Bulk Crystallization of GaN by HVPE on Small Seeds

The number and type of point defects in the growing crystal depend on microscopic processes of incorporation of basic growth units and impurities on the particular crystal faces. For HVPE, these growth mechanisms can be influenced by changing temperature, flows of reacting gases, and chemical environment in the system (carrier gas, impurities). 

The HVPE system used in this study was the horizontal home-built quartz reactor with the rotating-quartz susceptor. GaGl was supplied vertically, just over the surface of the susceptor. A growth temperature of about 1050 °C, temperature of GaCl synthesis of 870 °G, HGl flow in the range of 

5-24 ml min diluted in 500 ml min of N2, NH3 flow of 1200 ml min and 3000 ml min of N2 or H2 as carrier gases were applied for runs of 4-15 hours. The growth rates observed for this geometry and the set of conditions varied from 20-200 pm h and were dependent mainly on the flow of HCl. 

For the growth with a relatively high rate (100 pm or bigger), in N2 carrier gas, the HVPE GaN-high-pressure substrate system behaves like the one with a small lattice and/or thermal mismatch even for Mg-doped substrates, which according to the X-ray estimations are lattice matched to the pure GaN. This conclusion is based on the following observations  

On the other hand, there are observations indicating that the reasons for strain and defect generation in the considered system are related rather to the growth mechanisms than to the mismatch of high-pressure and HVPE-grown materials. These observations are as follows  

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