Interfacial Mixing Analysis for Strained Layer Superlattices by Atom Probe Tomography

Quantum wells and barriers with precise thicknesses and abrupt composition changes at their interfaces are critical for obtaining the desired emission wavelength from quantum cascade laser devices. High-resolution X-ray diffraction and transmission electron microscopy are commonly used to calibrate and characterize the layers’ thicknesses and compositions. A complementary technique, atom probe tomography, was employed here to obtain a direct measurement of the 3-dimensional spatially-resolved compositional profile in two InxGa1−xAs/InyAl1−yAs III-V strained-layer superlattice structures, both grown at 605 °C. Fitting the measured composition profiles to solutions to Fick’s Second Law yielded an average interdiffusion coefficient of 3.5 × 10−23 m2 s−1 at 605 °C. The extent of interdiffusion into each layer determined for these specific superlattices was 0.55 nm on average. The results suggest that quaternary active layers will form, rather than the intended ternary compounds, in structures with thicknesses and growth protocols that are typically designed for quantum cascade laser devices

III-V Superlattices on InP/Si metamorphic buffer Layers for λ≈4.8 μm quantum cascade lasers

Metalorganic chemical vapor deposition (MOCVD) growth of InP‐based quantum cascade laser (QCL) structures on a Si (001) substrate is demonstrated by employing a metamorphic InP buffer layer with InAs/InP quantum dots as dislocation filters. Calibration samples consist of a strain‐compensated 11.98 nm In0.365Al0.635As/14.8 nm In0.64Ga0.36As superlattice (SL) structure as well as 5‐stages of the λ ≈ 4.8 µm QCL active region, which are grown atop the metamorphic buffer and are used to assess the structural properties of the SL through high‐resolution X‐ray diffraction and high‐resolution transmission electron microscopy. Full QCL structures with 40‐stage active region are fabricated into edge‐emitting ridge‐waveguide structures and demonstrate low temperature electroluminescence with a FWHM of 48.6 meV