V. Komarnitskyy

Local lifetime control in silicon power diode by ion irradiation: introduction and stability of shallow donors

Enhanced formation of shallow donors (SDs) in hydrogen or helium-irradiated and subsequently annealed float-zone n-type silicon is investigated. Ion energies, irradiation fluences and annealing temperatures were chosen in ranges typically used for local lifetime control in silicon power devices. Introduced radiation defects and SDs were investigated by deep-level transient spectroscopy and C-V profiling. Results show that radiation damage produced by helium ions remarkably enhances formation of thermal donors (TDs) when the annealing temperature exceeds 375degC, i.e. when the majority of vacancy-related recombination centres anneal out. Proton irradiation introduces hydrogen donors (HDs) which form a Gaussian peak at the proton end-of-range. Their concentration linearly increases with proton fluence and changes dramatically during post-irradiation annealing between 100 and 200degC since HD constituents are reacting with radiation damage. Their annealing in this temperature range is influenced by the electric field. If annealing temperature exceeds 400degC, HDs disappear and the excessive shallow doping is caused, as in the case of helium irradiation, by TDs enhanced by radiation damage. Shallow doping introduced by both hydrogen and helium can have a detrimental influence on blocking voltage of power diodes if high irradiation fluences or wrong annealing conditions are chosen.

Accurate Identification of Radiation Defect Profiles in Silicon after Irradiation with Protons and Alpha-Particles in the MeV Range

Radiation defect profiles introduced in the low-doped float zone n-type silicon by irradiation with 1.8, 2.8 and 3.6 MeV protons and 8, 12 and 14.5 MeV alphas were studie d by a combination of the capacitance deep level transient spectroscopy and the reverse I-V profiling. Measured distributions of divacancies were compared with the profiles primary damage received from Monte Carlo simulation. It is shown that divacancy profiles foll ow in principle the simulated distribution of primary vacancies. However, the peak resulting from prot on irradiation significantly broadens its left edge towards the irradiated surface while the peak in the alpha-particle irradiated sample stays symmetrical. All divacancy profiles show a notice able broadening of the deeper side of the peak which grows with increasing energy and fluence. It is als o shown that the introduction rate of divacancies at the damage maximum increases with ion energy. Introduction The irradiation with high-energy protons and alphas became to be popular f or optimization of silicon power device parameters since it allows an introduction of a very narrow defe ct region where the carrier recombination is enhanced [1]. By choosing an appropriate ene rgy of the projectile, this region with locally reduced lifetime can be precisely placed only in that part of the device, where it is necessary. Switching parameters of ion irradiated devices ar e then improved without serious deterioration of static ones. Moreover, multiple ion irradiation can int roduce complex, custom-specific profiles of recombination centers to further optimiz e device characteristics and extend its safe operation area. Since many applications needs irra iation at substantially higher energies, the development of characterization methods capable to trac e electrically active defect within the whole device bulk is necessary. The aim of the paper is t o present a nondestructive electrical characterization of local damaged regions created by ion irradiation at energies that are covering the full depth of real silicon power device, i.e. hundreds of micr o eters. Compared to our previous studies [2-3], we used planar diodes with very low leakage (JR~10 Acm@VR=500V@303K) to increase sensitivity of the measurement and we characterize d divacancy profiles resulting both from the proton and alpha-particle irradiation. Experimental Radiation defect profiles were investigated in the low-doped (phosphorous c oncentration below 10 cm) <100>-oriented FZ n-type silicon substrate forming the n-base of the planar pnn diodes. The diodes were irradiated with 1.8, 2.8 and 3.6 MeV protons ( H) and 8, 12, and 14.5 MeV alphas ( He) using the 5 MeV Tandem accelerator in FZ Rossendorf. The irradia tion was performed at fluences ranging from 7 ×10 to 5×10 cm (H) and 1.4×10 to 1×10 (He). The energies and fluences for both types of irradiation were chosen in tha t way to produce an equivalent damage and to cover a typical range of energies used in practical pplications. The irradiation was performed at room temperature with a typical ion flux of 8 ×10 and 3×10 cms for H and He, resp. Diodes were tilted at 7 o off axis with respect to the incoming beam to minimize channeling. Solid State Phenomena Online: 2003-09-30 ISSN: 1662-9779, Vols. 95-96, pp 387-392 doi:10.4028/www.scientific.net/SSP.95-96.387

Electrical Characterization of Deep-Lying Donor Layers Created by Proton Implantation and Subsequent Annealing in N-Type Float Zone and Czochralski Silicon

The deep-lying donor layers created by proton implantation and subsequent isochronal annealing were investigated in silicon substrates with oxygen concentration changing from 2x10 cm to 1.4x10 cm. Implantation was performed with 700 keV and 1.8 MeV protons to fluence ranging from 1x10 to 1x10 cm. Results of C-V measurement showed that proton implantation introduces a Gaussian like distribution of shallow hydrogen donors that corresponds to the profile of implanted hydrogen obtained from the secondary ion mass spectroscopy measurement. Subsequent isochronal annealing leads to annealing out of hydrogen donors (~250°C) and formation of a series of hydrogen thermal donors (250-350°C). In substrates with enhanced concentration of oxygen, the radiation enhanced thermal donors and ordinary thermal donors (>400°C) were registered. It was shown that the introduction rate of hydrogen and thermal hydrogen donor layers is enhanced in materials with higher oxygen concentration. However, low oxygen concentration is preferred when better control over spatial distribution of the excess donor profiles is required.

InAs/GaAs quantum dot structures emitting in the 1.55 μm band

We investigated different capping layers covering InAs quantum dot structures grown on GaAs substrates by metalorganic vapor phase epitaxy in order to receive strong photoluminescence at 1.55 µm. Atomic force microscopy showed that uncovered InAs quantum dots are 4-5 nm high lenses with a broad luminescence peaking at 1.43 µm. The GaAs capping improves the quantum dot homogeneity but quantum dot dissolution causes blue shift of emitted light. On the other hand, proper engineering of InGaAs strain reducing layer allows to shift the photoluminescence maximum to 1.55 µm. Analysis of photoluminescence and microscopy data supported by calculation of quantum dot electron states shows that this is caused both by the change of the electronic-barrier structure and by the increase of the height of the overgrown quantum dots.

Radiation Defects and Thermal Donors Introduced in Silicon by Hydrogen and Helium Implantation and Subsequent Annealing

The effect of high-energy hydrogen and helium implantation and subsequent annealing on generation of radiation defects and shallow donors in the low-doped oxygen-rich FZ n-type silicon was investigated. Samples were implanted with 7 MeV 4He2+ or 1.8 MeV 1H+ to fluences ranging from 1x109 to 3x1011 cm-2 and 1.4x1010 to 5x1012cm-2, resp., and then isochronally annealed for 30 minutes in the temperature range up to 550°C. Results show that radiation damage produced by helium ions remarkably enhances formation of thermal donors (TDs) when annealing temperature exceeds 375°C, i.e. when the majority of vacancy-related recombination centers anneals out. The excess concentration of TDs is proportional to the helium fluence and peaks at 1.6x1014cm-3 if annealing temperature reaches 475°C. Proton irradiation itself introduces hydrogen donors (HDs) which form a Gaussian peak at the proton end-of-range. Formation and annealing of shallow and deep hydrogen-related levels are strongly influenced by electric field at annealing temperatures below 175°C. If annealing temperature exceeds 350°C, HDs disappear and the excessive shallow doping is caused, as in the case of helium irradiation, by radiation enhanced TDs.

Hydrogenated Radiation Defects in Silicon: Isotopic Effect of Hydrogen and Deuterium

The isotopic effect of hydrogen and deuterium on hydrogenation of radiation defects introduced in n-type float zone and Czochralski silicon by irradiation with high-energy alphas was investigated. Silicon diodes were first irradiated with 2.4 MeV alphas to a fluence of 1x1010 cm-2 and then hydrogen or deuterium was introduced by rf plasma treatment at 250°C. Reactions of hydrogen and deuterium with radiation defects were monitored by deep-level transient spectroscopy during subsequent isochronal annealing at temperatures ranging from 100 to 400°C. Results show that hydrogen rf plasma effectively neutralizes majority of vacancy related radiation defects created by alphas in both materials. In contrast with it, neutralization by deuterium plasma is substantially weaker. Disappearing of vacancy related defect levels due to hydrogen (deuterium) treatment is accompanied by introduction of two dominant deep levels at EC-0.309 eV and EC-0.365 eV. While hydrogenation significantly accelerates annealing of radiation defects especially in Czochralski material, deuteration has weaker effect and gives rise to new defect levels during annealing.

Low-Temperature Diffusion of Transition Metals at the Presence of Radiation Defects in Silicon

Low-temperature diffusion of Cr, Mo, Ni, Pd, Pt, and V in silicon diodes is compared in the range 450 - 800 oC. Before the diffusion, the diodes were implanted with high-energy He2+ to assess, if the radiation defects enhance the concentration of metal atoms at electrically active sites and what is the application potential for carrier lifetime control. The devices were characterized using AES, XPS, DLTS, OCVD carrier lifetime and diode electrical parameters. The metal atoms are divided into two groups. The Pt, Pd and V form deep levels in increased extent at the presence of radiation defects above 600 oC, which reduces the excess carrier lifetime. It is shown as a special case that the co-diffusion of Ni and V from a NiV surface layer results fully in the concentration enhancement of the V atoms. The enhancement of the acceptor level V-/0 (EC 0.203 eV) and donor level V0/+ (EC 0.442 eV) resembles the behavior of substitutional Pts. The second group is represented by the Mo and Cr. They easily form oxides, which can make their diffusion into a bulk more difficult or impossible. Only a slight enhancement of the Cr-related deep levels by the radiation defects has been found above 700 oC.

Radiation Defects in Silicon: Effect of Contamination by Platinum Atoms

The influence of platinum contamination on the stability of radiation defects produced by high-energy proton irradiation was investigated in the low-doped n-type float-zone oxygen rich silicon forming the base of power p+nn+ diodes. Platinum was first implanted and then in-diffused at different temperatures to obtain different levels of contamination. Diodes were then implanted with 1.8 MeV protons to a fluence of 2x1010 cm-2 and radiation defect reaction during isochronal annealing were investigated by deep-level transient spectroscopy. Results show that contamination of silicon by platinum atoms influences significantly both the introduction rates and the temperature stability of dominant radiation defects (vacancy-oxygen pairs, divacancies and VOH complexes).

Helium Irradiation for Advanced Lifetime Control in Silicon: New Recombination Centers and Their Interaction Stimulated by Isochronal Annealing

The article presents results of systematic investigation on annealing of radiation defects introduced into n-type oxygen-rich float-zone silicon by single (7 MeV) and double energy (7 and 7.6 MeV) alpha-particle irradiation with fluences form 8.5 times 108 to 1 times 1012 cm-2. Effect of isochronal anneal in the temperature range from 100 to 500degC on introduced defects and their interaction was studied by deep level transient spectroscopy. Shallow donor levels arising during annealing were investigated by C-V profiling. It is shown that formation of thermal donors (TDs) in the temperature range from 375 to 500degC is significantly enhanced by radiation damage (vacancy-oxygen clusters) produced by alpha-particle irradiation

Effect of proton and alpha irradiation on advanced silicon power devices: defect profiles and stability

cvut.cz Distribution 0/ divacancies in n-type float-zone silicon after irradiation with 1.83.6 Me V protons and 8 - 14.5 alphas was investigated and compared with profiles a/primary damage (vacancies) obtained by Monte Carlo simulation. It is shown that divacancy profiles follow in principle the simulated distribution of primary damage with exception of a small «lfjm) broadening of the defect peak. For both the projectiles, the yield of divacancies per generated vacancy at the defect maximum increases with ion energy while, at a half the projected range, an opposite tendency is observed. Radiation defect stability up to 550°C was studied by isochronal annealing. Results show that, up to 350°C, the divacancy is a dominant center affecting both the excess carrier generation and recombination.