The growth of Si-doped AlGaN on an AlN/sapphire substrate as an underlying layer was performed using LP-MOVPE. The AlGaN films were grown with different AlN mole fractions by changing the growth temperature. GaN and AlGaN with an AlN mole fraction of 0.28 were free from stress because of the 3D growth. In the case of AlGaN with an AlN mole fraction of nearly 0.4, the lattice mismatch between the AlGaN and underlying AlN had an adverse effect on the crystal quality. AlGaN with an AlN mole fraction of more than 0.6 was coherently grown on AlN, and in the samples with an AlN mole fraction of more than 0.6 the crystal quality was high because of the coherent growth on the underlying AlN. Moreover, AlGaN was subjected to Si doping. The carrier concentration increased linearly with the Si concentration up to a Si concentration of 2 x 1018 cm-3, indicating that the activation rate was approximately 1.
The structure of Si-doped AlGaN MQW targets was optimized for application to EB-pumped deep-UV light sources by the CL analysis. It was found that the optimum well and barrier layer thicknesses were 1.5 and 7 nm, respectively. We evaluated the deep-UV light emission from Si-doped AlGaN MQW targets that were pumped by a 10-kV, 5-mm-diameter EB. A deep-UV light output power of more than 15 mW with a conversion efficiency of more than 0.75% was achieved at a wavelength of 256 nm and an EB input power of 2.0 W. These results indicate the potential of using a p-type-AlGaN-free simple structure for AlGaN MQW targets for application to EB-pumped deep-UV light sources.