Inhomogeneity of Minority Carrier Lifetime in 4 H -SiC Substrates
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HYSICAL PROPERTIES OF CRYSTALS
Inhomogeneity of Minority Carrier Lifetime in 4H-SiC Substrates J. Y. Yua, X. L. Yanga,*, Y. Penga, X. F. Chena,**, X. B. Hua, and X. G. Xua a
State Key Laboratory of Crystal Materials, Shandong University, Jinan, 250100 China *e-mail: [email protected] **e-mail: [email protected] Received July 2, 2019; revised July 2, 2019; accepted November 26, 2019
Abstract—The minority carrier lifetimes in lightly N-doped n-type and V-doped semi-insulating 4H-SiC crystals were measured by microwave photo-conductance decay method. The resistivity mapping of the ntype 4H-SiC wafer lightly doped with nitrogen was examined by contactless resistivity measurement system to reveal the relationship between minority carrier lifetime and resistivity. Combining with the Raman spectroscopy and theoretical analysis of the nonequilibrium carrier recombination mechanism, it was found that the inhomogeneity of minority carrier lifetime in n-type 4H-SiC wafer was caused by inhomogeneous distribution of nitrogen concentration and the minority carrier lifetime was inversely proportional to the majority carrier concentration. It was also found that the minority carrier lifetime of V-doped semi-insulating 4H-SiC crystal was lower by one order of magnitude than that of N-doped n-type wafer. Second ion mass spectroscopy was used to examine the impurity concentration in different regions of V-doped semi-insulating 4HSiC. It confirmed that the inhomogeneity of minority carrier lifetime originated from the inhomogeneous distribution of electrically active impurity concentration. DOI: 10.1134/S1063774520070305
INTRODUCTION Silicon carbide (SiC) is a promising wide-bandgap semiconductor material which can be used as the substrates for the fabrication of high-power, hightemperature and high-frequency electronic devices due to its excellent physical properties such as high thermal conductivity, high breakdown electric field strength and high saturated electron drift velocity [1– 3]. The electrical conductivity of SiC single bulk can be changed by intentional doping in a wide range from a semi-insulating to a highly conductive material. This makes it possible to fabricate SiC-based and GaNbased field effect transistors with low-loss devices at microwave frequencies on SiC substrates. Otherwise, a key requirement for microwave devices is the use of an electrically passive, preferably semi-insulating, substrate which exhibits low dielectric loss. Therefore, attaining these electrical properties is non-trivial in SiC boule growth via physical vapor transport (PVT) [4, 5]. However, the electrical inhomogeneity still remains a crucial issue for commercial material. In the PVT technique, electrical inhomogeneity in the as-grown SiC crystals mainly results from nonuniform distribution of shallow and deep centers on the macroscopic scale. Even the small variations of the level defect concentrations can lead to the Fermi level pinned by different traps. This is equivalent to large variations of resistivity [6]. Qiang et al. [7] have
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