We proposed and investigated a hydrogen cleaning for decreasing pits and threading dislocations generated at interfaces of GaN on AlInN in Si-doped graded AlInN/GaN DBRs. We found that the hydrogen cleaning was very useful to suppress the threading dislocation generations, resulting in two orders of magnitude less than the case without the hydrogen cleaning. A high-quality conductive Si-doped AlInN/GaN DBR was obtained with the hydrogen cleaning, showing the maximum reflectivity of 99.8 %, a low pit density less than 106 cm-2, and a reasonably low vertical resistance of 15 Ω.

We developed an in-situ cavity length control of GaN-based vertical-cavity surface-emitting lasers (VCSELs) with an in-situ reflectivity spectra measurement. Firstly, a temperature dependence of a center wavelength of a 40-pair AlInN/GaN DBR was investigated, resulting in a 23 nm redshift from room temperature to GaN growth temperature of 1100℃. Secondly, a periodic oscillation of a reflectivity intensity during the GaN cavity growth on the DBR was clearly observed, providing precise cavity length information. Thirdly, based on both the results, we performed the in-situ GaN cavity length control, showing an accuracy within a 0.5% error. We finally demonstrated the in-situ cavity length control of an actual GaN-based VCSEL structure containing n-layers, a GaInN active region, and p-layers by selecting different resonance wavelengths along with the corresponding growth temperatures for the layers.

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