Carrier Concentration Temperature Dependence in 4H-SiC Substrate
The carrier concentration reflects the number of particles involved in conductivity in semiconductor materials. By testing the carrier concentration, we can evaluate the conductivity of the material and optimize the current carrying capacity and power consumption of the device accordingly. The variation of carrier concentration may also affect the band structure and electrical properties of materials, so testing it can help us comprehensively understand the performance characteristics of materials. The article mainly expounds the carrier concentration temperature dependence in 4H-SiC substrate.
1. About Semiconductor Carrier Concentration
Carrier concentration refers to the density of free electrons or holes (i.e. carriers) in semiconductor materials, which is the number of carriers per unit volume. In semiconductor physics, n is usually used to represent electron concentration, p is used to represent hole concentration, and the unit is the number of charge carriers per cubic centimeter (cm-3). The carrier concentration is affected by the following factors:
1) Doping: By doping specific impurity elements into semiconductors, the carrier concentration can be increased.
2) Temperature: An increase in temperature increases the probability of thermal excitation of electrons and holes in semiconductors, causing more electrons to transition to the conduction band and become free electrons, typically leading to an increase in carrier concentration.
2. Temperature Dependence of Carrier Concentration in N Type 4H-SiC
The carrier concentration temperature dependence in n-type 4H-SiC substrate measured by Hall test is shown in Fig. 1. The concentration of free charge carriers increases with temperature, indicating incomplete ionization. Secondary ion mass spectrometry (SIMS) showed that the N content of S1 SiC wafer was 5.8×1018 cm-3, and the N content of S2 SiC wafer was 4.5×1018 cm-3; If the temperature further increases, this should represent the maximum value of carrier concentration in Fig. 1.
Fig. 1 Temperature dependence of carrier concentration in semiconductor SiC substrates (S1, S2) measured by Hall test
3. Temperature Dependent Carrier Concentration in V Doped Semi-insulating 4H-SiC
Two V-doped semi insulating 4H-SiC substrates with different impurity concentrations were used for Hall testing. Fig. 2 and 3 show the relationship between the measured free carrier concentration and temperature for the two SiC substrate samples. From the curves in Fig. 2 and 3, it can be observed that the concentration of free charge carriers measured for V doped SiC #1 and SiC #2 remained n-type between 300 and 700K, and the electron concentration showed a significant upward trend with increasing temperature. For SiC substrate #1, there were fluctuations in the carrier concentration at 600K and 675K, indicating the occurrence of acceptor impurity compensation. For SiC wafer #2, there was one impurity compensation in the carrier concentration at 675K. Using SEM to observe the presence of boron element in both SiC wafers, compensation at 675K may be caused by boron impurities. The compensation of SiC #1 at 600K is due to the introduction of other acceptor impurities caused by environmental pollution during the growth process.
From the results, it can be seen that the doping concentration of semi-insulating SiC #2 is higher than that of semi-insulating SiC #1, but the experimentally measured carrier concentration is lower than that of SiC #1, indicating that the acceptor compensation in SiC #2 is more severe than that in SiC #1.
Fig. 2 Carrier concentration vs temperature relationship in semi-insulating SiC wafer #1
Fig. 3 Relationship of carrier concentration vs temperature in semi-insulating SiC substrate #2
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