Photoluminescence of Be implanted Si-doped GaAs

Degenerately doped n-type GaAs produces band-to-band luminescence with the peak energy dependent on the carrier concentration. In this study the photoluminescence of Si-doped GaAs is examined after implantation with high energy Be ions and annealing. The band-to-band peak energy in the unimplanted (reference) material is shown to be smaller than reported values in Te-doped GaAs of the same carrier concentration. This is attributed to compensation in the Si doped material as a result of its amphoteric nature. For the implanted samples, no luminescence was recorded for the unannealed samples or those annealed at 400°C and 500°C. Comparing the relative peak intensities from material annealed at 600°C for 15 min and 30 min indicates an increase in the number of As vacancies with anneal time. For samples annealed at 700°C and 800°C, the dominant luminescence is associated with Ga_As antisite defects. It is suggested that formation of these defects occurs predominantly only at these higher temperatures. Crystal recovery as measured by the luminescence intensity increased with both anneal temperature and time. For the implanted sample annealed at 800°C for 15 min, the dominant peak height was 25% of that from the reference sample.     

Temperature behavior and annealing of insulated gate transistors subjected to localized lifetime control by proton implantation

Localized lifetime control by proton implantation can result in a considerable improvement in the trade-off between device turn-off time and forward voltage when compared with the unlocalized method of electron irradiation. After a proton dose of 3 × 10¹¹cm⁻² at 3.1 MeV implanted here into insulated gate transistors, turn-off time is reduced by more than an order of magnitude compared to unimplanted devices. When the implanted devices are operated as high voltage switches at a current of 152 A cm⁻² and at a forward blocking voltage of 400 V, the following increases are observed by increasing device operating temperatures from 20 to 150°C, (a) forward voltage: 2.5 V to 2.7 V; (b) turn-off time: 0.78 μs to 1.23 μs; (c) leakage current: 20 nA to 1 mA. The physical mechanisms responsible for the qualitative temperature dependences are identified: MOS channel resistance for forward voltage, carrier capture cross-section for turn-off time, and generation and diffusion components of leakage current. Since no catastrophic or unrecoverable behavior is observed, normal device operation within the tested temperature range is possible. Isothermal annealing curves of turn-off time measured after annealing, and corresponding to a few hours annealing time, reveal that a constant turn-off time is reached after about an hour. The constant value increases with temperature, but is still below the unimplanted value after 4 h at 525°C. The turn-off time was verified to be constant even after 24 h of annealing at 200°C. Lifetime control by proton implantation seems to be more thermally stable than that caused by electon irradiation.     

Rapid thermal annealing of ion implanted cdte

Rapid thermal annealing of ion implantedn-type CdTe has been investigated. Samples were implanted with 60 keV Ar⁺ and As⁺ ions to a dose of 1 × 10¹⁴ cm⁻² and subjected to anneal sequences of 5-100s at temperatures of 350-650° C. Photoluminescence measurements have indicated that the implantation completely quenches the photoluminescence; however, anneals for only 5s at 350° C are sufficient to recover most of the features of the photoluminescence spectrum to that equivalent of unimplanted material. Luminescence spectral features associated with thermal annealing damage and substitutional As in inferred. Type conversion of the As⁺ implanted layer is observed and it has been shown that good diodes can be made, with the best behaviour resulting from a 5s anneal at 450° C. Research supported by the Natural Sciences and Engineering Research Council of Canada     

Reduction in minority carrier storage effect by fluorine ion implantation damage

Damage is produced in p-n diodes by fluorine ion implantation to reduce minority carrier storage effect. The switching time, reverse leakage current, andI-Vcharacteristics were investigated for annealing temperature between 450°C and 650°C. The accelation energy is 130 keV and doses are 10¹³-10¹⁵/cm². Annealing causes restoration in switching time, but leakage current increases with annealing temperature rise for doses more than 1 × 10¹⁴/cm². The best diodes indicate 1.5-order reduction in switching time and 10 nA in reverse leakage current. These properties, caused by implantation damage, are retained after long-cycle annealing at 450°C and are expected to be stable under practical use. These diodes can be obtained by annealing at 450°C and they furnish satisfactory diode performance.     

Promotion of radiative recombination in GaAs1—XPxby N-ion implantation

As a means of promoting radiative recombination in GaAs1-xPx, nitrogen doping by ion implantation has been evaluated. When the sample is impanted at room temperature, poor results are obtained. However, when the sample is heated up to 350°C during implantation, and annealed at 800°C for 1 h, photoluminescence spectra are obtained similar to those of GaAs1-xPxwith N incorporated during growth. For indirect-bandgap GaAs1-xPx(x = 0.52), the integrated intensity at 77 K of the implanted sample is more than 1000 times larger than that of an unimplanted sample. This shows that under appropriate conditions implanted N atoms are substituted for P atoms and become isoelectronic traps. This trap, under the proper annealing conditions, can enhance radiative recombination significantly.     

Transformation of electrically active defects as a result of annealing of silicon implanted with high-energy ions

Deep-level transient spectroscopy is used to study both the concentration profiles of defects introduced into silicon during the implantation of 14-MeV boron ions and the transformation of these defects as a result of subsequent annealing at temperatures in the range from 200 to 800°C. It is ascertained that implantation gives rise to a standard set of vacancy-containing radiation defects (the oxygen-vacancy and phosphorusvacancy complexes and divacancies) and to a center with the level located at E _c − 0.57 eV. Heat treatments at temperatures of 200–300°C bring about the disappearance of all vacancy-containing complexes at a distance from the surface h > 12−9 μm. Most likely, this phenomenon is caused by the decomposition of interstitial-containing complexes located at a depth h > 12−9 μm and their annihilation with the vacancy-containing complexes. Heat treatments at higher temperatures bring about both a further narrowing of the layer that still contains the vacancy-type defects to h ≈ 6 μm at 500°C and a change in the set of observable electrically active centers in the temperature range from 400 to 500°C. Specific features of the annealing of radiation defects after high-energy ion implantation are caused by spatial separation of the vacancy-and interstitial-containing defects. Original Russian Text ? I.V. Antonova, S.S. Shaĭmeev, S.A. Smagulova, 2006, published in Fizika i Tekhnika Poluprovodnikov, 2006, Vol. 40, No. 5, pp. 557–562.     

Diffusion of ion-implanted boron impurities into pre-amorphized silicon

Boron ion implantation into pre-amorphized silicon is studied. Pre-amorphization is performed either by F⁺ or Si⁺ implantation prior to B⁺ implantation at 10 keV with 3×10¹⁵ ions/cm². Broadening of the boron profile can be suppressed markedly in the pre-amorphized layers. For instance, the as-implanted depth at a B concentration of 1×10¹⁸ atoms/cm³ decreases from 0.19 to 0.1 μm for implantation into a pre-amorphized layer compared to B implantation into crystalline silicon. After annealing at 950°C, B atoms diffuse much more rapidly in the pre-amorphized layers than in the crystalline silicon case. Nevertheless, shallower junctions are obtained with the use of pre-amorphization. For dual F⁺ and B⁺ implantation at F⁺ doses above 1×10¹⁵ F⁺/cm², fluorine is found to segregate to the peak of the boron profile during annealing. Fluorine is also trapped at the peak of the as-implanted fluorine profile peak and near the amorphous–crystalline interface. The effects of fluorine dose and anneal temperature on the F precipitation are described and compared to results for BF⁺₂ implants.     

Formation and study of buried SiC layers with a high content of radiation defects

Protons with energy E=100 keV were implanted with doses ranging from 2×10¹⁷ to 4×10¹⁷ cm^?2 into 6H-and 4H-SiC n-type samples at room temperature. The samples were subjected to various types of postimplantation heat treatment in the temperature range 550–1500°C. The parameters of the samples were studied by measuring the capacitance-voltage and current-voltage characteristics and by analyzing the photoluminescence spectra. Blistering on the surface of the sample is observed after annealing the samples at a temperature of 800°C only after implantation of protons with a dose of ≤3×10¹⁷ cm^?2. A decrease in the resistivity of the compensated layer sets in after annealing at a temperature of ～1200°C and is completed after annealing at a temperature of ～1500°C. A drastic decrease in the photoluminescence intensity is observed after implantation for all types of samples. Recovery of the photoluminescence intensity sets in after annealing at temperatures ≥800°C and is complete after annealing at a temperature of 1500°C.     

Nanostructured thin films of the La0.7Sr0.3MnO3 manganite obtained using the extraction pyrolytic method

The extraction pyrolytic method is used to fabricate thin (100–300 nm) films of the lanthanum manganites La_0.7Sr_0.3MnO₃ on fused silica substrates. The films are deposited on the substrate using the alternate sessions of the centrifuging of solution and pyrolysis. The annealing of thin films at temperatures of greater than 650°C yields the single-phase La_0.7Sr_0.3MnO₃ material. It is demonstrated that the annealing temperature substantially affects the magnetic properties of the resulting films: the films exhibit the properties of spin glasses and ferromagnetic properties at temperatures of less than 700°C and greater than 700°C, respectively.     

Structural, electrical, and optical studies of GaAs implanted with MeV As or Ga Ions

The structural properties of GaAs implanted with high doses of 2 MeV arsenic or gallium ions with subsequent annealing at different temperatures were studied by transmission electron microscopy, Rutherford backscattering spectrometry-channeling, double crystal x-ray diffraction. Optical absorption, electrical conductivity, Hall effect and time-resolved photoluminescence were applied to monitor changes in electrical and optical characteristics of the material. An important conclusion from this investigation is that there was hardly any difference between materials implanted with gallium or arsenic. For implantation of either species, a large number of point defects was introduced and for a high enough dose a buried amorphous layer was formed. Hopping conduction and high absorption below band-to-band transition were observed for both cases. After low temperature annealing of the amorphous material, a high density of stacking faults and microtwins were found. Regrowth rates at the front and back amorphous-crystalline interfaces showed a significant difference. This was attributed to differences in local nonstoichiometry of the material at the upper and lower amorphous-crystalline interfaces. Structural studies showed the presence of some residual damage (a band of polycrystalline material in the center of the regrown area) with some associated strain even after annealing at high temperatures. Recovery to the conduction band transport in annealed samples was observed but mobilities, of the order of 2000 cmWs, were still smaller than in unimplanted GaAs. These results show that, in as-implanted material and even after annealing at lower temperatures, the point defects introduced by the implantation are responsible for the very short photocarrier lifetime. *On leave from Institute of Experimental Physics, Warsaw University, Poland.     

Compositional changes in erbium-implanted GaN films due to annealing

We have conducted a study of the material and infrared-luminescence properties of Er-implanted GaN thin films as a function of annealing. The GaN films, grown by metal-organic chemical-vapor deposition, were coimplanted with Er and O ions. After implantation, the films were furnace annealed at temperatures up to 1,100°C. Following each annealing stage, the samples were examined by photoluminescence (PL) measurements and secondary ion-mass spectrometry (SIMS) analysis. In the as-implanted samples, no PL signal near 1,540 nm could be detected with either above-bandgap or below-bandgap excitation. Only after annealing at temperatures above 900°C was the 1,540-nm luminescence detectable. Annealing at higher temperatures resulted first in an increase and then a decrease in the PL-signal intensities. The SIMS data showed that large concentrations of Al, O, and C atoms entered into the GaN films with high-temperature annealing. The stoichiometric changes in the GaN appear responsible for the changes in the Er-related luminescence.     

Low temperature processed mosfet's using laser recrystallized polycrystalline silicon films

An n-channel MOS transistor was fabricated on a laser recrystallized polycrystalline silicon film at temperatures below 630°C. The gate oxide was sputter deposited at 200°C. Lasers were used for substrate recrystallization, implantation damage annealing and dopant drive-in. An electron field effect mobility higher than 100 cm²/V · sec. was observed on the finished transistors. With 10 V applied to the gate of the transistors for 2 hr, less than a 20 mV shift in threshold voltage was observed.     

Controlled Growth and Properties of One‐Dimensional ZnO Nanostructures with Ce as Activator/Dopant

A large amount of one‐dimensional (1D) Ce‐doped ZnO nanostructures with different morphologies has been successfully synthesized by annealing a polymeric precursor at various temperatures. The evolution of the morphologies and microstructures was investigated by field‐emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), and high‐resolution TEM (HRTEM). The results show that the morphologies vary drastically with increasing synthesis temperature and the photoluminescence (PL) of the products depends on both the synthesis and measurement temperatures. The CeO layer forms first and becomes a catalytic center for the ZnO growth. At a synthesis temperature lower than the boiling point of Zn, Zn and O atoms can stack epitaxially along the CeO catalytic layer and form a bicrystal nanobelt‐like structure with a trapezoid‐like end and a concave growth fault center. At a synthesis temperature higher than the boiling point of Zn, however, nanowires with an incommensurately modulated superstructure are obtained due to the high reaction rate and the formation of a periodic separation of the CeO layer. As for the room‐temperature PL of ZnO, the incorporation of donor Ce leads to the disappearance of the green band and the appearance of a purplish‐blue emission peak, whose position shifts towards the red and whose intensity decreases with increasing synthesis temperature. Analysis of this temperature‐dependent luminescence indicates that the purplish‐blue emission of nanobelts prepared at 850 °C originates from a donor‐bound exciton emission, and, contrary to the nanowires, it undergoes a change from an emission of the electron–hole plasma (EHP) to an emission of the donor‐bound exciton with decreasing measurement temperature.     

Electrical and optical activation studies of Si-implanted GaN

Comprehensive and systematic electrical and optical activation studies of Si-implanted GaN were made as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with doses ranging from 1×10¹³ cm^?2 to 5×10¹⁵ cm^?2 at room temperature. The samples were proximity-cap annealed from 1050°C to 1350°C with a 500-Å-thick AlN cap in a nitrogen environment. The optimum anneal temperature for high dose implanted samples is approximately 1350°C, exhibiting nearly 100% electrical activation efficiency. For low dose (≤5×10¹⁴ cm^?2) samples, the electrical activation efficiencies continue to increase with an anneal temperature through 1350°C. Consistent with the electrical results, the photoluminescence (PL) measurements show excellent implantation damage recovery after annealing the samples at 1350°C for 20 sec, exhibiting a sharp neutral-donor-bound exciton peak along with a sharp donor-acceptor pair peak. The mobilities increase with anneal temperature, and the highest mobility obtained is 250 cm²/Vs. The results also indicate that the AlN cap protected the implanted GaN layer during high-temperature annealing without creating significant anneal-induced damage.     

Ion implantation and rapid thermal processing of Ill-V nitrides

Ion implantation doping and isolation coupled with rapid thermal annealing has played a critical role in the realization of high performance photonic and electronic devices in all mature semiconductor material systems. This is also expected to be the case for the binary III-V nitrides (InN, GaN, and A1N) and their alloys as the epitaxial material quality improves and more advanced device structures are fabricated. In this article, we review the recent developments in implant doping and isolation along with rapid thermal annealing of GaN and the In-containing ternary alloys InGaN and InAlN. In particular, the successful n- and p-type doping of GaN by ion implantation of Si and Mg+P, respectively, and subsequent high temperature rapid thermal anneals in excess of 1000°C is reviewed. In the area of implant isolation, N-implantation has been shown to compensate both n- and p-type GaN, N-, and O-implantation effectively compensates InAlN, and InGaN shows limited compensation with either N- or F-implantation. The effects of rapid thermal annealing on unimplanted material are also presented.     

Variable energy positron beam characterization of defects in as-grown and annealed low temperature grown GaAs

Variable energy positron annihilation measurements on as-grown and annealed GaAs grown by molecular beam epitaxy at temperatures between 230 and 350°C have been performed. Samples were subjected to either isochronal anneals to temperatures in the range 300 to 600°C or rapid thermal anneals to 700, 800, and 900°C. A significant increase in the S-parameter was observed for all samples annealed to temperatures greater than 400°C. The positron annihilation characteristics of the defect produced upon annealing are consistent with divacancies or larger vacancy clusters. The concentration of as-grown and anneal generated defects is found to decrease with increasing growth temperature.     

Micro-raman characterization of molecular-beam epitaxial ge heterolayers on Si substrates

Molecular-beam epitaxial germanium heterolayers on silicon are characterized by micro-Raman spectroscopy. The samples are angle-lapped to probe the near-interface region. A small positive shift in the germanium phonon frequency is observed near the interface compared with the surface of the 1 μm thick layer. This indicates that the misfit stress is not relaxed completely in the as-grown layers. The samples are annealed at 700°C, a temperature higher than the growth temperature, and then the germanium peak shifts toward lower frequency near the interface. This would be due to both thermal stress and formation of an interfacial alloy layer by the interdiffusion. After annealing at 850°C, the germanium peak shifts downward further because of the interdiffusion, and the peak due to the Si−Ge vibration is clearly observed near the interface.     

Effect of thermal annealing on the luminescence properties of ZnCdSe/ZnSe quantum-well structures

The thermal stability and luminescence properties of ZnCdSe/ZnSe quantum-well structures grown by molecular-beam epitaxy are investigated. A comparative analysis is made of the photoluminescence spectra of the structures before and after annealing. In the sample spectra after annealing (at 500 °C) a decrease in the intensity of the exciton luminescence line by more than two orders of magnitude, accompanied by an increase in the intensity of the deep levels, is observed. As a result of annealing at a lower temperature (about 400 °C), a narrowing of the exciton luminescence, accompanied by a shift of the maximum toward longer wavelengths, was detected. Fiz. Tekh. Poluprovodn. 31, 296–298 (February 1997)     

Investigation of techniques for minimizing resistivity of thin metallic films at submillimeter wavelengths

Experimental investigations of the substrate deposition temperature and annealing temperature influence on aluminum films deposited on diamond substrates were conducted. Tests were performed at direct current and at 101.55 GHz. Minimum resistivity levels, near theoretical predictions, occurred for deposition temperatures in the range of 50–160°C and for peak annealing temperatures of 100–120°C. Both colder and hotter substrate temperatures resulted in larger resistivity levels.     

Boron diffusion in silicon

Well-defined control of high-and low-temperature anneals of boron implanted in silicon is important in the calculation of shallow p-n junction profiles used in MOSFET's. Here, a sample matrix of boron implanted into silicon over a range of fluences and annealing temperatures is considered. The matrix of samples was measured by SIMS (secondary ion mass spectrometry). The measured profiles were compared with simulations from an annealing/diffusion model. Calculations of the annealed profiles were found to be in agreement with the SIMS data at temperatures greater than 1000°C. At lower temperatures, the profiles exhibit effects due to implantation damage which are not included in the diffusion model.