Reducing Structural Defect Densities in

We have obtained 4H-A1N on 4H-SiC (1120). Isopolytypic growth resulted in very small XRD linewidth, 90 arcsec, one of the lowest values ever reported for heteroepitaxial growth of nonpolar nitride layers. However, TEM studies showed that the 4H-A1N layers still contain high densities of SFs and partial TDs. Further reduction of the densities of these defects is desirable to develop 4H-A1N grown on 4H-SiC (1120) for device applications. 

The partial TDs originated from SFs, and the SFs originated from incomplete polytype replication of 4H-SiC to AlN. To further improve the AlN epdayer quality, it is necessary to enhance the polytype replication process (i.e. increase the fraction of AlN which is initially nucleated in the 4H structure). As clearly seen in the cross-sectional TEM images, SFs originate at the AlN/SiC interface, suggesting that control of the initial growth stage is absolutely crucial. 

To enhance the polytype replication process, we have introduced two key experimental procedures [23, 24]. The first is to prepare an atomically flat. 

The crystalline quality of the AlN layer was assessed by XRD measurements. Table 4.2 shows the FWHM of XRD 20 /a - and )-scans of AlN samples grown under various III/V ratios. For the measurement, receiving slit (acceptance angle of 30 arcsec) was attached. Both the 20/ )-scan and -scan FWHM values decreased with increasing III/V ratio. 

III/V ratio Very Al rich Slightly Al rich Slightly N-rich Very N-rich 

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