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Title: Diffusion length and junction spectroscopy analysis of low-temperature annealing of electron irradiation-induced deep levels in 4H-SiC

Abstract

The effects of low-temperature annealing in 8.2 MeV electron-irradiated 4H-SiC Schottky diodes were investigated. Deep-level transient spectroscopy and minority-carrier diffusion length (L{sub d}) measurements were carried out on not-irradiated samples and on irradiated samples before and after thermal treatments up to T=450 deg. C. We found that several deep levels in the upper half band gap (S1 with enthalpy E{sub T}=0.27 eV, S2 with E{sub T}=0.35 eV, S4 with E{sub T}=0.71 eV, and S5 with E{sub T}=0.96 eV) anneal out or modify at temperature values lower or equal to T=450 deg. C, whereby their progressive annealing out is accompanied by a net increase of L{sub d}, up to 50% of the value in the as-irradiated sample. We drew some conclusions regarding the microscopic nature of the defects related to the deep levels, according to their annealing behavior.

Authors:
; ; ; ; ;  [1];  [2]
  1. Dipartimento di Fisica, Universita di Bologna, Viale Berti Pichat 6/2, 40127 Bologna (Italy)
  2. (Italy)
Publication Date:
OSTI Identifier:
20787869
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 99; Journal Issue: 3; Other Information: DOI: 10.1063/1.2160708; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ANNEALING; DEEP LEVEL TRANSIENT SPECTROSCOPY; DIFFUSION LENGTH; ELECTRON BEAMS; ENTHALPY; IRRADIATION; MEV RANGE 01-10; SCHOTTKY BARRIER DIODES; SEMICONDUCTOR MATERIALS; SILICON CARBIDES; TEMPERATURE RANGE 0400-1000 K

Citation Formats

Castaldini, A., Cavallini, A., Rigutti, L., Pizzini, S., Le Donne, A., Binetti, S., and Dipartimento di Scienza dei Materiali, Universita di Milano Bicocca, Via Cozzi 53, 20125 Milan. Diffusion length and junction spectroscopy analysis of low-temperature annealing of electron irradiation-induced deep levels in 4H-SiC. United States: N. p., 2006. Web. doi:10.1063/1.2160708.
Castaldini, A., Cavallini, A., Rigutti, L., Pizzini, S., Le Donne, A., Binetti, S., & Dipartimento di Scienza dei Materiali, Universita di Milano Bicocca, Via Cozzi 53, 20125 Milan. Diffusion length and junction spectroscopy analysis of low-temperature annealing of electron irradiation-induced deep levels in 4H-SiC. United States. doi:10.1063/1.2160708.
Castaldini, A., Cavallini, A., Rigutti, L., Pizzini, S., Le Donne, A., Binetti, S., and Dipartimento di Scienza dei Materiali, Universita di Milano Bicocca, Via Cozzi 53, 20125 Milan. Wed . "Diffusion length and junction spectroscopy analysis of low-temperature annealing of electron irradiation-induced deep levels in 4H-SiC". United States. doi:10.1063/1.2160708.
@article{osti_20787869,
title = {Diffusion length and junction spectroscopy analysis of low-temperature annealing of electron irradiation-induced deep levels in 4H-SiC},
author = {Castaldini, A. and Cavallini, A. and Rigutti, L. and Pizzini, S. and Le Donne, A. and Binetti, S. and Dipartimento di Scienza dei Materiali, Universita di Milano Bicocca, Via Cozzi 53, 20125 Milan},
abstractNote = {The effects of low-temperature annealing in 8.2 MeV electron-irradiated 4H-SiC Schottky diodes were investigated. Deep-level transient spectroscopy and minority-carrier diffusion length (L{sub d}) measurements were carried out on not-irradiated samples and on irradiated samples before and after thermal treatments up to T=450 deg. C. We found that several deep levels in the upper half band gap (S1 with enthalpy E{sub T}=0.27 eV, S2 with E{sub T}=0.35 eV, S4 with E{sub T}=0.71 eV, and S5 with E{sub T}=0.96 eV) anneal out or modify at temperature values lower or equal to T=450 deg. C, whereby their progressive annealing out is accompanied by a net increase of L{sub d}, up to 50% of the value in the as-irradiated sample. We drew some conclusions regarding the microscopic nature of the defects related to the deep levels, according to their annealing behavior.},
doi = {10.1063/1.2160708},
journal = {Journal of Applied Physics},
number = 3,
volume = 99,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2006},
month = {Wed Feb 01 00:00:00 EST 2006}
}
  • Low temperature annealing of electron irradiation-induced deep levels in 4H-SiC is reported. The major deep level transient spectroscopy peak S2 associated with the energy level at E{sub c}-0.39 eV disappears in the temperature range 360-400 K, and some rearrangement of the peak S3, associated with the defect Z{sub 1}/Z{sub 2} with energy level at E{sub c}-0.5/E{sub c}-0.65 eV occurs in the temperature interval 400-470 K. A net free charge carrier concentration increase goes along with the disappearance of peak S2 at E{sub c}-0.39 eV, whereas the charge collection efficiency of the diode does not experience any significant change. An interpretationmore » of the annealing of peak S2 on a microscopic scale is given.« less
  • With low energy electron irradiation in the 80-250 keV range, we were able to create only those intrinsic defects related to the initial displacements of carbon atoms in the silicon carbide lattice. Radiation induced majority and minority carrier traps were analyzed using capacitance transient techniques. Four electron traps (EH1, Z{sub 1}/Z{sub 2}, EH3, and EH7) and one hole trap (HS2) were detected in the measured temperature range. Their concentrations show linear increase with the irradiation dose, indicating that no divacancies or di-interstitials are generated. None of the observed defects was found to be an intrinsic defect-impurity complex. The energy dependencemore » of the defect introduction rates and annealing behavior are presented and possible microscopic models for the defects are discussed. No further defects were detected for electron energies above the previously assigned threshold for the displacement of the silicon atom at 250 keV.« less
  • The effects on 4H-silicon carbide epilayers of irradiation with protons and electrons having particle energies, respectively, of 6.5 and 8.2 MeV were carefully studied and critically compared. In detail, the electronic levels associated with the irradiation-induced defects were analyzed by current-voltage characteristics and deep-level transient spectroscopy (DLTS) measurements up to 550 K. In the same temperature range the apparent free-carrier concentration was measured by capacitance-voltage characteristics in order to monitor compensation effects due to the deep levels associated with the induced defects. Introduction rate, enthalpy, and capture cross section of such deep levels were compared. We found that a setmore » of deep levels (at E{sub T}=0.39 eV, E{sub T}=0.65 eV, and E{sub T}=0.75 eV) is the same in both cases of proton and electron irradiations, whereas two other pairs of levels (S1, E{sub T}=0.20 eV and S1*, E{sub T}=0.23 eV; S5, E{sub T}=1.09 eV and S5*, E{sub T}=0.89 eV) appearing in the same temperature range within the DLTS spectra should be associated with different defect complexes according to the irradiation type. Some conclusions regarding the microscopic nature of the defects related to the deep levels have been drawn.« less
  • Effects of high-temperature annealing on deep-level defects in a high-purity semi-insulating 4H silicon carbide substrate have been studied by employing current-voltage, capacitance-voltage, junction spectroscopy, and chemical impurity analysis measurements. Secondary ion mass spectrometry data reveal that the substrate contains boron with concentration in the mid 10{sup 15 }cm{sup −3} range, while other impurities including nitrogen, aluminum, titanium, vanadium and chromium are below their detection limits (typically ∼10{sup 14 }cm{sup −3}). Schottky barrier diodes fabricated on substrates annealed at 1400–1700 °C exhibit metal/p-type semiconductor behavior with a current rectification of up to 8 orders of magnitude at bias voltages of ±3 V. With increasing annealingmore » temperature, the series resistance of the Schottky barrier diodes decreases, and the net acceptor concentration in the substrates increases approaching the chemical boron content. Admittance spectroscopy results unveil the presence of shallow boron acceptors and deep-level defects with levels in lower half of the bandgap. After the 1400 °C annealing, the boron acceptor still remains strongly compensated at room temperature by deep donor-like levels located close to mid-gap. However, the latter decrease in concentration with increasing annealing temperature and after 1700 °C, the boron acceptor is essentially uncompensated. Hence, the deep donors are decisive for the semi-insulating properties of the substrates, and their thermal evolution limits the thermal budget for device processing. The origin of the deep donors is not well-established, but substantial evidence supporting an assignment to carbon vacancies is presented.« less
  • In this study, the authors investigate deep levels, which are induced by reactive ion etching (RIE) of n-type/p-type 4H-SiC, by deep level transient spectroscopy (DLTS). The capacitance of a Schottky contact fabricated on as-etched p-type SiC is abnormally small due to compensation or deactivation of acceptors extending to a depth of {approx}14 {mu}m, which is nearly equal to the epilayer thickness. The value of the capacitance can recover to that of a Schottky contact on as-grown samples after annealing at 1000 deg. C. However, various kinds of defects, IN2 (E{sub C}-0.30 eV), EN (E{sub C}-1.6 eV), IP1 (E{sub V}+0.30 eV),more » IP2 (E{sub V}+0.39 eV), IP4 (HK0: E{sub V}+0.72 eV), IP5 (E{sub V}+0.85 eV), IP7 (E{sub V}+1.3 eV), and EP (E{sub V}+1.4 eV), remain at a high concentration (average of total defect concentration in the region ranging from 0.3 {mu}m to 1.0 {mu}m:{approx}5x10{sup 14} cm{sup -3}) even after annealing at 1000 deg. C. The concentration of all these defects generated by RIE, except for the IP4 (HK0) center, remarkably decreases by thermal oxidation. In addition, the HK0 center can also be reduced significantly by a subsequent annealing at 1400 deg. C in Ar.« less