Influence of Crystal Growth Conditions on Nitrogen Incorporation During PVT Growth of SiC
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1069-D01-04
Influence of Crystal Growth Conditions on Nitrogen Incorporation During PVT Growth of SiC Darren Hansen, and Mark Loboda Science and Technology, Dow Corning Compound Semiconductor Solutions, AUB1007, P.O. Box 994, Midland, MI 48686-0994, Midland, MI, 48686-0994 ABSTRACT The control and understanding of the incorporation of nitrogen during SiC PVT continues to play an important role in SiC crystal growth. Nitrogen acts both as a dopant and an impurity depending on the growth conditions and desired resistivity. Epitaxial growth by CVD provides some insight into N incorporation in terms of the face effects, temperature, and impact of the chemical species in terms of the C/Si ratio. This paper will present experimental results showing trends regarding nitrogen incorporation during SiC PVT. Various crystal growth processes operated under constant nitrogen partial pressures were found to produce wide ranges of SiC resistivity. These effects will be analyzed in light of the process impact on gas phase elemental composition (1), crystal stress (2), dopant activation (3) and crystal defectivity (4). The goal of this paper is to provide additional insights regarding nitrogen incorporation during SiC PVT, and in turn drive towards a more holistic approach to control the resistivity of 4H n+ SiC material, based on the understanding established from SiC epitaxy technology. INTRODUCTION SiC is a promising material because of its mechanical, electrical, and physical properties. 4H material in particular has a favorable bandgap, thermal conductivity, and carrier mobility relative to the other common SiC polytypes. In addition to the large amount of effort that has been placed on improving the overall defect densities of SiC materials, for example the reduction of micropipes, thermal decomposition voids, and polytype control, the electrical properties of the underlying SiC substrate are a critical aspect to the SiC substrate application in devices. For devices where the substrate actively conducts current as in some high power electronics the goal is to drive the resistivity of the SiC materials ever lower so that the SiC substrate does not negatively impact the overall device performance through introduction of parasitic resistances [2-12]. For high frequency devices, it is necessary to have the SiC material have minimum free carriers so as not to introduce loss into the overall device performance [13-20]. As a result of these two important applications it is becoming increasingly important to be able to manipulate the resistivity of the 4H substrate materials over a wide range of resistivities. The primary dopant for n-type 4H materials is N [2,4-12], although consideration has been given to P dopants as well [3,12]. To that end work to understand nitrogen incorporation in bulk growth by physical vapor transport (PVT) and epitaxial growth has occurred [1-12]. In epitaxial growth of SiC layers the dopant incorporation can be well understood in terms of a site competition model [1]. In this model dopants such as B, Al,
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