Kazuma Eto

Growth of Low Resistivity n-Type 4H-SiC Bulk Crystals by Sublimation Method Using Co-Doping Technique

The nitrogen (N) and aluminum (Al) co-doped growth of n-type 4H-SiC bulk crystals were performed by sublimation method. In the co-doping growth, we achieved the lowest resistivity of 6.9mWcm, and we also confirmed phenomenon of stacking faults suppression in spite of high N concentration more than 8 x 1019cm-3.

Growth of Low Resistivity p-Type 4H-SiC Crystals by Sublimation with Using Aluminum and Nitrogen Co-Doping

Low resistivity p-type SiC bulk crystals were grown by the sublimation method with using aluminum and nitrogen co-doping. In the sublimation growth of 4H-SiC, to obtain low-resistive p-type crystals are not easy because of the instability of 4H-SiC polytype with highly Al-doping. We have grown < 90 mΩcm p-type 4H-SiC bulk crystals with the co-doping condition. The results of SIMS and Raman spectroscopy show that high concentration of nitrogen co-doping could be effective to the stabilization of 4H polytype with p-type SiC growth.

Growth Study of p-Type 4H-SiC with Using Aluminum and Nitrogen Co-Doping by 2-Zone Heating Sublimation Method

p-type SiC crystals doped with aluminum and nitrogen were grown by the sublimation method. We found that Al and N co-doping is effective for stabilized growth of p-type 4H-SiC polytype. We studied the relationship of polytype of grown crystals and the condition of Al and N feeding during the crystal growth. p-type 4H-SiC with p~1 x 1018 cm-3 are stably-obtained with this method.

Hopping conduction range of heavily Al-doped 4H-SiC thick epilayers grown by CVD

To outline the hopping conduction range, the electrical characteristics of CVD-grown heavily Al-doped 4H-SiC thick epilayers (2.0 × 1019–4.0 × 1020 cm−3) were investigated in a wide temperature regime (20–900 K). It is found that, below 100 K, hopping conduction dominates the carrier transport for all epilayers, and the corresponding hopping conduction activation energy shows a maximum of ~30 meV at around 1.1 × 1020 cm−3. With increasing doping level, the temperature dependence of resistivity evolves and finally obeys the ~1/T1/4 law in the entire temperature regime, which gives direct evidence of variable-range hopping conduction.

Immobilization Phenomenon of Partials Surrounding Double Shockley Stacking Faults in Heavily Nitrogen Doped 4H-SiC Crystal with Thermal Anneal

The expansion behavior of double Shockley stacking faults (DSFs) was investigated in heavily nitrogen doped 4H-SiC crystals at high temperatures up to 1350°C. An immobilization phenomenon of partials surrounding DSFs was discovered by a thermal annealing at temperatures over 1275°C. The electric properties of SiC crystal were maintained after the partial dislocations were immobilized with a high temperature annealing. The mobile partial dislocations extended straight, but the immobile ones bent toward the glide direction. This immobilization phenomenon is significant and useful for achieving low-resistance SiC substrates without DSFs.

Comparison of Conduction Mechanisms in Heavily Al-Doped 4H-SiC and Heavily Al- and N-Codoped 4H-SiC

The conduction mechanism in heavily Al-doped or heavily Al-and N-codoped p-type 4H-SiC epilayers was investigated. In both the singly-doped and codoped samples with an Al concentration (CAl) between 4x1019 and 2x1020 cm-3, band and nearest-neighbor hopping (NNH) conductions appeared in high and low temperature ranges, respectively. The codoping of N donors makes the NNH conduction dominant at temperatures higher than in the singly-doped samples. In both the singly-doped and codoped samples with CAl between 1x1019 and 4x1019 cm-3, an unexpected conduction appeared between the regions of the band and NNH conductions.

Bulk growth of low resistivity n-type 4H-SiC using co-doping

The growth of n-type 4H-SiC crystal was performed by physical vapor transport (PVT) growth method by using nitrogen and aluminum (N-Al) co-doping. Resistivity of N-Al co-doped 4H-SiC was as low as 5.8 mΩcm. The dislocation densities of N-Al co-doped substrates were evaluated by synchrotron radiation X-ray topography (SXRT). In addition, epitaxial growth was performed on the N-Al co-doped substrates by chemical vapor deposition (CVD). No double Shockley type stacking fault was observed in the epitaxial layer.

Polarity Inversion of SiC(0001) during the Al Doped PVT Growth

We found that the polarity of the 4H-SiC is reversed from Si-face to C-face by high Al doping during the physical vapor transport (PVT) growth. KOH etching and deep ultraviolet (DUV) Raman spectroscopy were used to confirm the polarity of the grown crystals. The results show the polarity inversion is occurred in the samples grown on Si-face SiC with using Al doped SiC source material.