Abstract: The fabrication of diamond-based electronic devices requires that several active layers with different doping concentrations are grown in different reactors. In this paper, we have investigated the effect of interrupting and resuming the epitaxial growth of a homoepitaxial diamond film using high-power plasma CVD. It was found that long lifetime blue phosphorescence which is localized on regions with a high dislocation density is generated. Such phosphorescence is related to a higher uptake of impurities at the interface between two subsequent films, due to an increased surface roughness from etching at the epitaxial growth resumption. Etching was found to occur preferentially on threading dislocations leaving typical etch-pits. Cathodoluminescence helps identify boron as the main background impurity. Besides, the formation of new dislocations was observed on the facets of these etch-pits. The continuation of epitaxy on a roughened surface thus comes with a substantial decrease in crystal quality.
Abstract: The development of diamond based devices for high power electronic applications requires the growth of thick heavily boron doped diamond. During the growth of CVD single crystals, the final form of the film depends on the different crystalline faces growth rate with respect to each others. Three parameters (α, β and γ) which correspond to the displacement speeds of the {111}, {110} and {113} faces, normalized to the {100} displacement speed can be used into a 3D crystal growth model in order to predict the final crystal morphology. This model has been applied with success to intrinsic diamond, and is extended here to the growth of boron doped diamond. It is found that the addition of diborane gas promotes the appearance of large {110} and {113} faces limiting the usable top surface area and generally leading to stress and consequently to crystal breaking-up. By adding a small amount of oxygen (0.25%) to the feed gas, the {110} faces appearance can be inhibited and the crystal integrity preserved.
Abstract: Excitonic recombinations are investigated by cathodoluminescence in a series of homoepitaxial diamond layers doped with boron in the range (2 x 10(16))-(5 x 10(18)) at cm(-3). As opposed to earlier observations made on polycrystalline boron-doped diamond, we show that the ratio between the neutral-boron bound exciton and the free-exciton recombination intensities is proportional to the boron content up to 6 x 10(17) cm(-3) and starts to saturate above this value. The probability of an exciton in diamond being trapped by only one boron impurity is calculated and appears to be in good agreement with the observed saturation, suggesting the formation of excitons bound to near-neighbor boron pairs at high boron concentrations.
Abstract: We report a versatile method for engineering arrays of nitrogen-vacancy (NV) color centers in diamond at the nanoscale. The defects were produced in parallel by ion implantation through 80 nm diameter apertures patterned using electron beam lithography in a polymethyl methacrylate (PMMA) layer deposited on a diamond surface. The implantation was performed with CN − molecules that increased the NV defect-formation yield. This method could enable the realization of a solid-state coupled-spin array and could be used for positioning an optically active NV center on a photonic microstructure.
Abstract: The fabrication of diamond-based vertical power devices which are the most suited for high current applications requires the use of thick heavily boron-doped (B-doped) diamond single crystals. Although the growth of thin B-doped diamond films is well controlled over a large concentration range, little is known about the growth conditions leading to heavily doped thick single crystals. In this paper, it was found that the microwave power densities (MWPD) coupled to the plasma used to synthesize B-doped diamond by chemical vapor deposition is one of the key parameters allowing tuning doping efficiencies over two orders of magnitude. At high MWPD (above 100 W cm(-3)) the boron doping efficiency (DE) is extremely low while further increasing the boron concentration in the gas phase is no use as this leads to plasma instability. On the other hand, when low MWPD are used (<50 W cm(-3)), DE can be strongly increased but twinning and defects formation hampers the surface morphology. The use of intermediate MWPD densities has been demonstrated as the key in obtaining thick heavily B-doped diamond crystals (>10(20) cm(-3)) with good morphologies. (c) 2010 American Institute of Physics. [doi:10.1063/1.3511449]
Abstract: Even for samples exhibiting excellent electronic properties in terms of carrier mobility, sample-to-sample variability remains considerable and dislocation density is still very high, the latter characteristic being often related to damages induced either by the substrate polishing step or by substrate bulk dislocations. In order to limit the polishing effect, a pre-treatment based on H2/O2 plasma etching under relatively high pressure (a few 100 mbar) has been routinely used for several years. Nevertheless, those bulk dislocations present in the substrate that reach its surface lead to square etch-pit formation which depth can grow to several 100 nm, preventing the growth of smooth and flat thin films (<few µm). In order to overcome this limitation, we have focused our work on the identification of the crystallographic faces constitutive of the etch-pits. Starting from a geometrical model describing the diamond crystal morphology evolution, and by carefully choosing the initial growth conditions, we show that it is possible to fill the etch-pits rapidly and thus to recover the H2/O2 plasma pre-treatment advantages, even for thin film deposition with smooth surface.
Abstract: As quantum mechanics ventures into the world of applications and engineering, materials science faces the necessity to design matter to quantum grade purity. For such materials, quantum effects define their physical behaviour and open completely new (quantum) perspectives for applications. Carbon-based materials are particularly good examples, highlighted by the fascinating quantum properties of, for example, nanotubes(1) or graphene(2). Here, we demonstrate the synthesis and application of ultrapure isotopically controlled single-crystal chemical vapour deposition (CVD) diamond with a remarkably low concentration of paramagnetic impurities. The content of nuclear spins associated with the C-13 isotope was depleted to 0.3% and the concentration of other paramagnetic defects was measured to be <10(13) cm(-3). Being placed in such a spin-free lattice, single electron spins show the longest room-temperature spin dephasing times ever observed in solid-state systems (T-2 = 1.8 ms). This benchmark will potentially allow observation of coherent coupling between spins separated by a few tens of nanometres, making it a versatile material for room-temperature quantum information processing devices. We also show that single electron spins in the same isotopically engineered CVD diamond can be used to detect external magnetic fields with a sensitivity reaching 4 nT Hz(-1/2) and subnanometre spatial resolution.
Abstract: Several 65Â [mu]m thick epitaxial diamond films prepared on (100) Ib substrates by high power pulsed microwave plasma assisted chemical vapour deposition (HP-MPCVD) are studied as a function of surface treatments by cathodoluminescence (CL) and photoluminescence (PL) spectroscopies. They are either asgrown, or polished, or etched by a microwave oxygen plasma, or after applying subsequently the two last processes. In CL spectra, bands due to defects occur at 2.3Â eV, 3.07Â eV, 3.7Â eV and 4.7Â eV, the last one being specific of polished surfaces, with nearly no contrast in the luminescence image. A fundamental result consists in demonstrating that the defects induced by polishing can be removed by oxygen plasma etching. Additionally, in order to assess how luminescence spectra originate from a peculiar depth or not, a bevelled sample is studied. PL spectra are acquired on the sample side while CL spectra are measured at several points on the bevel top side till to the Ib substrate. Comparison of the two sets of result show that the H3 signal originates from the Ib substrate even if it is present in the CL spectra of the film. An analysis of the change in the intensity of the TO free exciton line, defect bands and H3 signal, along decreasing photon energies, as a function of the thickness of the remaining HP-PMPCVD film, is performed with the help of a model taking the diffusion of the unrecombined excitonic pairs and the re-excited photoluminescence into account. CL images recorded at specific wavelengths, which do not show inverted contrast, are also assessed. From these data, the exciton diffusion length is evaluated to 11Â [mu]m in the major part of the epitaxial layer except for the first 20Â [mu]m close to the Ib substrate where it decreases down to 2Â [mu]m. This study sheds light on the interpretation of luminescence spectra excited by an electron beam in undoped diamond layers. Defects bands due to damages induced by polishing and etching processes are also documented.
Abstract: The use of CVD diamond in electronics has very stringent requirements. For a CVD diamond industry to become viable it is mandatory to obtain very large growth rates (> 5 µm/h), all the while maintaining extremely high purity, a crystalline defect density as low as possible, and large usable surface areas. At the same time, one must keep the stress level within the growing crystal below acceptable limits to avoid crack formation and preserve the crystal structural integrity. These imperatives imply to work to improve both the plasma deposition process and the CVD diamond crystal growth. In this paper, we propose a three-pronged approach: (i) We use detailed plasma models to establish the influence of process parameters (in particular deposition pressure) on plasma chemistry in order to optimize film growth rate and diamond quality; (ii) We emphasize the need for careful substrate pre-treatment and selection (including choosing a single-sector face) to minimize defects in the growing films; (iii) We employ a 3D geometrical model to predict the crystal shape under given growth conditions, and exploit this knowledge to devise a growth strategy maximizing the usable film surface area while minimizing stresses inside the films.
Abstract: Highly Charged Ions (HCI) approaching surfaces at nm distances are known to extract a very large number of electrons from the target. Over dielectric surfaces, the positive holes left following the removal of the electrons cannot be immediately neutralized, thereby locally inducing a huge stress and creating permanent surface modifications on very small dots. We present in this paper experiments on the structural transformations induced by irradiation with HCI of graphite and diamond surfaces characterized using the Atomic Clock Property of the Hollow Atoms (ACPHA) technique. (C) 2008 Elsevier B.V. All rights reserved.
Notes: Times Cited: 0 xD;17th International Workshop on Inelastic Ion-Surface Collisions xD;SEP 21-26, 2008 xD;Porquerolles, FRANCE
Abstract: Plasma-assisted CVD homoepitaxial diamond growth is a process that must satisfy many stringent requirements to meet industrial applications, particularly in high-power electronics. Purity control and crystalline quality of the obtained samples are of paramount importance and their optimization is a subject of active research. In the process of such studies, we have obtained high purity CVD diamond monocrystals with unusual morphologies, namely with apparent {1 1 3} stable faces. This phenomenon has led us to examine the process of CVD diamond growth and build up a 3D geometrical model, presented here, describing the film growth as a function of time. The model has been able to successfully describe the morphology of our obtained crystals and can be used as a predictive tool to predetermine the shape and size of a diamond crystal grown in a given process configuration. This renders accessible control of desirable properties such as largest usable diamond surface area and/or film thickness, before the cutting and polishing manufacture steps take place. The two latter steps are more sensitive to the geometry of the growth sectors, which will be addressed in a companion paper. Our model, applicable to the growth of any cubic lattice material, establishes a complete mapping of the final morphology state of growing diamond, as a function of the growth rates of the crystalline planes considered, namely {1 0 0}, {1 1 1}, {1 1 0}, and {1 1 3} planes, all of which have been observed experimentally in diamond films. The model makes no claim as to the stability of the obtained faces, such as the occurrence of non-epitaxial crystallites or twinning. It is also possible to deduce transient behavior of the crystal morphology as growth time is increased. The model conclusions are presented in the form of a series of diagrams, which trace the existence (and dominance) boundaries of each face type, in presence of the others, and where each boundary crossing represent a topology change in terms of number of faces, edges and vertices. We validate the model by matching it against crystals published in the literature and illustrate its predictive value by suggesting ways to increase usable surface area of the diamond film.
Abstract: The growth of monocrystalline diamond films of electronic quality and large thickness (>few hundreds of microns) is an important issue in particular for high-power electronics. In this paper, we will describe the different key parameters necessary to reach this objective. First, we will examine the deposition process and establish that only microwave assisted diamond deposition plasma reactors can achieve the optimal growth conditions for the efficient generation of the precursor species to diamond growth. Next, we will consider the influence of the monocrystalline diamond substrate orientation and quality on the growth of the epitaxial layer, especially when the deposited material thickness exceeds 100 µm. The need to use a specific pre-treatment procedure of the substrate before the growth and its impact will also be discussed. Finally we will look at the growth conditions themselves and assess the influence of the process parameters, such as the substrate temperature, the methane concentration, the microwave power density and the eventual presence of nitrogen in the gas phase, on both the morphology and quality of the films on the one hand and the growth rate on the other hand. For this, we will introduce the concept of supersaturation and comment on its evolution as a function of the process parameters.
Abstract: Due to its unique physical properties, diamond is a very appealing material for the development of electronic devices and sensors. Its wide band gap (5.5 eV) endows diamond based devices with low thermal noise, low dark current levels and, in the case of radiation detectors, high visible-to-X-ray signal discrimination (visible blindness) as well as high sensitivity to energies greater than the band gap. Furthermore, due to its radiation hardness diamond is very interesting for applications in extreme environments, or as monitor of high fluency radiation beams. In this work the use of diamond based detectors for X-ray sensing is discussed. On purpose, some photo-conductors based on different diamond types have been tested at the DAFNE-L synchrotron radiation laboratory at Frascati. X-ray sensitivity spectra, linearity and stability of the response of these diamond devices have been measured in order to evidence the promising performance of such devices.
Abstract: In this study, homoepitaxial thick diamond films were grown by CVD at high microwave power densities for temperatures ranging from 800[no-break space][deg]C to 950[no-break space][deg]C and with nitrogen additions from 75 to 200[no-break space]ppm relative to the total gas flow. It was observed that there is a coupled effect of these two parameters on the growth mechanisms of the CVD diamond film. For a deposition temperature close to 875[no-break space][deg]C and for the lowest nitrogen concentration, the growth proceeded via a step flow mode identified by classical step bunching phenomena due to the presence of nitrogen and leading to the appearance of macro-steps. When nitrogen concentration was increased keeping the same temperature, the growth mode evolved from a step flow mode to a bidimensional nucleation mode, for which macro-steps are no longer observed. For higher growth temperatures (950[no-break space][deg]C), it was found that this growth mode transition still exists but appears for much higher nitrogen concentration. These different observations, associated with the resulting growth rates, are discussed in terms of surface modification induced by the presence of nitrogen impurity. It is shown in particular that an increase of nitrogen concentration is equivalent to an increase of the surface supersaturation, this effect being compensated by an increase of the deposition temperature.
Abstract: Brillouin light scattering has been used to investigate the elastic properties of high quality homoepitaxial diamond layers about 1[no-break space]mm thick that have been elaborated by microwave plasma assisted chemical vapour deposition. Taking advantage of the detection of different acoustic modes, a complete elastic characterization of the crystal has been achieved. Three single crystal elastic constants, namely, c11, (c11 - c12) / 2 and c44 have been selectively determined, respectively, from the frequency of the longitudinal and of the shear horizontal bulk modes travelling parallel to the film surface. These determinations are in agreement with the frequency of the observed surface modes and of the bulk waves propagating at different angles from a normal single crystal film plane and consistent with the properties of natural diamond. By adding a low amount of nitrogen ranging from 2 to 50[no-break space]ppm in the gas phase, the growth rates were increased from 6 to 33[no-break space][mu]m/h whereas the mechanical properties of the resulting layers remained close to those of natural diamond.
Abstract: In the preparation of high power diamond photoswitches, thick (more than 100 [mu]m) lightly nitrogen-doped single crystals were grown at LIMHP, for which Differential Interference Contrast Microscopy, Raman spectroscopy, photoluminescence, and cathodoluminescence have confirmed good morphology and very low but well-controlled impurity doping level. In order to evaluate the effect of nitrogen incorporation on the electronic properties of these films, photoconductivity measurements have been carried out. In an initial study, I-V and transient photocurrent measurements were conducted on several films with N-doping from 0 to 20 ppm intentionally added to the gas phase during growth, resulting into nitrogen concentrations lower than 100 ppb in the film. The results of these measurements are presented showing typical semiconductor behavior in terms of gain versus settling time, relatively high external quantum efficiency (EQE) and corresponding derived [mu][tau] (mobility x lifetime) product. In particular, samples with no nitrogen showed EQEs of several hundreds while their settling time was quite long (tens of seconds). However, samples with small nitrogen addition were observed to have settling times decreasing below a few seconds while EQEs close to 10 showed that a compromise could be found between efficiency and response time.
Abstract: Because of its high thermal conductivity and dielectric strength, diamond is a promising material for thermal management in high voltage, high power electronics. In this paper we present our investigation of CVD polycrystalline diamond films for heat sink applications. Dielectric strength and thermal conductivity have been measured at room temperature, for either home made or commercial samples. Though the measured dielectric strength remains lower than the 10 MV/cm expected value (greatly impacted by the surface polishing), the interest of diamond is confirmed.
Notes: Times Cited: 0 xD;2007 European Conference on Power Electronics and Applications xD;SEP 02-05, 2007 xD;Aalborg, DENMARK
Abstract: In this paper, the fast growth of three thick diamond single crystals using the chemical vapour deposition (CVD) method working in a pulsed mode is reported. After 48 h, a total of half a carat of uncoloured synthetic diamond was obtained. These crystals, exhibiting thicknesses of 430, 570 and 900 [mu]m, were then thoroughly analysed by a wide range of characterization techniques, such as Raman spectroscopy, UV and IR absorption, photoluminescence (PL) and cathodoluminescence (CL). All three samples turned out to be of relatively high quality but small differences in purity and quality could be detected. These appeared to be directly related to the slight inconsistence of the substrate temperature during growth that ranged from 800 to 900 [deg]C due to non-uniformity in the radial distribution of gas temperature. A higher contamination by residual nitrogen impurities has been evidenced for the two samples that were grown with the lowest temperature as confirmed by the PL and UV absorption spectra, as well as a lower free excitonic emission in CL. Finally a 900 [deg]C growth temperature was shown to be more favourable to good quality and fast growth rate.
Abstract: Single-crystal homoepitaxial diamond has been grown by chemical vapour deposition using a high-density microwave plasma. It has been shown that the growth rate can be increased by factors of up to 2.5 by adding small concentrations (2 to 10[no-break space]ppm) of nitrogen to the gas phase. Free-standing specimens up to 1.7[no-break space]mm thick have been characterised using optical absorption, cathodoluminescence, photoluminescence and Raman spectroscopies, and by electron paramagnetic resonance. These techniques all demonstrate that the colourless type IIa material is of excellent quality with total defect concentrations not exceeding 200[no-break space]ppb, and is ideally suited for optical and electronic applications.
Abstract: This is a detailed study of the process parameters that control the synthesis of homoepitaxial single-crystal diamond by chemical vapour deposition (CVD) using a microwave plasma-assisted reactor. The effects of substrate temperature, methane concentration and microwave power density on the surface morphology and purity of the synthesized diamond has been studied using diffraction enhanced and atomic force microscopy, Raman and photoluminescence (PL) spectroscopy. The effects of pulsing the input microwave is reported as well as the influence of adding small concentrations of nitrogen in the gas phase during growth. With no intentional nitrogen addition growth rates up to 16 [mu]m/h have been obtained in samples exhibiting relatively smooth surface morphologies and no indication of nitrogen contamination as measured by PL spectroscopy. Pulsing the microwave power allows an increase of near 40% in growth rate for the same average input power with no apparent degradation in purity. The addition of nitrogen up to 10 ppm results in an increase in growth rate of 150%. These samples remain of good colour (water clear) but exhibit distinct PL emission bands corresponding to the nitrogen-vacancy impurity centres. Single-crystal diamond samples of good colour up to 1.7 mm thick have been produced.
Abstract: In the last decade, progress in diamond growth by chemical vapor deposition (CVD) has resulted in significant improvement in the quality of synthetic single crystals. This article reports on the gemological and spectroscopic features of six synthetic type IIa diamonds grown for research purposes at the French Laboratoire d'Ingenierie des Materiaux et des Hautes Pressions (LIMHP-CNRS), and compares their diagnostic features to CVD-grown diamonds from other producers. Three of the six samples were nitrogen doped, whereas the other three were classified as high purity. A number of characteristics that are diagnostic of CVD synthetic diamond were present in the nitrogen-doped crystals, despite an absence of defect-related absorption features in the infrared region. Identification of the high-purity samples was more complicated, but it was still possible based on features in their photoluminescence spectra, their distinctive birefringence, and characteristic luminescence images.
Abstract: Owing to its exceptional properties, monocrystalline diamond is one possible interesting candidate for high-power electronic applications if a suitable and reproducible process allowing the deposition of high-quality thick films within a reasonable time is developed. In this paper, a Microwave Plasma-Assisted Chemical Vapour Deposition (MWPACVD) two-step process at high plasma density (microwave power 3200 W, pressure 220 mbar) has been successfully used on high-pressure high-temperature (HPHT) (100) substrates. It consisted in the etching of the diamond substrates with an O2/H2 plasma immediately followed by CVD diamond growth. Optimal growth conditions were determined leading to the synthesis of a 520-[mu]m-thick high-quality single-crystal homoepitaxial layer at growth rate of 6 [mu]m/h. This film exhibited a smooth surface with high optical clarity, and the photoluminescence (PL) spectrum was free from nitrogen- or silicon-related emission bands. Moreover, free exciton emission was clearly observed by cathodoluminescence (CL). Finally, the influence of small amounts of nitrogen was also investigated, which resulted in higher growth rate up to 33 [mu]m/h and films as thick as 1.7 mm. The relatively good quality of these films was confirmed by several appropriate characterizations, including Raman, photoluminescence and cathodoluminesence. The use of this process opens the way to the synthesis of thick high-quality single-crystal specimens for high-power electronic applications.
Notes: Proceedings of Diamond 2004, the 15th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes, Nitrides and Silicon Carbide
Abstract: Diamond has been identified as a very promising material for X and ultraviolet sensing. In this Letter, a photoconductive device based on a freestanding homoepitaxial chemically vapor deposition (CVD) single-crystal diamond 500 mu m thick has been tested. Photoconductive measurements in coplanar and transverse configurations have been performed to characterize the device sensitivity in the 140-250 nm spectral range. Very high sensitivity values were achieved in both configurations. The sensitivity in the transverse configuration is at least 300 times higher than in the coplanar configuration.
Notes: USA xD;Journal-Paper xD;English xD;P (Practical); X (Experimental) xD;0003-6951
Abstract: Depending on purity, diamond could exhibit very high breakdown threshold voltages, high free carrier mobilities and relatively high free carrier lifetimes. For these reasons, diamond has been considered to be well suited for radiation induced high power switching applications in continuous operation mode. Excitation using deep UV sources has been studied but it suffers from their intrinsic low conversion efficiency (below 0.1%). The other problem encountered with deep UV excitation, especially in a bulk configuration, is the short penetration length leading to poor collection efficiencies, polarization and space charge effects. Depending on energy, electron beam excitation should be more adapted for this kind of application. In the present study we report on the conductivity modulation induced by continuous electron beam excitation in CVD diamond samples as a function of electron beam energy and current. The current gain is found to depend strongly on the energy and current of the electron beam. At low electron beam currents continuous gains up to 180 have been measured for 30 keV electrons, believed to be the highest continuous gain ever reported.
Abstract: Owing to its semiconducting properties (wide band gap, high electron and hole mobility), diamond is an interesting material for UV and XUV photodetection. In the present study, we have characterized UV and evaluated XUV diamond photodetector efficiency using volume photoconductivity instead of usual surface interdigited devices. The detectors have been tested under over-gap (13 and 193 nm) as well as sub-gap nanosecond laser irradiation (266 nm). For each wavelength, electrical characteristics of the devices have been measured as a function of bias voltage and laser fluences. The particular sandwich configuration of the detectors has shown a charge effect under over-gap irradiation. This appears by the amplitude reduction of successive pulses, and also from the different response for AC and DC bias. The suitability of these devices is discussed, the final aim being to validate bulk structures for wide band imaging devices.
Abstract: Owing to its semiconducting properties (wide band gap, high electron and hole mobility), diamond is an interesting material for UV and XUV photodetection. In the present study, we have characterized UV and XUV diamond photodetector efficiency using bulk photoconductivity instead of usual coplanar devices. For comparisons, chemical vapor deposition diamond films of 200- mu m thickness have been fabricated for working either in bulk configuration (BC) or surface configuration. They have been tested under nanosecond laser irradiation in the gap region (over-gap 193 and 213 nm; sub-gap 266 nm). For each wavelength, photoconductive responses of devices have been measured as a function of bias voltage (AC and DC) and laser fluences. With BC linear responses are obtained up to 0.5 mJ/cm/sup 2/ at 193 nm and 40 mJ/cm/sup 2/ at 266 nm. However, with BC a space charge effect appears under 193- and 213-nm irradiation, reducing the sensitivity of the detector. Such drawback is overcome by using AC bias. The suitability of the devices for detecting UV laser pulses or intense laser pulses or intense XUV fast discharge lamp is discussed.
Notes: Netherlands xD;Conference-Paper; Journal-Paper xD;English xD;P (Practical); X (Experimental) xD;0925-9635
Abstract: Diamond is a wide band-gap material that, depending on purity may exhibit a short carrier lifetime and because of its strong lattice bonding it generally exhibits a high damage threshold. For these reasons it is considered to be suitable for fast and solar blind UV detectors. The use of highly oriented diamond (HOD) films should be advantageous over randomly oriented diamond (ROD) films because of the lower grain boundary density that should lead to an increase in the carrier mobility. In the present study, we compare the photoresponse of UV detectors made of HOD and ROD films using an ArF excimer pulsed laser and we measure the UV-visible discrimination factor of both types of diamond films using a tunable laser. Because the ROD film available for this study was considerably thinner than the respective HOD film, some of the conclusions of this paper are specific to this particular thickness ratio.
Abstract: Ultraviolet sensors were fabricated on a Si substrate using an undoped, highly oriented diamond film with Pt and Al interdigited electrodes with a gap length of 5, 10 and 15 mu m. Transient voltage outputs due to photocurrent of the sensors under a bias voltage of 20, 40 and 80 V were measured by the pulsed irradiation of an ArF excimer laser ( lambda =193 nm, pulse width=5 ns) or a dye laser ( lambda =313 nm, pulse width=7 ns). It was found that the transient voltage output by the ArF laser irradiation on a sensor (Pt electrodes with a 15- mu m gap) consisted of main and second peaks at 1.1 and 3.8 ns, respectively, when the bias voltage was 20 V. The FWHM was approximately 4 ns. The second peak was observed in the output signals of most sensors. On the other hand, the voltage output was two orders of magnitude weaker when the sensors were irradiated by the dye laser.
Notes: Netherlands xD;Conference-Paper; Journal-Paper xD;English xD;A (Application); X (Experimental) xD;0925-9635
Abstract: The characterization of semiconductor heterostructures from their mobility spectra has originally been proposed, some 12 years ago, as an improvement of Hall effect measurements. However, the application is far from being trivial and often leads to the occurrence of extra peaks without any physical interpretation. They are generally referred to as “mirror peaks” and are interpreted in terms of computational artifacts.The present paper comments upon such peaks from a set of data concerning van der Pauw test structures. Our main conclusion is that from an experimental point of view, the transverse component ([rho]xy) of the resistivity tensor is more precisely determined than the longitudinal one ([rho]xx). Thus, we are left with the possibility of artifacts within the experimental procedure.Starting from an adjustment of all available information ([rho]xx and [rho]xy), a preferential adjustment of [rho]xy leads to the disappearance of “mirror peaks”. As a matter of example, we report the study of an InP-based bilayered structure and show how the mobility spectrum evidences the highly conducting channel of a HEMT device.
Abstract: Recent progress has been made in the production of low-roughness Chemical Vapor Deposition (CVD) diamond films at temperatures less than 600[deg]C. These films are particularly suitable for cutting tool applications. Such progress was achieved by simultaneously promoting the renucleation process and controlling the growth process at low temperatures. In this paper, we show that below 700[deg]C (unlike what is usually observed at temperatures in the range of 750-900[deg]C), secondary nucleation does not occur easily even on (111) faces. This makes the growth of low roughness films difficult. We also report on the role of a thin gold layer deposited on top of a diamond film in favoring smoother film formation. This observation was seen to be due to the ability of the thin gold layer in promoting renucleation. Furthermore, the effect of the percentage of methane introduced in the feed gas was studied.
Abstract: We report the results of capacitance-voltage (C-V) and Deep Level Transient Spectroscopy (DLTS) measurements performed upon a Ga0.47In0.53As/InP quantum well structure. At room temperature, a conduction-band offset Delta E-c = (200+/-10)meV and charge densities sigma(1) = +/-(3+/-1)*10(11) times the electronic charge per cm(2) have been measured from C-V experiments. At lower temperature (T less than or equal to 150K) we have observed an important decrease of the band-offset, considerably larger than a pure thermal effect. We have shown that the explanation lies in the presence of a high concentration of deep traps located at the well-barrier interfaces. Two species A and B have been detected through DLTS experiments with activation energies E-tA = 90 meV and E-tB = 195 meV, respectively. The filling of these trap levels at low temperature lowers the band offset from 200 to 120 meV, owing to band repulsion effects.
Abstract: The paper reports a study of electrical properties of InP layers (<3 [mu]m thick) epitaxied by MOVPE and HVPE. The technique used is the so-called mobility spectrum method in which the maxima of carrier density are determined as a continuous function of mobility. A reduced conductivity tensor (RCT) adjustment allows to improve the accuracy in the determination of density and mobility values. In such layers, a high mobility channel, corresponding to the bulk material, is evidenced. However, low mobility channels are also detected and are interpreted in terms of the presence of defects (n-type for MOVPE and p-type for HVPE) at the substrate-layer interface. In the case of thin epitaxied layers on insulating substrate, the classical Hall data leads to a nonsignificant mean value of mobility while mobility spectrum technique improves the understanding of electrical properties at the layer-substrate interface.
Abstract: Rectifying contacts on n-InP using Zn based metallizations followed by moderate annealing temperature and time were studied. Diffusion of Zn atoms at the metal-semiconductor interface creates a thin p-InP layer. Pseudo-Schottky junctions were obtained with a significant barrier height enhancement, typically 0.2-0.25 eV. The metallization process involved throughout the present work leads to high quality Schottky diodes within a rather simple procedure similar to this generally used to obtain good ohmic contacts. It is shown in particular that the special requirements needed for a lot of electrical measurements (e.g. C-V characteristics or D.L.T.S.) can be matched without any extra complication. The behaviour of Schottky devices was thoroughly analysed as a function of the annealing procedure. Best performances were obtained by applying cumulative annealing sequences, increasing the temperature while decreasing the time of exposure. The homogeneity of the structures was attested from a satisfactory agreement between barrier heights deduced either from current or from capacitance measurements. A good linearity of C-2-V-T curves and low values of the series resistances were also obtained.
Abstract: Wide band gap semiconductors are discussed as materials for photonic or electron-beam controlled switches. Chemical vapour deposited (CVD) diamond has recently become the subject of intense research activity mainly due to its unique combination of thermal, mechanical and optoelectronical properties. The very high thermal conductivity, added to a high working temperature and a high dielectric strength, make CVD diamond as a promising candidate material, for high voltage electronics applications. Its semi conducting properties, such as wide band gap and high electron and hole mobilities are also noteworthy. The nature of CVD diamond is the most prominent obstacle against fabrication of any kind of electronic devices. This paper presents different grades of CVD diamond substrates and the comparison between them, especially between the natural Ha and other kind of CVD diamond. Dielectric strength investigation and surface conductivity with or without chemical treatment are presented, then the influence of the metal to diamond interface on the electronic properties have been investigated. Interdigitated planar contacts and plane back contacts have been photolithographically deposited on each sample, using different layered metals. The I(V) measurement allows to determine the optimal metallization for electronic applications. Finally, the authors investigate the response of metal-diamond-silicon components under UV illumination.
Notes: USA xD;Conference-Paper xD;English xD;P (Practical); X (Experimental)
