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.     

Resistors and diodes produced by Al-implantation in silicon

Al⁺-ions are implanted to obtain diodes and resistors with a sheet resistivity higher than 100 kΩ/□. Breakdown voltage of the diodes is between 240 V and 300 V. The conductivity of the resistors shows approximately a square root dependence on the implantation dose after a 500°C anneal. The temperature coefficient is α ≈ 3 × 10^?3 K^?1. The values are compared with results of B⁺-ion implantations.     

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.     

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.     

Comparison of p–n junction formed by BF2 and B implantation in silicon microstrip detector with low and high thermal budget: impact of fluorine on electrical characteristics

The influence of crystal damage on the electrical properties and the doping profile of the implanted p⁺–n junction has been studied at different annealing temperatures using process simulator TMA-SUPREM4. This was done by carrying out two different implantations; one with implantation dose of 10¹⁵ BF₂⁺ ions/cm² at an energy of 80 keV and other with 10¹⁵ B⁺ ions/cm² at 17.93 keV. Substrate orientation 1 1 1 of phosphorus-doped n-type Si wafers of resistivity 4 kΩ cm and tilt 7° was used, and isochronally annealing was performed in N₂ ambient for 180 min in temperature range between 400°C and 1350°C. The diode properties were analysed in terms of junction depth, sheet resistance. It has been found that for low thermal budget annealing, boron diffusion depth is insensitive to the variation in annealing temperature for BF₂⁺-implanted devices, whereas, boron diffusion depth increases continuously for B⁺-implanted devices. In BF₂⁺-implanted devices, fluorine diffusion improves the breakdown voltage of the silicon microstrip detector for annealing temperature upto 900°C.For high thermal budget annealing, it has been shown that the electrical characteristics of BF₂⁺-implanted devices is similar to that obtained in B⁺-implanted devices.     

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)     

Comparison of Solid-State Microwave Annealing with Conventional Furnace Annealing of Ion-Implanted SiC

Rapid solid-state microwave annealing was performed for the first time on N⁺-, Al⁺-, and B⁺-implanted SiC, and the results were compared with the conventional furnace annealing. For microwave annealing, temperatures up to 2,000 °C were attained with heating rates exceeding 600 °C/s. An 1,850 °C/35 s microwave anneal yielded a root-mean-square (RMS) surface roughness of 2 nm, which is lower than the 6 nm obtained for 1,500 °C/15 min conventional furnace annealing. For the Al implants, a minimum room-temperature sheet resistance (R _s ) of 7 kΩ/□ was measured upon microwave annealing. For the microwave annealing, Rutherford backscattering (RBS) measurements indicated a better structural quality, and secondary-ion-mass-spectrometry (SIMS) boron implant depth profiles showed reduced boron redistribution compared to the corresponding results of the furnace annealing.     

Elevated temperature nitrogen implants in 6H-SiC

Elevated temperature (700°C) N ion implantations were performed into 6H-SiC in the energy range of 50 keV-4 MeV. By analyzing the as-implanted depth distributions, the range statistics of the N⁺ in 6H-SiC have been established over this energy range. Annealing at 1500 and 1600°C for 15 min resulted in Rutherford backscattering spectrometry scattering yields at the virgin crystal level, indicating a good recovery of the crystalline quality of the material without any redistribution of the dopant. A maximum electron concentration of 2 × 10¹⁹ cm⁻³, at room temperature, has been measured even for high-dose implants. The p-n junction diodes made by N ion implantation into a p-type substrate have a forward turn-on voltage of 2.2 V, an ideality factor of 1.90, and a reverse breakdown voltage of 125 V with nA range leakage current for -10 V bias at room temperature. By probing many devices on the same substrate we found uniform forward and reverse characteristics across the crystal.     

Defects in annealed 1.5 MeV boron implanted p-type silicon

Effects of temperature and dosage on the evolution of extended defects during annealing of MeV ion-implanted Czochralski (CZ) p-type (001) silicon have been studied using transmission electron microcopy. Excess interstitials generated in a 1 10¹⁵ cm⁻²/1.5 MeV B⁺ implanted Si have been found to transform into extended interstitial {311} defects upon rapid thermal annealing at 800°C for 15 sec. During prolonged furnace annealing at 960°C for 1 h, some of the {311} defects grow longer at the expense of the smaller ones, and the average width of the defects seems to decrease at the same time. Formation of stable dislocation loops appears to occur only above a certain threshold annealing temperature (∼1000°C). The leakage current in diodes fabricated on 1.5 MeV B⁺ implanted wafers was found to be higher for a dosage of 1 10¹⁴cm⁻² and less, as compared to those fabricated with a dosage of 5 10¹⁴ cm⁻² and more. The difference in the observed leakage current has been attributed to the presence of dislocations in the active device region of the wafers that were implanted with the lower dosage.     

Characterization of phosphorus implantation in 4H-SiC

We report the characterization of phosphorus implantation in 4H-SiC. The implanted layers are characterized by analytical techniques (secondary ion mass spectrometry, transmission electron microscopy) as well as electrical and a sheet resistance value as low as 160 Ω/□ has been measured. We have also studied the effect of annealing time and temperature on activation of phosphorus implants. It has been shown to possible to obtain low sheet resistance (∼260 Ω/□) by annealing at a temperature as low as 1200°C. High-dose (∼ 4 × 10¹⁵ cm⁻²) implants are found to have a higher sheet resistance than that on lower dose implants which is attributed to the near-surface depletion of the dopant during high temperature anneal. Different implantation dosages were utilized for the experiments and subsequently junction rectifiers were fabricated. Forward characteristics of these diodes are observed to obey a generalized Sah-Noyce-Shockly multiple level recombination model with four shallow levels and one deep level.     

Comparison of current-voltage characteristics of n- and p-type 6H-SiC Schottky diodes

Current-voltage (I–V) characteristics of n- and p-type 6H−SiC Schottky diodes are compared in a temperature range of room temperature to 400°C. While the room temperature I–V characteristics of the n-type Schottky diode after turn-on is more or less linear up to ∼100 A/cm², the I–V characteristics of the p-type Schottky diode shows a non-linear behavior even after turn-on, indicating a variation in the on-state resistance with increase in forward current. For the first time it is shown that at high current densities (>125 A/cm²) the forward voltage drop across p-type Schottky diodes is lower than that across n-type Schottky diodes on 6H−SiC. High temperature measurements indicate that while the on-state resistance of n-type Schottky diodes increases with increase in temperature, the on-state resistance of p-type Schottky diodes decreases with increase in temperature up to ∼330 K.     

Effect of the post-As+-lmplantation thermal treatment on MBE HgCdTe optical properties

HgCdTe epilayers were grown by molecular beam epitaxy. A series of As⁺-implanted CdTe and HgCdTe epilayers annealed under different temperatures were investigated by photoluminescence spectroscopy. More As⁺ ions can occupy the Te sublattice after the samples were annealed at 450°C, and the acceptor level of As⁺ on the Te sublattice for HgCdTe material (x ≈ 0.39) is 31.5 meV. The Raman spectrum study indicates a recovery of the crystalline perfection after the post-As⁺-implantation thermal treatment.     

Short-wavelength photoluminescence of SiO2 layers implanted with high doses of Si+, Ge+, and Ar+ ions

The short-wavelength (400–700 nm) photoluminescence (PL) spectra of SiO₂ layers implanted with Si⁺, Ge⁺, and Ar⁺ ions in the dose range 3.2×10¹⁶–1.2×10¹⁷ cm⁻² are compared. After Ar⁺ implantation an extremely weak luminescence, which vanishes completely after annealing for 30 min at 400 °C or 20 ms at 1050 °C, was observed. After implantation of group-IV elements the luminescence intensities were 1 to 2 orders of magnitude higher, and the luminescence remained not only with annealings but it could also increase. The dose and heating dependences of the luminescence show that it is due to the formation of impurity clusters and this process is more likely to be of a percolation than a diffusion character. For both group-IV impurities an intense blue band and a weaker band in the orange part of the spectrum were observed immediately after implantation. The ratio of the excitation and emission energies of the blue luminescence is characteristic of oxygen vacancies in SiO₂; its properties are determined by the direct interaction of group-IV atoms. On this basis it is believed that the centers of blue PL are chains of Si (or Ge) atoms embedded in SiO₂. The orange luminescence remained after annealings only in the case of Si⁺ implantation. This is attributed directly to the nonphase precipitates of Si in the form of strongly developed nanometer-size clusters. Fiz. Tekh. Poluprovodn. 32, 439–444 (April 1998)     

Electron microscopic study on residual defects of Al+ or B+ implanted 4H-SiC

The residual defects of Al⁺- or B⁺-implanted 4H-SiC were studied in combination with annealing temperature and implantation temperature using cross-sectional transmission electron microscopy technique. Noticeable defects structure is not observed before post-implantation annealing. But after annealing, a lot of black spots appear in the implanted layer. These black spots are composed of a dislocation loop, parallel to {0001} of 4H-SiC, and strained area at the upper and lower sides of the dislocation loop. This defect structure and its size do not depend on implantation temperature and implanted ion species. The size of defect area depends only on post-implantation annealing temperature. The size grows, when post-annealing temperature is raised.     

Low-temperature processing of shallow junctions using epitaxial and polycrystalline CoSi2

Cobalt disilicide is grown epitaxially on (100) Si from a 15 nm Co/2 nm Ti bilayer by rapid thermal annealing (RTA) at 900°C. Polycrystalline CoSi₂ is grown on (100) Si using a 15 nm Co layer and the same annealing condition. Silicide/p⁺-Si/n-Si diodes are made using the silicide as dopant source:¹¹B⁺ ions are implanted at 3.5–7.5 kV and activated by RTA at 600–900°C. Shallow junctions with total junction depth (silicide plus p⁺ region) measured by high-resolution secondaryion mass spectroscopy of 100 nm are fabricated. Areal leakage current densities of 13 nA/cm² and 2 nA/cm² at a reverse bias of -5V are obtained for the epitaxial silicide and polycrystalline silicide junctions, respectively, after 700°C post-implant annealing.     

Radiation damage and annealing behaviour in Be+-implanted pure Ga(Al)Sb layers

Implantation of Be⁺ ions into GaAISb epilayers is used to realize thep ⁺ layer of the Ga_0.96Al_0.04Sb p⁺/Ga_0.96Al_0.04Sbn ⁻ /GaSbn ⁺ (1.55 /Μm) avalanche photodetector whose performances are detailed in Ref. (1). The GaAISb layers are grown using liquid phase epitaxy (LPE); the quality of these as-grown layers is shown through photoluminescence and channeling measurements. The last part of this paper is devoted to the damaging level in the Be⁺-implanted layers. Some annealing techniques are presented as a mean of restoration of the implanted layers. It is clear from the results that the Be⁺ ion implantation leads to a low damage level in this III-V compound.     

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     

The role of outdiffusion in the activation of high dose Mg implantations in InP

We have studied the annealing behaviour of magnesium implanted in indium phosphide. The activated fraction of dopants was found to depend strongly on implanted dose and substrate temperature during implantation. Low activation for high dose (10¹⁵ cm⁻²) implantations was found to be a result of pronounced outdiffusion (80%). We also found a large variation in the apparent activation energy for implantation temperatures between room temperature and 300° C.     

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.     

Growth and characterizations of InP self-assembled quantum dots embedded in InAIP grown on GaAs substrates

We report the characteristics of InP self-assembled quantum dots embedded in In_0.5Al_0.5P on GaAs substrates grown by metalorganic chemical vapor deposition. The InP quantum dots show increased average dot sizes and decreased dot densities, as the growth temperature increases from 475°C to 600°C with constant growth time. Above the growth temperature of 600°C, however, dramatically smaller and densely distributed self-assembled InP quantum dots are formed. The small InP quantum dots grown at 650°C are dislocation-free “coherent” regions with an average size of ∼20 nm (height) and a density of ∼1.5 × 10⁸ mm⁻². These InP quantum dots have a broad range of luminescence corresponding to red or organge in the visible spectrum.