Search

Accumulation of arsenic implantation-induced donor defects in heteroepitaxial Hg1−xCdxTe structures with the composition of the active layer xa = 0.30 was studied with the use of the Hall-effect measurements and mobility spectrum analysis. The studies allowed for identifying the carriers in the implantation-damaged n+-layer, namely, electrons with low and intermediate mobility, and for establishing the dependence of their concentration on the ion fluence. The electrically active implantation-induced defects in the studied structures, similar to the case of those with xa = 0.22, were identified as atoms of interstitial mercury captured by dislocation loops and quasi-point defects. In the material with xa = 0.30, a weak dependence of the concentration of low-mobility electrons on the fluence was observed. In general, a substantial difference in the properties of p+–n junctions formed as a result of arsenic implantation in the structures with xa = 0.30 and xa = 0.22 was established. The difference was explained by the effect of the graded-gap surface layer on the diffusion of charged defects released during the implantation.

Optical reflectance and bright-field and high-resolution transmission electron microscopy studies of radiation damage induced by implantation of arsenic ions with 190 keV and 350 keV energy and 1014 cm–2 fluence in molecular-beam epitaxy-grown Hg0.7Cd0.3Te films were performed. A similarity in defect pattern formed by arsenic implantation in Hg1−xCdxTe with x ≈ 0.2 and x ≈ 0.3 straight after the implantation was observed with formation of three nano-size defect layers containing dislocation loops of vacancy- and interstitial-types, single dislocations and lattice deformations. After post-implantation arsenic activation annealing, most of these defects in our Hg0.7Cd0.3Te films, in contrast to Hg0.8Cd0.2Te films, disappeared. This effect is explained by the reduced influence of the electric field of the graded-gap surface layer on the diffusion of charged point defects under annealing.

Results of a deep-level transient spectroscopy (DLTS) study of trapping states in Ni/Au Schottky diodes made on Si-doped GaN layers grown by metal–organic vapor-phase epitaxy (MOVPE) on highly conductive n-type Ammono-GaN substrates are reported. In all as-grown samples, the DLTS signals due to traps with the activation energies for electron emission (Eem) of about 0.26 and 0.60 eV (referred to as E1 and E3 traps, respectively) have been detected. It is found that the electric field (E) significantly enhances the electron emission rate (eem) for the E1 trap, while for the E3 trap the eem(E) dependence is not very strong. The eem(E) dependence for the E1 trap is found to be characteristic of attractive traps with spherically symmetric square well potential with a radius of about 2.9 ± 0.25 nm. The eem(E) dependence for the E3 trap is accounted for by a phonon-assisted tunneling mechanism. The zero-E Eem values for both traps are determined. Correlations between the concentrations of the E1 and E3 traps and concentrations of impurities (H, C, Si, O, Mg, and Fe) determined by secondary ion mass spectrometry in the samples are investigated. Charge states and origins of the E1 and E3 traps are discussed.

Coating magnesium alloys with nitride surface layers is a prospective way of improving their intrinsically poor surface properties, in particular, their tribological and corrosion resistance. These layers are usually produced using PVD methods using magnetron sputtering or arc evaporation. Even though the thus-produced layers significantly increase the wear resistance of the alloys, their effects on corrosion resistance are unsatisfactory because of the poor tightness, characteristic of PVD-produced products. Tightness acquires crucial significance when the substrate is a highly-active magnesium alloy, hence our idea to tighten the layers by subjecting them to a post-deposition chemical-hydrothermal-type treatment. This paper presents the results of our experiments with a new hybrid surface engineering method, using a final tightening pressure hydrothermal gas treatment in overheated steam of the composite titanium nitride layers PVD, produced on AZ91D magnesium alloy. The proposed method resulted in an outstanding improvement of the performance properties, in particular resistance to corrosion and wear, yielding values that exceed those exhibited by commercially anodized alloys and austenitic stainless 316L steel. The developed hybrid method produces new, high-performance corrosion and wear resistant, lightweight magnesium base materials, suitable for heavy duty applications.

The structural, optical, and electrical properties of ZnO are intimately intertwined. In the present work, the structural and transport properties of 100 nm thick polycrystalline ZnO films obtained by atomic layer deposition (ALD) at a growth temperature (Tg) of 100–300 °C were investigated. The electrical properties of the films showed a dependence on the substrate (a-Al2O3 or Si (100)) and a high sensitivity to Tg, related to the deviation of the film stoichiometry as demonstrated by the RT-Hall effect. The average crystallite size increased from 20–30 nm for as grown samples to 80–100 nm after rapid thermal annealing, which affects carrier scattering. The ZnO layers deposited on silicon showed lower strain and dislocation density than on sapphire at the same Tg. The calculated half crystallite size (D/2) was higher than the Debye length (LD) for all as grown and annealed ZnO films, except for annealed ZnO/Si films grown within the ALD window (100–200 °C), indicating different homogeneity of charge carrier distribution for annealed ZnO/Si and ZnO/a-Al2O3 layers. For as grown films the hydrogen impurity concentration detected via secondary ion mass spectrometry (SIMS) was 1021 cm−3 and was decreased by two orders of magnitude after annealing, accompanied by a decrease in Urbach energy in the ZnO/a-Al2O3 layers.

Understanding how Sb atoms are located in the ZnO crystal lattice and how they affect the layer parameters is essential to obtain p-type conductivity in ZnO:Sb. In this paper, the results of our extensive research (XPS, Raman, X-Ray, SIMS) of Sb doped ZnO films grown by Molecular Beam Epitaxy are presented. It is shown with use of high resolution X-ray Photoemission Spectroscopy (XPS) that three charge states of the Sb impurity: Sb3+, Sb5+, and Sb3− can exist in ZnO:Sb layers. The dominant charge state of Sb ions is 3 + while the contribution of 5 + is very low. The relative fraction of Sb atoms located at the Zn sites is about ∼90%, while ∼10% are incorporated in oxygen sites. It was found that increasing the Sb content in the layers increases the intensity of Raman modes at 511 cm−1, 533 cm−1, and 575 cm−1, which confirms their correlation with Sb doping. Additionally, a blue shift of the E2High Raman mode of ZnO was observed, related to the increase of strain in the oxygen sublattice. The relation between strain and stress for different Sb chemical states (Sb3+, Sb5+, Sb3−) in ZnO is calculated and compared with experimental results.

In this work, the Si+ doping of undoped GaN (n ∼1 × 1016 cm−3) on sapphire by a single step implantation or sequential implantation/recrystallization processes, to a total fluence of 1 × 1016 at/cm2 and subsequent activation annealing at 1100 °C for 2 min, were demonstrated and analysed. We proved that the multicycle implantation/recrystallization process is better in terms of structural and electrical parameters of implanted region than conventional single step implantation. Rutherford backscattering spectrometry in channeling geometry (RBS/c), McChasy simulations and atomic force microscopy (AFM) studies showed, that the proposed process does not deteriorate surface morphoplogy and leads to a significantly lower defect concentrations. Low resistivity ohmic contacts, with RC

In this work, we compared ion implantation n-type doping processes in GaN using Si+ or Ge+ ions, by conducting structural and electrical characterization. In the case of Ge+ implantation processes, we compared both the standard single implantation and the sequential doping technique. Analysis of RBS/c spectra and AFM images did not show surface degradation after each technological step (RMS

Diffusion of Be was investigated for the main crystallographic directions in HVPE-GaN: c [0001], m [10-10], and a [11-20]. Be was implanted into the samples at room temperature with a dose of 2.9e15 cm-2 with energy of 200 keV. Ultra-high pressure annealing (UHPA) was performed to repair the post-implantation damage and activate the dopant. The annealing was performed at different time (15 and 30 minutes) and temperature (1200 – 1400°C). Depth profiles of Be were measured by secondary ion mass spectrometry (SIMS). Diffusion coefficients were calculated using the complementary error function (erfc) or Boltzmann-Matano analysis. The determined diffusion coefficients were summarized in an Arrhenius plot: D(1/T). From this relation the pre-exponential factor D0 and the activation energy were calculated. In addition, it was possible to calculate the formation energy for interstitial Be as well as gallium vacancy defects.

Nominally 45 nm GaN:Mg/ 5 nm (Ga,Mn)N / 45 nm GaN:Mg trilayers structures prepared by molecular beam epitaxy on GaN-buffered Al2O3 substrates are investigated to verify whether the indirect co-doping by holes from the cladding layers can alter the spin-spin interaction in (Ga,Mn)N. The four investigated structures, differing with the Mg doping level, are carefully characterized at the nanoscale by HRTEM, EDX, and by SIMS. HRTEM decisively excluded a presence of foreign Mn-rich phases. The structures, up to medium Mg doping, show no Mg over-doping effects. Magnetic studies of these structures are aided by the employment of a dedicated experimental approach of the in situ compensation of the magnetic contribution from the substrate, allowing up to about fifty-fold reduction of this contribution. This technique, dedicated to these structures, simultaneously provides a tenfold reduction of temporal instabilities of the magnetometric unit and lowers the experimental jitter to merely $5 \times 10^{-7}$~emu at 70~kOe, vastly increasing the precision and the credibility of the results of the standard integral SQUID magnetometry in high magnetic fields. The magnetic characteristics of the trilayers structures established here prove identical with the already known properties of the thick (Ga,Mn)N single layers, namely (i) the low temperature ferromagnetism among Mn$^{3+}$ ions driven by superexchange and (ii) purely paramagnetic response at higher temperatures. The possible cause of the lack of any effects brought about by the adjacent Mg-doping is a presence of residual Mn in the cladding layers, resulting in the deactivation of the p-type doping intended there. This finding points out that a more intensive technological effort has to be exerted to promote the co-doping-driven carrier-mediated ferromagnetic coupling in Mn-enriched GaN, especially at elevated temperatures., 16 pages, 6 figures

Carrier species in arsenic-implanted p– and n–type Hg0.7Cd0.3Te films grown by molecular-beam epitaxy were investigated with the use of the Hall-effect studies and mobility spectrum analysis. The implantation was performed with ion energy 190 or 350 keV and ion fluence ranging from 1012 to 1015 cm−2. A substantial difference between carrier species in Hg0.7Cd0.3Te and Hg0.8Cd0.2Te films subjected to arsenic implantation and post-implantation activation annealing was established. In particular, arsenic implantation in p–type Hg0.7Cd0.3Te in most cases lead to the formation of n+–p– (not n+–n–p–) structures, and in n–type Hg0.7Cd0.3Te films post-implantation activation annealing lead to modification of the electrical parameters of the n–type ‘base’, in contrast to Hg0.8Cd0.2Te material studied earlier. The difference in carrier species formed in arsenic-implanted Hg0.7Cd0.3Te and Hg0.8Cd0.2Te films was tentatively explained by different background impurity concentrations in the films with different chemical composition.

The effect of growth temperature and precursor flows on the doping level and surface morphology of Ge-doped GaN layers was researched. The results show that germanium is more readily incorporated at low temperature, high growth rate and high V/III ratio, thus revealing a similar behavior to what was previously observed for indium. V-pit formation can be blocked at high temperature but also at low V/III ratio, the latter of which however causing step bunching.

The diffusion of beryllium in gallium nitride crystals grown in non-polar crystallographic directions by halide vapor phase epitaxy was investigated. The layers were crystallized on (10-10) and (11–20) planes of native ammonothermal substrates of the highest structural quality. The new-grown crystals were prepared to an epi-ready state, implanted with beryllium, and treated with ultra-high-pressure annealing. The crystallographic structure of all the samples before and after ion implantation as well as annealing processes was evaluated by X-ray diffraction measurements. The diffusion of beryllium was investigated by analyzing depth profiles obtained by secondary ion mass spectrometry. The diffusion profiles were box-shaped for both examined non-polar directions. Pre-exponential factors and activation energies for beryllium diffusion in non-polar gallium nitride were determined. A model related to point defect complexes, based on gallium vacancies and oxygen, was proposed for explaining the box-shaped beryllium diffusion profiles and the visible differences in the diffusion range between the two analyzed non-polar directions.

It is well known that ion implantation is one of the basic tools for semiconductor device fabrication. The implantation process itself damages, however, the crystallographic lattice of the semiconductor. Such damage can be removed by proper post-implantation annealing of the implanted material. Annealing also allows electrical activation of the dopant and creates areas of different electrical types in a semiconductor. However, such thermal treatment is particularly challenging in the case of gallium nitride since it decomposes at relatively low temperature (~800 °C) at atmospheric pressure. In order to remove the implantation damage in a GaN crystal structure, as well as activate the implanted dopants at ultra-high pressure, annealing process is proposed. It will be described in detail in this paper. P-type GaN implanted with magnesium will be briefly discussed. A possibility to analyze diffusion of any dopant in GaN will be proposed and demonstrated on the example of beryllium.

A multiple-quantum-well structure consisting of 40 periods of AlN/GaN:Si was investigated using a transmission electron microscope equipped with energy-dispersive X-ray spectroscopy. The thicknesses of the AlN barriers and the GaN quantum wells were 4 nm and 6 nm, respectively. The QW layers were doped with Si to a concentration of 1.3 × 10 19 c m - 3 (0.012 % at). The procedure for quantifying such a doping level using AlN as a standard is presented. The EDS results (0.013 % at) are compared with secondary ion mass spectrometry measurements (0.05 % at).

The possibility of inducing superconductivity in type-I Weyl semimetal through coupling its surface to a superconductor was investigated. A single crystal of NbP, grown by chemical vapor transport method, was carefully characterized by XRD, EDX, SEM, ARPES techniques and by electron transport measurements. The mobility spectrum of the carriers was determined. For the studies of interface transmission, the (001) surface of the crystal was covered by several hundred nm thick metallic layers of either Pb, or Nb, or In. DC current-voltage characteristics and AC differential conductance through the interfaces as a function of the DC bias were investigated. When the metals become superconducting, all three types of junctions show conductance increase, pointing out the Andreev reflection as a prevalent contribution to the subgap conductance. In the case of Pb-NbP and Nb-NbP junctions, the effect is satisfactorily described by modified Blonder-Tinkham-Klapwijk model. The absolute value of the conductance is much smaller than that for the bulk crystal, indicating that the transmission occurs through only a small part of the contact area. An opposite situation occurs in In-NbP junction, where the conductance at the peak reaches the bulk value indicating that almost whole contact area is transmitting and, additionally, a superconducting proximity phase is formed in the material. We interpret this as a result of indium diffusion into NbP, where the metal atoms penetrate the surface barrier and form very transparent superconductor-Weyl semimetal contact inside. However, further diffusion occurring already at room temperature leads to degradation of the effect, so it is observed only in the pristine structures. Despite of this, our observation directly demonstrates possibility of inducing superconductivity in a type-I Weyl semimetal., Accepted for Phys. Rev. B. 13 pages, 12 figures. Second version with major revisions. The title was changed. One author R. Jakiela added. New inset to Fig. 8(A). New fits in Fig. 8 (B) and Fig. 10 (B). Added figures 12 (C)-(E). Added Fig. 12 (F) with SIMS data. Rewritten chapters III-C-2 and III-C-3. Reference no. 38 removed, 11 new references: 9, 21, 22, 40-44, 46-49 were added

The dilute bismide alloy GaAs1-xBix has drawn significant attention from researchers interested in its fundamental properties and the potential for infrared optoelectronics applications. To extend the study of bismides, molecular-beam heteroepitaxy of nominally 1.0 eV bandgap bismide on Ge substrates is comprehensively investigated. Analysis of atomic-resolution anti-phase domain (APD) images in the direct-epitaxy revealed a high-density of Ga vacancies and a reduced Bi content at their boundaries. This likely played a key role in the preferential dissolution of Bi atoms from the APD interiors and Bi spiking in Ge during thermal annealing. Introduction of GaAs buffer on offcut Ge largely suppressed the formation of APDs, producing high-quality bismide with single-variant CuPtB-type ordered domains as large as 200 nm. Atomic-resolution X-ray imaging showed that 2-dimensional Bi-rich (111) planes contain up to x = 9% Bi. The anomalously early onset of localization found in the temperature-dependent photoluminescence suggests enhanced interactions among Bi states, as compared to non-ordered samples. Growth of large-domain single-variant ordered GaAs1-xBix films provides new prospects for detailed analysis of the structural modulation effects and may allow to further tailor properties of this alloy for optoelectronic applications.

Semi-insulating plates made from CdTe i Cd1−xZnxTe are currently used for preparing X and gamma radiation detectors. For many years there has been a search for another semiconductor based on CdTe, suitable for making large, monocrystalline, semi-insulating, and homogeneous detector plates. Recently, a series of investigations has been devoted to a possibility of using crystals based on CdTe with addition of magnesium (Mg), or selenium (Se) for X and gamma radiation detectors. In our previous paper [1] we presented results of investigation of CdTe with magnesium: Cd1−xMgxTe. In this paper we present results of investigation of crystals CdTe with selenium (Se) and with both selenium and manganese (Mn): CdTe1−xSex and Cd1−xMnxTe1−ySey.

In recent years, a series of investigations has been devoted to a possibility of using crystals based on CdTe with addition of magnesium (Mg) for X and gamma radiation detectors. Since we have had wide technological possibilities of preparing crystals and investigating their properties, we performed crystallizations of the crystals mentioned above. Thereafter, we investigated selected properties of the obtained materials. The crystallization processes were performed by using the Low Pressure Bridgman (LPB) method. The elements used: Cd, Te, Mg were of the highest purity available at present. In order to obtain reliable conclusions the crystallization processes were carried out at identical technological conditions. The details of our technological method and the results of the investigation of physical properties of the samples are presented below.

Theoretical predictions of high hydrogen diffusivity in p-GaN layers were confirmed in many experiments for samples grown by Metalorganic Vapor Phase Epitaxy (MOVPE). In this technology, p-GaN has a high concentration of hydrogen incorporated during the growth. In this work, we confirm that also in hydrogen-free p-GaN grown by Plasma Assisted Molecular Beam Epitaxy (PAMBE) the hydrogen diffusion during H2+NH3 annealing is much higher than in n-type layers. Additionally, we have compared hydrogen diffusion for samples of different dislocation density and we have found no effect of these defects. The photoluminescence of the PAMBE-grown p-GaN exhibited the following change after annealing in H2+NH3 atmosphere: the blue luminescence decrease and yellow luminescence increase.

In this paper the current understanding of defects in acceptor doped ZnO is briefly reviewed. The results of investigations of ZnO:As/n-GaN heterojunctions which have been successfully fabricated by plasma assisted molecular beam epitaxy method are presented. The electrical properties of the junctions, as well as deep levels, have been studied by means of current-voltage (I-V), capacitance-voltage (C-V) characteristics and deep level transient spectroscopy (DLTS). Electrical measurements were supplemented by photoluminescence- (PL) along with secondary ion mass spectrometry (SIMS) and X-ray photoemission spectroscopy (XPS) investigations. The I-V measurements allowed for detailed analysis of current mechanisms, through which the presence of trap states in the investigated junction was confirmed. The C-V results proved that the depletion region of the diode is located within the ZnO:As layer. The DLTS measurements revealed the presence of three hole trap related signals. The activation energies and capture cross sections of these traps were determined and their possible origin has been ascribed. Obtained results allowed for better identification of defects found in the case of the analyzed heterostructure, as well as the studies of its electronic properties.

Ion implantation can be applied to form the electrical isolation in AlGaAs/GaAs Quantum Cascade Laser (QCL) instead of mesa etching. In this paper, we present in detail the designing of hydrogen implant isolation scheme, alongside with its verification and study of thermal stability by structural and electrical characterization techniques. Our scheme employed 4 µm thick metallic mask made mainly of gold which also served as contact layer, and 640 keV hydrogen implantation to a fluency of 1 × 10 15 cm −2 . We obtained the sheet resistivity R SH of (1.5 ± 0.9) × 10 9 Ω/□. The critical temperature for the hydrogen implant isolation fabrication of the AlGaAs/GaAs QCL was determined to be 310 ℃. Defect density dropped to residual levels after 1 min annealing at 300 ℃ and 400 ℃, while the material was still resistive with R SH above 10 8 Ω/□. Based on our simulated vacancy maps we concluded that the minimum width of the masking structure should be at least 5 µm to avoid the effects of lateral isolation for the given implantation conditions. The QCL device fabricated with this isolation scheme operated with threshold current densities of 6 kA/cm 2 at the temperature of 77 K. Ultimately, we confirmed the applicability of hydrogen implant isolation for the manufacturing of optical devices.

This paper discusses possible contributions to the nominal n–type behavior of ZnO films grown by the Atomic Layer Deposition (ALD). The room–temperature photoluminescence (RT PL) and Secondary Ion Mass Spectroscopy (SIMS) investigations suggest an important role played by the zinc–related defects in their electrical behavior. This is also supported by increasing electron concentration, which changes from 1.7 × 1017 cm−3 to 8.6 × 1019 cm−3 with increasing ZnO growth temperature. The ellipsometry studies show that the absorption edge shifts with increasing growth temperature from 3.27 eV to 3.34 eV, indicating the self–compensation and the Burstein–Moss effect, whereas the maximal extinction coefficient k remains at the level of k = 0.5. After the rapid thermal processing (RTP) in oxygen and nitrogen–rich atmosphere significant changes in the defect–related RT PL were observed, suggesting the contributions of defects of miscellaneous origin in different spectral range, i.e., RTP annealing in N2 results in the defect–related luminescence peaked at 520–560 nm, i.e. 2.23–2.38 eV (ascribed to the defects involving oxygen vacancies), whereas similar treatment performed in O2 atmosphere activates the luminescence in the vicinity of 650–730 nm, i.e. 1.70–1.90 eV, where the zinc–related (presumably VZn) defects are efficient radiative centers.

In recent years, a series of investigations has been devoted to a possibility of using crystals based on CdTe with addition of magnesium (Mg), selenium (Se), or manganese (Mn) for X and gamma radiation detectors. In the literature there are contradictory data with respect to the segregation of Mg in (Cd,Mg)Te and Se in Cd(Te,Se) and to the possibility of obtaining materials with a homogeneous composition without grains and twins. We have wide technological possibilities of preparing crystals and investigating some of their properties. Thus, we performed crystallizations of (Cd,Mg)Te, Cd(Te,Se), (Cd,Mn)(Te,Se), and (Cd,Mn)Te compounds. The aim of our studies was to check whether any of the investigated materials may be easily obtained by the Low Pressure Bridgman (LPB) method in the form of large, homogeneous, high resistivity single crystals with as few as possible twins, subgrains, and tellurium inclusions. The crystallization processes were performed by using the LPB method. The elements used: Cd, Te, Mn, Mg, and Se were of the highest purity available at that time. In order to obtain reliable conclusions the crystallization processes were carried out under identical technological conditions. The details of our technological method and the results of the investigation of physical properties of the samples are presented below.

The aim of this study is to establish the measured concentration of vanadium actually present in the doped crystals as a function of the vanadium concentration determined on the basis of its amount introduced into our (Cd,Mn)Te and CdTe crystals during the growth process. For (Cd,Mn)Te the expected concentration of vanadium varied from 1014 cm−3 to 1020 cm−3. The measurements were performed using the Secondary Ion Mass Spectrometry (SIMS). The measured results for vanadium concentrations from 1014 cm−3 to 3 × 1018 cm−3 differ from the intended ones by not more than a factor of 2 and exhibit the linear relationship. For concentrations above 3 × 1018 cm−3 the measured vanadium concentrations are lower than the nominal ones by more than a factor of 10.

Vertical structures based on Pd Schottky contacts to a ZnO/AZO bilayer have been realized and electrically characterized. Following a preliminary annealing study on the separated ZnO and AZO layers the ZnO/AZO bilayer was first annealed at 450 °C for 30 min to reduce the carrier concentration and then functionalized with a H2O2 dip prior to Pd deposition. On the basis of Atomic Force Microscopy, Transmission electron Microscopy and Capacitance vs Voltage measurements it has been found that the H2O2 treatment lowers the surface roughness and creates a ~ 200 nm thick layer formed by ZnO crystallites with grain size ≲ 10 nm embedded into an amorphous matrix with reduced carrier concentration. However, contrary to what previously reported no formation of ZnO2 has been observed. The obtained Schottky contacts showed a rectification ratio ≳ 10 2 at −2 V/+2 V with a detailed analysis based on the differential approach pointing to field enhanced emission from defective channels as the main leaking mechanisms.

Highly-doped ZnO:Al,N films were grown under oxygen-rich conditions on Si substrates by magnetron sputtering using a layer-by-layer growth technique. An investigation of the highly-doped ZnO:Al,N films is attractive for obtaining p -type conductivity in ZnO films as well as for an improvement of performance of ZnO-based ultraviolet (UV) detectors. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES) and Secondary ion mass spectrometry (SIMS) were used for the samples characterization. An effect of high Al and N doping on structure and electronic properties of ZnO films was studied and discussed.

The paper presents results of investigations of optical absorption spatial changes in congruent bulk LiNbO3 crystals in 300–800 nm spectral region along Х, Y, Z directions caused by high-temperature (400–700 оС) annealing in Н2 and, subsequently, in air. As it is shown, the coloration/discoloration processes are anisotropic: a maximal depth of coloration is observed for Z direction and a minimal one – for X direction. The reversibility of optical properties with respect to the annealing atmosphere changes as well as results of investigations by SIMS and IR spectroscopy methods suggest that the oxygen loss/incorporation. processes play a major role in the coloration/discoloration. The additional absorption spectrum caused by reduction consists of three bands, whose nature is associated with different point defects: 350–410 nm – defects in anion sublattice, 500–520 nm – bipolarons; 700–750 nm – bound polarons. Individual contributions of the bands to the additional absorption spectra depend on the annealing temperature and on the distance from the crystal surface. During reduction lithium oxide is leaving the crystal which leads to the formation of Li2O-depleted structural phase LiNb3O8 in near-surface regions. Experimentally obtained distribution of depth-dependent additional absorption in reduced crystals was successfully approximated basing on the oxygen vacancies diffusion model and solution of differential equations set describing a quasichemical reaction of bipolarons formation due to the oxygen loss in LiNbO3 crystal. On the other hand, this model does not allow to describe accurately the depth-dependent discoloration after oxidizing annealing of previously reduced lithium niobate crystals.

Infrared (IR) reflectance spectroscopy is applied to study Si-doped multilayer n+/n0/n+-GaN structure grown on GaN buffer with GaN-template/sapphire substrate. Analysis of the investigated structure by photo-etching, SEM, and SIMS methods showed the existence of the additional layer with the drastic difference in Si and O doping levels and located between the epitaxial GaN buffer and template. Simulation of the experimental reflectivity spectra was performed in a wide frequency range. It is shown that the modeling of IR reflectance spectrum using 2 × 2 transfer matrix method and including into analysis the additional layer make it possible to obtain the best fitting of the experimental spectrum, which follows in the evaluation of GaN layer thicknesses which are in good agreement with the SEM and SIMS data. Spectral dependence of plasmon-LO-phonon coupled modes for each GaN layer is obtained from the spectral dependence of dielectric of Si doping impurity, which is attributed to compensation effects by the acceptor states.

ZnO:Al-hydroquinone (AZO-HQ) films were grown on poly(ethylene terephthalate) (PET) substrates by atomic and molecular layer deposition (ALD/MLD). Organic contents in the films varied from 0 to ≈4 vol%. Structural and electrical investigations of the films were carried out. Electrical measurements were performed under film bending. The piezoresistive effect in the films with different organic contents was observed and described. Critical bend radius, critical strain, and piezoresistive coefficient values were related to the film microstructure. The piezoresistivity was found to be enhanced for the deformations of ZnO crystallites along the a-axis whereas higher critical strain was influenced by long crystallites oriented in the deformation direction. AZO-HQ films having 2 vol% of the organic content are characterized by the lowest critical bend radius and the highest critical strain among the films under study. Keywords: Zinc oxide, Molecular layer deposition, Electrical properties, Piezoresistive effect

A defect study was performed on arsenic-implanted Hg 1-x Cd x Te ( x = 0.23–0.30) films with graded-gap surface layers, grown with molecular-beam epitaxy on GaAs and Si substrates and designed for fabrication of ‘ p + – n’- type photodiodes. First, formation of n + – p structure was investigated in p -type material, in order to study radiation-induced donor defects. Next, formation of p + – n structure was investigated in the course of implantation in n -type material and arsenic activation annealing. Influence of the graded-gap surface layer was found to be expressed in the degree of saturation of the concentration of radiation-induced defects, with results obtained on arsenic- and boron-implanted material differing due to the difference in the ion masses.

This paper is devoted to the electrophysical diagnostics of the ZnO-based rectifying structures in which the semiconducting oxide layer has been obtained by the low-temperature (80 °C ≤ T ≤ 130 °C) Atomic Layer Deposition (ALD) process. For the growth of examined diodes an organic compound (diethylzinc, DEZn) was used as a zinc precursor. As an oxygen source either deionized (in case of Schottky rectifiers as well as for n-type part of homojunction) or ammonia water (for the p-type layer of homojunction) was applied. In order to improve the basic electrical parameters of these structures (with a particular interest in the rectification (ION/IOFF) ratio) a solution based on inserting the thin dielectric layer (HfO2 or Al2O3) either below the Ag Schottky contact or between the homodiode parts, respectively, has been tested. Through comparing the electrical properties of Ag/HfO2/ZnO/ITO Schottky diodes and ZnO homojunctions as well as modeling their room-temperature current–voltage (I–V) characteristics according to the differential approach it has been proven that the optimal interlayer thickness allowing to achieve the ION/IOFF parameter as high as 104–105 for approximately ± 2 V polarization voltage range is about 2.5–5-nm. Additionally, involving the theoretical studies, the dominant carrier transport mechanisms were identified to be the monopolar injection, tunneling/trapping phenomena occurring in the dielectric layer and bimolecular recombination. The achieved results predestine the examined structures to be applied in the modern electronic devices, where stable in time and good quality diodes are required.

This paper describes two types of MOCVD-grown n-type GaN layers (Samples A and B) with similar carrier concentration but behaved differently under galvanic photo-etching. In order to understand this behavior, Transmission Electron Microscopy (TEM) for cross-section and plan-view samples, Secondary Ion Mass Spectroscopy (SIMS) and photoluminescence (PL) techniques were applied. SIMS studies showed that Si, C and O are approximately at the same concentration in both samples, but Sample B also contained Fe and Mg. Both GaN samples were grown on sapphire substrate with Ga growth polarity, which was confirmed by Convergent Beam Electron Diffraction (CBED). Despite a smaller layer thickness in Sample B, the density of edge dislocations is almost one order of magnitude lower than in Sample A. In addition, planar defects formed in this sample in the transition area between the undoped buffer and Si doped layers resulted in a substantial decrease in the density of screw dislocations at the sample surface. These planar defects most probably gave rise to the PL lines observed at 3.42 eV and 3.32 eV. The new PL lines that only appeared in Sample B might be related to Mg impurities found in this sample. There were no detectable gettering of these impurities at dislocations using different diffraction conditions. However, Fe rich platelets were found only in Sample B due to the presence of Fe as well as hexagonal features, similar to defects reported earlier in highly Mg-doped GaN. These structural and chemical non-uniformities between the two GaN samples can explain their different etching behaviors. This paper demonstrates that samples with similar carrier concentrations do not necessarily ensure similar structural and optical properties and that additional material characterization are needed to ensure that devices built on such samples have similar performance.

Zinc oxide films single, double and triple doped with arsenic, arsenic and nitrogen, arsenic, nitrogen and antimony, were grown by plasma assisted molecular beam epitaxy. Differently doped ZnO samples were post-growth annealed in oxygen or argon atmospheres. Incorporation of impurities into ZnO layers was confirmed by the results of secondary ion mass spectrometry measurements. The high resolution X-ray photoelectron spectroscopy (XPS) studies of arsenic 3d state revealed three arsenic states at the binding energy of ∼41 eV, 44.2 and 45.6 eV which we attribute to As deep acceptor, As Zn -2V Zn shallow acceptor, and to As Zn donor, respectively. Concentration of the As O species was found to be low in all samples. The relative fractions of arsenic chemical states in As-doped ZnO layers, were altered as a result of doping by antimony and/or nitrogen and post grown annealing in argon and oxygen atmosphere.

Low temperature (at 100 °C and below) growth of ZnO thin films by atomic layer deposition (ALD) is demonstrated. Properties of the layers grown with two different oxygen reagents: ozone and water are compared. Diethylzinc (DEZ) was used as metal precursor. Electrical and structural properties of films obtained at several different growth temperatures, ranging from 50 °C to 250 °C were analyzed. It turned out that the film grown in the water-based process at 250 °C and all films grown with ozone have more ordered crystallographic structure with the privileged growth direction (001) perpendicular to the substrate than water-based samples grown in temperatures 100−200 °C. Higher free electron concentration at room temperature was observed for ozone-based samples grown at 100 °C and 150 °C in comparison to water-based samples obtained at the same growth temperature. Low value of resistivity in case of ozone-based samples grown at 100 °C is a promising result, however lower electron mobility requires further optimization.

HVPE can be used for growing thin, up to 200 µm, GaN layers of high purity and low free carrier concentration. Deposition of such material on conductive n-type GaN seeds results in a structure which is the basis of some vertically operating electronic devices. It should be stressed that thickness of this GaN with low free carrier concentration influences the breakdown voltage of the devices. Therefore, HVPE becomes the main epitaxial technology for crystallizing such layers. The method allows to crystalize GaN with a relatively high growth rate of about 100 µm/h. It makes this technology crucial for preparing transistor structures with breakdown voltage higher than a few or several kV. The main goal of this paper is to investigate implantation of beryllium (Be) acceptors into thin (10-100 µm) unintentionally doped layers of GaN crystallized by HVPE on native seeds. A nitride structure comprising of an n-type layer of low free carrier concentration with implanted regions with p-type conductivity or semi-insulating and a highly conductive n-type substrate will be obtained. Basic parameters of HVPE-GaN growth processes (reagent flows, growth temperature) as well as parameters of ion implantation will be determined. Post-implantation damage, which occurs in implanted layers, will be removed by high-temperature (1400-1480°C) annealing at high nitrogen pressure (1 GPa). Basic structural, optical, and electrical parameters of implanted and annealed GaN will be investigated. The samples will be characterized prior to and after ion implantation.