We have determined the structure of AlSb and GaSb (001) surfaces prepared by molecular beam epitaxy under typical Sb-rich device growth conditions. Within the range of flux and temperature where the diffraction pattern is nominally ͑1 3 3͒, we find that there are actually three distinct, stable ͑4 3 3͒ surface reconstructions. The three structures differ from any previously proposed for these growth conditions, with two of the reconstructions incorporating mixed III-V dimers within the Sb surface layer. These heterodimers appear to play an important role in island nucleation and growth. PACS numbers: 68.35.Bs, 61.16.Ch, 73.61.Ey, 81.15.Hi The surface reconstruction on a semiconducting material is the starting point for understanding the mechanisms of growth from the vapor. The steric and energetic landscape of the surface reconstruction determines the kinetic factors for adsorption, diffusion, and desorption, and provides the template for island nucleation [1]. These factors are critical to our understanding of growth and the formation of interfaces between materials, particularly for the case of III-V semiconductor quantum heterostructures, which are key components in a wide range of optical and high frequency electronic devices under development. Many of the most promising applications require extremely thin layers, so that even submonolayer variations in film thickness and interfacial roughness can dramatically affect the ultimate device performance [2,3]. To achieve the level of morphological control needed to reproducibly fabricate optimized III-V devices, a detailed understanding of the relevant surface reconstructions and the mechanisms by which epitaxy proceeds is essential.The structure of III-As and III-P (001) surfaces under typical device growth conditions (V͞III flux . 1) has been generally established [4,5]. For the much-studied case of GaAs, the extensive experimental and theoretical knowledge accumulated about the surface structure has led to significant progress in understanding the atomistic mechanisms of growth during molecular beam epitaxy (MBE) [6,7]. In contrast, the III-Sb device surfaces are poorly understood, despite their demonstrated potential for a variety of advanced electronic and optoelectronic applications [8]. Although the surface structures have been determined for atypical, extreme Sb-rich conditions-InSb and AlSb have the c͑4 3 4͒ structure common to the arsenides, and GaSb reconstructs into unusual, metallic ͑n 3 5͒ structures [9,10]-even after more than 20 years of study [11], the atomic-scale structures under more typical growth conditions have yet to be resolved. During device growth both GaSb and AlSb usually exhibit a ͑1 3 3͒-like reflection high-energy electron diffraction (RHEED) pattern, with the GaSb RHEED further delineated into distinct c͑2 3 6͒ and ͑1 3 3͒ (higher temperature/lower Sb flux) regimes [12,13]. Simple Sb-dimer row models for these reconstructions have been proposed [13,14], but scanning tunneling microscopy (STM) studies of the III-Sb(001) surfaces...
We have studied the evolution of AlSb-on-InAs͑001͒ surfaces and interfaces grown by molecular-beam epitaxy using in situ scanning tunneling microscopy. We find that forming InSb-like interfacial bonds on an InAs͑001͒-͑2ϫ4͒ surface creates surface roughness because the surface In coverage inherent to the ͑2ϫ4͒ reconstruction is insufficient to form a complete InSb͑001͒-͑1ϫ3͒-like surface layer. This morphological roughness can be eliminated by depositing additional In to compensate for the different compositions of the reconstructions. We have also grown three different 5-monolayer-thick films of AlSb on the InSb-like interface to study the effect of growth conditions on the film surface morphology. The AlSb surface can be improved by either raising the growth temperature or by growing the film using migration-enhanced epitaxy. Finally, we present electrical characterization of InAs/AlSb/GaSb resonant interband tunneling devices fabricated with different growth procedures. The possible effects of various growth procedures on interfacial quality and device properties are discussed.
We report a technique for nanofabrication in the InAs/GaSb/AlSb 6.1 Å material system that utilizes the large difference in the surface Fermi level pinning position for InAs [Efs(InAs)] compared with that for AlSb. An InAs/AlSb single quantum well is capped with a 3 nm, intentionally p-doped InAs layer. As a result of its construction and a relatively low Efs(InAs) there are no free carriers in the InAs/AlSb single quantum well making the quantum well insulating as-grown. Simply by selectively removing the thin p-doped InAs cap layer with a wet etch, the surface Fermi level becomes pinned on AlSb and shifted upward by half an electron volt. This results in a drastic change in band bending and creates a conducting electron channel in the buried InAs quantum well. We demonstrate with experiment and the support of a self-consistent band bending calculation that this scheme is highly effective for nanofabrication.
We describe a ternary antimonide superlattice photodiode with a 21 μm cutoff wavelength. The active region consists of 150 periods of 10 monolayers (MLs) of In0.07Ga0.93Sb and 19 MLs of InAs with InSb-like interfacial bonds. The device has a detectivity of 3×109 cm√Hz/W, dynamic impedance-area product of 0.18 Ω cm2, and peak external quantum efficiency of 3% at 40 K. X-ray diffraction and cross-sectional scanning tunneling microscopy show the structure to have a high degree of order with abrupt interfaces. A simulation of the absorption spectrum effectively reproduces the observed spectrum.
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