Dopant Concentration Distribution Research Articles

Microstructural Gradational Properties of Sn-Doped Gallium Oxide Heteroepitaxial Layers Grown Using Mist Chemical Vapor Deposition.

This study examined the microstructural gradation in Sn-doped, n-type Ga2O3 epitaxial layers grown on a two-inch sapphire substrate using horizontal hot-wall mist chemical vapor deposition (mist CVD). The results revealed that, compared to a single Ga2O3 layer grown using a conventional single-step growth, the double Ga2O3 layers grown using a two-step growth process exhibited excellent thickness uniformity, surface roughness, and crystal quality. In addition, the spatial gradient of carrier concentration in the upper layer of the double layers was significantly affected by the mist flow velocity at the surface, regardless of the dopant concentration distribution of the underlying layer. Furthermore, the electrical properties of the single Ga2O3 layer could be attributed to various scattering mechanisms, whereas the carrier mobility of the double Ga2O3 layers could be attributed to Coulomb scattering owing to the heavily doped condition. It strongly suggests the two-step-grown, lightly-Sn-doped Ga2O3 layer is feasible for high power electronic devices.

Valence states and dielectric properties of fine-grained BaTiO3 ceramics co-doped with double valence-variable europium and chromium

(Ba1–xEux)(Ti1–xCrx)O3 (x = 0.01‒0.05) (BETC) and (Ba1–xEux)(Ti1.01–xCrx–0.01)O3 (x = 0.02‒0.05) (BETC1) ceramics with single-phase perovskite structures were prepared using a mixed-oxides method. The structure, microstructure, site occupations, valence states of Eu/Cr, and dielectric properties of these ceramics were investigated using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, fluorescence spectroscopy, emission spectroscopy, electron paramagnetic resonance, and dielectric measurements. The mixed valence states of Eu3+/Eu2+ and Cr3+/Cr5+ were confirmed. Co-doping with Eu and Cr greatly inhibited the grain growth of BaTiO3 ceramics, resulting in a fine-grained microstructure (0.7 µm). Two permittivity peaks of BETC with x ≥ 0.02 were characteristic of an inhomogeneous dopant concentration distribution forming a core–shell structure. For BETC1, the mixed valence states and site occupations of Eu/Cr were analyzed to elucidate an expansion in the unit-cell volume, very high Eu/Cr ratio (= 3.5) in coarser grains, regular diffuse phase transition behavior, rapid Tm-shifting rate of − 24 °C/at% (Eu/Cr), higher ε′RT (= 4550), and lower tan δ (= 0.0196) in BETC1, as well as the destruction of the core-shell structure in BETC.

Ytterbium-doped double-cladding fiber with 35 kW output power, fabricated by chelate gas phase deposition technique

A ytterbium-doped double-cladding fiber was successfully fabricated by a chelate gas phase deposited technique. The measurement results of dopant concentration distribution and refractive index of preform indicate that radial and longitudinal homogeneity could be controlled perfectly with this technique. The absorption coefficients of fiber are 0.39 dB/m at 915nm and 1.02 dB/m at 976nm respectively. Using this fiber as the laser amplifier stage, 3592W output power at 1080nm with 72.5% slope efficiency was obtained with end-pump technique, which is close to the test results of Nufern commercial fiber. The results demonstrate that the chelate gas phase deposition technique is a relatively promising technique for high quality gain fiber fabrication.

Influence of Adsorption of Dopant on Distribution of the Dopant in A P-N-Junction

It has been shown, that manufacturing diffu- sive- and implanted-junction rectifiers in a semiconductor heterostructure and optimization of annealing give us possi- bility to increase sharpness of p-n-junction and homogeneity of dopant distribution in doped area. In this paper we con- sider influence of adsorption of dopant in the heterostructure on distribution of dopant concentration in the p-n-junction. Based on results of modeling we show, that adsorption of dopant gives us possibility to decrease both sharpness of the p-n-junction and homogeneity of dopant distribution in enriched by the dopant area.

Laser-silicon interaction for selective emitter formation in photovoltaics. I. Numerical model and validation

Laser doping to form selective emitters offers an attractive method to increase the performance of silicon wafer based photovoltaics. However, the effect of processing conditions, such as laser power and travel speed, on molten zone geometry and the phosphorus dopant profile is not well understood. A mathematical model is developed to quantitatively investigate and understand how processing parameters impact the heat and mass transfer and fluid flow during laser doping using continuous wave lasers. Calculated molten zone dimensions and dopant concentration profiles are in good agreement with independent experimental data reported in the literature. The mechanisms for heat (conduction) and mass (convection) transport are examined, which lays the foundation for quantitatively understanding the effect of processing conditions on molten zone geometry and dopant concentration distribution. The validated model and insight into heat and mass transport mechanisms also provide the bases for developing process maps, which are presented in part II. These maps illustrate the effects of output power and travel speed on molten zone geometry, average dopant concentration, dopant profile shape, and sheet resistance.

Single crystal growth by axial vibrational control technique in Czochralski configuration

Application of the axial vibration control technique to the Czochralski crystal growth (AVC–CZ) by submerging an oscillating baffle into the melt under the crystal for the large diameter crystal growth was studied. The configuration of the submerged vibrating baffle was optimized to enlarge the growing crystal diameter while keeping control on heat–mass transfer in the melt. The equalization of melt composition in the crucible whole volume and dopant concentration distribution in AVC–CZ grown NaNO3 single crystal was demonstrated.

Suppression of conductivity in Mn-doped ZnO thin films

We studied the dopant concentration distribution and conductivity in ZnO:Mn films grown by metalorganic chemical vapor deposition. The ion beam, surface, and microstructural properties of undoped ZnO films were compared with Mn-doped ZnO films. Suppression of ZnO conductivity was observed for Mn doping up to ∼4.5 at. %. The presence of Mn2+, confirmed by x-ray photoelectron spectroscopy, is correlated with the reduction in conductivity. Variable-temperature Hall effect measurements yield an activation energy of 170 meV, consistent with deep donors in the bulk or at the interface. The results suggest that the incorporation of substitutional Mn suppresses the formation of native defects such as oxygen vacancies.

Numerical study on the dopant concentration and refractive index profile evolution in an optical fiber manufacturing process

The index of refraction is an important property of optical fibers, since it directly affects the bandwidth and optical loss during information transmission. The refractive index is governed by the dopant concentration distribution across the fiber cross section, which is strongly influenced by the processing conditions. An understanding of the effects of process parameters on the dopant concentration profile evolution is important to design the drawing process for tailored refractive index and optical transmission characteristics. Although the heat and momentum transport in optical fiber drawing have been studied extensively, little has been reported in the open literature on dopant concentration and index of refraction profile development during processing. This paper presents a two-dimensional numerical analysis on the flow, heat and mass transfer phenomena involved in the drawing and cooling process of glass optical fibers using a finite difference approach based on primitive variables. The effects of several important parameters are investigated in terms of nondimensional groups, including: fiber draw speed, inert gas velocity, furnace dimensions, gas properties, and dopant properties on the flow, temperature and dopant concentration distribution.

Static and high-frequency transverse electrical conductivity of isotypical silicon structures obtained by direct bonding

The possibility of using the results of measuring the quasi-static current-voltage characteristics and high-frequency impedance of symmetrically doped bicrystal structures obtained by direct bonding to simultaneously determine the electrical parameters of the bonding interface [differential density of the surface states ν(E)] and the near-boundary layers (the dopant-concentration distribution in the vicinity of the boundary) is discussed. Attention is given to the fact that the ratio of static current to high-frequency conductivity is extremely sensitive to the presence of “punch-throughs” (regions with enhanced electrical conductivity) in the potential barrier of the bonding interface. It is shown experimentally that the electrical conductivity of actual bicrystal structures obtained by direct bonding of silicon is governed to a large extent by the presence of such “punch-throughs,” which should be taken into account, in addition to the possible doping of interfacial layers in the course of bonding, when determining the dependence ν(E).

Dopant diffusion in phases with a moving interface

We consider the diffusion of a dopant through a moving interface in the suicide film-Si system during silicide layer growth. The dopant concentration distribution is derived in analytical form by the integral Fourier transform method with subsequent reduction of the dopant redistribution problem to numerical solution of two integral equations. The results are presented in the form of curves plotting the time dependence of dopant concentration on both sides of the interface for various values of diffusion coefficients and interface velocity. The effect of physical parameters on the variation of dopant concentration near the interface is demonstrated.

Axial dopant distribution and its control in bulk crystal growth

It is shown that Czochralski-grown bulk crystals can be made to have a uniform dopant concentration axially (in the direction of the growth) by properly adding undoped polysilicon to the melt. The rate of addition is constant with the crystal pulling. A relationship is derived for the axial distribution of dopant concentration in floating-zone bulk crystals. It is in turn used to specify a prescribed axial dopant distribution in the original rod that will yield a uniform axial dopant profile upon completion of the zone growth. The results are applicable to silicon and other semiconductor crystals.

For the Growth of 3 Inch D-Shaped GaAs Crystals by a Modified Horizontal Bridgman Process

Doped with silicon or zinc, 3 inch D-shaped GaAs crystals were grown by the modified two-temperature horizontal Bridgman (M2T-HB) technique. Then (1&10) wafers were sliced axially from the chunk of silicon-doped 3 inch GaAs crystals and chemically etched to reveal the growth striations of solid/liquid interfaces. Three-dimensional, numerical simulations of the solidification process for growing 3 inch crystals by the M2T-HB system were performed and compared with the etched (110) wafers from experiments. The heat- and mass-transfer mechanism through the melt is the combination of convection, conduction and radiation. The finite volume approach and the continuum model are employed to determine the position and shape of the interface of the solid/melt, dopant concentration and the temperature field in the crystal and melt. Two methods for computing the dopant concentration are (a) solving the transport equation of full mass concentration and (b) using the simplified model of equilibrium. The computed solidification fronts and the dopant distributions agree successfully with the experimental data, and the axial distribution of dopant concentration as well as flow and temperature fields are computed for information of the crystal quality.

Dopant incorporation during liquid phase epitaxy

A quantitative treatment of nonequilibrium dopant incorporation during the growth by conventional liquid phase epitaxy (LPE) as well as by electroepitaxy has been put forward. Analytical expression for the stationary distribution of dopant concentration and potential in the solid near the liquid metal-semiconductor interface is derived. On this basis the effect of the Schottky barrier height, supplied voltage, diffusion coefficient in the solid, and growth rate on the incorporation of the donor impurities is calculated. The experimental verification of the proposed model can be easily carried out as all the dependences are plotted versus normalized variables.