Raman Characterization of Carrier Concentrations of Al-implanted 4H-SiC with Low Carrier Concentration by Photo-Generated Carrier Effect

Abstract

In this work, 4H SiC samples with a multilayer structure (shallow implanted layer in a lowly doped n-type epitaxial layer grown on a highly doped thick substrate) were investigated by Raman scattering. First, Raman depth profiling was performed to identify characteristic peaks for the different layers. Then, Raman scattering was used to characterize the carrier concentration of the samples. In contrast to the conventional Raman scattering measuring method of the Longitudinal Optical Plasmon Coupled (LOPC) mode, which is only suitable to characterize carrier concentrations in the range from 2 × 1016 to 5 × 1018 cm−3, in this work, Raman scattering, which is based on exciting photons with an energy above the band gap of 4H-SiC, was used. The proposed method was evaluated and approved for different Al-implanted samples. It was found that with increasing laser power the Al-implanted layers lead to a consistent redshift of the LOPC Raman peak compared to the peak of the non-implanted layer, which might be explained by a consistent change in effective photo-generated carrier concentration. Besides, it could be demonstrated that the lower concentration limit of the conventional approach can be extended to a value of 5 × 1015 cm−3 with the approach presented here.

Validation of Raman spectroscopy as a tool for mapping transport parameters in inhomogeneous N‐doped 4H‐SiC

“…The increase of carrier concentration due to laser excitation has also been reported for Al-implanted 4H-SiC. 38 Thus, the carrier concentration n eff,R measured at the position of the laser spot on the sample is larger than in the transport experiment without illumination. This effect is more pronounced at low temperatures as the fraction of photons absorbed also depends on the number of D 0 states available or in other words the occupation of the impurity band, which decreases with increasing temperature.…”

KPFM - Raman Spectroscopy Coupled Technique for the Characterization of Wide Bandgap Semiconductor Devices

“…This area, called the Junction Termination Extension (JTE), is designed to avoid the abrupt increase of the electric field at the P + emitter edge. The fabrication process and static electrical characteristics of these 5 kV 4H-SiC PiN diodes are detailed in [6,7]. The diodes crosssection is shown in Fig.…”

“…2A and optical images are presented in Fig 2B . The identification of this area of interest is obtained using KPFM thanks to the variation of the second derivative of the capacitance which gives information on the location of the charges [4]. Raman spectroscopy was already used to measure dopant concentration in specific areas [6]. Compared to conventional techniques such as C-V, SIMS (Secondary Ion Mass Spectrometry) or Hall effect, Raman spectroscopy is a non-contact, non-destructive and easy to implement alternative to investigate doped areas.…”

Depth Profiling of Ion-Implanted 4H–SiC Using Confocal Raman Spectroscopy

“…De Biasio demonstrated the use of Raman spectroscopy for the determination of carrier concentrations in epitaxial layers and substrates in n-type 4H-SiC obtained by doping during epitaxial growth without a detailed explanation of the overlap of the longitudinal optical (LO) mode and the longitudinal optical phonon-plasmon coupled (LOPC) mode [16]. Tao Liu et al studied the phenomenon of photo-generated carriers excited by ultraviolet light (325 nm line) and calculated the carrier concentrations of the epitaxial layer [17]. However, the research did not focus on the epitaxial layer thickness, the variation of the LOPC peak position in the depth direction, and the influence of different doping concentrations on the position of the LOPC peak.…”