Abstract
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.
Highlights
Quantum cascade laser (QCL) devices employ conduction band engineering to obtain a desired emission wavelength
For strain-compensated superlattices (SLs), minor thickness variations can lead to an imbalance in the overall strain-thickness product, which may result in strain relaxation in the several-microns-thick active region
The thickness of the bilayer motif strain the superlattice, which is not seen in the simulation for pattern, the targeted strain compensated and itsin average composition can be determined from the HRXRD
Summary
Quantum cascade laser (QCL) devices employ conduction band engineering to obtain a desired emission wavelength They contain active regions consisting of 30–40 repetitions of a complex motif composed of quantum wells and barriers of various compositions and thicknesses in the range of 1–5 nm each [1]. A desirable feature of QCLs, being intersubband transition devices, is the tunability of the emission wavelength through the design of the thickness and composition of each layer within a chosen material system These structures are sensitive to small deviations from the designed thicknesses and compositions, which can alter the emission wavelength through changes in the electron wavefunctions in the conduction band [2]. These simulations can provide an accurate measurement of the periodicity of the SL and the composition of the motif averaged over its volume
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
