4H-SiC Schottky barrier diodes (SBDs) were exposed to 5.4 MeV alpha particles with fluences of 2.55× 1011 cm−2, 5.11 × 1011 cm−2 and 7.67 × 1011 cm−2, respectively. Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) was used to determine the structure and cross-sectional elemental composition of the device, while current–voltage and capacitance–voltage profiling were used to determine the primary electrical device-characteristics before and after irradiation. EDS revealed the presence of a <1 μm Ti layer, covered by 5 μm Al layer, in intimate contact with the SiC. Deep level transient spectroscopy (DLTS), performed in the temperature range 15–310 K, revealed one dominant peak around 50 K (Ec - 0.07 eV) in the unirradiated samples. This peak showed asymmetry suggesting that it may consist of more than one defect. Notably, Z1/2, the carbon vacancy-related (Vc) defect commonly observed in as-grown n-type 4H-SiC, was not detected in the unirradiated reference sample. After irradiation, a broad peak emerged around 280 K (at 80 Hz), most likely Z1/2, having a shoulder around 180 K, was detected. Increasing the fluence resulted in a corresponding decrease in the concentration of the electron trap observed around 50 K (Ec - 0.07 eV), while the concentration increases for the defect detected around 280 K. Notably, the concentration of Z1/2 was found to be strongly fluence dependent and linked to what we believe is a related to a silicon vacancy transition, labelled S1/2 in literature. Laplace DLTS confirmed that the peak observed around 50 K is composed of multiple defects.

This study investigates the effect of bismuth (Bi) doping on the structural, optical and electrical properties of ZnO nanorods prepared using a chemical bath deposition process. X-ray diffraction shows that the prepared nanorods are crystalline, and that Bi is successfully incorporated into the ZnO lattice. Scanning electron microscopy reveals an enhancement in the growth-rate upon Bi doping while X-ray photoelectron spectroscopy confirms the presence of Bi2O3 for Bi concentrations ≥ 2 at.%. Room temperature UV and deep-level emission peaks are observed in the as-grown ZnO nanorods. Following annealing at 573 K, in oxygen, only sharp UV luminescence peaks remain. Additinally, a blueshift in the optical band gap is observed following Bi doping. The current–voltage characteristics of the fabricated Schottky diodes show improved rectification behaviour after Bi doping. The best device is obtained at 3 at.% Bi with a Schottky barrier height and an ideality factor of 0.70 eV and 1.86, respectively.

In this study, both deep level transient spectroscopy (DLTS) and admittance spectroscopy (AS) have been used to study the properties of electrically active deep level centers present in GaNAs/GaAs quantum wells (QWs) embedded in p-i-n solar cells. The structures were grown by molecular beam epitaxy (MBE). In particular, the electrical properties of samples with Si (n-type) doping of the QWs were investigated. DLTS revealed four deep level centers in the material, whereas only three were detected by AS. NextNano++ simulation software was used to model the sample band-diagrams to provide reasoning for the origin of the signals produced by both techniques.

In this paper, the growth of ZnO nanorods on bare and NiO-coated p-Si substrates is reported. A two-step chemical bath deposition process has been used to grow the nanorods. X-ray diffraction and scanning probe microscopy confirmed that the NiO films were polycrystalline, and that the average grain size correlated with the NiO layer thickness. The ZnO nanorod morphology, orientation and optical properties seemed to be unaffected by the intermediate NiO layer thickness. Current-voltage measurements confirmed the rectifying behavior of all the ZnO/NiO/Si heterostructures. The inclusion of a NiO layer between the substrate and the ZnO nanorods are shown to cause a reduction in both the forward and reverse bias currents. This is in qualitative agreement with the band diagram of these heterostructures, which suggests that the intermediate NiO layer should act as an electron blocking layer.

A comprehensive understanding of defects in semiconductors remains of primary importance. In this paper the effectiveness of two of the most commonly used semiconductor defect spectroscopy techniques, viz. deep level transient spectroscopy (DLTS) and admittance spectroscopy (AS) are reviewed. The analysis of defects present in commercially available SiC diodes shows that admittance spectroscopy allows the identification of deep traps with reduced measurement effort compared to deep Level Transient Spectroscopy (DLTS). Besides the N-donor, well-studied intrinsic defects were detected in these diodes. Determination of their activation energy and defect density, using the two techniques, confirm that the sensitivity of AS is comparable to that of DLTS while, due to its well defined peak shape, the spectroscopic resolution is superior. Additionally, admittance spectroscopy can analyze faster emission processes which make the study of shallow defects more practical and even that of shallow dopant levels, possible. A comparative summary for the relevant spectroscopic features of the two capacitance methods are presented.

Zinc oxide (ZnO) nanorods have been synthesized by a two-step chemical bath deposition process on silicon substrates having different dopant densities and orientations. Scanning electron microscopy and X-ray diffraction analysis reveal that the orientation of the Si substrate does not affect the orientation, distribution or crystallinity of the nanostructures. The electrical properties of the ZnO/Si heterojunction are also investigated by current–voltage (I–V) measurements. The ideality factor is found to be 2.6 at 295K, indicating that complex current transport mechanisms are at play. Temperature dependent I–V characteristics have been used to determine the dominant transport mechanism. The experimental results suggest that in the low bias region the current is dominated by a trap assisted multi-step tunneling process.

Variable laser power and temperature dependent photoluminescence (PL) measurements were used to identify some of the optical transitions and impurity-related emissions for chemically treated (Br-methanol, (NH4)(2)S + S or [(NH4)(2)S/(NH4)(2)SO4] + S solutions) or oxidised (annealed in oxygen) bulk n-InAs (111)A. A combination of PL and X-ray photoelectron spectroscopy (XPS) measurements before and after various treatments was used to identify the chemical nature of the impurities giving rise to bound exciton recombination in InAs (111). Band-to-band transitions have been observed at 0.4185 eV. In addition, two shallow neutral donor bound excitons ascribed to atomic oxygen (at 0.412 eV) and to sulphur (at 0.414 eV), have been detected after treatment

Self-assembled ZnO nanorods have been synthesized on a seeded Si substrate by a simple chemical bath deposition method at a temperature of 80°C. Room-temperature photoluminescence analysis revealed material of high optical quality with a low density of defects that can be reduced by post growth annealing. Current–voltage measurements on these devices showed excellent rectification. Junction characteristics were also studied using capacitance–voltage measurements and showed that the junction characteristics are mainly determined by the properties of the p-Si substrate. Based on the energy band diagram and possible interface states at the junction, it was suggested that the current transport in the device is predominantly determined by hopping of charge carriers between localized states through a multi-step tunneling process.

In this study, ZnS coated ZnO nanorods were synthesized using a simple, cost effective two-step chemical method. A continuous coating of ZnS on a ZnO nanorod, having a uniform thickness, is demonstrated using high resolution transmission electron microscopy, electron energy loss spectroscopy and selected area diffraction (SAD). These core-shell structures can be produced at relatively low temperatures (75 degrees C) and within relatively short times (3 h). The ZnS coating exhibits a polycrystalline structure with a lattice parameter of 5.35 angstrom, which is 1.1% smaller than the unstrained cubic zinc-blende structure. The SAD pattern taken at the ZnO-ZnS interface exhibits a partial epitaxial relationship, where (1 0 - 1 0) ZnO//(1 1 1) ZnS. Our detailed analysis shows that the ZnS shell comprises two different regions: a ZnS rich inner shell region is produced via the first sulphidation process, followed by a mixture of ZnO and ZnS in the outer shell region during the second treatment. From the detailed microscopy results a growth mechanism is proposed for each step of the sulphidation process. The results are complemented by room temperature photoluminescence spectroscopy. Strong emission from free excitons in ZnO is observed at 3.27 eV before ZnS coating, while a composite band peaking at 2.9 eV is measured after sulphidation. The origin of the latter will be discussed. (C) 2014 Elsevier B.V. All rights reserved.

The temperature dependent transport characteristics of Pd/n-GaSb:Te Schottky contacts with low and saturating reverse current are investigated by means of current-voltage measurements between 80 K and 320 K. The apparent barrier height and ideality factor increase with a decrease in temperature. Neither thermionic nor thermionic field emission can explain the low temperature characteristics of these diodes. Instead, evidence is presented for barrier inhomogeneity across the metal/semiconductor contact. A plot of the barrier height, phi(b) vs. 1/2kT revealed a double Gaussian distribution for the barrier height with phi(b,mean) assuming values of 0.59 eV +/- 0.07 (80-140 K) and 0.25 eV +/- 0.12 (140-320 K) respectively. (C) 2014 Elsevier B.V. All rights reserved.

Three prominent electron traps, 0.167 eV, 0.243 eV, and 0.295 eV below the conduction band minimum were detected in Te doped MOCVD grown n-GaSb using an Au Schottky barrier diode. The free carrier concentration of the ∼3 μm epilayer grown on n+ (>1018 cm−3) substrate, confirmed by Hall and capacitance-voltage measurements, was 5–7 × 1016 cm−3. The low doping concentration of the epitaxial layers was achieved using diethyl tellurium as the dopant source. Defect concentration profiles suggest that Ec-0.167 eV and Ec-0.243 are predominantly confined to the surface of the epilayer and that the concentration, thereof, approximates the free carrier concentration of the material close to the metal-semiconductor interface.

X-ray photoelectron spectroscopy, field emission scanning electron microscopy, Raman and photoluminescence spectroscopy were used to evaluate the surface properties of n-type InAs (111)A etched in a 1% Br–methanol solution. Etching completely removes the native oxides from the surface and enhances the photoluminescence response. The adsorption of bromine onto the InAs surface leads to the formation of In–Brx and As–Brx bonds (x = 1, 2, 3) as inferred from changes in the In 3d3/2;5/2 and As 3d core level binding energies. The etch rate is found to decrease due to strong anisotropic effects and the high volatility of the bromine species. A 1 min Br–methanol etch was found to enhance the photoluminescence intensity by a factor of 3, probably due to a reduction in the surface state density upon de-oxidation of the surface. This is thought to be due to reductions in the surface state density. The presence of native oxides enhances both the surface accumulation layer and the surface state density.

Inductively coupled Ar plasma etching of n-type (Si doped) Gallium Arsenide (GaAs) introduces several electron traps, Ec – 0.04 eV (labelled E1′), Ec – 0.19 eV, Ec – 0.31 eV, Ec – 0.53 eV, and Ec – 0.61 eV (behaving like the well documented M3 and labelled M3′ in this study), of which the metastable defects Ec – 0.04 eV (E1′), and Ec – 0.07 eV are novel. Furthermore, E1′ and M3′ exhibit strong field enhanced carrier emission. Double-correlation deep level transient spectroscopy was used to investigate the field dependent emission behaviour of these two defects. It is shown that for both traps, the observed enhanced emission is due to phonon assisted tunnelling. The latter observation is contrary to the literature reports suggesting that enhanced carrier emission for M3 occurs via the Poole-Frenkel mechanism.

A sulphur based chemical, [(NH4)(2)S/(NH4)(2)SO4] to which S has been added, not previously reported for the treatment of (1 0 0) n-GaSb surfaces, is introduced and benchmarked against the commonly used passivants Na2S center dot 9H(2)O and (NH4)(2)S. The surfaces of the treated material were studied by scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). It has been found that the native oxides present on the GaSb surface are more effectively removed when treated with ([(NH4)(2)S/(NH4)(2)SO4] + S) than with (NH4)(2)S or Na2S center dot 9H(2)O, as evidenced by the ratio of the O-506 (eV) to Sb-457 eV AES peaks. XPS results reveal that Sb2S3/Sb(2)S5 "replaces" Sb2O3/Sb(2)O5, suggesting that sulphur atoms substitute oxygen atoms in Sb2O3/Sb(2)O5 to form Sb S. It seems sulphurization only partially removes Ga2O3. Treatment with ([(NH4)(2)S/(NH4)(2)SO4] + S) also results in a noteworthy improvement in the current-voltage (I-V) characteristics of Au/n-GaSb Schottky contacts compared to those fabricated on as-received material. (C) 2012 Elsevier B. V. All rights reserved.

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—0.046eV, Ec—0.186eV, Ec—0.314eV. Ec—0.528eV and Ec—0.605eV) were detected. The metastable defect Ec—0.046eV having a trap signature similar to E1 is observed for the first time. Ec—0.314eV and Ec—0.605eV are metastable and appear to be similar to the M3 and M4 defects present in dc H-plasma exposed GaAs.

Bulk (1 0 0) n-GaSb surfaces have been treated with a sulphur based solution ((NH4)2S/(NH4)2SO4) to which sulphur has been added, not previously reported for the passivation of GaSb surfaces. Au/n-GaSb Schottky barrier diodes (SBDs) fabricated on the treated material show significant improvement compared to that of the similar SBDs on the as-received material as evidenced by the lower ideality factor (n), higher barrier height (ϕb) and lower contact resistance obtained. Additionally, the reverse leakage current, although not saturating, has been reduced by almost an order of magnitude at −0.2 V. The sample surfaces were studied by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The native oxide, Sb–O, present on the as-received material is effectively removed on treating with ([(NH4)2S/(NH4)2SO4]+S) and (NH4)2S. Analysis of the as-received surface by XPS, prior to and after argon sputtering, suggests that the native oxide layer is ≤8.5 nm.

An alternative sulphur blended [(NH4)2S04/(NH4)2S] solution is reported for stabilizing the bulk GaSb (100) surface. Scanning electron microscopy of treated surfaces shows a significant improvement in morphology over untreated surfaces. Dektak step profiling reveals that sulphurization causes a non-linear time dependent etching effect accompanied by smoothening of the surface while the photoluminescence is enhanced three-fold after a 30 minute treatment. The surface state density (Nss) distributions were calculated from forward IV characteristics of Au/n-GaSb Schottky structures. Surface state densities of 10cm, at midgap, were calculated, with treated surfaces showing about 3 times less than untreated. Treatment apparently unpins the fermi level in Au/n-GaSb Schottky structures as evidenced by a larger barrier height. Additionally, treatment also reduces the reverse leakage current. The reverse current however does not saturate with applied reverse bias. This may be attributed to either quantum mechanical tunnelling or near surface recombination via surface states not completely passivated (or removed) by the sulphurization.

The reaction of halogen-based etchants with n-InAs (111)A and the resulting surface morphology and surface electronic structure are investigated using field emission scanning electron microscopy and Raman spectroscopy. Using the intensity ratio of the unscreened longitudinal optical (LO) phonon to the transverse optical (TO) phonon in the Raman spectrum, a significant reduction in band bending is deduced after exposure of the InAs surface to HCl:H2O, Br–methanol and I–ethanol for moderate times and concentrations. These procedures also lead to smooth and defect-free InAs surfaces. The improvements in surface properties are reversed, however, if the concentrations of the etchants are increased or the etch time is too long. In the worst cases, pit formation and inverted pyramids with {111} side facets are observed. The influence of the etchant concentration and etch time on the morphological and electronic properties of the etched surfaces is reported.