![]() ![]() Thus, it is plausible that 50 ML-InAs films are coherently strained to the GaSb substrate. 1(c), no significant change in the d 110 value is observed below 50 ML (17.5 nm). In the nearly lattice-matched system of InAs on GaSb(111)A (lattice mismatch ≈0.61%), as shown in Fig. Thus, it is likely that the lattice mismatch of InAs/Si (11.5%) is too large to be accommodated by elastic deformation of thin InAs films. This indicates that, on the Si(111) substrate, the InAs film was nucleated with its inherent lattice constant, and that pseudomorhic InAs layers are not formed. The spacing of streaks is quite close to the value of bulk InAs, and remains almost unchanged throughout the growth (<50 ML). A new set of streaks from the InAs film appeared in the RHEED patterns at the very early stage of the growth (~0.6 ML), in addition to those from the Si substrate. 1(b) is the variation in the d 110 value for the InAs growth on the Si(111) substrate. However, the strain relaxation processes between the two systems are quite different. Similarly to the case for InAs/GaAs(111)A, the InAs film is two-dimensionally grown on the In-terminated Si(111) substrate 9. On the other hand, the peak width of x-ray rocking curve is insensitive to the density of threading defects. Our x-ray diffraction (XRD) measurements revealed that the residual strain in InAs film is responsible for the peak broadening in XRD profiles. The in-plane compressive strain in InAs on GaAs (lattice mismatch of 7.2%) gradually relaxed as the growth proceeds, but the strain is not fully relaxed even in the 100nm-thick InAs film. Fully-strained pseudomorphic InAs layers continue to grow above ~50 ML on the nearly lattice matched GaSb substrates (lattice mismatch of −0.61%), while in the InAs/Si system with the largest lattice mismatch of 11.4%, mostly-relaxed InAs films are formed even at the very initial stage of the growth. While the InAs(111)A film grows in a layer-by-layer mode on all substrates irrespective of the lattice mismatch, the strain relaxation process behaves differently depending on the lattice mismatch. This paper reports the strain relaxation processes and structural properties of InAs films heteroepitaxially grown on the lattice-mismatched substrates of GaAs(111)A, Si(111), and GaSb(111)A. However, strain relaxation processes of InAs are far from being completely understood, and the crystalline quality of InAs has not been studied in detail. This technique has a great advantage, especially for the growth on Si(111), because the formation of antiphase domain boundaries in InAs films is suppressed, in contrast with the growth on the (001)-oriented substrate. The novel growth technique has been successfully applied to the layer-by-layer growth of InAs on Si(111) 9, GaSb growth on InAs/Si(111) 10, and to the improvement of the crystalline quality of InGaAs 11 and GaSb 12 on InAs/GaAs(111)A. Similar strain relaxation has been reported for GaSb/GaAs(001) heteroepitaxy, which is known for so-called interfacial misfit array growth 8. The layer-by-layer growth of the (111)A-oriented InAs film is accompanied by the formation of a misfit dislocation network at the InAs/GaAs interface 6, so that the generation of defects in the film is strongly suppressed. On the other hand, the use of the (111)A-oriented GaAs substrates forces the InAs film to grow in a layer-by-layer mode 5, 6, 7. The SK growth occurs also in the InAs/GaAs(001) system having lattice mismatch of 7.2%: InAs islands are formed at the film thickness of 1.6 ML 4. It has been reported that the islanding in the Ge/Si system is effectively suppressed by introducing As and Sb as surfactant species 1, 2, 3. Thus, significant efforts have been devoted to suppress the strain-induced islanding and strain-relieving defects. The island formation is highly undesirable, because it prevents the growth of smooth films and introduces nucleation centers for defects. A prototypical example of such a system is Ge on Si (lattice mismatch ≈4.2%), in which layer-by-layer growth is limited to 3–4 monolayer (ML). Heteroepitaxy in lattice-mismatched systems usually follows a Stranski-Krastanov (SK) growth mode: a pseudomorphic two-dimensional layer is formed below a certain critical thickness, and is followed by the formation of three-dimensional islands. The flexibility in the choice of materials for the formation of heterostructures is often limited by lattice mismatch. Heteroepitaxy of semiconductors has opened up new possibilities for band-structure engineering and novel devices, including strained-layer structures. ![]()
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