The comparative studies of chemical vapor deposition grown epitaxial layers and of sublimation sandwich method grown 4H-
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237 Mat. Res. Soc. Symp. Proc. Vol. 572 0 1999 Materials Research
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EXPERIMENTAL DETAILS
The six samples used in this study are listed, with their net doping concentrations and their growth methods, in Table I. Table I. List of samples with their net doping concentration and growth methods. Sample # ND - NA ( x 1017 cm"3 ) Growth method 5500 5635 5722 5929 5930 5931
0.0015 0.0015 2.0 4.0 7.0 4.0
CVD CVD SSM SSM SSM SSM
Samples 5500 and 5635 were grown by chemical vapor deposition and obtained from Cree Research Inc. and from Northrop-Grumman Science and Technology center respectively. The other four samples were SSM grown 4H-SiC and obtained from the Institute of Semiconductors, Kiev, Ukraine. After the usual cleaning in RCA solutions, Ni was sputtered onto the back side of the samples and annealed at 9000 C to form the ohmic contact. Circular Schottky diodes were then fabricated on the thin films as described elsewhere'. Capacitancevoltage ( C-V ) measurements were made with a 1 MHz capacitance meter. The net doping concentrations listed in Table I were determined from the C-V data. The thermal admittance spectroscopy ( TAS ) is described in detail in reference 6. In this experiment, the conductance and the capacitance are measured as functions of frequency and temperature. TAS measurements were made at frequencies ranging from 100 Hz to 1 MHz, and a temperature range of 5 K to 300 K. RESULTS AND DISCUSSION 4 -....
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° 3.1o
120
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r ,-
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L. .inflections W 4-. (3 3.4z
N
60
U
respectively. The activation energies
40
3.2
•.were obtained from the plots of ln(e/T 2)
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