High-speed high-quality epitaxial growth of N and B codoped 6H-SiC by closed sublimation method
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High-speed high-quality epitaxial growth of N and B codoped 6H-SiC by closed sublimation method
T. Maeda1, Y. Nakamura1, M. Iwaya1, S. Kamiyama1, H. Amano1, I. Akasaki1, T. Furusho2 , H. Kinoshita2, M. Yoshimoto3, Fac. Sci. and Technol., 21st COE “Nano-Factory” Meijo Univ.1, SiXON Ltd．2 Kyoto Institute of Technology 3
ABSTRACT N and B codoped 6H-SiC epilayers were grown by the closed sublimation method, the growth rate of which was as high as 100 µm/h. Donor acceptor (DA) pair emission at different temperatures was investigated for two samples with different B concentrations. The integrated photon count obtained from the photoluminescence (PL) spectra of the samples having high B concentration increases with temperature. To estimate the internal quantum efficiency, we measured the PL integrated photon counts of GaN at 10 K as a reference. The integrated PL photon count of 6H-SiC DA-doped epilayer at 250 K is almost comparable to that of GaN at 10 K, which is thought to be almost 100% because of the freezing of the nonradiative recombination at low temperature. This result implies that the internal quantum efficiency of the 6H-SiC DA-doped epilayer exceeds 95%. INTRODUCTION White-light-emitting diodes (LEDs), which are composed of nitride-based blue LED and yellow phosphor such as YAG:Ce [1], have been applied as the backlight source of small LCD displays. They are also expected to be used in general lighting applications. However, the present white LEDs have problems of low luminous efficiency, low color rendering index, and low luminous flux compared with existing light sources such as fluorescent lamps. In this paper, we propose a donor and acceptor (DA)-doped 6H-SiC substrate as a new phosphor. Since SiC has superior electric and thermal conductivities, it is suitable as a substrate of high-power LEDs. Because of the solid-state medium of SiC crystal, it has no light scattering loss and no inhomogeneous distribution of color, which are the current problems in the use of powder phosphor materials. It is known that the DA-doped SiC shows strong donor and acceptor pair (DAP) emission upon photoexcitation. When a nitrogen donor and boron acceptor are doped
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in to a 6H-SiC crystal, yellow to orange light emission by photoexcitation can be obtained [2]. The SiC-based blue LEDs were also fabricated using emission from the N and Al [3] DAP. However, the efficiency of DAP emission in SiC has not been clarified. 6H-SiC is an indirect band-gap material, so it has a small light absorption coefficient and low light emission rate compared with a direct band-gap material such as GaN. However an increase in volume and optimization of impurity concentrations may improve the quantum efficiency of DA-doped SiC epilayers. In this study, we investigate the optical properties of 6H-SiC epilayers doped with N and B of different concentrations. The quantum efficiency of the DAP emission from 6H-SiC is also discussed. EXPERIMENT DA-doped 6H-SiC epilayers were grown by the closed sublimation method [4-6]
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