The effect of boron,oxygen, and fluorine in ion implanted GaAs

Effects of boron, fluorine, and oxygen in GaAs have been investigated by electrical characterization using current-voltage, capacitance-voltage and deep level transient spectroscopy techniques. Ion implantation at 100 keV energy was conducted with doses of 10¹¹ and 10¹²/cm². Carrier compensation was observed in each implanted sample. The compensation effect strongly depended on ion implantation condition and ion species. More free carriers were compensated for higher dose and heavier species; however, severe surface damage would also be induced that degrade electrical performance. Rapid thermal annealing treatment showed the heavier ion implanted samples to be more thermally stable. Defect levels for each implanted species were compared and identified. A native shallow defect E4 was easily removed by ion implantation. In higher dose and heavier ion implantation, both electron and hole traps were induced. However, in some cases, heavier ion implantation also removed native defects. Acceptor-type surface states were created by implantation that degrade material electrical characteristics and also reduce the effect of compensation. The damage induced traps were mostly point-defects or point-defect/impurity complexes as evidenced by sensitivity to heat treatment.     

Characterization of silicon ion-implantation damage in single-strained-layer (InGa)As/GaAs quantum wells

We have characterized the structural effects of silicon ion implantation and controlled-atmosphere annealing on single quantum wells of In_0.14Ga_0.86As strained to match the in-plane lattice spacing of bulk GaAs. Cantilever-beam techniques were applied to measure implantation-induced stresses, while Rutherford backscattering, double-crystal x-ray diffraction, and cross-sectional transmission electron microscopy were applied to characterize the resulting microstructure. Samples were examined in both the as-implanted state and also after implantation and annealing under an arsenic overpressure at 800° C for 10 minutes. For implants whose energies produced maximum implanted ion density near the center of the 20 nm-thick quantum well, a maximum in the implantation-induced stresses were observed to occur at a silicon ion fluence of 1 × 10¹⁴/cm². Annealing of the implanted samples resulted in small dislocation loops in the ion range zone with survival of the strained quantum well. Electrical activation of the implants was found to be similar to identical implants into bulk GaAs.     

The influence of dose and protecting mask on electrically active defects induced by ion implantation in silicon

We present a study of electrically active defects induced by ion implantation, for two dopants: arsenic and phosphorous. Our analysis technique is Deep Level Transient Spectroscopy (D.L.T.S.). We have studied the generation of defects by direct implantation, and indirect implantation, that is through an SiO₂ layer. We follow the defect spectrum evolution for different doses (10⁸ to 10¹⁴ atoms/cm²) and for different annealing temperatures (from room temperature up to 800° C). The comparison of our results with other published ones allows us to improve the knowledge about the role of a protecting oxide layer, the influence of moderate thermal annealing, and the effect of oxygen on deep centers produced by ion bombardment.     

Aluminum and boron ion implantations into 6H-SiC epilayers

Aluminum and boron ion implantations into n-type 6H-SiC epilayers have been systematically investigated. Redistribution of implanted atoms during high-temperature annealing at 1500°C is negligibly small. The critical implant dose for amorphization is estimated to be 1 × 10¹⁵ cm⁻² for Al⁺ implantation and 5 × 10¹⁵ cm^-2 for B⁺ implantation. By Al⁺ implantation followed with 1500°C-annealing, p-type layers with a sheet resistance of 22 kΩ/^— can be obtained. B⁺ implantation results in the formation of highly resistive layers, which may be attributed to the deep B acceptor level.     

Rapid Thermal annealing of si implanted GaAs

Rapid thermal annealing (RTA) with incoherent light from tungsten lamps shows high potential relative to the conventional furnace annealing (FA) to activate the implanted dopant. Due to the short time annealing, it could completely eliminate the re-diffusion of dopant and host atom. For the Si implantation with dose of 2 × 10¹⁴ cm², the electrical activity of 78% for RTA was higher than that of the FA. But for this short time, some defects measured by deep level transient spectroscopy (DLTS) were hard to remove. A two-step annealing was suggested by the combination of high temperature RTA (1000° C) and FA (700° C). After the post-FA, the defects would be removed to a great extent, and the electrical activity of dopant also increased. With the dose of 2 x 1013 cm^-2, the activity attained after the two step annealing was 92.5%, which may be the highest value according to our knowledge for rapid thermal annealing on Si ion implanted GaAs.     

Effect of ion doping on the dislocation-related photoluminescence in Si+-implanted silicon

The study is concerned with the effect of the additional implantation of Si samples with C⁺, O⁺, B⁺, P⁺, and Ge⁺ impurity ions followed by annealing at 800°C on the behavior of the dislocation photoluminescence line D1, induced in the samples by implantation with Si⁺ ions at a stabilized temperature followed by annealing in an oxidizing Cl-containing atmosphere. It is established that the intensity of the D1 line strongly depends on the type of incorporated atoms and the dose of additional implantation. An increase in the D1 line intensity is observed upon implantation with oxygen and boron; at the same time, in other cases, the D1 luminescence line is found to be quenched. The mechanisms of such behavior, specifically, the role of oxygen and its interaction with implanted impurities are discussed.     

Deep levels in Si-implanted and rapid thermal annealed semi-insulating gaAs

Deep levels have been investigated in Si-implanted and rapid-thermal-annealed semiinsulating GaAs:Cr, which was grown by a horizontal Bridgman method. Samples were implanted with a Si-dose of (1 - 5) x 10¹² ions cm^-2 with 100 keV energy, and treated by a two-step rapid thermal annealing process at 900 and 800° C. After these processes, three electron deep levels at 0.81, 0.53 and 0.62 eV below the conduction band and three hole deep levels at 0.89, 0.64 and 0.42 eV above the valence band were observed. The new deep levels E_c - 0.53 eV, E_c - 0.62 eV, andEv + 0.64 eV in fact, dominate the implantation and/or the thermally damaged region, but are not found in the bulk. These results indicate that high-density deep levels may be induced near or within the implanted region by rapid heating and cooling, and that these defects may effect carrier activation.     

The behaviour of boron molecular ion implants into silicon

Implants of boron molecular ions into silicon have been studied using a variety of experimental techniques, but with emphasis on sheet resistance annealing characteristics and transmission electron microscopy. Boron halide compound molecules have been implanted and equivalent dose sequential implants of atomic species used as control conditions. The implants studied were B⁺, BCl₂⁺, BCl⁺, Cl⁺ + B⁺, BF₂⁺, BF⁺ and B⁺ + F⁺ at 25 keV/B atom and B⁺, BBr₂⁺ and Br₂⁺ + B⁺ at 12 keV/B atom.The implantation of molecular ions enables conditions of varying damage to be studied with constant dose, dose rate and energy of the dopant species. In addition to damage effects the halogen atoms produce species effects in the implanted zone. The escape of the halogen atoms has been measured as a function of the annealing temperature.The significant differences which exist between the behaviour of silicon implanted with these various conditions are considered with reference to the damage structures observed by transmission electron microscopy. The boron-fluorine molecular implants are shown to offer some advantages as a means of implanting boron.     

Effect of O+ implantation on silicon-silicon dioxide interface properties

A detailed investigation has been made by the MOS capacitance method, into the mechanism by which the fixed positive surface state charge, due to silicon rich oxide near SiSiO₂ interface, is controlled by O⁺ implantation into the oxide near the SiSiO₂ interface, and subsequent heat treatment. High dosage implantation of 3 × 10¹³ O⁺ ions cm^?2 results in damage in oxide which is occured by 450°C annealing. However, low dosage implantation of 3 × 10^?2 produces no detectable damage in the oxide, and increases the effective positive charge in the oxide at Si'SiO₂ interface. It is shown that prolonged 450°C heat treatment of 0⁺ ion implanted oxides results in an oxygen-silicon reaction in the silicon enriched oxide layer and reduces the fixed positive surface state charge. Subsequent heat treatments at 838°C increase the positive surface state charge to the original pre-ion implantation values, hence converting the oxide into the original silicon rich condition.     

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)     

Ultra-shallow P+/N junctions formed by recoil implantation

The concept of recoil implantation is proposed to facilitate fabrication of ultrashallow p⁺/n junctions. In this method, a thin boron film is first deposited onto the Si wafer surface. Then the boron atoms are knocked into the Si substrate by Ge implantation or Ar plasma source ion implantation. Dopant activation and damage removal are achieved via rapid thermal annealing. Preliminary results show the realization of sub-100 nm deep p⁺/n junctions with this technique. Monte Carlo simulations were performed to predict the recoiled boron profiles, and agree well with the experimental results.     

Effect of the insulator-gallium arsenide boundary on the behavior of silicon in the course of radiation annealing

The depth-concentration profiles n(x) of ²⁸Si implanted into semiinsulating GaAs (E ₁=50 keV, F ₁=8.75×10¹² cm^?2; E ₂=75 keV, F ₂=1.88×10¹² cm^?2) were studied by C-V measurements after the electron-beam annealing (P=7.6 W/cm², t=10 s). Prior to annealing, the samples were coated with protective insulating films (SiO₂:Sm; SiO₂ deposited by monosilane oxidation, or Si₃N₄) or were not coated. It was found that the implant profiles observed upon the electron-beam annealing extend to deeper layers as compared to the calculated curves or the profiles upon thermal annealing (800°C, 30 min). The profile depth depends on the type of insulating coating. The maximum “broadening” was observed in the electron-beam-annealed GaAs without insulating coating, and the minimum, in the sample with a protective SiO₂:Sm layer. The n(x) curves can be divided into two parts, adjacent to and distant from the interphase boundary. The diffusion parameters and the degree of electric activation of the implanted Si atoms are greater in the second region than in the first one. The experimental results are interpreted assuming the presence of thermoelastic stresses at the insulator-semiconductor boundary in GaAs.     

Impurity centers of tin in glassy arsenic chalcogenides

¹¹⁹Sn atoms produced by radioactive decay of ¹¹⁹Sb impurity atoms in the structure of As _x S_{1 − x} and As _x Se_{1 − x} glasses are stabilized in the form of Sn²⁺ and Sn⁴⁺ ions at arsenic sites and correspond to ionized states of the amphoteric two-electron center with negative correlation energy (Sn²⁺ is an ionized acceptor, and Sn⁴⁺ is an ionized donor), whereas the neutral state of the Sn³⁺ center is unstable. The fraction of Sn⁴⁺ states increases with chalcogen content in glass. ¹¹⁹Sn atoms produced by radioactive decay of ^119m Te impurity atoms in the structure of As _x S_{1 − x} and As _x Se_{1 − x} glasses are stabilized at chalcogen sites (they are electrically inactive) and arsenic sites, and the fraction of arsenic atoms decreases with the chalcogen content in glass.     

Electrical and cathodoluminescence measurements on ion implanted donor layers in GaAs

GaAs has been doped by the ion implantation of silicon, sulphur, selenium and tin. After annealing at 700°C, the layers were n-type in all cases but with the heavier ions, selenium and tin, it was necessary to implant above room temperature. Van der Pauw measurements showed that for all the impurities the surface concentration of free electrons as a function of ion dose reached a maximum of approximately 10¹³ electron/cm² with an average Hall mobility of 2000 cm²/V sec. The spatial distributions of active donors were obtained from both differential Hall measurements and capacitance measurements on reverse biased Schottky barriers. The maximum carrier density measured was 10¹⁸/cm³ at the peak of the distribution of tin ions implanted at 200°C. With selenium and tin implants the concentration and mobility of free electrons and the depth of the donor distribution were dose dependent. The cathodoluminescence spectra from implanted layers were dominated by broad low energy bands due to recombination at defects. A V_Ga-Si complex was thought to be responsible for one of the most intense bands at 1·18 eV. The results indicate that under certain conditions both defects and impurities migrate into the substrate.     

Electrical properties of He+ ion-implanted GaInP

The electrical properties of high resistivity GaInP layers produced by He⁺ ion implantation have been studied. Thick high-resistivity layers (ρ > 10⁷ Ω-cm) were obtained using multi-energy implants (80 keV, 120 keV, and 150 keV). Current-voltage (I-V) measurements of mesa diodes with two ohmic contacts indicate that in the temperature range from 200 to 300K, the dominant current flow mechanism in both n-type and p-type implanted materials is Poole-Frenkel emission, especially in the range of high electric field (>10⁵ V/cm). The thermal activation energy E_a and the potential barrier height Φ_o of the generated deep levels are 0.16±0.005 eV and 0.33±0.005 eV, respectively. At low temperature, the hopping current dominates at low and moderate applied electric fields, and the I-V curves show an ohmic characteristic. The high-temperature annealing behavior of the implanted GaInP indicates that the compensation of free carriers in the material is dominated by damage-related levels, which are annealed out at high temperatures. In regard to typical alloying cycles of metal contacts in device fabrication, it is worth noting that the resistivity is still as high as 2 × 10⁸ Ω-cm for n-type samples (5 × 10⁷ Ω-cm for p-type) after 350°C annealing, which suggests that multi-energy He⁺ implantation is suitable for implant isolation in the GaInP device technology.     

The electrical properties of zinc implanted GaAs

The electrical properties of zinc implanted GaAs have been measured as a function of ion dose, ion energy, implant temperature and annealing temperature and time using either evaporated aluminium layers or pyrolytically deposited Si₃N₄ as the encapsulant during annealing. The electrical profiles depend on all the above variables and thus profiles can be tailored by varying the relative magnitudes of these parameters. It is important to note that hole concentrations in excess of 1 × 10¹⁹ cm^?3 can be obtained following an anneal at temperatures as low as 650°C. Also, at the same annealing temperature, profile depths can be varied from 0.2 to about 1 μm by correct choice of implantation parameters. Aluminium coatings are acceptable for annealing temperatures up to 700°C but Si₃N₄ is required at higher temperatures.     

Beryllium and sulfur ion-implanted profiles in gaas

Atomic profiles of ion-implanted Be and S in GaAs have been measured as a function of implant fluence and annealing temperature. Concentration versus depth profiles were ob-tained by means of secondary ion mass spectrometry (SIMS) techniques. Pyrolytically deposited and sputter-coated Si0₂ and Si₃N₄ films were used as encapsulants for the 500 to 900° annealing study. Semi-insulating GaAs was implanted with 200 keV³⁴S⁺ to fluences of 1 × 10¹⁴ and 5₂× 10¹⁴/cm², and 100 keV⁹Be⁺ in the 1 × 10¹³ to 1 × 10¹⁵/cm² fluence range. The S profiles did not change significantly after annealing at 800°C, although there was some skewing after annealing above 600°C. In contrast, the Be profiles showed significant changes and a decrease in the peak concentration for the ≥ 5 × 10^T4/cm² implants after a 700°C anneal. After a 800°C anneal the Be profile was essentially flat with a monotonic decrease from the surface into the implanted re-gion and a 900°C anneal caused a further decrease in the Be concentration. Profiles of Be implants of ≤ 1 × 10¹⁴/cm² did not change significantly after annealing indicating that the higher fluence cases were related to solubility effects. This work supported by the Naval Electronic Systems Command and the Office of Naval Research.     

Implantation of sodium ions into germanium

The donor properties of Na atoms introduced by ion implantation into p-Ge with the resistivity 20–40 Ω cm are established for the first time. Na profiles implanted into Ge (the energies 70 and 77 keV and the doses (0.8, 3, 30) × 10¹⁴ cm⁻²) are studied. The doses and annealing temperatures at which the thermoprobe detects n-type conductivity on the sample surface are established. After implantation, the profiles exhibit an extended tail. The depth of the concentration maximum is in good agreement with the calculated mean projected range of Na ions R _p . Annealing for 30 min at temperatures of 250–700°C brings about a redistribution of Na atoms with the formation of segregation peaks at a depth, which is dependent on the ion dose, and is accompanied by the diffusion of Na atoms to the surface with subsequent evaporation. After annealing at 700°C less than 7% of the implanted ions remain in the matrix. The shape of the profile tail portions measured after annealing at temperatures 300–400°C is indicative of the diffusion of a small fraction of Na atoms into the depth of the sample.     

Current transport in fluorine implanted GaAs

Effects of fluorine implantation in GaAs have been investigated by electrical characterization. Ion implantation at 100 keV energy was conducted with doses of 10¹¹ and 10¹²/cm². The effect of fluorine implantation on current-voltage (I-V) characteristics of Schottky diodes was significant. Carrier compensation was observed after implantation by the improved I-V characteristics. The lower dose implanted samples showed thermionic emission dominated characteristics in the measurement temperature range of 300 to 100K. The starting wafer and the low dose implanted samples after rapid thermal annealing (RTA) showed similar I-V properties with excess current in the lower temperature range dominated by recombination. The higher dose implanted samples showed increased excess current in the whole temperature range which may result from the severe damage-induced surface recombination. These samples after RTA treatment did not recover from implantation damage as in the low dose implantation case. However, very good I-V characteristics were seen in the higher dose implanted samples after RTA. The influence of the higher dose ion implantation was to produce more thermal stability. The results show the potential application of fluorine implantation in GaAs device fabrication.     

Carrier compensation in O+ implanted n-type GaAs

Results of electrical measurements on 1 MeV O⁺ implanted n-type GaAs are reported. After annealing the implanted material it is found that the free carrier compenasation rate (k), defined by Favennec[1] as the number of carriers removed per oxygen atom, can be dependent upon both the starting material and the implanted dose.