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We have studied the In x Ga 1−x As/In y Al 1−y As (001) interface using first-principles ab-initio pseudopotential calculations, focusing on the effects of alloy composition and strain state on the electronic properties. In particular we estimate a valence band offset (VBO) of 0.11 eV (InGaAs higher), including spin-orbit and self-energy corrections, for a strain-compensated configuration with homogenous composition x = y = 0.75 on a lattice-matched substrate. Unintentional composition fluctuations which are typically limited to a few percent and different short-range order effects give rise only to small variations on the VBO, of the order of 0.1 eV or less, whereas intentional substantial changes in the alloys composition allow to achieve a high tunability of band offsets.We predict a VBO varying in a range of about 1.1 eV for interfaces between the pure arsenides in different strain states as extreme cases of composition variation at In x Ga 1−x As/In y Al 1−y As heterostructures. GaAs, AlAs, and InAs form the family of common-anion III-V conventional semiconductors covering the widest possible range of energy gaps, apart from nitrides.1 They are therefore particularly suitable to be combined into alloys to form In x Ga 1−x As/In y Al 1−y As heterojunctions whose electronic properties can be easily tailored according to the technological needs, acting on composition to control and intentionally modify the valence and conduction band offsets (VBO and CBO), namely for band-offset engineering. 2,3,4,5The use of alloys in heterojunctions has also some drawbacks. Beside controlled variations in the average composition, unintentional composition inhomogeneities could be present in epitaxially grown alloys and heterostructures, as detected by tunneling microscope techniques. 6,7,8 Their origin can be ascribed to several mechanisms: inhomogeneous incorporation of the alloy components during growth, atomic diffusion at the surface during growth induced by strain inhomogeneities arising from stress relaxation and/or interface roughening, and also post-growth atomic interdiffusion with or without thermal annealing.Although in high-quality alloy-based nanostructures and devices such inhomogeneities are minimized, their residual occurrence can affect the electronic and optical properties. 6,9,10,11,12 Another source of variations of the electronic properties in alloy-based heterojunctions is the occurrence of spontaneous ordering in the constituting alloys. In the last years considerable theoretical and experimental effort have been devoted in investigating the effect on the band alignments and related properties. 13,14,15,16 It is important for device design not only to predict the value of band offsets at heterojunctions with given composition, but also to estimate the effects of both composition fluctuations and ordering. We address this problem here, focusing on the In x Ga 1−x As/In y Al 1−y As heterojunction and studying by accurate ab-initio simulations: (i) the band offsets at a given nominal composition x...
We have studied the In x Ga 1−x As/In y Al 1−y As (001) interface using first-principles ab-initio pseudopotential calculations, focusing on the effects of alloy composition and strain state on the electronic properties. In particular we estimate a valence band offset (VBO) of 0.11 eV (InGaAs higher), including spin-orbit and self-energy corrections, for a strain-compensated configuration with homogenous composition x = y = 0.75 on a lattice-matched substrate. Unintentional composition fluctuations which are typically limited to a few percent and different short-range order effects give rise only to small variations on the VBO, of the order of 0.1 eV or less, whereas intentional substantial changes in the alloys composition allow to achieve a high tunability of band offsets.We predict a VBO varying in a range of about 1.1 eV for interfaces between the pure arsenides in different strain states as extreme cases of composition variation at In x Ga 1−x As/In y Al 1−y As heterostructures. GaAs, AlAs, and InAs form the family of common-anion III-V conventional semiconductors covering the widest possible range of energy gaps, apart from nitrides.1 They are therefore particularly suitable to be combined into alloys to form In x Ga 1−x As/In y Al 1−y As heterojunctions whose electronic properties can be easily tailored according to the technological needs, acting on composition to control and intentionally modify the valence and conduction band offsets (VBO and CBO), namely for band-offset engineering. 2,3,4,5The use of alloys in heterojunctions has also some drawbacks. Beside controlled variations in the average composition, unintentional composition inhomogeneities could be present in epitaxially grown alloys and heterostructures, as detected by tunneling microscope techniques. 6,7,8 Their origin can be ascribed to several mechanisms: inhomogeneous incorporation of the alloy components during growth, atomic diffusion at the surface during growth induced by strain inhomogeneities arising from stress relaxation and/or interface roughening, and also post-growth atomic interdiffusion with or without thermal annealing.Although in high-quality alloy-based nanostructures and devices such inhomogeneities are minimized, their residual occurrence can affect the electronic and optical properties. 6,9,10,11,12 Another source of variations of the electronic properties in alloy-based heterojunctions is the occurrence of spontaneous ordering in the constituting alloys. In the last years considerable theoretical and experimental effort have been devoted in investigating the effect on the band alignments and related properties. 13,14,15,16 It is important for device design not only to predict the value of band offsets at heterojunctions with given composition, but also to estimate the effects of both composition fluctuations and ordering. We address this problem here, focusing on the In x Ga 1−x As/In y Al 1−y As heterojunction and studying by accurate ab-initio simulations: (i) the band offsets at a given nominal composition x...
In scanning frequency comb microscopy, a mode-locked ultrafast laser is focused on the tunneling junction of a scanning tunneling microscope to generate a microwave frequency comb (MFC) with hundreds of measurable harmonics that is superimposed on the dc tunneling current when the sample is metallic. With semiconductor samples, each laser pulse creates a surface charge that may have a radius of less than 1 nm, and this charge is rapidly dispersed by intense electrostatic repulsion. Time or frequency-domain measurements of the resulting pulse train with semiconductors, or hyperspectral measurements of the MFC with metals, may be used to determine the properties near the surface of a sample with atomic resolution.
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