Table of contents

Partially relaxed InGaAs/GaAs heterostructures with a small lattice mismatch have been studied by means of atomic force microscopy and high-resolution x-ray diffractometry. Additionally, electron-beam induced current in a scanning electron microscope and transmission electron microscopy have been employed to investigate misfit dislocations formed at the (001) heterostructure interface. The measurements revealed a direct correlation between the surface cross-hatched morphology and the arrangement of interfacial misfit dislocations. The reciprocal lattice mapping and the rocking curve techniques employed for the samples aligned with either the or the [110] crystallographic direction perpendicular to the diffraction plane revealed anisotropic misfit strain relaxation of the InGaAs layers. This anisotropy results from an asymmetry in the formation of the α and β types of misfit dislocations oriented along the and [110] directions, respectively, which differ in their core structures. The misfit strain anisotropy causes a distortion of the unit cell of the layer and lowers its symmetry to orthorhombic.

In this paper we demonstrate the parallel application of light beam induced current (LBIC) and lock-in infrared thermography for the investigation of strong shunting regions in multicrystalline silicon solar cells. Usually both mappings are not correlated, but in this case the shunts could be imaged by both techniques. If for a locally generated photocurrent the conductance through a shunt lying nearby is comparable to that across the emitter into the current amplifier, local shunts become visible in the LBIC as dark regions. After the rear contact of the cell was removed, the LBIC technique was performed from the rear side of the cell. The images point to the existence of inversion layers along grain boundaries crossing the bulk of the cell. Obviously, these inversion layers represent the dominant material-induced shunt type in multicrystalline silicon solar cells. Moreover, it has been shown that cracks may lead to shunts.

By means of a contactless microwave phase shift technique, the minority carrier lifetime and surface recombination velocity were measured in multicrystalline silicon wafers containing iron and chromium. The bulk lifetime can be deduced, leading to the determination of the concentration of interstitial iron [Fe_i ] associated with boron, after pair dissociation annealing at 210 °C. It is found that [Fe_i ] is higher in the vicinity of extended defects but decreases at the defects because the iron segregates irrespective of boron concentration and does not form pairs.

Micro-Raman imaging has been used extensively for characterizing semiconductors. This paper reviews recent developments in the use of Raman microscopy for studying structural and electronic properties of semiconductor crystals and composites. Some results for recent Raman imaging measurements are outlined and discussed.

Silicon and gallium arsenide indentations have been investigated by using Raman spectroscopy. This perfect tool permits the study of the strain field within and around the indentation with 3D-micrometric resolution. By mapping both indented materials, we show that the strain varies strongly in GaAs and is constant in Si within indentations. With the selected orientation of GaAs, the two observed phonons provide a way to determine the local symmetry of the strain in all the area of the fingerprint. In Si, the quite constant value within the indentation, always reported in the literature with low laser power, seems to be correlated with the metastable phases created. To provide evidence for this fact, we have selected samples which favour metastable phases over amorphous, allowing the study of the correlation of the Raman peaks associated with metastable crystalline Si phases (Si-XII) and associated with diamond Si-I. The frequency shift plot of the 355 cm⁻¹ band as a function of the Si-I Raman band frequency at 522 cm⁻¹ exhibits a negative slope. The strains in both phases have an opposite sign. This accurate observation provides an insight into the origin of the surprising high strain in silicon.

Mg⁺ ions were implanted at room temperature in n-type hexagonal GaN for the device isolation purposes. The implantation dose varied from 7.5 × 10¹² to 10¹⁶ ions cm⁻². We performed resonance Raman spectroscopy and DC electrical measurements in order to monitor the structural and electrical changes of non-annealed and annealed implanted GaN samples. Annealing was carried out at 900 °C for 30 s, these conditions being used to achieve good Ohmic contacts. The aim was to determine, on the one hand, the influence of ion doses on the device isolation and, on the other, to establish the order of the technological steps which should be made between ion implantation and Ohmic contact annealing. On increasing the implantation dose from 7.5 × 10¹² to 2 × 10¹⁴ ions cm⁻², an increase in the electrical isolation and a decrease in the photoluminescence (PL) were observed. For the highest dose, the implanted layer became conductive owing to a hopping mechanism and only the first-order phonon lines remained observable. After annealing, the implanted samples became conductive and the PL reappeared or increased compared with the non-annealed samples at same implantation doses, except for the sample implanted at the highest dose, which became insulating. Then, it is possible to achieve device electrical isolation by using a lower ion dose without thermal annealing or using a higher ion dose with thermal annealing.

Ion beam induced charge microscopy (IBIC microscopy) has been established recently as an analytical tool for the characterization of various types of semiconductor devices. In this paper the potential of IBIC microscopy for the analysis of deeply buried structures of high power devices under biases of more than 2 kV is discussed. Such data are useful in the design process of high power devices because excessive fields at device edge regions or within protection elements (e.g. field ring structures) can be avoided.

Since charge collection efficiency within depleted pn junctions is typically 100% for IBIC analysis, the contrast due to E-field variations within the large depletion regions of high power devices is limited. Here we will introduce a new approach for enhancing this contrast by using the temporal information from the IBIC signals gained with a transient IBIC set-up. Simulations and experimental data will be compared to evaluate the suitability of the new approach. The device used here is a high voltage diode with a field ring structure which was analysed using a 2 MeV proton beam.

We present frontal ion beam induced charge imaging on a cadmium zinc telluride device using a 2.05 MeV He microbeam. Two sets of voltage-dependent 3 mm × 3 mm scans over the device cathode were acquired at room temperature and 250 K respectively and the corresponding charge collection efficiency (CCE) images extracted. The reduction of CCE due to electron transport with reduced bias voltage can be described using a simplified Hecht equation. This allows us to measure the mobility–lifetime product for electrons (μ_eτ_e) and so produce high-resolution μ_eτ_e images at 296 and 250 K. At 296 K, CCE values up to 96% were observed for an electric field of 3570 V cm⁻¹. In general, the CCE values at 250 K are lower than the comparable values at 296 K with μ_eτ_e decreasing from 4.7 × 10⁻⁴ to 1.2 × 10⁻⁴ cm² V⁻¹, about 1/4 of its original value. Additionally, we observe an increase in CCE at 250 K due to previous irradiation of the material, caused by partial filling of electron traps by the ion beam.

The dynamic mode of scanning electron microscopy (SEM) cathodoluminescence (CL) based on computer-aided acquisition and fast processing of image data is introduced as a unique method to reveal glide dislocations as extended mobile recombination centres in several III/V and II/VI semiconductors with zincblende and wurtzite lattice structure respectively. Local plastic deformation by in situ scratching or indentation at low-index sample surfaces is shown to be easily used to generate and propagate individual single dislocations of various types. Dislocation dynamics and defect-related recombination activity, as simultaneously observed at separate moving dislocation segments having screw- or edge-type structure, are considered by analysing the CL movies taken.

Our results give evidence of a complex relationship between dynamic and recombination active defect properties depending on the structure of the dislocation and the material studied. In particular, polar A(g) and B(g) dislocations are clearly different in respect of both their dynamics and recombination active behaviour, as discussed for fresh glide dislocations in ZnO and GaAs samples.

We investigate the microstructure of Cu(In,Ga)Se₂ thin films with different preferred grain orientations (textures). The films are grown by coevaporation from elemental sources. We analyse the electro-optical properties of the films with a cathodoluminescence spectrometer attached to a transmission electron microscope. {112} textured films show sharp contrasts at the grain boundaries, whereas grain boundaries in {220/204} textured films give only very weak contrasts indicating a preferential population of electronically rather inactive grain boundaries.

p–n junctions were fabricated in diamond and cubic BN for ultraviolet light emitting diodes. These junctions were characterized by means of cathodoluminescence (CL) and electron-beam-induced current (EBIC). The line profile of CL spectra clearly revealed the different doping regions. EBIC profiles showed the band profile of these structures. The comparison of CL and EBIC results confirmed that, in both cases, the electrical fields exist at the interfaces between p and n regions. The light emitted from these structures under the current injection was compared with CL spectra from the p and n regions. It is noted that EBIC and CL are a suitable tool for the characterization of p–n junction devices of wide-gap materials with small minority carrier diffusion length.

An Si complex formation is observed in unintentionally doped as well as n-type doped GaAs layers grown laterally on GaAs seeds deposited on (100) Si substrates. The free carrier concentration was accurately assessed by previous Raman studies. Particularly interesting was the observation of a doped stripe nearby the GaAs seed in the unintentionally doped layers. In this work the formation of the complexes in both kinds of doped samples was analysed by means of SEM-cathodoluminescence (CL) studies. Different bands, indicative of the presence of more than one Si-related transition, have been observed in the infrared spectral region. The distribution of some of the related complexes at the different depths along the growth axis was analysed by depth-resolved CL. The nature of the emission levels has been investigated by power dependent CL studies, allowing to correlate them to DAP transitions. The Si autodoping origin of the doped stripes on the unintentionally doped samples was also confirmed.

The cathodoluminescence (CL) technique is used to analyse the radiative recombination properties of four distinct silicon carbide (SiC) samples: a 6H-SiC n⁺-type Lely wafer, two off-axis 4H-SiC epitaxial layers of n type and p type, and a ()-oriented 4H-SiC n⁺-type substrate. The CL spectra, recorded at various temperatures and at various excitation conditions, show strong differences between the polytypes, indicating a better homogeneous distribution of radiative centres inside the 6H polytype than in the 4H one, and also between the different orientations. For the ()-oriented 4H sample, luminescence features decrease when the excitation intensity increases, probably due to a more significant indirect transition band. The CL spectra also vary for the same sample, due to the impurity and the microscopic defect density variations. Comparisons between two local spectra taken in two distinct areas of the ()-oriented 4H sample, and with images obtained by x-ray topography in the same areas, allow us to establish that some structural defects are involved in luminescence centres. A deep centre involved in green luminescence (at 1.80 eV) is found to be associated with basal plane dislocations with the Burgers vector .

Self-organized GaN/AlN stacked quantum dots (QDs) have been studied by means of cathodoluminescence (CL), near field scanning optical microscopy (NSOM), photoluminescence, μ-Raman, and transmission electron microscopy. Assignment of the optical emissions was made on the basis of the structural parameters, power-dependent optical studies and depth-resolved CL.

Power-dependent studies allowed us to distinguish between quantum confined and buffer emissions. On increasing the power injection conditions, a QD-size-dependent blue shift due to the screening of the internal electric fields was found together with a trend to saturation observed in the high injection limit. The possible evidence of excited states has also been shown by power-dependent photoluminescence and CL. Different blue shifts in specimens with different numbers of stacked layers suggested possible different residual strain values as confirmed by μ-Raman studies.

Depth-resolved CL investigations performed at constant power injection per unit volume allowed us to distinguish between QD layers with different nominal GaN coverages and a linear dependence of peak energy versus GaN monolayer number has also been found. Adding 1 ML of GaN resulted in an average shift of about 150 meV.

The existence of QDs with different size distributions along the growth axis was also found. The observations were confirmed by NSOM spectroscopy.

Hydrogen incorporation in n-type Si-doped GaAs epilayers is a well-known process which leads to the neutralization of the active Si impurities with the formation of SiH complexes. Recently, we have shown that SiH complex dissociation and, consequently, Si-dopant reactivation could occur when the epilayers are exposed to an electron beam.

Two epilayers have been studied: the first is a 0.35 µm thick hydrogenated Si-doped GaAs epilayer and the second is Si planar-doped AlGaAs/GaAs/InGaAs heterostructures.

Firstly, Hall effect measurements have been carried out on the epilayers exposed, after RF hydrogen plasma exposition, to increasing electron doses with different injection energies. For the 2D heterostructures, we have observed that the free carrier density N_s does not vary significantly for weak electron densities. This reactivation presents a threshold value, contrary to the 0.35 µm epilayer in which N_s varies quite linearly. It will be shown that such phenomena might be attributed to the filling of surface states as the dopants are progressively reactivated.

Then, using a high spatial resolution electron beam lithography system, nanometric conductive patterns have been fabricated starting from hydrogenated epilayers. Electric measurements have been performed and the results obtained show that about 15 nm spatial resolution could be expected.

In conclusion, taking into account this spatial resolution, the high spatial contrast of conductivity which could be expected due to the existence of an electron dose threshold, and the high mobility of the AlGaAs/GaAs/InGaAs heterostructure, the effects described in this paper could open a new way for the fabrication of III–V 1D or 2D mesoscopic structures for electronic or optoelectronic applications.

CdSe/ZnSe structures containing 1 or 15 thin (3–5 monolayers) CdSe layers were studied by cathodoluminescence (CL) and deep level transient spectroscopy (DLTS). The DLTS spectra consisted of peaks from deep levels (DLs) and an additional intense peak due to electron emission from the ground quantized level in the CdSe layers. Activation energy of this additional peak correlated with an energy of the CdSe-layer emission line in the CL spectra. Electron-beam irradiation of the structure during the growth process was found to influence the DLTS and CL spectra of the CdSe layers, shifting the CdSe-layer emission line to the long-wave side. The obtained results are explained using the assumption that e-beam irradiation stimulates the formation of quantum dots of various sizes in the CdSe layers.

In this study we report applications of the synchrotron radiation based x-ray microprobe techniques, x-ray beam induced current (XBIC) and microprobe x-ray fluorescence (μ-XRF), to the analysis of the recombination activity and spatial distribution of transition metals in silicon. A combination of these two techniques enables one to study the elemental nature of defects and impurities and their recombination activity in situ and to map metal clusters with a micron-scale resolution. The correspondence between XBIC data and the data obtained by conventional recombination-sensitive mapping techniques such as electron beam induced current and laser beam induced current is demonstrated. An approach that allows determination of the depth of metal precipitates from several XBIC/μ-XRF images taken for different sample orientations is suggested and is experimentally demonstrated.

Pr₂O₃ is one of the most promising hetero-oxides that are the candidates of choice to replace SiO₂ as the gate dielectric material for sub-0.1 µm CMOS technology. In order to enable process integration, however, hetero-oxides require substantial characterization. In particular, the basic interaction mechanisms at the interface to the silicon substrate are the key issues. A solid knowledge of these mechanisms is required to address reliability arguments. The challenges in material science are to understand the chemical bonding of the hetero-oxides and Si on a microscopic scale. We report on the specific variations in the electronic structure which are evident in the valence band features around resonant excitation at the Pr 4d threshold. We also determine the valance band discontinuities at the Pr₂O₃/Si(001) interface and follow the changes in the surface potentials to develop a band scheme, a prerequisite to understanding the properties of charge transport across that interface.

The applicability of tunnelling spectroscopy by scanning tunnelling microscopy (STM) to semiconductor nanoobjects is addressed through two examples: chemically synthesized PbSe nanocrystals and cleaved InAs quantum dots (QDs) embedded in a GaAs matrix. In the case of free-standing nanocrystals on a metallic substrate, measurements of the conductance at low temperature provides the electronic structures of the nanocrystals in the conduction band and a broad transition range is found for the density of states as a function of the nanocrystal dimensions. Use of the scanning ability of the STM also allows the acquisition of spectroscopic images. At room temperature, current images obtained on cleaved InAs QDs for different samples voltages show the formation of standing wave patterns, which are identified as the probability density of the ground and first excited states. Such results open the opportunity to study the electronic structure of more complicated systems based on the assembly of semiconductor nanoobjects such as coupled QDs.

Scanning tunnelling microscopy (STM) and current imaging tunnelling current spectroscopy (CITS) methods were performed on polycrystalline diamond films grown on silicon substrates grown by microwave plasma-enhanced chemical vapour deposition. Large tunnelling currents were observed at some grain boundaries and crystal surfaces with secondary grains. Following atomic force microscopy (AFM) measurements, we performed scanning probe contact current (SPCC) measurements to investigate the spatial variation of electrical resistance on the surface by using an AFM cantilever in contact mode. The conducting grain boundaries and facets were observed on both boron-doped and undoped samples. For microscale characterization of the field emission properties, we performed scanning probe field emission current (SPFEC) measurements. From the results of STM/CITS, AFM/SPCC and SPFEC, it is concluded that the specific grain boundaries and facets on polycrystalline diamonds work as initial points of electron emission and cause high field emission current through a conducting pass formed in the bulk.

Off-axis and in-line electron holography have been used to determine the electrical properties of a silicon p–n junction. Specimens were prepared for transmission electron microscopy (TEM) by focused ion beam (FIB) thinning and examined in a biasing holder, with holograms recorded as a function of specimen thickness and applied reverse bias. The data revealed the important role played by the surfaces of the thin TEM sample which affect the electrostatic potential distribution within the specimen. The presence of electrically inactive layers, corresponding to the FIB-damaged amorphous surface and an additional crystalline layer, was inferred from the experimental results. Such effects must be taken into account if electron holography is to be used in a reproducible and quantitative way for the examination of semiconductor devices.

Two-dimensional dopant profiling is being strongly demanded by the semiconductor industry, and several techniques have been developed in recent years. We compare the performance of electron holography in a transmission electron microscope with other microscopic techniques. The advantages of electron holography are the high spatial resolution of a few nanometres and the direct interpretability of the measured two-dimensional electrostatic potential requiring no simulation. We demonstrate the detection of a 0.5 monolayer of boron in silicon and silicon germanium. We image a 35 nm wide potential dip of 25 mV in a boron-doped specimen, corresponding to detection of a 2 × 10¹⁷ B cm⁻³ dip between peaks of 2 × 10¹⁸ B cm⁻³. Moreover, we illustrate directly by electron holography the existence of a potential barrier at NiSi₂ precipitates in silicon, which was predicted earlier by the electron-beam-induced current technique.

Electron beam induced current (EBIC) investigations of plastically deformed silicon in the temperature range from 90 K to 300 K were carried out. It is found that the dislocation trails left behind moving dislocations are the main defects revealed by the EBIC in crystals deformed in clean conditions. With an increase of the contamination level, the dislocation contrast in p-type samples increases. It is observed that the EBIC contrasts of both dislocations and dislocation trails increase with cooling in p-type silicon, while in n-type samples the EBIC contrasts exhibit the opposite trends for both defects.

The links between the electrical activity and the atomic structure of various Ge grain boundaries (GBs) are investigated. The atomic structure is studied using high resolution electron microscopy, while the electrical activity is evaluated thanks to the measurement of minority carrier lifetime by means of the contactless microwave phase shift technique. Results show that in the Σ = 51 GB the electrical activity depends on the atomic structure connected to the configuration of the grain boundary, i.e. tilt, twist or mixed. Lower energy structures such as Σ = 3 and 9 GBs appear not to be recombinant.

Multicrystalline silicon (mc-Si) manufactured by a multi-stage solidification control casting method has been characterized by the electron beam induced current (EBIC) method. The average diffusion length of the ingot was over 250 µm, which was much longer than that of conventional mc-Si. The EBIC study revealed that the electrical activities of grain boundaries (GBs) varied with the ingot position due to the impurity contamination level. The main impurity detected was iron. The concentration of iron in the central position was much lower than that at the bottom and top positions. GBs in the central position showed no significant EBIC contrast at 300 K, suggesting low contamination level. GBs in the top and bottom positions, however, showed strong EBIC contrast at 300 K, suggesting high contamination level. At 100 K, a denuded zone with bright contrast developed around GBs in the top and bottom positions. The existence of the denuded zone suggested that impurities were gettered at the GBs. It was considered that the variation of the diffusion length in the ingot was related to the variation of recombination activities of GBs in the different positions, which mainly depended on the impurity contamination.

Electrically active defects in epitaxial, n-type, 4H-SiC have been investigated by electron-beam-induced current (EBIC) in the scanning electron microscope. Several defects, mainly nanopipes, 6H polytype inclusions and triangular, carrot-like, defects were detected by different techniques, including atomic force microscopy and cathodoluminescence. However, EBIC images reveal that only nanopipes are electrically active. The hole diffusion length (L) was calculated at different temperatures from EBIC line scans recorded in defect-free regions. L values of 3.1 ± 0.2 and 4.8 ± 0.3 µm were respectively estimated at 295 and 420 K. A strong decrease of the diffusion length was observed in the proximity of the nanopipes.

High-resolution photoinduced transient spectroscopy has been applied to study grown-in defect centres in semi-insulating InP:Fe. The defect structure of crystals characterized by various values of Hall mobility has been compared. A number of defect centres with activation energies ranging from 10 to 640 meV were detected. They include shallow donor and acceptor impurities, native defects, shallow impurity–native defect complexes and iron-related defects. It was found that the Hall mobility is mainly affected by the shallow donor concentration which determines the ratio [Fe²⁺]/[Fe³⁺]. The electron lifetime is determined either by the iron concentration or the concentration of shallow impurities.

We report the results of our study of the electron irradiation effect (E = 6 MeV, ) on the galvanomagnetic ( K,  T) properties of gallium-doped PbTe, and Pb_1−ySn_yTe (y = 0.19,0.23) narrow-gap semiconductors. Depending on the features of the initial electronic structure of the alloys, a p–n-inversion, a transition from metal to insulating or from insulating to metal-type conductivity and an increase in the free electron density under electron irradiation were revealed. The rate of defect generation under irradiation was found to be abnormally high for A⁴B⁶ materials. The activation character of the temperature dependences of the galvanomagnetic parameters, caused by the presence of deep gallium-induced defect levels in the gap, was observed for the alloys in the insulating state. The results were explained assuming that electron irradiation of gallium-doped PbTe-based alloys creates primarily donor-like defects, which leads to an increase of the electron concentration and a change in the occupancy of the allowed and localized bands. Additionally, electron irradiation seems to cause a change in the charge activity of gallium centres within the bulk, providing a high rate of defect generation.

In situ cathodoluminescence experiments on GaN quantum dots (QDs) show that the area concerned with the degradation is much larger than that where electron–hole pairs are created. It is also shown that an increase in the beam current density leads to a slower degradation of the QDs' optical properties.

The luminescence of GaSb and AlGaSb layers grown on GaAs substrates by metal organic vapour phase epitaxy has been studied by means of cathodoluminescence (CL) using a scanning electron microscope. CL plane-view analysis reveals a distribution of defects, as misfit dislocations, in some of the structures. The luminescence bands observed in the GaSb layers are related to near band edge recombination and to an excess of Ga. In the case of AlGaSb/GaSb heterostructure emission bands related to the ternary compound and to donor–acceptor recombination are detected. In addition, with the aid of a scanning tunnelling microscope (STM), local electronic properties, such as conductance and surface energy gap, were studied in sample cross-sections. The results obtained from imaging and spectroscopy modes of STM enabled us to image the single AlGaSb layer.

Polycrystalline samples of titanium oxide were prepared by thermal sintering, in argon and air atmospheres at temperatures ranging from 1100 to 1500 °C, from powders of anatase and rutile phases. The samples sintered in argon were further treated in oxygen at the temperature of 800 °C for intervals of time up to 8 h. The luminescence emission of the initial powders was situated in the green region, with the peak at 580 nm. The sintering treatment in argon leads to a decrease of the luminescence intensity that appears as a broad band peaked at 550 nm in the case of anatase and as a band peaked at 450 nm in the case of the rutile phase. The sintering treatment in air causes the quenching of the emission in the visible region. In both cases, a sharp and intense emission appears in the infrared region at 800 nm for rutile and 820 nm for the anatase phase.

The blue emission is sensitive to the treatment in oxygen atmosphere which causes mainly an intensity increase of the band at 450 nm. The treatment in oxygen results in the reconstruction of the polycrystalline sample surface as hexagonal shape protrusions and large terraces.

Dark cathodoluminescence (CL) defect contrasts observed in CL video movies taken on GaAs and ZnO samples disclose the intrinsic recombination properties of glide dislocations during their slip motion. This way, the kinematical SEM CL microscopy provides, for the first time, direct information on the possible relationship between the dynamics and electronic activity of glide dislocations as expected from structural alterations or kink processes related to defect movement. The dark CL defect contrasts observed for various dislocation types in both materials indicate defect-bound non-radiative excess carrier recombination. Quantitative CL contrast analysis is performed to discover differences in the recombination strength of distinct dislocation structures resulting from the type and dynamic state of the glide dislocations studied.

The luminescence band at 0.95 eV has been identified as originating from the transition within (Si_GaV_GaSi_Ga) complexes by comparing cathodoluminescence and positron annihilation spectra. The upper and lower energy levels of the molecule-like defect complexes are suggested to lie at 22 meV below the conduction band and at about 0.5 eV above the valence band, respectively.

The incorporation of phosphorus (P) dopants as donor atoms in chemical vapour deposition (CVD) diamond is studied by cathodoluminescence (CL). P-doped and undoped samples with identical CVD growth conditions are analysed. Variations in the spectral emission of the doped diamond are observed depending on the orientation of growth sectors. Indeed, strain relaxation through crack generation induces the formation of a faceted topography of the substrate surface. Centres associated with P incorporation seem to be responsible for the change in the CL spectral emission in the non-(111) facets. This indicates that n-type diamond can probably be grown on other than (111) orientation. Excitonic emission from liquid He to room temperature is observed for both samples as a result of the high quality n-doped growth.

Undoped ZnO single crystals were implanted with multiple-energy N⁺ ions ranging from 50 to 380 keV with doses from 10¹² to 10¹⁴ cm⁻². Positron annihilation measurements show that vacancy defects are introduced in the implanted layers. The concentration of the vacancy defects increases with increasing ion dose. The annealing behaviour of the defects can be divided into four stages, which correspond to the formation and recovery of large vacancy clusters and the formation and disappearance of vacancy–impurity complexes, respectively. All the implantation-induced defects are removed by annealing at 1200 °C. Cathodoluminescence measurements show that the ion-implantation-induced defects act as nonradiative recombination centres to suppress the ultraviolet (UV) emission. After annealing, these defects disappear gradually and the UV emission reappears, which coincides with positron annihilation measurements. Hall measurements reveal that after N⁺ implantation, the ZnO layer still shows n-type conductivity.

Nitrogen-doped chemical vapour deposited diamond-like carbon (DLC) films were treated by reactive ion etching system under various conditions of CHF₃ gas successively after pre-treatment with oxygen. Atomic force microscopy and Raman spectroscopy were carried out in order to characterize the surface morphology and chemical bond, respectively. Scanning tunnelling microscopy was used in order to investigate the surface state of the DLC films at the nanoscale level. Scanning probe field emission current measurement was performed in order to obtain the emission current mapping. The emission sites appeared to a great extent after the surface treatment by CHF₃ gas and a clear activation effect was observed. We confirmed that the surface treatment using CHF₃ gas affected not only the appearance of emission sites but also the activation process.