Abstract
A new method for the rapid determination of layer thicknesses in semiconductor Bragg mirrors for vertical cavity surface emitting lasers (VCSEL) has been developed. The photoluminescence spectrum of a complete VCSEL structure for a wavelength of 980 nm is measured in the wafer plane at room temperature with the excitation being normal to the specimen. In the spectrum from 850 to 1000 nm three regions can be distinguished; the long wavelength part of the spectrum (λ > 950 nm) gives iriformation about the quantum well emission, the shorter part (λ > 850 nm) stems from luminescence of heavily doped p type GaAs. A pronounced structure in the range from 900 to 950 nm arises from constructive interference of light generated in the GaAs layers and leaving the specimen parallel to the surface near the angle of total reflection. From the wavelength of these peaks the layer thicknesses within the Bragg mirror can be calculated with high precision.
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