Digital metamorphic alloys

Abstract

We have combined thin layers of constituent materials such that they act in a mechanically similar fashion as a random alloy. We term this combination of many thin layers of constituent materials as digital metamorphic alloy ͑DMA͒. The constituent materials can be elemental ͑e.g., Si, Ge͒ or binary ͑e.g., GaP, GaAs, InP, InAs, etc.͒ semiconductors. The DMAs are used to replace alloys in a metamorphic buffer layer. Such a DMA buffer potentially has superior thermal conductivities to, and avoids material growth-related problems associated with, conventional compositionally graded random-alloy metamorphic buffers. The method of fabricating DMAs with binary III-V materials is described. Lattice-constant grading from GaAs to InP has been carried out using both the DMA concept, and a hybrid analog-buffer/DMA approach.

A versatile digitally-graded buffer structure for metamorphic device applications

“…Moreover, a closer look at the X-TEM image reveals that a number of MDs in the In 0.82 Al 0.18 As layers preferentially nucleated near the In 0.52 Al 0.48 As/In 0.82 Al 0.18 As interfaces. These results indicate the strain relaxation pattern is dramatically modified in comparison to that in linearly-or step-graded metamorphic buffer structures, where high density TDs extend through the whole buffer regions are frequently observed [18,22]. Stacking faults were observed in the followed 400 nm In 0.82 Al 0.18 As layer with much reduced densities of MDs, TDs and glides, indicates a low residual strain at the end of DGMB region.…”

“…steps, staircases or superlattices) is also demonstrated to be helpful in lowering the TDD to some extent, despite very clear understandings on the defect suppression mechanisms are generally lacking. Moreover, an extensive exploitation of superlattices in the metamorphic buffer layer has also been exploited [18], where an InP/GaAs binary digital alloy superlattice structure was grown to grade the lattice constant from GaAs to InP. However, the effectiveness in control of strain relaxation is still subject to confirmation due to the fact that the superlattice constituents with thin thicknesses below the critical values remain strained.…”

The Effect of Buffer Types on the In0.82Ga0.18As Epitaxial Layer Grown on an InP (100) Substrate

“…Many efforts using low-pressure metalorganic chemical vapor deposition [ 10 ], molecular beam epitaxy [ 11 ], or low-pressure metalorganic vapor phase epitaxy [ 12 ] with different types of buffer structures have been made, thus the qualities of InGaAs materials have been effectively evaluated. In previous reports, various buffer structures, which were implemented to reduce the dislocation density, have been explored, including a thick uniform buffer [ 13 ], a compositionally linearly-graded or step-graded buffer [ 14 , 15 , 16 , 17 ], and a digitally graded buffer [ 18 ]. For example, an In 0.8 Ga 0.2 As buffer layer was introduced between an In 0.8 Ga 0.2 As epitaxial layer and an InP (100) substrate and showed that the heterostructure with a buffer thickness of 100 nm had the optimum properties [ 10 ].…”

InAlAs Graded Metamorphic Buffer with Digital Alloy Intermediate Layers

“…Various dislocation restriction techniques have been implemented to reduce the TD density of metamorphic buffer, such as the use of a thick uniform buffer, 1) a continuously graded 2,3) or step-graded buffer, 4,5) and a digitally graded buffer. 6) Also, overshoot 7) or reverse steps 8) in the graded buffer were proved beneficial for the full relaxation of residual strain, while Be doping 9) and dilute nitride buffers 10) were suggested to further reduce the TD density. Moreover, a built-in strain field, which arises from strained 11) or strain-compensated supperlattice (SL) 12) and strain-driven quantum dots, 13) was reported to bend the dislocation propagation and thereby decrease the TD density.…”