Photoluminescence of Si3N4 films implanted with Ge+ and Ar+ ions

The room-temperature photoluminescence emission and excitation spectra of Si₃N₄ films implanted with Ge⁺ and Ar⁺ ions were investigated as a function of the ion dose and temperature of subsequent annealing. It was established that the implantation of bond-forming Ge atoms during annealing right up to temperature T _a=1000 °C stimulates the formation of centers emitting in the green and violet regions of the spectrum. Implantation of inert Ar⁺ ions introduces predominantly nonradiative defect centers. Comparative analysis of the photoluminescence spectra, Rutherford backscattering data, and Raman scattering spectra shows that the radiative recombination is due not to quantum-well effects in Ge nanocrystals but rather recombination at the defects ≡Si-Si≡, ≡Si-Ge≡, and ≡Ge-Ge≡. Fiz. Tekh. Poluprovodn. 33, 559–566 (May 1999)     

Effect of ion dose and annealing mode on photoluminescence from SiO2 implanted with Si ions

This paper discusses the photoluminescence spectra of 500-nm-thick layers of SiO₂ implanted with Si ions at doses of 1.6×10¹⁶, 4×10¹⁶, and 1.6×10¹⁷ cm⁻² and then annealed in the steady-state region (30 min) and pulsed regime (1 s and 20 ms). Structural changes were monitored by high-resolution electron microscopy and Raman scattering. It was found that when the ion dose was decreased from 4×10¹⁶ cm⁻² to 1.6×10¹⁶ cm⁻², generation of centers that luminesce weakly in the visible ceased. Moreover, subsequent anneals no longer led to the formation of silicon nanocrystallites or centers that luminesce strongly in the infrared. Annealing after heavy ion doses affected the photoluminescence spectrum in the following ways, depending on the anneal temperature: growth (up to ∼700 °C), quenching (at 800–900 °C), and the appearance of a very intense photoluminescence band near 820 nm (at >900 °C). The last stage corresponds to the appearance of Si nanocrystallites. The dose dependence is explained by a loss of stability brought on by segregation of Si from SiO₂ and interactions between the excess Si atoms, which form percolation clusters. At low heating levels, the distinctive features of the anneals originate predominantly with the percolation Si clusters; above ∼700 °C these clusters are converted into amorphous Si-phase nanoprecipitates, which emit no photoluminescence. At temperatures above 900 °C the Si nanocrystallites that form emit in a strong luminescence band because of the quantum-well effect. The difference between the rates of percolation and conversion of the clusters into nanoprecipitates allows the precipitation of Si to be controlled by combinations of these annealings. Fiz. Tekh. Poluprovodn. 32, 1371–1377 (November 1998)     

Lateral schottky GaN rectifiers formed by Si<Superscript>+</Superscript> ion implantation

Type conversion of p-GaN by direct Si⁺ ion implantation and subsequent annealing was demonstrated by the fabrication of lateral Schottky diodes. The Si⁺ activation percentage was measured as a function of annealing time (30–300 sec) and temperature (1,000–1,200°C), reaching a maximum of ∼30% for 1,200°C, 2-min anneals. The resulting n-type carrier concentration was 1.1×10¹⁸ cm⁻³ for a moderate Si⁺ ion dose of ∼2×10¹⁴ cm⁻². The lateral Schottky diodes displayed a negative temperature coefficient of −0.15 V·K for reverse breakdown voltage.     

Multimodal luminescence spectra of ion-implanted silica

The main luminescence bands in silica SiO₂ are the red luminescence R (650 nm, 1.9 eV) of the non-bridging oxygen hole center, and the blue band B (460 nm, 2.7 eV) and ultraviolet luminescence UV (290 nm, 4.3 eV), both commonly related to oxygen-deficient centers. In the present work, we will enhance or replace either the first or second constituent of SiO₂, i.e., silicon or oxygen, isoelectronically by additional implantation of the respective ions. Thus, thermally oxidized SiO₂ layers have been implanted by different ions of the IV group (C, Si, Ge, Sn, Pb) and of the VI group (O, S, Se) with doses up to 5 × 10¹⁶ cm⁻², leading to an atomic dopant fraction of about 4 at % at the half depth of the SiO₂ layers. Very surprisingly, the cathodoluminescence spectra of oxygen-and sulfur-implanted SiO₂ layers show, besides the characteristic bands, a sharp and intensive multimodal structure beginning at the green region at 500 nm up to the near infrared. The energy step differences of the sublevels equal on average 120 meV, and indicate vibration associated electronic states, probably of O ₂ ⁻ interstitial molecules. The text was submitted by the authors in English.     

Optical and Magnetic Properties of ZnO:V Prepared by Ion Implantation

We report on the optical and magnetic properties of the magnetic semiconductor Zn(V)O fabricated by implantation of 195 keV ₅₁V⁺ ions into bulk ZnO:Al grown by a hydrothermal technique. Two sets of the samples, containing N _d –N _a ∼ 10¹⁵ cm⁻³ and 10¹⁸ cm⁻³, were implanted to doses of 1 × 10¹⁵ cm⁻², 3 × 10¹⁵ cm⁻², and 1 × 10¹⁶ cm⁻². The ion implantation was performed at 573 K. To remove irradiation-induced defects, the samples were annealed in air at 1073 K. Photoluminescence (PL) measurements of Zn(V)O films were carried out at temperatures from 10 K to 300 K. The effects of implantation dose and free carrier concentration on the magnetic properties of Zn(V)O were studied using a superconducting quantum interference device magnetometer. Ferromagnetism has been observed in annealed highly conductive samples implanted to 1 × 10¹⁶ cm⁻². The PL studies of ZnO bulk samples implanted with V⁺ have revealed that thermal annealing at 1073 K restores to a large extent the optical quality of the material. A new emission line centered at 3.307 eV has been found in the PL spectrum of the highly conductive samples implanted to the dose of 1 × 10¹⁶ cm⁻², which is most probably due to complexes involving V ions.     

Effect of ion irradiation of amorphous-silicon films on their crystallization

The change in the structure of amorphous Si films implanted with inert-gas ions and chemically active impurity was investigated by transmission electron microscopy and electron diffraction methods. It was shown that as a result of radiation-induced formation of thermally stable vacancy complexes, Si films irradiated with Ar⁺ and P⁺ ions with doses above 7×10¹⁵ cm⁻² do not crystallize up to temperature 680 °C. It was established that crystallization of Si films after implantation of lower doses of P⁺ ions accelerates the growth of grains in the films as a compared with the unirradiated films. A model of the mechanism by which the ion irradiation influences the crystallization of Si films is discussed. Fiz. Tekh. Poluprovodn. 32, 349–352 (March 1998)     

Influence of laser recrystallization and hydrogen annealing on electrical characteristics of polysilicon

 Asenic ions are implanted with doses of 5×10~(11)—5×10~(15)/cm~2 into LPCVD polysilicon films on SiO_2 isolating substrate.The polysilicon films have been recrystallized with CW Ar~+ laser before implantation.Electrical measurements show that the resistivity is lowered and the mobility is increased significantly at low doping concentration(～10~(17)As~+/cm~3).Plasma hydrogen annealing is performed on laser-recrystallized samples.The electrical characteristics of plasma hydrogen annealed samples are close to that of single crystalline silicon.It is found that the resistivity decreases from 1.2 Ω.cm to 0.45 Ω.cm,the mobility rises from 62 cm~2/V.s to 271 cm~2/V.s,the electrical activation energy reduces from 0.03 eV to -0.007 eV and the trapping state density at the grain boundary drops from 3.7×10~(11)/cm~2 to 1.7×10~(11)/cm~2.Based on the existing theoretical models for conduction in polysilicon, a new formula for large grain polysilicon has been proposed,with the help of which,a good agreement between theory and experimental results is achieved within the doping concentration range from 10~(16)/cm~3 to 10~(20)/cm~3.     

Doping and impurity compensation by ion implantation in a-SiGe films

This paper discusses the electrical properties of a-SiGe films (N _Ge∼2.2 at. %) prepared by co-evaporation of Si and Ge from separate sources and doped by ion implantation of substitutional impurities (B⁺ and P⁺), as well as the results of controlled impurity compensation by ion-beam doping. It was found that B⁺ and P⁺ implantation into a-SiGe films in the dose range 1.3×10¹⁴–1.3×10¹⁷ cm⁻², followed by annealing at 350 °C, increased the conductivity of these films from 10⁻⁹ to 10⁻⁴ and to 10⁻⁵ S/cm for B⁺ and P⁺, respectively. The position of the Fermi level could be varied from (E _v+0.27) to (E _c−0.19) eV. These investigations indicate that compensation of pre-doped a-SiGe films by ion implantation is feasible and reproducible. It is also found that higher doping efficiency of a-SiGe films is obtained by using boron than by using phosphorus. Fiz. Tekh. Poluprovodn. 32, 1260–1262 (October 1998)     

Activation analytical investigation of contamination and cross-contamination in ion implantation

In silicon layers, implanted at 100–150 keV with P⁺, As⁺ and Ar⁺ ions, considerable Fe, Cr, Ni, Co and Cu were detected by means of neutron activation analysis. With the elements of the Fe group, concentrations up to 5.10¹⁴cm⁻² were obtained, whereby the relationship of these elements to each other corresponds to the composition of the stainless steel apertures used. The contamination of the layers is dose dependent. In accordance with the sputter rates, As⁺ ion implanted layers are more contaminated than those implanted by P⁺ or Ar⁺ ions. Additionally, the implanting process introduces, besides the contamination with heavy metals, dopants from the previous implantation. This so-called cross-contamination amounted to approx. 0.3 % of the implanted ion dose. Essential parts of this work were presented at the symposium on “Solid State Device Technology” Munster, 1977     

Effect of successive implantation of Ag+(Cu+) and Xe+ ions on the recombination properties of CdxHg1−x Te crystals

The effect of successive double implantation of Ag⁺(Cu⁺) and Xe⁺ ions on the recombination properties of Cd_xHg_1−x Te (0.2<x<0.3) crystals has been investigated. It is shown that after implantation of ions of one chemical element, followed by diffusion thermal annealing at temperatures below 150–200 K, recombination through local levels lying 30±5 meV below the conduction band bottom dominates. Successive double implantation of Ag⁺(Cu⁺) and Xe⁺ ions followed by diffusion thermal annealing changes the course of the temperature dependence of the lifetime of the nonequilibrium charge carriers. It was determined that for Cd_xHg_1−x Te crystals with x⋍0.20–0.25 in the temperature interval 700–200 K the lifetime of the nonequilibrium charge carriers is low (τ<0.15 μs) and does not depend on the temperature. For Cd_xHg_1−x Te crystals with x⋍0.3 recombination of nonequilibrium charge carriers occurs through two types of levels: in the temperature range 140–200 K — deep levels E _t1⋍E _c −51 meV and at lower temperatures (77–140 K) — through shallower levels E _t2⋍E _c −(16±2) meV. Fiz. Tekh. Poluprovodn. 31, 786–789 (July 1997)     

Scanning spreading resistance microscopy of defect engineered low dose SIMOX samples

Modification of SiO₂ precipitate formation by defect engineering of SIMOX (separation by implanted oxygen) process was studied using cross section scanning spreading resistance microscopy (SSRM). Firstly, open volume defects, nanocavities, have been introduced by He⁺ ion implantation in the region, where SiO₂ precipitates were subsequently formed. Secondly, dual (simultaneous) oxygen (O⁺) and silicon (Si⁺) implantation was used to modify SiO₂ reaction kinetics too. The results show that the He-induced nanocavities enhance the SiO₂ formation presumably releasing excess strain associated with Si oxidation, while the use of a dual O⁺/Si⁺ beam do not influence significantly the oxidation kinetics in the initial state of the SIMOX process in our samples. Overall, SSRM was shown to be a suitable method for observation of the early stage of buried oxide formation in Si, since it measures the local resistivity, the main functional parameter of a SIMOX structure.     

Radiation hardness of porous silicon

The effect of irradiation by 300-keV Ar⁺ ions on the properties of electrochemically produced porous silicon is studied at doses of 5×10¹⁴–1×10¹⁶ cm⁻². Raman scattering and photoluminescence data are used to show that the radiation hardness of porous silicon layers is substantially greater than that of single crystal silicon. Fiz. Tekh. Poluprovodn. 31, 1126–1129 (September 1997)     

Effect of in situ photoexcitation of n-type Si as a result of ion implantation at low doses on the formation of radiation defects

The effect of in situ photoexcitation of the electronic subsystem of a semiconductor as a result of implantation of low ion doses on the formation of complexes of radiation defects in n-type Si is investigated by the DLTS method. The n-type Si samples were irradiated with 150-keV O ₂ ⁺ and N ₂ ⁺ ions at the same dose 10¹¹ cm⁻² and Ar⁺ ions at doses 7×10¹⁰ and 2×10¹¹ cm⁻². With the exception of the latter case, the ion energy and dose were chosen so as to produce approximately the same number of initially displaced Si atoms and the same depth distribution of such atoms from the target surface. The temperature of the n-type Si samples during irradiation was 300 or 600 K. Photoexcitation of the semiconductor was performed using UV radiation with various power densities. It is shown that radiative heating of the samples during ion implantation suppresses the formation of radiation-defect complexes, while photoexcitation of n-type Si, in contrast, intensifies their formation. It is found that the effect of illumination increases with decreasing ion mass and with increasing target temperature. The effect of UV illumination on defect formation in n-type Si as a function of sample temperature during ion implantation is established. It is found that the density of divacancies in n-type Si saturates with increasing illumination intensity. Fiz. Tekh. Poluprovodn. 33, 537–541 (May 1999)     

Hot-implantation of nitrogen donors into p- type α-SiC and characterization of n+-p junction

N⁺ implantation into p-type a-SiC (6H-SiC, 4H-SiC) epilayers at elevated temperatures was investigated and compared with implantation at room temperature (RT). When the implant dose exceeded 4 × 10₁₅ cm₋₂, a complete amorphous layer was formed in RT implantation and severe damage remained even after post implantation annealing at 1500°C. By employing hot implantation at 500~800°C, the formation of a complete amorphous layer was suppressed and the residual damage after annealing was significantly reduced. For implant doses higher than 10¹⁵ cm⁻², the sheet resistance of implanted layers was much reduced by hot implantation. The lowest sheet resistance of 542Ω/ was obtained by implantation at 500 ~ 800°C with a 4 × 10¹⁵ cm⁻² dose. Characterization of n⁺-p junctions fabricated by N⁺ implantation into p-type epilayers was carried out in detail. The net doping concentration in the region close to the junction showed a linearly graded profile. The forward current was clearly divided into two components of diffusion and recombination. A high breakdown voltage of 615 ∼ 810V, that is almost an ideal value, was obtained, even if the implant dose exceeded 10¹⁵ cm⁻². By employing hot implantation at 800°C, the reverse leakage current was significantly reduced.     

Low-temperature photoluminescence in holmium-doped silicon

In this paper the photoluminescence (PL) of holmium-doped silicon is discussed. The silicon was first implanted with holmium ions at energies of 1–2 MeV and doses of 1×10¹³–3×10¹⁴ cm⁻², and then annealed at temperatures of 620–900 °C for 0.5–1 h. In order to increase the concentration of electrically and optically active centers, the silicon was implanted a second time with oxygen ions at energies of 0.14–0.29 MeV and doses of 1×10¹⁴–3×10¹⁵ cm⁻². Several photoluminescence lines, which are attributable to the transitions of electrons from the first excited state of the Ho³⁺ ion (⁵ I ₇) to the ground state (⁵ I ₈), were observed. The amplitudes of the most intense lines, which correspond to transitions at frequencies 5119 and 5103 cm⁻¹, decreased by more than an order of magnitude in the temperature range 4.2−78 K. The PL intensity of the holmium ions increased with increasing concentrations of the implanted rare-earth ions and oxygen. Fiz. Tekh. Poluprovodn. 33, 420–422 (April 1999)     

Degradation of MOS tunnel structures at high current density

The stability of tunneling-thin (2–3 nm) SiO₂ films during prolonged flow of high-density currents (10²–10³ A/cm²) was investigated. A sharp increase in the charge which a tunneling MOS structure is capable of transmitting without degradation on switching from Fowler-Nordheim injection to direct tunneling (10³ C/cm² and 10⁷ C/cm², respectively) was observed. The degradation of SiO₂ films was investigated using Al/SiO₂/n-Si/p ⁺-Si thyristor structures with a positive bias on the semiconductor, i.e., with reverse bias of the MOS structure. The use of these devices accounted for the uniformity of the current distribution over the area and made it possible to monitor the state of the insulator layer by measuring the device gain in the phototransistor mode. Fiz. Tekh. Poluprovodn. 32, 743–747 (June 1998)     

Special features of the excitation spectra and kinetics of photoluminescence of the Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>:Er/Si structures with relaxed heterolayers

Luminescent properties of heteroepitaxial Si_{1 − x} Ge _x :Er/Si structures with relaxed heterolayers are studied. The results of combined studies of the excitation spectra and kinetics of photoluminescence (PL) are used to single out the components providing the largest contribution to the PL signal of the Si_{1 − x} Ge _x :Er/Si structures in the wavelength region of 1.54 μm. It is shown that relaxation of elastic stresses in the Si_{1 − x} Ge _x :Er heterolayer affects only slightly the kinetic characteristics of erbium luminescence and manifests itself in insignificant contribution of the defects and defect-impurity complexes to the luminescent response of the Si_{1 − x} Ge _x :Er/Si structures. In the excitation spectra of the erbium PL, special features related to the possibility of the rare-earth impurity excitation at energies lower than the band gap of the Si_{1 − x} Ge _x solid solution are revealed. It is shown that a peak the width of which depends on the band gap of the solid solution and the extent of its relaxation is observed in the excitation spectra of the erbium-related PL in the Si_{1 − x} Ge _x :Er/Si structures in the wavelength region of 1040–1050 nm. The observed specific features are accounted for by involvement of intermediate levels in the band gap of the Si_{1 − x} Ge _x :Er solid solution in the process of excitation of an Er³⁺ ion.     

Microwave field-effect transistors from sulphur-implanted GaAs

Sulphur implanation into semi-insulating Cr doped GaAs has been used to fabricate MESFETs with 1.5 μm gatelength showing microwave gain equivalent to epitaxial FETs (MAG = 9 dB at 10 GHz) but higher noise. Room temperature implantation of S at an energy of 30 keV and a dose of 5 × 10¹² cm^?2, sputtered SiO₂ and Si₃N₄ as encapsulants and heat treatments from 820 to 900°C have been used. Electrical activation was found to depend critically on the substrate material. Si₃N₄-encapsulation gave slightly higher electrical activation than SiO₂.     

Effect of annealing on the optical and structural properties of GaN:Er

The effect of annealing on the optical and structural properties of gallium nitride layers grown by metalorganic chemical vapor deposition and implanted with 0.8 to 2.0-MeV erbium ions at doses of (1−4)×10¹⁴ cm⁻² is investigated. Additional implantation of 0.11 to 0.28-MeV oxygen ions at doses of (1−4)×10¹⁵ cm⁻² is performed on some samples. Measurements of the Rutherford backscattering of protons show that amorphization of the gallium nitride layers does not occur at the erbium implantation doses investigated. The formation of erbium-related luminescence centers which emit at 1.54 μm ends before the defect structure of the implanted layers is restored during a postimplantation anneal in the temperature range 700–1300 °C. Fiz. Tekh. Poluprovodn. 33, 674–676 (June 1999)     

Effect of electron and neutron bombardment on the orange luminescence spectra of not specially doped and copper-doped cadmium sulfide single crystals

CdS single crystals which were not specially doped and which were doped with copper (N _Cu=10¹⁸ cm⁻³) have been investigated. It is concluded on the basis of an analysis of the dose dependences of the orange luminescence intensity (λ _M=605 nm) of “pure” and doped samples upon bombardment by electrons with E=1.2 MeV and by fast reactor neutrons that the centers responsible for this luminescence are complex in nature. They consist of interstitial cadmium atoms and oxygen atoms. Electron bombardment of CdS:Cu single crystals results in the formation of new centers which are responsible for luminescence with λ _M=570 and 545 nm. Fiz. Tekh. Poluprovodn. 31, 390–392 (April 1997)