In-situ structural controls during the GaN-based VCSEL growths

GaN-based VCSELs have been developed towards light sources in retinal scanning displays and so on. One of the biggest issues in VCSEL fabrication is to align three wavelengths, (1) a DBR center wavelength, (2) a cavity resonance wavelength, and (3) a gain peak wavelength. Typically, all of them are determined during the epitaxial growth. Therefore, in-situ measurements during the growth could be a key to solve the issue. In order to fabricate AlInN/GaN DBRs as designed, an InN mole fraction in AlInN must be controlled. We have used an in-situ wafer curvature measurement to monitor the InN mole fraction during the DBR growth, leading to a precise determination of the InN mole faction value within ±0.1% range. Next, we developed a control of the cavity resonance wavelength (cavity length). We used an in-situ reflectivity spectra measurement. As a result, a difference between a measured resonance wavelength and the designed wavelength was only 2 nm, corresponding to a 0.5% error. The above two in-situ measurements are powerful tools for in-situ controls of alloy compositions and thicknesses, drastically improving the reproducibility of the VCSEL performances.