Abstract:
Dislocation generation due to lattice mismatch in heterostructures is an issue in the development of new devices requiring exceptional crystalline quality. The particular importance of these compounds arises from the growing interest in THz technology, where a wide variety of devices such as THz sensors, emitters, transistors, and photomixers have been developed. Major research efforts are still being made to achieve improved characteristics. Some researchers have proposed the use of linear graded layers that absorb dislocations upon reaching a thickness zc after which there are no more dislocations. Graded layer engineering has shown that using and optimizing nonlinear metamorphic layers can absorb and further extend the defect-free zone above zc.
In this work, the growth by molecular beam epitaxy of graded In1-xGaxAs/GaAs structures to achieve high crystal quality and promote band bending near the surface, which can enhance THz radiation emission, is studied. In1-xGaxAs hyperbolic tangent concentration profiles developed by adjusting the growth temperature as a function of the alloy's In content is proposed. Due to the nature of the growth, indium segregation is present at the surface. High-temperature annealing is performed to remove this segregated indium.
Laser pump excitation was used to study the THz emission of GaAs, InAs, and graded samples. The band bending in the tangent-hyperbolic InxGa1-xAs graded layers causes a depth dependence of the effective mass and the built-in electric fields, which consequently modify the THz emission.
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