Nitrogen-doped Layer Research Articles

Degenerate layers in epitaxial ZnO films grown on sapphire substrates

ZnO films were grown on low-temperature (LT) buffer layers on sapphire a-plane (11–20) substrates by radical source molecular-beam epitaxy. The LT buffer layers were found to effect the electrical properties of subsequently grown undoped ZnO films, and their presence was found to be indispensable for the growth of films with low carrier concentrations and high mobilities. Temperature-dependent Hall measurements showed the existence of a degenerate region related to the LT buffer layers. It was found that the effects of degenerate layers could be reduced by using annealing treatments and nitrogen doping of the LT buffer layers. The dominant residual donor energy of 110 meV was found to be different than previously reported. The carrier concentration of a ZnO film fabricated using a nitrogen-doped buffer layer was 7.5×1016 cm−3 with a mobility of 132 cm2/V s at room temperature.

Effects of low temperature buffer layer treatments on the growth of high quality ZnO films

ZnO films were grown on sapphire substrates by radical source molecular beam epitaxy (RS-MBE). ZnO low temperature buffer layers were subjected to various treatments. High quality ZnO films were obtained by vacuum annealing plus nitrogen doping of the buffer layer. The carrier concentration of the ZnO film fabricated using this buffer layer was 7.5 × 1016 cm−3 with a mobility of 132 cm2/V sec at RT. Temperature dependent Hall measurements showed implied the existence of degenerate (untreated) buffer layers. Using a nitrogen-doped buffer layer to reduce the influence of the degenerate layer, a donor energy of 110 meV was estimated from temperature dependent Hall measurements. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoluminescence studies of undoped and nitrogen-doped ZnO layers grown by plasma-assisted epitaxy

Nitrogen-doped ZnO layers grown on C-sapphire at 400°C by plasma-assisted epitaxy in oxygen and nitrogen mixed gas plasma were studied by photoluminescence measurements comparing to undoped ZnO layers grown in pure oxygen plasma. A new luminescence was observed around 3.27 eV with phonon-replicas at 20 K and we concluded that they are due to shallow donor–acceptor pair emission by excitation power dependence of the peak energy. The donor and acceptor levels were assigned as shallow levels located at 40 meV below conduction bandedge and 135 meV above valence bandedge, respectively. It was also indicated that Zn-rich condition should be given for efficient nitrogen-acceptor doping.

The Study of Modified Layers in SiCOH Dielectrics using Spectroscopic Ellipsometry

AbstractThe current challenge in designing new low-k dielectrics is realizing sufficient mechanical and chemical stability such that the material can be integrated into current damascene schemes. The material of interest in this study is a nonporous SiCOH composite (carbon-doped silicon oxide, also known as organosilicate glass “OSG”) for use as an intermetal dielectric (IMD). During integration of this IMD, processing steps such as etch, resist strip and chemicalmechanical polishing for planarization may chemically alter the outer layer of the dielectric. Here, spectroscopic ellipsometry is used to characterize the modified layer of SiCOH films after exposure to different resist strip plasmas. The data are analyzed based on a 2-layer model, consisting of a carbon-deficient layer on the surface of the low-k SiCOH dielectric. This model is supported by XPS and FTIR data. The effects of two types of plasma etch chemistry on the formation of this modified layer were studied, and differences between the two chemistries were found. The 2-layer model accurately describes the modifications produced by the oxidizing plasma, but its description of the modified layer formed by the plasma involving nitrogen is not complete. A 3-layer model with an additional nitrogen-doped layer is suggested.

Characteristics of Nitrogen-Doped GaAsP Light-Emitting Diodes

The characteristics of nitrogen-doped GaAsP light-emitting diodes grown by hydride vapor-phase epitaxy are described. The light output, forward voltage and degradation to provide the performance required, are investigated as functions of the structural parameters of the GaAsP layers. The parameters studied are the carrier concentrations in the nitrogen-doped and middle GaAsP layers, and the total thickness of the GaAsP layer. The GaAsP layer consists of nitrogen-doped and middle layers. The characteristics are discussed using the electroluminescence emission decay time, electroluminescent spectrum and aging test result. The effects of total thickness on the characteristics are discussed with the aid of calculations of stress. The study confirms that the characteristics depend systematically on the parameters and that nitrogen-doped and middle layers play important roles in the diode performance.

Raman study of Zn1−xBexSe/GaAs systems with low Be content (x⩽0.20)

We present an experimental and theoretical investigation of the Raman line shape of long-wavelength phonons with longitudinal optical (LO) symmetry from both sides of Zn1−xBexSe/GaAs (001) heterojunctions with special emphasis on samples with low Be content (x⩽0.20). First the built-in p-type LO phonon–plasmon (LO–P) coupled mode at the near-interfacial substrate is used as a sensitive probe to investigate the interfacial quality. The corresponding hole gas is reinforced when the ZnBeSe layers are nominally p doped by nitrogen. This provides clear evidence for effective hole transfer across the junction, and thereby indicates a minimized density of interfacial defects. In the nitrogen-doped layers hole densities as high as 1017 cm−3, in accordance with capacitance–voltage measurements, are directly inferred from clear weakening of the ZnSe-like LO mode due to LO–P coupling. Concerning the intrinsic properties of the alloys, we demonstrate that the asymmetric broadening of the ZnSe-like LO mode is determined by topological disorder only, and not by other possible mechanisms such as structural disorder, nonhomogeneity in the alloy composition, a distribution of tensile strain, or a Fano-type interference. This reveals a high structural quality that parallels the high interfacial quality. We also show that a spatial correlation model with Gaussian distribution applies to Zn1−xBexSe. Most of this study is supported by a quantitative treatment. We extend the phenomenological approach of Hon and Faust to equations of motion and polarization derived from the modified-random-element-isodisplacement model in order to achieve line shape analysis of the alloy-related LO and LO–P modes.

Nitrogen passivation by implantation-induced point defects in 4H–SiC epitaxial layers

Ion implantation causes damage to the crystal lattice resulting in the loss of free charge carriers. In this study, low dose implantations using different ions and implantation doses are made to resolve the initial carrier loss in nitrogen-doped epitaxial layers. A strong dependence of compensation on nitrogen concentration is seen, showing that nitrogen is passivated by implantation-induced point defects. An activation energy of 3.2 eV for the dissociation of the passivated nitrogen center is obtained.

Improved degradation stability of blue-green II-VI light-emitting diodes with excluded nitrogen-doped ZnSe-based layers

Degradation characteristics of p-i-n BeZnSe/Zn(Be)CdSe light-emitting diodes were investigated. Undoped short-period superlattices, which provide efficient hole transport from the p+-BeTe:N near-contact region (hole injector) into the active region, were used instead of the p-doped BeZnSe:N emitter. It is demonstrated that this makes it possible to considerably lengthen the operating life of the light-emitting diodes at highest direct current densities (∼4.5 kA/cm2) at room temperature.

Cadmium Telluride Solar Cells on Molybdenum Substrates

ABSTRACTWe report on the development of Mo/CdTe/CdS/indium-tin-oxide, thin-film solar cells grown by radio-frequency magnetron sputtering. This is an inverted configuration compared to the conventional glass/tin-oxide/CdS/CdTe/metal cells. Molybdenum was chosen as a substrate because its thermal expansion coefficient and the work function are close to those of CdTe. We have achieved AM1.5 conversion efficiencies of 7.8 percent on 0.05 cm2 area devices. Our best cells had a nitrogen-doped ZnTe layer between the molybdenum and the CdTe for a somewhat improved back contact. However, we observe a significant rollover in the IV curve in forward current that indicates a back-diode effect. This implies the need for improvement of the electronic properties of the molybdenum - CdTe and possibly CdS - ITO interfaces.

Nitrogen-induced defects in ZnO : N grown on sapphire substrate by gas source MBE

Nitrogen-doped ZnO layers were grown on sapphire substrates by radical source molecular beam epitaxy by simultaneously introducing O 2 and N 2 via a RF radical source. Reflection high-energy electron diffraction and X-ray diffraction measurements revealed that high N 2/O 2 flow ratios induced growth twins into the ZnO layer. A nitrogen-doped ZnO fabricated using a N 2/O 2 flow ratio of 10% was found to have a chemical nitrogen concentration of 1×10 19 cm −3. However, type conversion from n-type to p-type did not occur while large nitrogen incorporation was observed to induce extended defects.

Diamond junction FETs based on δ-doped channels

Abstract Diamond junction field effect transistors (FETs) utilizing δ-boron-doped diamond films were fabricated and analyzed. In order to allow full charge modulation by the gate, the total channel sheet charge must not exceed the order of 1013 cm−2. However, boron doping shows full activation only for concentrations above ca 1020 cm−3 [1] . This yields a thickness for a fully activated channel in the range of ca 1 nm. To approach such narrow doping spikes any parasitic boron doping tails need to be eliminated. One possible way of achieving this is to compensate boron doping with nitrogen doping, an extremely deep donor. This results in the formation of a pn-junction, where the nitrogen doped part is not activated at room temperature and which therefore represents a semi-insulating (lossy) dielectric at low temperature and high frequency. At elevated temperature and low frequency the nitrogen doped layer becomes conducting acting as a series resistor to the interfacial pn-junction. Using this concept of a lossy dielectric pn-junction in the δ-doped channel FET, two gate diode configurations were investigated. In the first the nitrogen doped (Ib) synthetic diamond substrate served as a large area back gate, while in the second the nitrogen doped gate layer was grown on top of the δ-channel. The devices show high drain currents of up to 100 mA mm−1 and full channel modulation even at moderate operation temperatures of 200–250 °C. By extrapolation a current density of 1 A mm−1 is expected for a 0.25 μm gate length device.

Spectroscopic evidence of the formation of N–H and N–D complexes in plasma hydrogenated and deuterated ZnTe:N layers

Homoepitaxially grown nitrogen-doped ZnTe layers have been exposed to a hydrogen (deuterium) plasma. After hydrogen (deuterium) diffusion, an infrared absorption band appears at 3346 cm−1 (2489 cm−1). It is assigned to the vibrational stretching mode of the N–H (N–D) bond. It is also shown that the absence of such detectable bands in heteroepitaxially grown ZnTe/CdZnTe layers can be explained by thermal strains originating from the difference between the ZnTe and the CdZnTe thermal expansion coefficients.

Nitrogen in germanium

The known properties of nitrogen as an impurity in, and as an alloy element of, the germanium network are reviewed in this article. Amorphous and crystalline germanium–nitrogen alloys are interesting materials with potential applications for protective coatings and window layers for solar conversion devices. They may also act as effective diffusion masks for III-V electronic devices. The existing data are compared with similar properties of other group IV nitrides, in particular with silicon nitride. To a certain extent, the general picture mirrors the one found in Si–N systems, as expected from the similar valence structure of both elemental semiconductors. However, important differences appear in the deposition methods and alloy composition, the optical properties of as grown films, and the electrical behavior of nitrogen-doped amorphous layers. Structural studies are reviewed, including band structure calculations and the energies of nitrogen-related defects, which are compared with experimental data. Many important aspects of the electronic structure of Ge–N alloys are not yet completely understood and deserve a more careful investigation, in particular the structure of defects associated with N inclusion. The N doping of the a-Ge:H network appears to be very effective, the activation energy of the most effectively doped samples becoming around 120 meV. This is not the case with N-doped a-Si:H, the reasons for the difference remaining an open question. The lack of data on stoichiometric β-Ge3N4 prevents any reasonable assessment on the possible uses of the alloy in electronic and ceramic applications.

Enhancement of magnesium incorporation in nitrogen doped ZnMgSSe grown by molecular beam epitaxy

Effect of nitrogen plasma on magnesium incorporation has been investigated for ZnMgSSe based p- n junction device grown on (0 0 1) GaAs substrates by molecular beam epitaxy. It was found that magnesium composition in a nitrogen-doped p-type ZnMgSSe layer was larger than that in an n-type ZnMgSSe layer. The magnesium composition increased with increasing nitrogen content in p-type ZnMgSSe. To obtain p- and n-type ZnMgSSe layers of symmetric composition, magnesium beam flux should be reduced during growth of nitrogen-doped p-type ZnMgSSe layer to compensate this enhanced incorporation of magnesium in the nitrogen-doped ZnMgSSe layer.

Photon assisted growth of nitrogen-doped CdTe and the effects of hydrogen incorporation during growth

Nitrogen doping in CdTe epilayers grown by photo-assisted molecular beam epitaxy was demonstrated using an rf plasma source. The effect of the presence of atomic hydrogen during growth of undoped and nitrogen-doped CdTe was investigated. The layers were characterized using photoluminescence spectros-copy (PL), Hall effect, secondary ion mass spectroscopy (SIMS), Fourier transform infrared spectroscopy, and atomic force microscopy. PL confirmed the incorporation of nitrogen as acceptors. While p-type carrier concentrations greater than 1018 cm−3 were easily obtained, SIMS measurements indicated that nitrogen was concentrated near the undoped-doped and epilayer-substrate interfaces which complicates interpretation of activation efficiency. Hydrogen incorporation was found to be enhanced by the presence of nitrogen. Infrared absorption measurements strongly suggested the formation of N-H complexes. Hall measurements indicated that complexes are formed which are donor-like in nature. The presence of atomic hydrogen during growth radically changed the low temperature photoluminescence in both undoped and nitrogen-doped layers. Exciton-related luminescence was quenched at low temperature. Nitrogenrelated donor-acceptor pair luminescence was also absent from the N-doped hydrogenated layers, consistent with complex formation. Copper (a cation-site acceptor) donor-acceptor pair luminescence appeared to be enhanced by hydrogenation.

P-type doping of CdTe with a nitrogen plasma source

We report here on the growth and the characterization of p-type CdTe grown by molecular beam epitaxy on (001) Cd0.96Zn0.04Te substrates. Nitrogen has been used as a dopant, which is activated in an electron cyclotron resonance plasma source. The carrier concentration was determined using a C/V profiler. Nitrogen has been successfully incorporated substitutionally and hole densities up to 2.6×1017 cm−3 have been achieved. In addition we present data from x-ray diffraction and photoluminescence, which demonstrate the effect of self-compensation on the nitrogen-doped CdTe layers.

Hydrogenation of undoped and nitrogen-doped CdTe grown by molecular beam epitaxy

The effect of atomic hydrogen during the growth of undoped and nitrogen-doped CdTe by photon-assisted molecular beam epitaxy was investigated. Hydrogen incorporation is enhanced by the presence of nitrogen. Infrared absorption measurements strongly suggest the formation of N–H complexes. Hall measurements indicate that the complexes are donorlike in nature. Hydrogenation radically changes the low temperature photoluminescence in both undoped and nitrogen-doped layers. Exciton-related luminescence is quenched at low temperature. Nitrogen-related donor-acceptor pair luminescence is also absent from N-doped hydrogenated layers, consistent with complex formation. Copper donor–acceptor pair luminescence appears to be enhanced by hydrogen.

Sharp photoluminescence lines from nitrogen atomic-layer-doped GaAs

We performed nitrogen atomic-layer doping into GaAs grown by molecular beam epitaxy using nitrogen molecules (N2) cracked by a hot tungsten filament. While uniformly nitrogen-doped GaAs layers show relatively weak nitrogen-related photoluminescence lines, nitrogen atomic-layer-doped GaAs layers show a series of sharp and strong photoluminescence lines. The dominant photoluminescence line was observed at 1.4437 eV, where an exciton bound to the nitrogen isotropic traps has the highest binding energy.

Raman Scattering by Acceptors and Donors in p-Type ZnSe

Raman spectroscopy is used to study dopants introduced into ZnSe to produce p-type material. Special attention is paid to nitrogen-doped epitaxial layers and Raman scattering involving the electronic levels of nitrogen acceptors is reported. In these layers spin-flip scattering by electrons at a new type of donor centre at a depth of about 50 meV is also observed. This new donor is believed to play an important role in the compensation process that limits the net acceptor concentrations attainable in this material.

Characteristics of sub-1/4-μm gate surface channel PMOSFET's using a multilayer gate structure of boron-doped poly-Si on thin nitrogen-doped poly-Si

This paper reports the effects of a new p/sup +/ gate structure (MBN gate) on the properties of surface channel PMOSFET's with an extremely thin gate oxide. The MBN gate is a multilayer gate structure of boron-doped poly Si on thin nitrogen-doped poly-Si. The thin nitrogen-doped Si layer effectively suppresses boron diffusion, so that the gate poly Si can be doped with boron in high concentration without the fear of boron penetration. Gate depletion effects are well suppressed. Effective hole mobility is improved due to the reduction of the initial interface state density. The hot-hole induced interface state generation is shown to be the dominant clause of degradation in the 1/4-/spl mu/m level PMOSFET's, and less Gm degradation is found in the MBN-gate PMOSFET's than in conventional p/sup +/-gate PMOSFET's. Finally, with respect to the reliability of the gate oxide, a conventional p/sup +/ gate with boron penetration exhibits an increase in short-time defect related breakdown during constant-current FN stressing. Short-time defect-related breakdown is not observed in the MBN gate but a slight decrease in charge to breakdown. >