Growths of AlInN Single Layers and Distributed Bragg Reflectors for VCSELs
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Growths of AlInN Single Layers and Distributed Bragg Reflectors for VCSELs
Y. Kozuka1, K. Ikeyama1, T. Yasuda1, T. Takeuchi1, S. Kamiyama1, M. Iwaya1, I. Akasaki1, 2 1
Faculty of Science and Technology, Meijo University
2
Akasaki Research Center, Nagoya University
ABSTRACT We investigated MOVPE growth conditions for AlInN layers with high growth rates and obtained 0.5µm/h with smooth surfaces. We found that short gas mixing time, relatively high growth temperature, and very low In/Al supply ratio were key growth parameters in order to obtain the AlInN layers with high growth rate and smooth surface simultaneously. AlInN/GaN DBRs grown under such growth conditions showed smooth surfaces and a reflectivity of over 99%. INTRODUCTION (0001)-oriented Al0.83In0.17N is lattice-matched to GaN, showing a larger bandgap and a smaller refractive index compared to those of GaN. Therefore, it is favorable to utilize the AlInN layers in various devices, such as field-effect transistors, edge emitting lasers, and vertical cavity surface emitting lasers (VCSELs) with distributed Bragg reflectors (DBRs) 1, 2. Especially the lattice matched, AlInN/GaN DBR is the most favorable candidate for high reflective mirrors in nitride-based VCSELs since the lattice-matched multiple layers inhibit material degradations due to cracks and misfit dislocations. So far, AlInN/GaN DBRs with peak reflectivity over 99% in both the UV and the visible regions have been reported3-6. On the other hand, a typical growth rate of AlInN by metal organic vapor phase epitaxy (MOVPE) is very low, less than 0.2µm/h, and the fastest one reported so far is still 0.25µm/h7. In principle the low growth rate is required to enhance species migrations on the surface because the growth temperature of AlInN is much lower than that of AlN, resulting in insufficient migrations. Due to such a low growth rate, it takes over 20 hours to fabricate a 40 pair AlInN/GaN DBR which shows over 99% reflectivity. In this study, we systematically investigated the MOVPE growth conditions for AlInN layers with high growth rates, targeting 0.5µm/h. We then grew 40pair AlInN/GaN DBRs on GaN templates with sapphire substrates and on GaN substrates using our optimized growth condition of AlInN.
EXPERIMENTAL DETAILS We conducted two different experiments to optimize the MOVPE growth conditions for AlInN with high growth rate. One is gas mixing time dependence, and the other is growth temperature and In/Al supply ratio dependences. The first experiment was originally intended to just increase growth rate of AlInN layers due to a small parasitic reaction between Trimethylaluminum (TMAl) and ammonia caused by a shorter gas mixing time in a reactor. We changed the gas mixing time from 0.017 to 0.13 seconds with various growth pressures from 75 torr to 300 torr. The sample with the longest gas mixing time, 0.13 seconds, was grown by another reactor which had a larger chamber. Thus, the sample was grown with long gas mixing time but low growth pressure, 113 torr. The sample structure on a sapp
