Evaluating Epitaxy Quality in Compound Semiconductors Using AC-STEM/EDS
Assessing epitaxial growth uniformity for AlGaN based UV laser diodes and GaAs based vertical cavity surface emitting lasers.
Fine control over structural and compositional uniformity during epitaxial growth of compound semiconductors is critical for developing reliable and efficient devices. III-V materials offer a platform for a wide range of devices that can be tailored to specific electro-optical needs by alloying to the appropriate composition. However, many different types of defects and nonuniformities can occur during growth that severely hinder final device performance especially at interfaces and compositionally graded layers. Thus, it is important to evaluate epitaxy quality before device fabrication steps.
In this application note, we will discuss the importance of assessing epitaxial growth uniformity for AlGaN based UV laser diodes and GaAs based vertical cavity surface emitting lasers. By employing aberration-corrected scanning transmission electron microscopy (AC-STEM) we show that we can clearly observe differences in epitaxial layer roughness and composition with atomic level precision.
STEM imaging and EDS analysis in a thick AlGaN epitaxial layer grown on a GaN substrate.
The figure above shows a thick AlGaN layer grown on a GaN substrate via MOCVD for laser use. Although the gas flow inputs were unchanged through growth, we observe streaks of bright contrast in the HAADF (Z-contrast) image through the AlGaN layer. The HAADF Z-contrast image intensity scales with the total atomic weight in each column (average atomic number x density). Thus, local changes in intensity are tied to compositional variation. Download the application note to learn more.
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