Real-time controlled epitaxy of vertical cavity surface emitting lasers (VCSELs) using a standard pyrometer

For the reproducible growth of VCSELs by MBE a growth rate control of better than ± 0.3% is necessary. To achieve this high accuracy, a real-time monitoring of the growth is essential. In our work on 0.98 μm VCSELs the standard pyrometer read-out is used as a simple and inexpensive tool to maintain the centre wavelength of the Bragg reflectors as well as the cavity resonance precisely within ± 2 nm. During growth the pyrometer signal is oscillating mainly for layers with different refractive indices. The correlation of the phase information and the period of the oscillation with ex-situ reflection measurements obtained in a series of calibration samples provides precise information on the actual growth rate. Practically this is done by fitting real-time the minima and maxima of the oscillating temperature. The obtained information can be used to adjust the growth rates by varying the source temperatures. For the regrowth of patterned laser structures this technique proved successful as well.