| Research Abstract |
In this year, we started fundamental research on crystal growth of 2-, 3- and 4-alloy nitrides including In atom such as InN/Si, InAs/Si and InGaNAs/Si before actually proceeding crystal growth of 5-alloy nitrides such as AlInGaNAs heteroepitaxial layers with higher crystalline quality on Si substrates. Because crystal growth of alloy nitrides including In atom at high temperature is difficult because of high evaporation of In metal as a source. With increasing the content of In atoms in alloy films, it was evident that the crystalline qualities of alloy films would be much degraded. Moreover, even simple InN films did not emit the band-edge PL emission at 8.5 K. Before investigating the research on crystal growth of 5-alloy nitrides, we decided to solve these problems in the first place. Therefore, we investigated the optimum growth conditions of InN films grown on Si substrates by electron cyclotron molecular beam epitaxy. We found the optimum growth conditions that InN film grown at 500 ℃ on the 10 nm-thick InN buffer layer at a growth temperature of 250 ℃ and under nitrogen plasma with twice of the usual 357 nm-plasma emission and the weakest 391 nm-plasma emission intensities is essential to obtain hexagonal-InN with the highest crystalline quality. Moreover, the substrate nitridation before growth promoted crystal growth of hexagonal-InN and dramatically improved crystalline quality. Unless the substrate nitridation, it is evident that the quality of the films would be degraded and become amorphous. Moreover, we annealed the samples at high temperatures using infrared light imaging furnace and tried the improvement of crystalline quality. As a result, the crystalline quality was much improved with increasing the anneal temperature. However, anneals higher than 550 ℃ abruptly degraded the surface morphologies of the films probably because of re-evaporation of N atoms from the surfaces of InN films.
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