Papers by Keyword: n-Type Doping

Abstract: We report the study of the effect of the growth rate and of the doping on the stress and the defect density of a Cubic Silicon Carbide (3C-SiC) bulk layer grown at low temperature on a silicon substrate. After the growth process, the silicon substrate was melt inside the CVD reactor used for the deposition and then the intrinsic stress was measured by the curvature of the wafer without influence of the thermal stress between silicon and 3C-SiC. A considerable increase of the curvature was observed increasing the doping of the layer. The average stress is compressive and then produces a convex bow. At the same time, the average quality of the grown material deteriorates increasing the doping concentration. Using μ-Raman measurement in cross-section of the 3C-SiC grown samples, it was possible to observe the dependence of the stress and of the quality of the material as a function of the thickness and of the growth rate, due to the variation of the growth rate during the process. In particular, the increase of the growth rate produced both an increase of the stress and a decrease of the material quality. Furthermore, the increase of the doping concentration produced both an increase of the stress and a further deterioration of the crystal quality.

Abstract: In this study, influence of both Si/H₂ ratio and C/Si ratio on growth rate uniformity and carrier concentration uniformity of n-type 4H-SiC epitaxial films grown by high speed wafer rotation vertical CVD tool was investigated. It was found that changes in radial profile of the growth rate and the carrier concentration obtained by varying Si/H₂ ratio showed quite similar behavior to those obtained by varying C/Si ratio. Such a similar trend would suggest that the distribution of local C/Si ratio near the wafer surface changes depending on total Si/H₂ ratio similarly to total C/Si ratio. Additionally, by using this relationship, both the growth rate uniformity of 49.2 μm/h ±1.78% (1.15% σ/mean) and carrier concentration uniformity of 1.08 ×10¹⁶cm^-3 ±6.15% (3.40% σ/mean) was achieved.

Abstract: After presenting an exhaustive experimental study of aluminum incorporation in epitaxial 4H-SiC and 3CSiC films grown by chemical vapor deposition (CVD), we focalize once more on what is called site competition effects. We observed that the influence of C/Si ratio on dopant (Al, N) incorporation in SiC was qualitatively different depending on whether the growth experiments were performed in “low temperature” (LT) or “high temperature” (HT) regime. Partial explanation of observed phenomena basing on thermal evolution of carbon coverage of SiC surface is proposed.

Abstract: The depth profiles of n-type doping concentration in thick (>100 μm) and low-doped (< 4 × 10¹⁴ cm^-3) 4H-SiC epilayers grown by chemical vapor deposition (CVD) were investigated. The variation in doping concentration during epitaxial growth are considered to be caused by: (1) variation in gas flow due to parasitic deposition, (2) variation in precursor decomposition rate due to change in reactor temperature, (3) variation in dopant incorporation rate due to change in wafer temperature, and (4) variation in supply of background dopants. By controlling all these parameters, a constant depth profile in thick (> 100um) epilayers was realized.

Abstract: We review two ex-situ doping methods to achieve high n-type doping up to mid-10¹⁹ cm^-3 in Ge-on-Si thin films. For both, delta doping and ion implantation, rapid thermal annealing is used to diffuse phosphorus from a diffusion source into the single crystal Ge layer. The diffusion mechanism is studied and we find that dopant enhanced diffusion in in-situ doped Ge attributes to the high doping level. A band gap narrowing effect is observed in highly doped n-type Ge through photoluminescence measurements by determining the photoluminescence peak shift. An empirical linear expression of the direct band gap narrowing shift with carrier concentration is proposed.

Abstract: This paper investigates n-type doping of point-defect compensated high purity semi-insulating (HPSI) 4H-SiC using a pulsed laser (10 ns FWHM @ 260 nm) for the introduction of nitrogen to shallow depths. A thermal model is presented using COMSOL Multiphysics featuring nonlinear temperature dependent material properties and a volumetric heat source term that takes into account the laser absorption depth for common ultraviolet irradiating wavelengths. The temperature distribution in the material and the amount of time that the surface and near-surface regions are at high temperature determines how many laser pulses are required to dope to the desired depth, and simulation results are presented and fit to measured data. The simulations and measured data show that for shallow doping a short wavelength ultraviolet laser should be used to localize the heat at the surface so the dopant can’t diffuse deep into the material. The laser enhanced diffusion process has been used to incorporate nitrogen into HPSI 4H-SiC with a measured surface concentration greater than 10²⁰ cm^-3 and a nonlinear thermal model was built.

Abstract: This work presents the crystalline quality investigation of 3C-SiC unseeded crystals grown from vapor phase. Samples were polished after different crystallographic planes from crystals grown with or without nitrogen flow. The structural and optical investigation showed that the central part of the samples exhibited a very good crystalline quality. The best samples proved to be the {100} growth sectors where the only defects found were stacking faults with a defect density under 103 cm-1. At the edges, i.e. between two adjacent growth sectors, structural investigation by transmission electron microscopy revealed stacking faults and hexagonal polytype inclusions. The nitrogen doping was found not to have an influence on the crystalline quality.

Abstract: In this paper, field emission from ZnO was studied by morphological and electronic design. By fabricating ZnO into nanopin structure with sharp tip, we can obtain low threshold and high emission current density. By doping ZnO with gallium, we can lift up the Fermi level and increase the conductivity to enhance the field emission. The fabrication of nanostructures and analysis of field emission will be discussed.

Abstract: The n-type doping of diamond with phosphorus suffers from defects reducing the electron mobilities and inducing some degree of compensation. In addition, the relatively high ionization energy (0.6 eV) of phosphorus severely limits the electrical activity of the dopants. Here, we present two recent advances of the n-type doping of diamond. One is based on the significant reduction of the compensation ratio of highly compensated phosphorus-doped diamond by thermal annealings. The second one presents the possibility of converting p-type boron-doped diamond into n-type by deuterium diffusion and formation of deuterium-related shallow donors with ionization energy of 0.33 eV.