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We have used confocal Raman spectroscopy, atomic force microscopy (AFM), Binary collision approximations and Deep level transient spectroscopy (DLTS) to study the defects introduced in n-type 4H-SiC by 167 MeV Xe26+ ions (swift heavy ions (SHIs)). Moderately doped epitaxial layers were irradiated with SHIs to a fluence of 5 × 1011 cm−2 at room temperature. Raman spectroscopy was used to investigate the effects of irradiation on the crystal structure. Raman intensity reduced after irradiation but the overall bond structure was conserved. Cluster spectra from confocal Raman spectroscopy showed a damage impact that was consistent with SRIM simulations. AFM showed that the incident radiation resulted in elongated protrusions. The virgin samples contained the E0.09, E0.12, E0.15 and E0.65 as the only electrically active defects. After irradiation the E0.40 and E0.71 defects were introduced.

ZnO thin films were prepared using the sol-gel spin coating technique. The structure was investigated using X-ray diffraction (XRD). The XRD spectra exhibited typical randomly orientated structure with a slight preference for growth along the (002) plane and a crystallite size of ∼ 48 nm. The Schottky barrier diodes were fabricated on the synthesized ZnO thin films. The electrical properties before and after irradiating the devices with alpha particle irradiation were characterized using current-voltage (I-V), capacitance-voltage (C-V), deep-level transient spectroscopy (DLTS) and Laplace-transform deep-level transient spectroscopy (L-DLTS) techniques. Pd/ZnO/n-Si/AuSb Schottky diodes exhibited good rectifying properties. Before irradiation, the DLTS spectra revealed one defect E 4 with activation enthalpy 0.41 eV. After irradiation, there is a new defect E α with the activation enthalpy 0.35 eV. Laplace-transform deep-level transient spectroscopy (L-DLTS) revealed the fine structure of the E α to be made up of 0.53 eV and 0.36 eV defects.

Au Schottky barrier contacts (SBDs) were DC sputter deposited on Si doped n-type GaAs at a power of 150 W. Deep-level transient spectroscopy (DLTS) and Laplace DLTS were used to characterize the sputter-induced defects near the surface of the GaAs. In this study, I-V and C-V measurements showed that the sputter deposited diodes had a significantly lower barrier height and a higher free carrier density. Using DLTS, it was found that this sample contained seven defects – three of them were metastable while one of the others was highly dopant dependent. The energy levels of these defects are Ec – 0.046 eV, Ec – 0.22 eV, Ec – 0.30 eV, Ec – 0.55 eV, Ec – 0.56 eV, Ec – 0.83 eV and Ec – 0.84 eV. The EL2 defect was not observed in the sputtered samples, but one of the sputter-induced defects emitted in the same range as the EL2, however, it had two components and their DLTS signatures (Ec – 0.83 eV and Ec – 0.84 eV) differed significantly from that of the EL2. By applying different bias conditions (−2 V and zero V) for annealing procedures, the metastable defects (Ec – 0.30 eV and Ec – 0.56 eV) were transformed into each other. The pre-factor obtained from transformation rate of Ec – 0.56 eV → Ec – 0.30 eV under reverse bias was 3 × 1015 s−1 which is related to free carrier emission.

Ni/4H-SiC Schottky barrier diodes have been irradiated by 5.4-MeV helium ions at cryogenic temperatures and their electrical characteristics investigated. Only the prominent native defects (E0.11, E0.16, and E0.65) were observed before and after low-temperature irradiation at 50 K, with a baseline on the spectrum observed starting at 190 K. Low-temperature irradiation reduced the concentration of native E0.11 and E0.16 defects. After annealing at 380 K, E0.37, E0.58, E0.62, E0.73, and E0.92 defects were observed. These results show that E0.62, an acceptor level of the Z1 center, and E0.73, an acceptor level of the Z2 center, are both secondary defects which are not formed directly from the irradiation process but from succeeding thermal reactions. An interpretation of the formation of the secondary defects is given.

We have characterised the deep level defects present before and after annealing the proton-irradiated Ni/nitrogen-doped 4H-SiC Schottky barrier diodes (SBDs) using deep level transient spectroscopy. The bombardment of the sample was carried out at a fluence of 1.0 × 1012 cm−2. The quality of the Ni/4H-SiC SBDs was evaluated before and after proton irradiation and annealing by current–voltage (I-V) and capacitance–voltage (C-V) measurements, carried out at room temperature (300 K). The I-V and C-V results revealed extensive degradation of the diodes properties after proton irradiation at the aforementioned fluence. Rectification properties of the Ni/4H-SiC SBDs recovered gradually after annealing in flowing argon at temperatures varying from 125 to 625 °C. The presence of four electron traps (Ec – 0.10, Ec – 0.13, Ec – 0.18 and Ec – 0.69 eV) was observed in as-grown Ni/4H-SiC SBDs. Deep level defects, Ec – 0.42 and Ec – 0.76 eV, were revealed after annealing the proton-irradiated SBDs up to 225 °C. The two defects observed at 225 °C later annealed out at 425 °C, causing a significant change in the spectrum. The annealing out of Ec – 0.42 and Ec – 0.76 eV at 425 °C was concurrent with detection of two electron traps, Ec – 0.31 and Ec – 0.62 eV. We speculate that the defects Ec – 0.42 and Ec – 0.76 eV have a link or relationship with defects Ec – 0.31 and Ec – 0.62 eV, respectively. The defect, Ec – 0.31 eV, was stable up to high-temperature annealing and was attributed to a carbon interstitial.

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.

We have investigated the current-voltage ( I-V ) characteristics of nickel (Ni), cobalt (Co), tungsten (W) and palladium (Pd) Schottky contacts on n-type 4 H -SiC in the 300–800 K temperature range. Results extracted from I-V measurements of Schottky barrier diodes showed that barrier height ( Ф Bo ) and ideality factor ( n ) were strongly dependent on temperature. Schottky barrier heights for contacts of all the metals showed an increase with temperature between 300 K and 800 K. This was attributed to barrier inhomogeneities at the interface between the metal and the semiconductor, which resulted in a distribution of barrier heights at the interface. Ideality factors of Ni, Co and Pd decreased from 1.6 to 1.0 and for W the ideality factor decreased from 1.1 to 1.0 when the temperature was increased from 300 K to 800 K respectively. The device parameters were compared to assess advantages and disadvantages of the metals for envisaged applications.

Primary defects introduced in boron-doped silicon by an alpha-particle source with a fluence rate of 7 × 106 cm−2 s−1 at cryogenic temperatures were investigated using deep-level transient spectroscopy (DLTS). The data showed that the defects observed between 35 K and 120 K were not detectable when irradiation was carried out at room temperature. The defect levels were observed at 0.10 eV, 0.14 eV and 0.18 eV above the valence band maximum. These levels were attributed to the boron-substitutional vacancy complex, the mono vacancy and a vacancy-related defect respectively.

Au/Ni (20:80) Schottky barrier diodes (SBDs) were resistively evaporated on nitrogen-doped n –type 4 H -SiC. Current-voltage ( I-V ) and capacitance-voltage ( C-V ) characteristics of the SDBs were investigated before and after bombardment with 1.8 MeV proton irradiation at a fluence of 2.0 × 10 12 cm –2 . The measurements were carried out in the temperature range 40–300 K in steps of 20 K. Results obtained at room temperature (300 K) showed highly rectifying devices before and after bombardment. It was observed that the proton irradiation induced an increase of ideality factor from 1.05 to 1.13, a decrease in Schottky barrier height from 1.40 to 1.22 eV, an increase in series resistance from 10 to 66 Ω and a noticeable increase of the saturation current from 3.0 × 10 –21 to 6.8 × 10 –17 A. The increase in saturation current after proton irradiation was attributed to the presence of interfacial states created by irradiation-induced defects. Thermionic emission dominated the I-V characteristics in the temperature range 120–300 K but the I-V characteristics deviated from thermionic emission theory at temperatures below 120 K for devices both before and after irradiation. The variation of the SBDs characteristics with temperature was attributed to the presence of lateral inhomogeneities of the SBH. Modified Richardson constants were determined from a Gaussian distribution of barrier heights to be 133 and 165 A cm –2 K –2 before and after irradiation, respectively.

The electronic and thermal properties of defects introduced during electron beam deposition (EBD) followed by isochronal annealing of titanium (Ti) contacts on p-Si were investigated. In this work, EBD-deposited Ti Schottky contacts were annealed within a temperature range of 200–400 °C. Current-voltage ( I - V ) measurements were conducted to monitor the change in electrical characteristics with every annealing step. A barrier height of 0.55 eV was measured on the as-deposited sample. Deep level transient spectroscopy (DLTS) and Laplace-DLTS techniques were employed to identify the defects introduced after EBD and isochronal annealing of the Ti Schottky contacts. DLTS revealed that the main defects introduced during metallization were hole traps H(0.05), H(0.23) and H(0.38). Annealing at 300 °C removed the two hole traps H(0.05) and (0.38). Atomic force microscopy (AFM) was performed on the contacts to monitor their surface topology. The surface of the contacts became rougher as the annealing temperature increased. The slight increase in root-mean-square roughness of the contacts with increasing annealing temperature may be attributed to outdiffusion of Si into Ti layers.

We have used deep level transient spectroscopy (DLTS) and Laplace DLTS (L-DLTS) to characterize the electrically active point defects introduced in n -type gallium arsenide by electron beam exposure prior to Schottky metallization. The GaAs crystals were exposed to incident electrons at sub-threshold energies which are deemed low and insufficient to form defects through ion solid interactions. DLTS revealed a set of electron traps different from those commonly observed in n -GaAs after particle irradiation. These different signatures from the same radiation type suggest that different mechanisms are responsible for defect formation in the two electron irradiation processes. An analysis of the conditions under which the defects were formed was done to distil a number of possible defect formation mechanisms using the experimental evidence obtained.

The effect of high energy electron (HEE) irradiation on nickel Schottky contacts fabricated on lowly-doped n -type 4 H -SiC was investigated by deep level transient spectroscopy (DLTS) and high resolution Laplace-DLTS. The Schottky contacts were deposited by resistive evaporation of nickel and were observed to be of good rectification quality from current-voltage measurements. DLTS was performed up to 350K to investigate the presence of defects before and after HEE irradiation. HEE irradiation was observed to induce three deep level defects below 350 K at 0.42 eV, 0.62 eV and 0.76 eV below the conduction band minimum. These deep level defects are labelled E 0.42 , E 0.62 and E 0.76 . Defects E 0.42 and E 0.76 were observed after the same electron fluence and were annealed out at the same temperature, suggesting that the defects could be strongly related. The effect of HEE irradiation and annealing on as-grown defects was also investigated and is reported.

Deep-level transient spectroscopy measurements on β-Ga 2 O 3 crystals reveal the presence of three defect signatures labeled E 2 a, E 2 b, and E 3 with activation energies at around 0.66 eV, 0.73 eV, and 0.95 eV below the conduction band edge. Using secondary ion mass spectrometry, a correlation between the defect concentration associated with E 3 and the Ti concentration present in the samples was found. Particularly, it is found that E 3 is the dominant Ti-related defect in β-Ga 2 O 3 and is associated with a single Ti atom. This finding is further corroborated by hybrid functional calculations that predict Ti substituting on an octahedral Ga site, denoted as Ti GaII, to be a good candidate for E 3. Moreover, the deep level transient spectroscopy results show that the level previously labeled E 2 and attributed to Fe substituting on a gallium site (Fe Ga) consists of two overlapping signatures labeled E 2 a and E 2 b. We tentatively assign E 2 a and E 2 b to Fe substituting for Ga on a tetrahedral or an octahedral site, respectively.

Deep level transient spectroscopy (DLTS) was used to characterise Cs implanted GaN grown by hydride vapour phase epitaxy (HVPE). This implantation was done at room temperature using energy of 360 keV to a fluence of 10–11 cm−2. A defect with activation energy of 0.19 eV below the conduction band and an apparent capture cross section of 1.1 × 10–15 cm2 was induced. This defect has previously been observed after rare earth element (Eu, Er and Pr) implantation. It has also been reported after electron, proton and He ion implantation.

Deep level transient spectroscopy was used to study the defects induced by alpha-particle irradiation from an Am241 source in antimony doped n-type germanium. Previous investigations of the well know Sb-vacancy defect have led to the discovery of a second defect with very similar emission properties, referred to as the E′. Although both defects have similar emission rates, they have very different annealing properties. In this study we further investigated these properties of the E′ in Sb doped samples irradiated at 270 K with alpha particles from an Am241 source. Laplace deep level transient spectroscopy was used to determine the concentration of each defect. An isothermal annealing study of the E′ was carried out in the temperature range 300 K to 325 K in 5 K increments, while the Sb-vacancy was annealed out completely at 410 K onwards, long after the E′ was completely annealed out. The annealing activation energy was determined through isothermal annealing profiles for both the Sb-Vacancy and the E′ as 1.05 eV and 0.73 eV respectively with a prefactor of 2.05 × 109 s−1 and 2.7 × 108 s−1.

We have studied the defects introduced in n -type 4H-SiC during electron beam deposition (EBD) of tungsten by deep-level transient spectroscopy (DLTS). The results from current-voltage and capacitance-voltage measurements showed deviations from ideality due to damage, but were still well suited to a DLTS study. We compared the electrical properties of six electrically active defects observed in EBD Schottky barrier diodes with those introduced in resistively evaporated material on the same material, as-grown, as well as after high energy electron irradiation (HEEI). We observed that EBD introduced two electrically active defects with energies E C – 0.42 and E C – 0.70 eV in the 4H-SiC at and near the interface with the tungsten. The defects introduced by EBD had properties similar to defect attributed to the silicon or carbon vacancy, introduced during HEEI of 4H-SiC. EBD was also responsible for the increase in concentration of a defect attributed to nitrogen impurities (E C – 0.10) as well as a defect linked to the carbon vacancy (E C – 0.67). Annealing at 400 °C in Ar ambient removed these two defects introduced during the EBD.

The effect of high energy electron 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.

In this study n-type GaN was subjected to irradiation. This irradiation was performed by Xe+26 of 167 MeV to a fluence of 1010 cm−2 at room temperature. Irradiation resulted in an increase in the reverse current by about 10 orders of magnitude. This has been explained by the generation/recombination centers formed during irradiation. Using the deep level transient spectroscopy (DLTS) technique, two defects were identified after irradiation with activation energies of 0.07 and 0.48 eV below the conduction band. These defects have similar signatures to other defects observed after electron irradiation, thermal annealing and In doping.

The deep level transient spectroscopy (DLTS) technique was used to investigate the effects of electron beam exposure (EBE) on n-GaN. A defect with activation energy of 0.12 eV and capture cross section of 8.0×10–16 cm2 was induced by the exposure. The defect was similar to defects induced by other irradiation techniques such as proton, electron, and gamma irradiation. In comparison to GaN, the EBE induced defects in other materials such as Si and SiC are similar to those induced by other irradiation methods.

In this paper, we report on defects introduced in epitaxially grown n-type silicon (Si) during electron beam exposure. The defects observed were electrically characterized using deep-level transient spectroscopy (DLTS) and high- resolution Laplace DLTS. In this process, Si samples were first exposed to the conditions of electron beam deposition (EBD) without depositing a metal. In this paper, this process is called electron beam exposure (EBE). After 50 minutes of EBE, gold Schottky contacts were fabricated using a resistive deposition method. The defect levels E(0.11) and E(0.17) seem to be associated with the carbon interstitial-substitutional pair CiCs. The CiCs-defect is a bistable defect with an amphoteric character in two defect configurations: A and B. The transition from configuration A to B and vice versa is made possible by a simple bond-switching transformation. A defect level E(0.21) was observed, but the defect’s structure is not clear. E(0.41) and E(0.45) were also observed, associated with a divacancy and a phosphorous interstitial, respectively. E(0.47) and E(x) were observed, but their structures are still a subject of speculation.

The effects of isochronal annealing on the electrical, morphological and structural characteristics of Au/Ni/4H-SiC Schottky barrier diodes (SBDs) have been studied. Current–voltage (I–V), capacitance–voltage (C–V), deep-level transient spectroscopy, scanning electron microscope (SEM) and X-ray diffraction measurements were employed to study the thermal effect on the characteristics of the SBDs. Prior to thermal annealing of Schottky contacts, the I–V measurements results confirmed the good rectification behaviour with ideality factor of 1.06, Schottky barrier height of 1.20 eV and series resistance of 7 Ω. The rectification properties after annealing was maintained up to an annealing temperature of 500 °C, but deviated slightly above 500 °C. The uncompensated ionized donor concentration decreased with annealing temperature, which could be attributed to out-diffusion of the 4H-SiC into the Au/Ni contacts and decrease in bonding due to formation of nickel silicides. We observed the presence of four deep-level defects with energies 0.09, 0.11, 0.16 and 0.65 eV below the conduction band before and after the isochronal annealing up to 600 °C. The conclusion drawn was that annealing did not affect the number of deep-level defects present in Au/Ni/4H-SiC contacts. The variations in electrical properties of the devices were attributed to the phase transformations and interfacial reactions that occurred after isochronal annealing.

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, ϕ I V =0.85 eV and ϕ C V =0.96 eV, respectively. ϕ I V 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 ϕ C V 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.

National Research Foundation (NRF) of South African (Grant specific unique reference number (UID) 78838).

The evolution of Ni/Au and Ni/Ir/Au metal contacts deposited on AlGaN was investigated at different annealing temperatures. The samples were studied with electrical and chemical composition techniques. I–V characteristics of the Schottky diodes were optimum after 500 and 600 °C annealing for Ni/Au and Ni/Ir/Au based diodes, respectively. The depth profiles of the contacts were measured by x-ray photoelectron spectroscopy and time of flight secondary ion mass spectroscopy. These chemical composition techniques were used to examine the evolution of the metal contacts in order to verify the influence the metals have on the electrical properties of the diodes. The insertion of Ir as a diffusion barrier between Ni and Au effected the electrical properties, improving the stability of the contacts at high temperatures. Gold diffused into the AlGaN film, degrading the electrical properties of the Ni/Au diode. At 500 °C, the insertion of Ir, however, prevented the in-diffusion of Au into the AlGaN substrate.

We report on the analysis of current voltage ( I–V ) measurements performed on Pd/ZnO Schottky barrier diodes (SBDs) in the 80–320 K temperature range. Assuming thermionic emission (TE) theory, the forward bias I–V characteristics were analysed to extract Pd/ZnO Schottky diode parameters. Comparing Cheung’s method in the extraction of the series resistance with Ohm’s law, it was observed that at lower temperatures (T 200 K). The barrier height and the ideality factor decreased and increased, respectively, with decrease in temperature, attributed to the existence of barrier height inhomogeneity. Such inhomogeneity was explained based on TE with the assumption of Gaussian distribution of barrier heights with a mean barrier height of 0.99 eV and a standard deviation of 0.02 eV. A mean barrier height of 0.11 eV and Richardson constant value of 37 A cm − 2 K −2 were determined from the modified Richardson plot that considers the Gaussian distribution of barrier heights.

Current–voltage, capacitance–voltage and conventional deep level transient spectroscopy at temperature ranges from 40 to 300 K have been employed to study the influence of alpha-particle irradiation from an 241 Am source on Ni/4H–SiC Schottky contacts. The nickel Schottky barrier diodes were resistively evaporated on n-type 4H–SiC samples of doping density of 7.1 × 10 15 cm −3 . It was observed that radiation damage caused an increase in ideality factors of the samples from 1.04 to 1.07, an increase in Schottky barrier height from 1.25 to 1.31 eV, an increase in series resistance from 48 to 270 Ω but a decrease in saturation current density from 55 to 9 × 10 −12 A m −2 from I – V plots at 300 K. The free carrier concentration of the sample decreased slightly after irradiation. Conventional DLTS showed peaks due to four deep levels for as-grown and five deep levels after irradiation. The Richardson constant, as determined from a modified Richardson plot assuming a Gaussian distribution of barrier heights for the as-grown and irradiated samples were 133 and 151 A cm −2 K −2 , respectively. These values are similar to literature values.

The influence of high energy electron (HEE) irradiation from a Sr-90 radio-nuclide on n-type Ni/4H–SiC samples of doping density 7.1×1015 cm−3 has been investigated over the temperature range 40–300 K. Current–voltage (I–V), capacitance–voltage (C–V) and deep level transient spectroscopy (DLTS) were used to characterize the devices before and after irradiation at a fluence of 6×1014 electrons-cm−2. For both devices, the I–V characteristics were well described by thermionic emission (TE) in the temperature range 120–300 K, but deviated from TE theory at temperature below 120 K. The current flowing through the interface at a bias of 2.0 V from pure thermionic emission to thermionic field emission within the depletion region with the free carrier concentrations of the devices decreased from 7.8×1015 to 6.8×1015 cm−3 after HEE irradiation. The modified Richardson constants were determined from the Gaussian distribution of the barrier height across the contact and found to be 133 and 163 A cm−2 K−2 for as-deposited and irradiated diodes, respectively. Three new defects with energies 0.22, 0.40 and 0.71 eV appeared after HEE irradiation. Richardson constants were significantly less than the theoretical value which was ascribed to a small active device area.

Deep level transient spectroscopy (DLTS) was used to characterize the defects introduced in n-type, N-doped, 4H-SiC while being exposed to electron beam evaporation conditions. This was done by heating a tungsten source using an electron beam current of 100 mA, which was not sufficient to evaporate tungsten. Two new defects were introduced during the exposure of 4H-SiC samples to electron beam deposition conditions (without metal deposition) after resistively evaporated nickel Schottky contacts. We established the identity of these defects by comparing their signatures to those of high energy particle irradiation induced defects of the same materials. The defect E0.42 had acceptor-like behaviour and could be attributed to be a silicon or carbon vacancy. The E0.71 had intrinsic nature and was linked to a carbon vacancy and/or carbon interstials.

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 × 10 10 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.

We report on a systematic investigation of temperature dependent current–voltage (I–V) characteristics of Pd/ZnO Schottky barrier diodes in the 30–300 K temperature range. The ideality factor was observed to decrease with increase in temperature, whilst the barrier height increases with increase in temperature. The observed trend has been attributed to barrier inhomogeneities, which results in a distribution of barrier heights at the interface. Using the dependence of saturation current values on temperature, we have calculated the Richardson constant (A⁎) which was investigated in the two distinct temperature regions: 140–200 K and 210–300 K and values of 3×10−12 and 3×10−9 A cm−2 K−2 were obtained, respectively. A mean barrier height of 0.97 eV was obtained in the 140–300 K temperature range. Applying the barrier height inhomogeneities correction, the value of A⁎ was obtained from the modified Richardson plots as 39.43 and 39.03 A cm−2 K−2 in the 140–200 K and 210–300 K temperature range. The modified Richardson constant (A⁎⁎) has proved to be strongly affected by barrier inhomogeneities and dependent on contact quality.

Ions arriving at a semiconductor surface with very low energy (2 - 8 eV) are interacting with defects deep inside the semiconductor. Several different defects were removed or modified in Sb-doped germanium, of which the E–center has the highest concentration. The low fluence and low energy of the plasma ions implies that the energy has to be able to travel in a localized way to be able to interact with defects up to a few microns below the semiconductor surface. After eliminating other possibilities (electric field, light, heat) we now conclude that moving intrinsic localized modes (ILMs), as a mechanism of longdistance energy transport, are the most likely cause. This would be striking evidence of the importance of ILMs in crystals and opens the way to further experiments to probe ILM properties both in semiconductors and in the metals used for contacts. Although most of the measurements have been performed on germanium, similar effects have been found in silicon. MICINN South African National Research Foundation European Regional Development Fund, Centre of Excellence Mesosystems: Theory and Applications

SA Research Chairs Initiative of the Department of Science and Technology, National Research Foundation and the NMMU.

The capture barrier energy of the E-center deep level defect introduced in Pd/Sb-doped Ge by alpha-particle irradiation has been studied. Palladium Schottky barrier diodes (SBDs) fabricated by resistive evaporation technique were successfully characterised by current-voltage (I-V), capacitance-voltage (C-V), conventional and Laplace deep level transient spectroscopy. The rectification quality of Schottky contacts before and after irradiation was confirmed by I-V and C-V results. The ideality factor and doping density were determined to be in the range of 1.23 to 1.46 and 3.55 × 1015 to 5.25 × 1015 cm−3, respectively before and after irradiating the device with alpha-particles. The thermal emission activation energy and the apparent capture cross section of the E-center were determined from the Arrhenius plot to be 0.37 eV and 1.3 × 10−15 cm2, respectively. The capture barrier energyand the true capture cross section of the E-center were calculated to be 0.052 eV and 2.25 × 10−17 cm2, respectively from the experimental findings after varying the pulse width at different temperature range from 145 to 180 K in steps of 5 K.

Inductively coupled plasma (ICP) etching of germanium introduces a single defect, the E 0.31 electron trap, for a large range of argon partial pressures from 4×10 –3 to 6.5×10 –4 mbar that correspond to ion energies of 8 to 60 eV. Ge of three crystallographic orientations, (1 0 0), (1 1 0) and (1 1 1), treated with 20 and 60 eV ICP had defect concentration profiles that were similar in appearance, with a maximum concentration of 10 14 cm −3 extending more than a µm into the material, approximately three orders of magnitude deeper than what TRIM simulations predicted. All profiles were measured using Laplace deep level transient spectroscopy (L-DLTS), a technique that is sensitive to defect concentrations as low as 10 11 cm −3 . Isochronal annealing of samples showed concentration curves broadening after a 400 K anneal and decreasing to the 10 13 cm −3 level after a 450 K anneal. Unannealed samples measured after a year exhibited similar decreases in defect concentration without broadening of their profiles. A 550 K anneal lowered the defect concentration to levels below the L-DLTS detection limit. Thereafter additional plasma treatment of the surface failed to reintroduce this defect indicating that the structure required for the formation of E 0.31 was no longer present in the region under observation.

An AlGaN-based front illuminated intrinsically solar-blind ultraviolet four-quadrant Schottky detector was fabricated and characterized. A layered ohmic structure was deposited followed by a multi-step annealing method. Ultraviolet transmissive iridium oxide was used as the Schottky barrier material and formed by a two-step annealing method. Au contacts were deposited on the Schottky contacts and annealed. The detector was mounted onto a commercial chip carrier and wires were epoxy bonded from the ohmic and Au contacts to the carrier strips. The detector had an average ideality factor of 1.97±0.08, a Schottky barrier height of (1.22±0.07) eV, a reverse leakage current density of (2.1±4) nA/cm 2 , a series resistance of ( 120 ± 30 ) Ω and a free carrier concentration of ( 1.6 ± 0.3 ) × 10 18 cm − 3 . Spectral characterization on the photosensitive area of 7.3 × 10 − 3 cm 2 yielded a cut-off wavelength at (275±5)nm (4.59 eV to 4.23 eV) for each quadrant, corresponding to the absorption edge of a (46±3)% Al content AlGaN-based material. The detector had an average responsivity of (28±2) mA/W and a quantum efficiency of (14±1)% at 250 nm. The ultraviolet-to-visible and near-infrared rejection ratio was between 10 3 and 10 5 for most of the quadrants. Characterization showed uniformity across the quadrants, proving the detector feasible for implementation in future ultraviolet-sensitive electro-optic devices.

Barrier height inhomogeneities on Pd/n-type 4H-SiC Schottky barrier diodes in the 300–800 K temperature range have been investigated. Palladium is known to form silicide above 673 K. Temperature dependent current-voltage (I-V) characteristics were analyzed. Barrier height (BH) and ideality factor (n) were found to be strongly temperature dependent. Barrier height increased, whilst ideality factor decreased with increasing in temperature and the Richardson plot showed some deviation from linearity. This was attributed to barrier inhomogeneities at the metal-semiconductor interface which resulted in a distribution of barrier heights. From the modified Richardson plot, the modified Richardson constant, A** was found to be 155 Acm−2K−2 and 87 Acm-2 K−2 in the 300–525 K and the 550–800 K temperature ranges respectively.

The defects introduced in epitaxially grown p-type silicon (Si) during electron beam exposure were electrically characterised using deep level transient spectroscopy (DLTS) and high resolution Laplace-DLTS. In this process, Si samples were first exposed to the conditions of electron beam deposition (EBD) without metal deposition. This is called electron beam exposure (EBE) herein. After 50 minutes of EBE, nickel (Ni) Schottky contacts were fabricated using the resistive deposition method. The defect level observed using the Ni contacts had an activation energy of H(0.55). This defect has an activation energy similar to that of the I-defect. The defect level is similar to that of the HB4, a boron related defect. DLTS depth profiling revealed that H(0.55) could be detected up to a depth of 0.8 μm below the junction. We found that exposing the samples to EBD conditions without metal deposition introduced a defect which was not introduced by the EBD method. We also observed that the damage caused by EBE extended deeper into the material compared to that caused by EBD.

We report on in situ space charge spectroscopy measurements on low-temperature proton-bombarded n-type gallium nitride thin film samples. The scope of this study was to investigate the introduction and annealing dynamics of radiation-induced lattice damage. Using optical excitation allowed for the detection of electronic defect states in the entire GaN bandgap and to detect unstable primary defects that would have been invisible in thermal space charge spectroscopic measurements. The introduction of compensating acceptor-like primary defects by the bombardment was observed and manifested as a decrease in the sample capacitance. After the bombardment the concentrations of deep-levels and acceptor states were monitored by deep-level transient spectroscopy and photo-capacitance measurements while the temperature was increased. It was found that annealing and reactions of primary bombardment-induced defects occurs even below room-temperature which might account for the radiation-hardness of GaN.

We have used deep level transient spectroscopy (DLTS) and high resolution DLTS to characterize the defects introduced in epitaxially grown n-type, P-doped, Si during electron beam deposition (EBD) of Pt for Schottky contact formation. The identity of some of these defects could be established by comparing their properties to those of well-known defects introduced by high energy electron irradiation of the same material. The most prominent EBD-induced defects thus identified were the E-center (VP center), the A-center (VO center), interstitial carbon (Ci), and the interstitial carbon–substitutional carbon (CiCs) pair. EBD also introduced some defects that were not observed after high energy electron irradiation. DLTS depth profiling revealed that the main defects, VO and VP, could be detected up to 0.5 µm below the metal–Si interface. Shielding the sample from particles originating in the region of the electron beam significantly reduced defect introduction and resulted in Schottky contacts with improved rectification properties. Finally, we have found that exposing the sample to EBD conditions, without actually depositing metal, introduced a different set of electron traps, not introduced by the EBD process.

The South African Research Chair’s Initiative of the Department of Science and Technology, National Research Foundation, as well as by the Nelson Mandela Metropolitan University (NMMU).

Intrinsically solar-blind ultraviolet (UV) AlGaN-based Schottky photodiodes were fabricated using Iridium oxide (IrO2) as the Schottky barrier material. The Ir Schottky contacts were annealed at 700 °C under O2 ambient and the photodiodes characterized with an optoelectronic system. The main parameters extracted from I–V measurements were an average ideality factor of 1.38, a Schottky barrier height of 1.52 eV, a reverse leakage current density at −1 V bias of 5.2 nA/cm2 and series resistance of 250 Ω . After spectral characterization, it was found that annealing, alone, of the Ir contact to form the more UV transmissive IrO2 does not always improve the responsivity. The deposition of a Au probe contact on the IrO2 contact increased the responsivity from 40 mA/W to 52 mA/W at 275 nm with respect to the annealed Ir contact. However, the ideality factor degraded to 1.57, Schottky barrier height lowered to 1.19 eV, reverse leakage current density increased to 49 nA/cm2 and series resistance decreased to 100 Ω with the addition of the Au contact. The radiation hardness of AlGaN was also confirmed after studying the effects of 5.4 MeV He-ion irradiation using 241Am for a total fluence of 3 × 10 13 cm−2.

We report on the studies carried out on hydrogen peroxide treated melt-grown, bulk single crystal ZnO samples. Results show the existence of two shallow donors in the as-received ZnO samples with energy levels (37.8±0.3) meV that has been suggested as Zni related and possibly H-complex related and (54.5±0.9) meV, which has been assigned to an Al-related donor. Annealing studies performed on the hydrogen peroxide treated samples reveal the existence of a conductive channel in the samples in which new energy levels have been observed, Zn vacancies, related to the Group I elements, XZn. The surface donor volume concentration of the conductive channel was calculated from a theory developed by Look (2007) [1] . Results indicate an increase in the surface volume concentration with increasing annealing temperature from 60×1017 cm−3 at 200 °C to 4.37×1018 cm-3 at 800 °C.

The variation in electrical characteristics of Au/n-Ge (1 0 0) Schottky contacts have been systematically investigated as a function of temperature using current-voltage (IV) measurements in the tempera- ture range 140-300 K. The I-V characteristics of the diodes indicate very strong temperature dependence. While the ideality factor n decreases, the zero-bias Schottky barrier height (SBH) (FB) increases with the increasing temperature. The I-V characteristics are analyzed using the thermionic emission (TE) model and the assumption of a Gaussian distribution of the barrier heights due to barrier inhomogeneities at the metal-semiconductor interface. The zero-bias barrier height FB vs. 1/2 kT plot has been used to show the evidence of a Gaussian distribution of barrier heights and values of FB¼ 0.615 eV and standard deviation ss0¼0.0858 eV for the mean barrier height and zero-bias standard deviation have been obtained from this plot, respectively. The Richardson constant and the mean barrier height from the modified Richardson plot were obtained as 1.37 A cm � 2 K � 2 and 0.639 eV, respectively. This Richardson constant is much smaller than the reported of 50 A cm � 2 K � 2 . This may be due to greater inhomogeneities at the interface.

Ruthenium (Ru) Schottky contacts were fabricated on n-Ge (1 0 0) by electron beam deposition. Current–voltage (I–V), deep level transient spectroscopy (DLTS), and Laplace-DLTS techniques were used to characterise the as-deposited and annealed Ru/n-Ge (1 0 0) Schottky contacts. The variation of the electrical properties of the Ru samples annealed between 25 °C and 575 °C indicates the formation of two phases of ruthenium germanide. After Ru Schottky contacts fabrication, an electron trap at 0.38 eV below the conduction band with capture cross section of 1.0×10−14 cm−2 is the only detectable electron trap. The hole traps at 0.09, 0.15, 0.27 and 0.30 eV above the valence band with capture cross sections of 7.8×10−13 cm−2, 7.1×10−13 cm−2, 2.4×10−13 cm−2 and 6.2×10−13 cm−2, respectively, were observed in the as-deposited Ru Schottky contacts. The hole trap H(0.30) is the prominent single acceptor level of the E-centre, and H(0.09) is the third charge state of the E-centre. H(0.27) shows some reverse annealing and reaches a maximum concentration at 225 °C and anneals out after 350 °C. This trap is strongly believed to be V–Sb2 complex formed from the annealing of V–Sb defect centre.

Deep Level Transient Spectroscopy (DLTS) was used to measure the field enhanced emission rate from a defect introduced in n-type Ge. The defect was introduced through low energy (±80 eV) inductively coupled plasma (ICP) etching using Ar. The defect, named EP0.31, had an energy level 0.31 eV below the conduction band. Models of Pons and Makram-Ebeid (1979) [2] and Ganichev and Prettl (1997) [3] , which describe emission due to phonon assisted tunneling, were fitted to the observed electric field dependence of the emission rate. The model of Pons and Makram-Ebeid fitted the measured emission rate more accurately than Ganichev and Prettl. However the model of Ganichev and Prettl has only two parameters, while the model of Pons and Makram-Ebeid has four. Both models showed a transition in the dominant emission mechanism from a weak electron–phonon coupling below 152.5 K to a strong electron–phonon coupling above 155 K. After the application of a χ2 goodness of fit test, it was determined that the model of Pons and Makram-Ebeid describes the data well, while that of Ganichev and Prettl does not.

We oxidized a Ni/Au metal bi-layer contact fabricated on HVPE Al0.18Ga0.82N from 373 K to 573 K in 100 K steps. In the range 1 kHz to 2 MHz, the Capacitance–Voltage–Frequency (C–V–f) measurements reveal a frequency dispersion of the capacitance and the presence of an anomalous peak at 0.4 V owing to the presence of interface states in the as deposited contact system. The dispersion was progressively removed by O2 anneals from temperatures as low as 373 K. These changes are accompanied by an improvement in the overall quality of the Schottky system: the ideality factor, n, improves from 2.09 to 1.26; the Schottky barrier height (SBH), determined by the Norde [1] method, increases from 0.72 eV to 1.54 eV. From the Nicollian and Goetzberger model [2] , we calculated the energy distribution of the density of interface states, NSS. Around 1 eV above the Al0.18Ga0.82N valence band, NSS, decreases from 2.3×1012 eV−1 cm−2 for the un-annealed diodes to 1.3×1012 eV−1 cm−2 after the 573 K anneal. Our results suggest the formation of an insulating NiO leading to a MIS structure for the oxidized Au/Ni/Al0.18Ga0.82N contact.

The electronic properties of defects introduced by low energy inductively coupled Ar plasma etching of n-type (Si doped) GaAs were investigated by deep level transient spectroscopy (DLTS) and Laplace DLTS. Several prominent electron traps (Ec—0.046 eV, Ec—0.186 eV, Ec—0.314 eV. Ec—0.528 eV and Ec—0.605 eV) were detected. The metastable defect Ec—0.046 eV having a trap signature similar to E1 is observed for the first time. Ec—0.314 eV and Ec—0.605 eV are metastable and appear to be similar to the M3 and M4 defects present in dc H-plasma exposed GaAs.

Iridium (Ir) Schottky barrier diodes were deposited on bulk grown (1 0 0) Sb-doped n-type germanium by using the electron beam deposition system. Electrical characterization of these contacts using current–voltage (I–V) and capacitance–voltage (C–V) measurements was performed under various annealing conditions. The variation of the electrical properties of these Schottky diodes can be attributed to combined effects of interfacial reaction and phase transformation during the annealing process. Thermal stability of the Ir/n-Ge (1 0 0) was observed up to annealing temperature of 500 °C. Furthermore, structural characterization of these samples was performed by using a scanning electron microscopy (SEM) at different annealing temperatures. Results have also revealed that the onset temperature for agglomeration in a 20 nm Ir/n-Ge (1 0 0) system occurs between 600 and 700 °C.