temperatures with a fluence of Φ=1×10¹⁷ Si/cm². The annealing temperature was varied between 350 and 900 °C in order to form the Si precipitates. PL measurements, with a 488 nm Ar laser as an excitation source, show two superimposed broad PL bands centered around 760 and 900 nm. The maximum PL yield is achieved for the samples annealed at 475 °C. Transmission electron microscopy (TEM) measurements show the formation of amorphous nanoclusters and their evolution with the annealing temperature.