8 research outputs found
The fine structure of electron irradiation induced EL2-like defects in n-GaAs
Defects induced by electron irradiation in n-GaAs have been studied using deep level transient spectroscopy
(DLTS) and Laplace DLTS (L-DLTS). The E0.83 (EL2) is the only defect observed prior to
irradiation. Ru/n-GaAs Schottky diodes were irradiated with high energy electrons from a Sr-90 radionuclide
up to a fluence of 2.45 1013 cm 2. The prominent electron irradiation induced defects,
E0.04, E0.14, E0.38, and E0.63, were observed together with the metastable E0.17. Using L-DLTS, we
observed the fine structure of a broad base EL2-like defect peak. This was found to be made up of
the E0.75, E0.83, and E0.85 defects. Our study reveals that high energy electron irradiation increases
the concentration of the E0.83 defect and introduces a family of defects with electronic properties
similar to those of the EL2.The authors gratefully acknowledge the financial
support of the South African National Research Foundation
(NRF) and the University of Pretoria.The South African National Research Foundation
(NRF) and the University of Pretoria.http://scitation.aip.org/content/aip/journal/japam2016Physic
The effect of high temperatures on the electrical characteristics of Au/n-GaAs Schottky diodes
In this study, the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of Au/n-GaAs Schottky diodes have been measured over a wide temperature range, 80–480 K. The diodes were rectifying throughout the range and showed good thermal stability. Room temperature values for the ideality factor, I–V barrier height and C–V barrier height were found to be n =1.10, ϕIVϕIV=0.85 eV and ϕCVϕCV=0.96 eV, respectively. ϕIVϕIV increases and n decreases with an increase in temperature. We investigated the effect of elevated temperatures on the barrier height and ideality factor by measuring the diodes at a high temperature (annealing mode) then immediately afterwards measuring at room temperature (post annealing mode). The measurements indicate I–V characteristics that degrade permanently above 300 K. Permanent changes to the C–V characteristics were observed only above 400 K. We also noted a discrepancy in the C–V barrier height and carrier concentration between 340 and 400 K, which we attribute to the influence of the EL2 defect (positioned 0.83 eV below the conduction band minima) on the free carrier density. Consequently, we were able to fit the ϕCVϕCV versus temperature curve into two regions with temperature coefficients −6.9×10−4 eV/K and −2.2×10−4 eV/K above and below 400 K.The University of Pretoria and the South African National Research Foundation grant#88021.http://www.journals.elsevier.com/physica-b-condensed-matter2017-01-31hb2016Physic
Electrical characterization of deep levels created by bombarding nitrogen-doped 4HSiC with alpha-particle irradiation
Deep-level transient spectroscopy (DLTS) and Laplace-DLTS were used to investigate the
effect of alpha-particle irradiation on the electrical properties of nitrogen-doped 4H-SiC. The
samples were bombarded with alpha-particles at room temperature (300 K) using an
americium-241 (241Am) radionuclide source. DLTS revealed the presence of four deep levels
in the as-grown samples, E0.09, E0.11, E0.16 and E0.65. After irradiation with a fluence of 4.1 ×
1010 alpha-particles-cm–2, DLTS measurements indicated the presence of two new deep
levels, E0.39 and E0.62 with energy level, EC – 0.39 eV and EC –0.62 eV, with an apparent
capture cross sections of 2×10–16 and 2×10–14 cm2, respectively. Furthermore, irradiation with
fluence of 8.9×1010 alpha-particles-cm–2 resulted in disappearance of shallow defects due to a
lowering of the Fermi level. These defects -
minutes. Defects, E0.39 and E0.42 with close emission rates were attributed to silicon or carbon
vacancy and could only be separated by using high resolution Laplace-DLTS. The DLTS
peaks at EC – (0.55-0.70) eV (known as Z1/Z2) were attributed to an isolated carbon vacancy
(VC).This work is based on the research supported in part by the National Research Foundation (NRF) of South African (Grant specific unique reference number (UID) 78838).http://www.elsevier.com/locate/nimb2017-03-31hb2016Physic
Electrical characterization of 5.4 MeV alpha-particle irradiated 4H-SiC with low doping density
Nickel Schottky diodes were fabricated on 4H-SiC. The diodes had excellent current rectification with
about ten orders of magnitude between 50 V and +2 V. The ideality factor was obtained as 1.05 which
signifies the dominance of the thermionic emission process in charge transport across the barrier. Deep
level transient spectroscopy revealed the presence of four deep level defects in the 30–350 K temperature
range. The diodes were then irradiated with 5.4 MeV alpha particles up to fluence of 2.6 1010 cm 2.
Current–voltage and capacitance–voltage measurements revealed degraded diode characteristics after
irradiation. DLTS revealed the presence of three more energy levels with activation enthalpies of
0.42 eV, 0.62 eV and 0.76 eV below the conduction band. These levels were however only realized after
annealing the irradiated sample at 200 C and they annealed out at 400 C. The defect depth concentration
was determined for some of the observed defects.National Research Foundation (NRF) of South Africa.http://www.elsevier.com/locate/nimb2016-09-30hb201
Electrical characterization of electron irradiated and annealed lowly-doped 4H-SiC
Please read abstract in the article.The University of Pretoria; Postdoctoral Fellowship Program of the University of Pretoria and the National Research Foundation (NRF) of South Africa.http://www.elsevier.com/locate/nimb2018-10-15hj2017Physic
Electrical characterization of high energy electron irradiated Ni/4H-SiC Schottky barrier diodes
The effect of high energy electron (HEE) irradiation on Ni/4H-SiC Schottky barrier diodes was evaluated by
current-voltage (I-V) and capacitance-voltage (C-V) measurements at room temperature. Electron irradiation
was achieved by using a radioactive strontium source with peak emission energy of 2.3 MeV. Irradiation was
performed in fluence steps of 4.9 × 1013 cm–2 until a total fluence of 5.4 × 1014 cm–2 was reached. The Schottky
barrier height determined from (I-V) measurements was not significantly changed by irradiation while that
obtained from (C-V) measurements increased with irradiation. The ideality factor was obtained before
irradiation as 1.05 and this value did not significantly change as a result of irradiation. The series resistance
increased from 47 Ω before irradiation to 74 Ω after a total electron fluence of 5.4 × 1014 cm–2. The net donor
concentration decreased with increasing irradiation fluence from 4.6 × 1014 cm–3 to 3.0 × 1014 cm–3 from which
the carrier removal rate was calculated to be 0.37 cm–1.National Research Foundation (NRF) of South Africahttp://link.springer.com/journal/116642017-08-31hb2016Physic
Laplace current deep level transient spectroscopy measurements of defect states in methylammonium lead bromide single crystals
We present a measurement of the energies and capture cross-sections of defect states in methylammonium
lead bromide (MAPbBr3) single crystals. Using Laplace current deep level transient spectroscopy
(I-DLTS), two prominent defects were observed with energies 0.17 eV and 0.20 eV from
the band edges, and further I-DLTS measurements confirmed that these two defects are bulk defects.
These results show qualitative agreement with theoretical predictions, whereby all of the observed
defects behave as traps rather than as generation-recombination centers. These results provide one
explanation for the high efficiencies and open-circuit voltages obtained from devices made with lead
halide perovskites.The Israel Ministry of
Science’s Tashtiot program.and the NRF Nanotechnology Flagship
Program (Project No. 88021).http://scitation.aip.org/content/aip/journal/jap2018-10-30am2017Physic
Electrical characterization of defects introduced during sputter deposition of tungsten on n type 4H-SiC
We have studied the defects introduced in n-type 4H-SiC during sputter deposition of tungsten using deep-level transient spectroscopy (DLTS). Current-voltage and capacitance-voltage measurements showed a deterioration of diode thermionic emission characteristics due to the sputter deposition. Two electrically active defects E0.29 and E0.69 were introduced. Depth profiling revealed that sputter deposition increases the concentration of the native Z1 defect. A comparison with prominent irradiation and process induced defects showed that the E0.29 was unique and introduced during sputter deposition only. The E0.69 may be silicon vacancy related defect.The South African National Research Foundation and the University of Pretoria.http://www.elsevier.com/locate/mssp2019-07-01hj2018Physic