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Current–voltage (IV) and capacitance–voltage (CV) measurement techniques have successfully been employed to study the effects of annealing highly rectifying Pd/ZnO Schottky contacts. IV results reveal a decrease in the contact quality with increasing annealing temperature as confirmed by a decrease in the zero bias barrier height and an increase in the reverse current measured at −1.5 V. An average barrier height of (0.77 ± 0.02) eV has been calculated by assuming pure thermionic emission for the as-deposited material and as (0.56 ± 0.03) eV after annealing at 550 °C. The reverse current has been measured as (2.10 ± 0.01) × 10−10 A for the as-deposited and increases by 5 orders of magnitude after annealing at 550 °C to (1.56 ± 0.01) × 10−5 A. The depletion layer width measured at −2.0 V has shown a strong dependence on thermal annealing as it decreases from 1.09 μm after annealing at 200 °C to 0.24 μm after annealing at 500 °C, resulting in the modification of the dopant concentration within the depletion region and hence the current flowing through the interface from pure thermionic emission to thermionic field emission with the donor concentrations increasing from 6.90 × 1015 cm−3 at 200 °C to 6.06 × 1016 cm−3 after annealing at 550 °C. This increase in the volume concentration has been explained as an effect of a conductive channel that shifts closer to the surface after sample annealing. The series resistance has been observed to decrease with increase in annealing temperature. The Pd contacts have shown high stability up to an annealing temperature of 250 °C as revealed by the IV and CV characteristics after which the quality of the contacts deteriorates with increase in annealing temperature.

Deep level transient spectroscopy (DLTS) and Laplace-DLTS have been used to investigate the defects created in Sb doped Ge after irradiation with 2 MeV protons having a fluence of 1×1013 protons/cm2. The results show that proton irradiation resulted in primary hole traps at EV +0.15 and EV +0.30 eV and electron traps at EC −0.38, EC −0.32, EC −0.31, EC −0.22, EC −0.20, EC −0.17, EC −0.15 and EC −0.04 eV. Defects observed in this study are compared with those introduced in similar samples after MeV electron irradiation reported earlier. EC −0.31, EC −0.17 and EC −0.04, and EV +0.15 eV were not observed previously in similar samples after high energy irradiation. Results from this study suggest that although similar defects are introduced by electron and proton irradiation, traps introduced by the latter are dose dependent.

In this study a comparison is made between the optical and electrical properties of Ni/Au and Ni/Ir/Au Schottky photodiodes based on Al0.35Ga0.65N. The effects of inserting Ir between Ni and Au are of particular interest. The comparison in the properties is done after annealing the photodiodes at different temperatures in an argon gas ambient. The reverse current decreased with annealing temperature up to 400 °C for the Ni/Au Schottky photodiode and up to 500 °C for the Ni/Ir/Au photodiode. The Schottky barrier heights increased with increasing annealing temperature. The responsivity of the Ni/Au photodiode was higher than that of the Ni/Ir/Au photodiode. The transmission of the Ni/Au metal layer improved with increasing annealing temperature up to 500 °C and the best transmission of the Ni/Ir/Au metal layer was after 400 °C annealing.

We computed the homogeneous Schottky barrier height (SBH) at ideality factor (n) = 1.0 of Ni/nGe (100) Schottky diodes (SDs). The SDs were identically prepared by using resistive evaporation of Ni on n-Ge (100). The SBHs and n of these diodes (24 dots) were calculated from their experimental forward bias current-voltage (I-V ) and reverse bias capacitance-voltage (C-V ) measurements at room temperature. Even though the Schottky diodes were identically prepared, the values of the SBH from the I-V characteristics varied from 0.487 to 0.508 eV, the ideality factor varied from 1.34 to 1.53, and the SBH from the C 2 -V characteristics varied from 0.358 to 0.418 eV. The Gaussian fits of the experimental SBH distributions obtained from the C 2 -V and the I-V characteristics yielded mean SBH values of 0.401 ± 0.015 and 0.503 ± 0.006 eV, respectively. Furthermore, a homogeneous SBH value of approximately 0.535 eV was also computed from an extrapolation of a linear plot of the experimental SBHs versus the ideality factors. The homogeneous SBHs, rather than the eective SBHs, of individual contacts or mean values should be used to discuss the theories and the physical mechanisms that determine the SBHs of SDs.

Copyright: 2011 Elsevier. This is the post-print version of the work. The definitive version is published in Materials Science in Semiconductor Processing, vol. 13(5-6), pp 371-375

Boron carbide (B4C) coatings on diamond offer potential for obtaining homogeneous B4C-diamond composites with improved properties. A method was developed for coating diamond particles with B4C at 1150 °C under argon atmosphere for dwell times of 2–6 hours in a powder mixture of boric acid (H3BO3) and amorphous boron. The B4C coating showed very good adhesion to the diamond substrate, and an unusual five-fold symmetry thought to be due to a twinned growth mechanism. The sudden onset of nucleation at T > 1000 °C is ascribed to the stabilising effect of hydrogen from the decomposition of H3BO3 on the diamond surface reactivity.

We would like to thank the National Research Foundation (NRF) of South Africa for the financial support.

Defects introduced by the solid state reactions between tungsten and silicon carbide have been studied using deep level transient spectroscopy (DLTS) and Laplace DLTS. W/4H-SiC Schottky barrier diodes were isochronally annealed in the 100–1100 °C temperature range. Phase composition transitions and the associated evolution in the surface morphology were investigated using x-ray diffraction (XRD) and scanning electron microscopy (SEM). After annealing at 1100 °C, the E0.08, E0.15, E0.23, E0.34, E0.35, E0.61, E0.67, and E0.82 defects were observed. Our study reveals that products of thermal reactions at the interface between tungsten and n-4H-SiC may migrate into the semiconductor, resulting in electrically active defect states in the bandgap.

Platinum (Pt) and titanium (Ti) Schottky barrier diodes were fabricated on bulk grown (1 0 0) Sb-doped n-type germanium using the electron beam whereas nickel (Ni) contacts were fabricated using the resistive evaporation system. Electrical characterization of these contacts using current–voltage ( I–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. The results have also revealed that Pt Schottky contacts are of a high quality, with low reverse currents in the order of (10 −5 to 10 −6 ) A and as-deposited ideality factors as low as 1.09. Furthermore, the samples microstructural characterization was performed by scanning electron microscopy (SEM) at different annealing temperatures. From the results, it can be concluded that the onset temperature in 30 nm Ni- and Pt/n-Ge (1 0 0) systems occurs at 500–600 °C and 600–700 °C, respectively.

We have etched Sb-doped n-type (111) oriented Ge by inductively coupled plasma (ICP), using argon, and subsequently studied the defects that this process introduced as well as the effect of this etching on Schottky barrier diode quality. Deep level transient spectroscopy (DLTS) revealed that ICP etching introduced only one prominent defect, EP 0.31 , in Ge with a level at 0.31 eV below the conduction band. The properties of this defect are different to those of defects introduced by other particle-related processing steps, e.g. sputter deposition and electron beam deposition, that each introduces a different set of defects. DLTS depth profiling revealed the EP 0.31 concentration was a maximum (3.6 × 10 13 cm − 3 ) close to the Ge surface and then it decreased more or less exponentially into the Ge. Annealing at 250 °C reduced the EP 0.31 concentration to below the DLTS detection limit. Finally, current–voltage ( I – V ) measurements as a function of temperature revealed that the quality of Schottky contacts fabricated on the ICP-etched surfaces was excellent at − 100 K the reverse leakage current at − 1 V was below 10 13 A (the detection limit of our I – V instrumentation).

SiOC films made by the inductively coupled plasma chemical vapor deposition were researched the relationship between the dielectric constant and the chemical shift. SiOC film had the main Si-O-C bond with the molecule vibration mode in the range of 930∼1230 cm-1 which consists of C-O and Si-O bonds related to the cross link formation according to the dissociation and recombination. The C-O bond originated from the elongation effect by the neighboring highly electronegative oxygen atoms at terminal C-H bond in Si-CH3 of 1270 cm-1. However, the Si-O bond was formed from the second ionic sites recombined after the dissociation of Si-CH3 of 1270 cm-1. Increment of Si-O bond in the Si-O-C main bond contributed to increase the hardness and decrease the roughness because of the decreasing of the carbon content witch is related to the space effect. The dielectric constant of SiOC film was decreased by lowering the polarization which consists of the ionic and electronic polarity. Increment of Si-O bond in a right shoulder at the main bond was interpreted by the red shift observed in FTIR spectra. Moreover, the increment of Si-O bond and decrement of carbon content induced to decrease the ionic polarity and then decreased the dielectric constant (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Temperature dependent current–voltage (I–V) and capacitance–voltage (C–V) measurements have been performed on Pd/ZnO Schottky barrier diodes in the range 60–300 K. The room temperature values for the zero bias barrier height from the I–V measurements (FI–V) was found to be 0.52 eV and from the C–V measurements (FC–V) as 3.83 eV. From the temperature dependence of forward bias I–V, the barrier height was observed to increase with temperature, a trend that disagrees with the negative temperature coefficient for semiconductor material. The C–V barrier height decreases with temperature, a trend that is in agreement with the negative temperature coefficient of semiconductor material. This has enabled us to fit two curves in two regions (60–120 K and 140–300 K). We have attributed this behaviour to a defect observed by DLTS with energy level 0.31 eV below the conduction band and defect concentration of between 4 � 10 16 and 6 � 10 16 cm � 3 that traps carriers, influencing the determination of the barrier height.

Inductively coupled plasma (ICP) etching has been used primarily on compound semiconductors. There are however compelling reasons to study the effects of ICP etching on Ge. Pd Schottky barrier diodes (SBDs) were resistively evaporated onto Ge (111) that was ICP etched at a rate of 60 ˚ A per minute for three or ten minute intervals. Although plasma cleaning is known to introduce defects that were observed with DLTS, the diodes exhibited excellent current–voltage characteristics when cooled down to 80 K. Current–temperature (IT) scans that were recorded from 20 K up to 300 K after cooling under reverse bias showed no effect of recombination/generation (RG). On the other hand, IT scans that were recorded after cooling under zero or forward bias clearly exhibited RG effects in the 100–240 K temperature range. This effect was found to be completely reversible. In addition, ICP etching leads to superior devices when compared to devices manufactured by RF sputter deposition.

Three n-type single crystal hydrothermally grown ZnO samples with resistivities of 5.1±0.6, 15±2 and 220±20 Ω cm, respectively, have been electrically characterized using thermal admittance spectroscopy ( TAS ). The presence of three main donors: two shallow ones D 1 and D 2 and a deeper one D 3 with activation energies of ∼30, ∼50 and ∼290 meV, respectively, are detected. In addition, the TAS spectra reveal the presence of a fourth level, D X , with a peak amplitude in the conductance spectra that decreases with the temperature occurrence. It is shown that this anomalous behavior is consistent with D X being a negative-U defect of donor-type. An activation energy of ∼80 meV for the ++/+ transition, a capture cross section equal to ∼3×10 −17 cm 2 and an energy barrier for atomic reconfiguration of ∼0.25 eV, respectively, deduced according to the assignment of D X to a negative-U defect. A tentative assignment of the D X defect with oxygen vacancies is discussed.

Deep-level transient spectroscopy (DLTS) measurements were used to characterize the electrical properties of MOCVD grown, europium- (Eu) and xenon- (Xe) implanted GaN films on sapphire substrates. Implantation energy was 80 keV with a fluence of 110 14 cm 2 along a channeled crystallographic direction. Defect levels were observed at EC 0.19 eV for both Eu- and Xe-implantation which were predicted to be a rare-earth related donor level by theoretical calculations. Other defect levels are observed with energy levels located at 0.22, 0.68, 0.49, 0.60, 0.77 eV and 0.48, 0.64, 0.45, 0.72 eV below the conduction band for Eu and Xe implantation, respectively. Some of these levels have similar defect signatures and can be related to other implantation related defects introduced in erbium, praseodymium and helium implantations.

Ar + and He + ions were implanted into Ge samples with (1 0 0), (1 1 0), (1 1 1) and (1 1 2) orientations at 15 K with fluences ranging from 1×10 11 to 1×10 14 cm −2 for the Ar + ions and fluences ranging from 1×10 12 to 6×10 15 cm −2 for the He + ions. The Rutherford backscattering (RBS) technique in the channelling orientation was used to study the damage built-up in situ. Implantation and RBS measurements were performed without changing the target temperature. The samples were mounted on a four axis goniometer cooled by a close cycle He cryostat. The implantations were performed with the surface being tilt 7° off the ion beam direction to prevent channelling effects. After each 300 keV Ar + and 40 keV He + implantation, RBS analysis was performed with 1.4 MeV He + ions. For both the implantation ions, there is about no difference between the values found for the damage efficiency per ion for the four different orientations. This together with the high value (around 5 times higher than that found in Si), gives rise to the assumption of amorphous pocket formation per incident ion, i.e. direct impact amorphization, already at low implantation fluences. At higher fluences, when collision cascades overlap, there is a growth of the already amorphized regions.

Commercial O-face (0 0 0 1) ZnO single crystals were implanted with 200 keV Ar ions. The ion fluences applied cover a wide range from 5 × 10 11 to 7 × 10 16 cm −2 . The implantation and the subsequent damage analysis by Rutherford backscattering spectrometry (RBS) in channelling geometry were performed in a special target chamber at 15 K without changing the target temperature of the sample. To analyse the measured channelling spectra the computer code DICADA was used to calculate the relative concentration of displaced lattice atoms. Four stages of the damage evolution can be identified. At low ion fluences up to about 2 × 10 13 cm −2 the defect concentration increases nearly linearly with rising fluence (stage I). There are strong indications that only point defects are produced, the absolute concentration of which is reasonably given by SRIM calculations using displacement energies of E d (Zn) = 65 eV and E d (O) = 50 eV. In a second stage the defect concentration remains almost constant at a value of about 0.02, which can be interpreted by a balance between production and recombination of point defects. For ion fluences around 5 × 10 15 cm −2 a second significant increase of the defect concentration is observed (stage III). Within stage IV at fluences above 10 16 cm −2 the defect concentration tends again to saturate at a level of about 0.5 which is well below amorphisation. Within stages III and IV the damage formation is strongly governed by the implanted ions and it is appropriate to conclude that the damage consists of a mixture of point defects and dislocation loops.

The electronic properties of defects introduced unintentionally, during electron beam deposition (EBD) of Ti and Mo on Cz grown, B-doped Si and those deliberately introduced by proton and electron irradiation are presented in this paper. Deep level transient spectroscopy (DLTS) studies on the samples revealed the following primary hole traps at 0.32 eV and 0.54 eV above the valence band after EBD processing, 0.15 eV, 0.32 eV after proton irradiation and 0.17 eV, 0.23 eV, 0.33 eV and 0.60 eV after electron irradiation. The comparison of the defect levels showed one common defect level at 0.32 eV above the valence band in the three radiation processed samples, and this hole trap is boron related. Most of the defect levels, created in these three samples, are not similar. Higher defect introduction rates were recorded for the proton when compared to the electron irradiation induced primary deep level states. We have also briefly discussed the annealing behaviour of these primary defect levels.

Temperature dependent current–voltage ( I – V ) and Hall measurements were performed on Pd/ZnO Schottky barrier diodes in the range 20–300 K. The apparent Richardson constant was found to be 8.60 × 10 - 9 A K - 2 cm - 2 in the 60–160 K temperature range, and mean barrier height of 0.50 eV in the 180–300 K temperature range. After barrier height inhomogeneities correction, the Richardson constant and the mean barrier height were obtained as 167 A K - 2 cm - 2 and 0.61 eV in the temperature range 80–180 K, respectively. A defect level with energy at 0.12 eV below the conduction band was observed using the saturation current plot and ( 0.11 ± 0.01 ) eV using deep level transient spectroscopy measurements.

We have studied the defects introduced in n-type Ge during electron beam deposition (EBD) and sputter deposition (SD) by deep-level transient spectroscopy (DLTS) and evaluated their influence on the rectification quality of Schottky contacts by current–voltage (I–V) measurements. I–V measurements demonstrated that the quality of sputter-deposited diodes are poorer than those of diodes formed by EBD. The highest quality Schottky diodes were formed by resistive evaporation that introduced no defects in Ge. In the case of EBD of metals the main defect introduced during metallization was the V–Sb complex, also introduced during by electron irradiation. The concentrations of the EBD-induced defects depend on the metal used: metals that required a higher electron beam intensity to evaporate, e.g. Ru, resulted in larger defect concentrations than metals requiring lower electron beam intensity, e.g. Au. All the EBD-induced defects can be removed by annealing at temperatures above 325 °C. Sputter deposition introduces several electrically active defects near the surface of Ge. All these defects have also been observed after high-energy electron irradiation. However, the V–Sb centre introduced by EBD was not observed after sputter deposition. Annealing at 250 °C in Ar removed all the defects introduced during sputter deposition.

Various Schottky metal contacts were deposited on bulk grown (111) Sb-doped n-type Germanium. The Schottky contacts were deposited by resistive evaporation, electron beam deposition and RF sputter deposition. Current–voltage (IV) and capacitance–voltage (CV) measurements revealed differences in the diode performance that suggested damage caused to the germanium semiconductor crystal by the more energetic deposition methods of electron beam deposition and sputter deposition. Subsequent annealing improved the diode performance thus succeeding in removing some of the defects introduced, but not all. Sputter deposition produced the poorest diodes highlighting this as the most damaging process. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ar+ ions were implanted into Ge samples with (100), (110), (111) and (112) orientations at 15 K with fluences ranging from 1 × 1011 to 1 × 1014 cm−2. The Rutherford backscattering (RBS) technique in the channelling orientation was used to study the damage build-up in situ. Implantation and RBS measurements were performed without changing the target temperature. The samples were mounted on a four axis goniometer cooled by a close cycle He cryostat. The implantations were performed with the surface being tilted 7° off the ion beam direction to prevent channelling effects. After each 300 keV Ar+ implantation, RBS analysis performed with 1.4 MeV He+ ions. The damage efficiency per ion was found to be Pa =4.5 × 10−14 cm−2. There is no significant difference in the values found for the four different orientations. This, together with the high value (5 times higher than that found in Si), gives rise to the assumption of amorphous pocket formation per incident ion, i.e. direct impact amorphisation, already at low implantation fluences. At higher fluences, when collision cascades overlap, there is a growth of the already amorphised regions. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Samples of as-manufactured and annealed zinc oxide (ZnO) grown by melt-growth, seeded chemical vapour transport (SCVT) growth and hydrogen-implanted hydrothermal ZnO were investigated via the temperature dependent Hall technique. The conduction in the melt-grown sample appeared to be dominated by two donors with activation energies of about 70 meV and 44 meV, the former disappearing with annealing above 550 oC. Only one dominant donor of about 80 meV was found in the SCVT-grown sample and it showed little change with annealing. Surface conduction effects were observed only in the SCVT-grown sample. Hydrogen-implanted hydrothermal ZnO layers were found to have only one dominant donor with activation energy of about 45 meV that was stable up to annealing temperatures of about 300 oC. The acceptor concentration was found to increase considerably with annealing above 300 oC. We attempt to interpret these results by considering theoretical predictions for the various native and extrinsic defects expected to occur in our samples. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The etch rates of various etches and the resulting morphology of the Ge (111) surface have been investigated using atomic force microscopy (AFM) techniques and the oxidation rate of the germanium after etching was monitored by ellipsometry. The effect of the etch on the stability of Pd Schottky barrier diodes (SBDs) was monitored over a period of time using current voltage measurements. It was found that those etches with high etch rates produced much rougher surfaces which in turn showed significant variation in the leakage currents of SBDs deposited on these surfaces. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We have measured the electrical characteristics of electron irradiation-induced defects in n-type (1 1 0), (1 1 1) and (1 0 0) germanium doped with antimony (Sb) by deep-level transient spectroscopy (DLTS) and Laplace-DLTS. The following electron traps at 0.04, 0.15, 0.20, 0.21, 0.23, 0.31 and 0.38 eV below the conduction band were observed and two hole traps at 0.09 and 0.30 eV above the valence band were recorded in the low doping (1014 cm−3) samples. In the higher doping (1015 cm−3) samples, similar electron traps were observed but the electron trap at 0.04 eV below the conduction band and hole trap at 0.09 eV above the valence band was not observed. The electron trap at 0.38 eV is identified as the (V–Sb)−−/− center and the hole trap at 0.30 eV assigned the (V–Sb)0/− appeared in almost equal concentrations in the higher-doped samples but in the lowest-doped samples the hole trap (V–Sb)0/− was more dominant. We have also presented the annealing behavior of these electron-induced defects.

When using Schottky barrier diodes (SBDs) on silicon (Si) to study the thermal stability of radiation-induced defects, point defects injection into the silicon substrate can occur at temperatures where silicidation occurs. These injected point defects can react with the radiation-induced defects and may lead to an incorrect picture of annealing studies of these defects. In order to overcome this problem, we have annealed (1) ruthenium (Ru), cobalt (Co), nickel (Ni) and platinum (Pt) SBDs to form stable silicides on phosphorus (P) doped Si and (2) have measured the electrical characteristics of defects introduced during diodes fabrication by electron beam deposition (EBD), using conventional and (high resolution) Laplace (L-) deep level transient spectroscopy (DLTS). A primary electron trap at 0.48 eV below the conduction band was observed after EBD processing of the contacts. Isochronal annealing of the SBDs at 350 °C, annealed-in defects 0.05, 0.09, 0.18 and 0.28 eV below the conduction band. All the EBD-induced defects were removed after annealing at 600 °C. Primary defect depth profile versus annealing temperature results are also presented in this study.

The authors have investigated by deep level transient spectroscopy the electron traps introduced in n-type Ge during sputter deposition of Au Schottky contacts. They have compared the properties of these defects with those introduced in the same material during high-energy electron irradiation. They found that sputter deposition introduces several electrically active defects near the surface of Ge. All these defects have also been observed after high-energy electron irradiation. However, the main defect introduced by electron irradiation, the V-Sb center, was not observed after sputter deposition. Annealing at 250°C in Ar removed the defects introduced during sputter deposition.

ZnO Schottky barrier diodes (SBD's) were fabricated with 20/80/40/80 nm Ti/Al/Pt/Au ohmic contacts on the O face and circular 0.5 mm in diameter 50 nm thick Ru Schottky contacts in the Zn face. The carrier concentration of the ZnO prior to irradiation was approximately 5 × 10 16 cm -3 . These diodes were irradiated with 1.8 MeV He + with fluences ranging from 1 × 10 12 cm -2 to 2 × 10 13 cm -2 . Deep level transient spectroscopy (DLTS) was used to study the defects introduced. These measurements revealed that this irradiation introduced a defect with an energy level at 0.55 eV below the conduction band. The introduction rate of this defect for 1.8 MeV He + ions was calculated to be 220 ± 20 cm -1 . This appears to be the same defect that is introduced during proton irradiation of ZnO.

Schottky barrier diodes (SBD’s) were fabricated with 20/80/40/80 nm Ti/Al/Pt/Au ohmic contacts on the O face and circular 0.5 mm in diameter, 50 nm thick Ru Schottky contacts in the Zn face. Current ( I ) deep level transient spectroscopy ( I -DLTS) was used to study the shallow level defects introduced during 1.8 MeV proton irradiations with fluences ranging from 1 × 10 13 cm −2 to 2.4 × 10 14 cm −2 . These measurements revealed that this irradiation introduced a defect with an energy level at 0.03–0.036 eV below the conduction band and with an electron capture cross section of 9 × 10 −16 to about 1.4 × 10 −15 cm 2 . This defect may be hydrogen-related as theory has predicted that hydrogen forms a shallow donor in ZnO, or it may be due to the Zn I , as it was reported that electron irradiation with an energy of >1.6 MeV produces the Zn I in ZnO which is a shallow level defect at 0.03 eV below the conduction band.

Using a combination of etch rate, photoconductance, and deep level transient spectroscopy (DLTS) measurements, the authors have investigated the use of reactive ion etching (RIE) of dielectrics and Si in CHF3∕O2 and CHF3∕Ar plasmas for photovoltaic applications. The radio frequency power (rf-power) and gas flow rate dependencies have shown that the addition of either O2 or Ar to CHF3 can be used effectively to change the etch selectivity between SiO2 and Si3N4. The effective carrier lifetime of samples degraded upon exposure to a CHF3-based plasma, reflecting the introduction of recombination centers in the near-surface region. The extent of minority carrier lifetime degradation was similar in both types of plasmas, suggesting that the same defects were responsible for the increased recombination. However, the rf-power dependence of lifetime degradation in n- and p-type Si was different. Moreover, the lifetime degradation did not exhibit a linear rf-power dependence, suggesting that primary defects were not the dominant recombination centers responsible for the decrease in lifetime. Indeed, DLTS measurements have shown that secondary defects were formed in samples exposed to the plasma after annealing at 400°C, the temperature at which a SiN:H layer is deposited on samples to passivate their surfaces. The minority carrier lifetime degradation in RIE processed samples could be partially avoided using post-RIE chemical treatments.

We have investigated by deep level transient spectroscopy the hole and electron trap defects introduced in n -type Ge during electron beam deposition (EBD) of Pt Schottky contacts. We have also compared the properties of these defects with those introduced in the same material during high-energy electron irradiation. Our results show EBD introduces several electrically active defects at and near the surface of Ge. The main defect introduced during EBD has electronic properties similar to those of the V–Sb complex, or E-center, introduced during high-energy electron irradiation of Ge. Annealing at 325 °C in Ar removed all the defects introduced during EBD.

The authors gratefully acknowledge financial support from the UK Engineering and Physical Sciences Research Council and the South African National Research Foundation.

We have measured the electrical and annealing properties of defects created in epitaxial and Czochralski-grown Si doped with either B or Ga by electron irradiation using both conventional and Laplace deep level transient spectroscopy (L)-DLTS. With L-DLTS, we have been able to resolve several defects that cannot be resolved using conventional DLTS. L-DLTS provides a new avenue to study defect introduction rates and annealing kinetics in B- and Ga-doped Si. The isochronal annealing behaviour of the defects was also investigated.

We have investigated and compared the defects in ZnO grown by two methods, namely seeded chemical vapour transport (SCVT) and melt-growth (MG), using conventional deep level transient spectroscopy (DLTS) and high resolution (Laplace) DLTS with Au and Ru Schottky barrier diodes. Both materials contained two prominent defects, E1, at E C –0.12 eV and E3 at E C –0.29 eV. The SCVT ZnO has E1 as the main defect with a concentration of about 10 16 cm −3 , while the MG ZnO has E3 as the main defect with a concentration of above 10 16 cm −3 . It has been speculated that this defect is the oxygen vacancy in ZnO. High resolution Laplace DLTS suggests that this level could consist of two closely spaced levels but with different capture cross-sections. The relative concentrations of these defects were found to vary across the region probed by DLTS. The E1 and E3 defects also showed opposite trends in an electric field: an increase in electric field enhanced emission from E1 whereas it slowed down emission from E3. The peak splitting and field dependence may, however, be a consequence of a non-exponential transient. Finally, etching in HCl:H 2 O did not affect the defect concentrations or introduce additional defects in ZnO in the MG ZnO.

In this study, various surface cleaning techniques for the removal of contaminants from GaN were investigated. Auger electron spectroscopy (AES) analysis was used to monitor the presence of surface contaminants and atomic force microscopy (AFM) was used to monitor surface roughness. AES analysis showed that KOH was effective in removing carbon (C). Comparing the topographies of GaN surfaces cleaned in HCl, KOH and (NH4)2S in aqueous solutions; it has been found that surfaces cleaned in (NH4)2S is the best cleaned, have the lowest values of both C and O, RMS roughness and Ga/N ratio. The nearly complete removal of C and O were achieved by heating the samples in AES in vacuum.

The thermal stability and electronic properties of the vacancy-donor complexes, often referred to as the E centres, have been studied in silicon, unstrained silicon-germanium and pure germanium. The E centres have been introduced by electron irradiation or gamma rays. In silicon, Laplace deep level transient spectroscopy has been used to separate the E centre emission from the di-vacancy, thus enabling very reliable data to be obtained for the vacancy complexes with P, As and Sb. In pure Ge only the E centres associated with P and Sb are reported and in Ge rich SiGe only V-P. In all the samples measured the thermal stability of V-Sb has been found to be significantly higher than V-P. With regard to the energy levels, the activation energy of electron emission from the single-acceptor level of the E centre in silicon are for V-Sb 0.40 eV and for V-P 0.46 eV. For the pure Ge case, the single acceptor is a hole trap with emission to the valence band having energies for V-P of 0.35 eV and V-Sb of 0.31 eV. Similar values are found for Ge rich SiGe. The double-acceptor state is not seen in silicon but in germanium produces a state with an activation energy for electron emission of 0.30 eV for V-P and 0.38 eV for V-Sb. This is also reflected in the Ge rich alloys of SiGe:P that have been measured in this work.

We have used thermally stimulated capacitance (TSCAP) and optical deep level transient spectroscopy (O-DLTS) to detect and characterise hole traps in n-type GaN grown by epitaxial lateral overgrowth (ELOG) organo-metallic vapour phase epitaxy (OMVPE). Semi-transparent Ni Schottky barrier diodes (SBDs) were used to probe the space charge region of the GaN layer. Optical excitation was achieved using an ultraviolet light emitting diode with sub-bandgap energy photons at a wavelength of 380 nm. Two hole traps with activation enthalpies of 0.25 eV and 0.85 eV with respect to the valence band were found to be present in concentrations of 5 × 10 14 and 2 × 10 15 cm -3 . This is almost two orders of magnitude higher than the concentration of the electron traps present in this material. We have also found that 1.8 MeV proton implantation introduced additional shallow level hole traps with activation enthalpies of 0.19 eV and 0.23 eV, respectively.

Deep level transient spectroscopy (DLTS) measurements on as-grown GaN layers on sapphire substrates commonly reveal three dominant traps, viz. the 0.65 eV, 0.61 eV and 0.27 eV levels below the conduction band. These deep levels are normally attributed to the native defects that are present in the as-grown layers. We have previously observed that the E c - 0.61 eV level behaves in an almost similar manner to bistable defects during bias-on/bias-off anneals. It is proposed that this is due to the presence of a negatively charged mobile species in the material that drifts under the influence of an electric field and is able to passivated the E c - 0.61 eV level. Defect profiles of the level under zero bias and under different reverse bias conditions showed changes in the defect profile distributions that further confirms the mobile defect/ion theory. The reactivation kinetics of the E c - 0.61 eV defect level has also been studied and results indicate that the energy required to reactivate the level is E Reac = 0.96 ± 0.03 eV with an attempt frequency v 0 = 6 x 10 10±1 s -1 , while the reverse transformation of this level requires E Pass = 0.93 ± 0.06 eV and an attempt frequency of v 0 = 7 × 10 11±1 s -1 .

We detected electron traps in AlGaN photodetectors with carrier densities (5–9) × 1017 cm−3 using DLTS and thermal admittance spectroscopy (TAS). The electron traps P2 and P1, as detected by DLTS in AlGaN with an Aluminium (Al) content of 41% are located at 0.57 eV and at 0.27 eV respectively, below the conduction band minima. The same pair of traps is detected in samples with 12% Al content; these levels are situated at 0.54 eV and 0.16 eV below the conduction band, respectively. TAS in the sample set with Al mole fraction of 12%, yielded a level at EC − 0.15 eV. In all our samples, independent of the Al mole fraction, we find P1 always has a concentration higher than P2's. We believe the trap P2 is the same as the defect, E1, detected by Wang et al. [1] in as grown GaN; and, P1 is the 0.61 eV level reported by Gotz et al. [2]. 1.8 MeV He-ion irradiation, up to a dose of 5.5 × 1012 cm−2, results in the uniform removal of free carriers at a rate of 24000 cm−1. We were unable to detect any significant defect(s) responsible for this compensation, however, we believe the culprits are acceptor-type defects. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this paper we describe the behaviour of the E2 defect in GaAs as measured by a digital DLTS system at temperatures much lower than those at which the defect is normally observed in analogue DLTS systems. We found that, at temperatures below approximately 40 K, the emission rate of the E2 defect became essentially temperature independent. We show that this behaviour is due to a competing mechanism, involving thermal radiation from the outer shroud of the cryostat, emptying the E2. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Metal-oxide-semiconductor (MOS) structures were formed on n-ZnO and the electrical properties were compared to Au Schottky barrier diodes (SBDs) on similar ZnO. After evaporating Ni onto either ZnO, Si or glass, the thin films were oxidised to produce transparent, resisitive layers. The structure and composition of these layers were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron microscopy. The electrical properties were investigated by variable temperature current–voltage ( I – V ) and four-point probe measurements, whereas the optical properties were investigated by photospectrometry. The influence of oxidation temperature on the resistivity of the nickel oxide layers was used to optimise the processing conditions. NiO layers had a maximum resistivity of approximately 100 Ω cm after oxidation and bandgap of 3.5–3.6 eV at room temperature. The rectifying qualities of the junctions (using Pd gates) were sufficient for DLTS measurements of ZnO in the temperature range 20–390 K.

It has previously been found that, for example, 2.0 MeV protons at room temperature introduces two main electron traps at introduction rates of 400 and 600 cm –1 , respectively and reduces the carrier density at a rate of 40 cm –1 in gallium nitride (GaN). In this paper, we report on the behaviour of the ideality factor, barrier height and reverse leakage current of the Schottky barrier diodes (SBDs) fabricated on GaN and aluminium gallium nitride as a function of temperature as well as incident proton fluence. We also report the introduction rates of defects and the removal rate of free carriers when bombarding the SBDs at 300°C and compare these observations with the results obtained for room temperature bombardment.

Deep-level transient spectroscopy (DLTS) on HVPE grown n-GaN revealed three dominant traps below the conduction band, commonly associated with HVPE-grown material. In this study, it was found that the concentration of the EC−0.61 eV level is dependent on the biasing conditions: zero bias annealing at 370 K decreases the concentration of the 0.61 eV level to a non-zero value, while reverse bias annealing increases the concentration within the region probed. The change in the defect concentration becomes lower for thicker GaN layers with a lower density of threading dislocations. We tentatively ascribe this behaviour to the neutralisation of the 0.61 eV level by a mobile defect species, which is associated with dislocations present in the material.

We have used electrical measurements Deep level transient spectroscopy (DLTS) complemented by high-resolution X-ray diffraction (HRXRD) and Rutherford backscattering spectroscopy (RBS) measurements for assessment of the defects introduced in p-Si1-xGex during 160keV erbium ion implantation. From deep-level transient spectroscopy, it was observed that two prominent defects with discrete energy levels above the valence band, were introduced during Er ion implantation. The observed defects have similar signatures as those introduced during alpha-particle irradiation and electron beam metal deposition, indicating that these defects are more likely not related to Er but only to implantation induced damage such as primary defects. The generated defects expand the Si1-xGex lattice in the implanted region, which results in the presence of the tail in the high-resolution X-ray diffraction spectra. After rapid thermal annealing (RTA) at 850degreesC for 30 s in nitrogen ambient, a reduction in defect density as well as a relaxation of the Si1-xGex lattice is observed for all x values. A dominant Er-related sharp emission in the 1.541 mum region was observed at room temperature and neither the intensity of the Er emission nor the emission peak position were influenced by the Ge content or the strain relaxation in the epilayers.

We have used deep level transient spectroscopy to study the electric-field-enhanced electron emission rate from a defect S1 observed in impurity-free disordered n-GaAs. The field dependence of emission rate could be well described by the electron emission from a Gaussian potential well with ground energy state ∼0.25 eV. The phonon-assisted tunneling model with a triangular barrier could also adequately fit our experimental data for a large localized quasi-stationary energy level of ∼0.57 eV. Our modeling shows that a medium-range potential is associated with S1, showing it cannot be a point defect. The possible complex structure of S1 is discussed in terms of the arsenic antisite, As Ga , and the arsenic interstitial, As i , based on our results and by drawing on the theoretical modeling of defects in nonstoichiometric (As-rich) GaAs.

Capacitance transient techniques, combined with ab initio modeling, were employed to study the electronic properties and structure of vacancy–oxygen (VO) complexes in unstrained Czochralski-grown Si1−xGex crystals (0

Hydrogen-ion implantation was studied for Mg-doped hexagonal GaN grown on sapphire. Low temperature photoluminescence spectroscopy (PL) shows two significant features; the implantation-annealing induced yellow band (YL) and a remarkable sharp excitonic peak. In the region 1.73–1.79 eV well resolved optical transitions were observed, which resemble the well known R1 and R2 emission bands from Cr3+ in Al2O3 (ruby). Structural and electronic changes were monitored by inelastic light scattering (ILS) spectroscopy. At high implantation dose and high annealing temperature we observed well resolved bands at 320, 380 and 640 cm−1. The latter band ‘splits’ into 645 and 672 bands at the highest implantation dose. Additionally, implantation-annealing induced band was observed at 430 cm−1. This band was not observed before. Besides these, four of the six Raman allowed modes are present in the spectra: 2A1, E1 and E2. Second order Raman spectroscopy yields several bands in the region 860–1470 cm−1. On the high energy side of the spectra, we monitor luminescence bands at 1.878, 1.85, 1.836 eV and for the first time observed a 1.8 eV band. Using a group-theoretical approach we assign symmetries of the first order phonons at k=0 as well as some experimentally observed second order symmetry allowed modes.

Cadmium sulfide (CdS) thin films were electrodeposited on two conducting oxide substrates from aqueous solutions at temperatures between 30 and 90 °C. The as-deposited films were characterized using scanning electron microscopy, transmission electron diffraction, atomic force microscopy and Raman spectroscopy and were found to be crystalline at all temperatures. The microstructural development of the films is also discussed based on field emission scanning electron microscopy and atomic force microscopy studies. The composition of the films was found to be independent of the deposition temperature, with a slight difference in the Cd/S ratio on the different substrates.