Top and side emission from double heterostructure LED's and lasers

The characteristics of light emitted perpendicular to the junction plane (top emission) have been compared with light emitted along the junction plane (side emission) for LED's with active layer carrier concentrations ranging from 10
¹⁶
to ≳ 10
¹⁹
cm
^-3
. Although the top emission always consisted of a single spectral peak, the side emission was often double-peaked. From experimental data and theoretical considerations it was established that double-peaked spectra arise from the absorption and geometrical properties of the epitaxial layers and do not indicate that different recombination mechanisms are operating. In order to compare LED structures with laser structures, a new laser device was prepared in which spectra could be taken perpendicular to the junction plane and compared with conventional spectra obtained from the side mirrors. It was found that lasing occurred only within the longer wavelength peak, an observation which was predicted from the LED data.