Structural and Electrical Properties of Beryllium Implanted Silicon Carbide
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INTRODUCTION Silicon carbide (SiC) is a promising material for high temperature, high frequency, and high power device applications. Group II elements are commonly used as acceptor dopants for this semiconductor. Investigations on p-type SiC doped with these elements, however, revealed poor electrical characteristics due to high acceptor ionization energies and low hole mobilities [1-5]. Therefore, alternative dopants with a higher electrical activation are highly desirable. Due to the low mass and high solubility in the SiC lattice [6], beryllium (Be) can be used for the production of thick p-type layers applying ion implantation. However, there have been very few reports on Be doped SiC [7-12]. Be is known to be an electrically active impurity, i.e., a doubly charged acceptor in SiC [10]. Two acceptor levels at 0.42 and 0.6 eV, respectively, were determined by Hall measurements [8]. Further, one deep level at 0.38 eV was obtained by I-V measurements on p-n junctions produced by Be implantation [12]. However, the precision of these results is questionable because that data analysis is based on simplified model assumtions. Despite the fact that Be has been successfully applied in the fabrication of diodes [11,12], much is still unknown about the structure of this dopant in the SiC lattice. In this paper, we report on structural and electrical properties of Be implanted SiC. Samples were characterized by secondary ion mass spectrometry (SIMS), Rutherford backscattering spectrometry / channeling (RBS/C), deep level transient spectroscopy (DLTS), resistivity and Hall measurements. EXPERIMENT Epitaxial layers ([0001] orientation, n-type, off-axis, thickness: 10 tun, carrier concentration: lxl016 cm-) grown on 6H-SiC substrates as purchased from Cree Research [13] were used as starting material. 9Be+ was implanted applying energies between 50 and 590 keV (see Table I) in order to obtain a box-shaped profile. Samples were maintained at room temperature (RT), and 117 Mat. Res. Soc. Symp. Proc. Vol. 572 © 1999 Materials Research Society
were tilted 7' with respect to the ion beam to minimize channeling effects during implantation. Ion range and nuclear energy distributions were obtained by Monte Carlo (MC) simulations using the TRIM code (SRIM-98, full cascade) [14]. A mean displacement energy of 25 eV for both Si and C atoms was applied. The concentration profile and the nuclear energy density distribution are shown in Fig. 1. The critical energy density for the amorphization of SiC crystal at RT (2x 1021 keV/cm 3 [15]) is indicated by the dashed line. Ion energy (keV)
-2
Ion fluence (104 cm 2)
50
0.61
75 100 130
0.62 0.63 0.84
170 210 260 320 400 490
0.74 0.85 0.80 1.00 1.03 0.94
590
1.52
g
C0l
1019
o10187 0 C
09
4D1017 00
101
300
600
900
12000
Depth (nm)
Table I. Schedule used for Be implantation.
Fig. 1. Total nuclear energy distribution and total dopant concentration for Be implanted SiC as calculated using TRIM
To repair the crystal damage and activate the implanted dopant, samples were ann
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