High Frequency Electron Spin Resonance Study of Hydrogenated Microcrystalline Silicon
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A19.9.1
High Frequency Electron Spin Resonance Study of Hydrogenated Microcrystalline Silicon
Takashi Ehara School of Science and Engineering, Ishinomaki Senshu University 1 Shinmoto, Minamisakai, Ishinomaki, Miyagi 986-8580, Japan
ABSTRACT Dangling bond defects (DB) in hydrogenated microcrystalline silicon (µc-Si:H) have been studied by X-band (9 GHz) Q-band (33 GHz) and W-band (90 GHz) electron spin resonance (ESR) spectroscopy. In X-band ESR spectra, all the samples showed asymmetric dangling bond defect signal at g = 2.005 – 2.006. The DB signal shape shows little dependence on substrate temperature in the X-band electron spin resonance (ESR) spectra. In the Q-band and W-band ESR spectra, existence of two centers in DB signals is clearly indicated by the shape of the spectra. The Q-band ESR spectra shape reviles that the peak of one center is at g = 2.0055 and the other is around at g = 2.0060. In addition, the DB signal showed dependence on substrate temperature. The dependence of the DB signals can be explained by difference of intensity ratio of the peaks by these two centers. The signal at g = 2.0060 is consistent with the asymmetric ESR signal observed in the microcrystalline silicon embedded in SiO2. W-band ESR measurement indicates that the signal observed at g = 2.0060 is due to single inhomogeneous species and does not consist of plural species.
INTRODUCTION µc-Si:H has been recognized as promising materials for optical devices. In the µc-Si:H, DB are very important to control its electrical properties. The µc-Si:H is a heterogeneous material that consists of small crystallites with size in the order of 5 – 30 nm which are embedded in columns structure with a diameter of 50 – 200 nm [1,2]. In such mixed phase structure, ESR
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spectroscopy is an important method to study a particular electronic state, because the techniques are sensitive to the microscopic environment of this state. Previously, deconvolution of the ESR spectra of the DB in the µc-Si:H into two species has been reported [3]. This result supports the existence of plural kinds of the DB in the µc-Si:H. In addition, we have reported the high frequency ESR study of unhydrogenated µc-Si that showed the spectra could not be explained by single paramagnetic species [4]. In the present work, the DB in the µc-Si:H is studied by high resolution Q-band and W-band ESR spectroscopy. The details of the spectra are studied also by comparison with microcrystalline silicon embedded in SiO2 [5].
EXPERIMENTAL DETAILS The µc-Si:H films were prepared by the plasma enhanced chemical vapor deposition (PECVD) method using hydrogen diluted SiH4 gas at a concentration of 2 % and a feed rate of 50 sccm. The rf power and the deposition pressure were 100 W (13.56 MHz) and 133 Pa, respectively. Substrate temperatures were ranged from 70 to 270°C. The deposition time was 15 hours and thickness of the samples were about 1.0 µm. The microcrystalline embedded in SiO2 samples were prepared by the rf co-sputtering of Si and SiO2 followed by the thermal anneali
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