Semiconductor nanowires based on non-nitride III-V compounds can be synthesized under certain growth conditions to favor the appearance of wurtzite crystal phase. Despite the reports in literature of ab initio band structures for these wurtzite compounds, we still lack effective multiband models and parameter sets that can be simply used to investigate physical properties of such systems, for instance, under quantum confinement effects. In order to address this deficiency, in this study we calculate the ab initio band structure of bulk InAs and InP in wurtzite phase and develop an 8$\times$8 k.p Hamiltonian to describe the energy bands around $Γ$ point. We show that our k.p model is robust and can be fitted to describe the important features of the ab initio band structure. The correct description of the spin splitting effects that arise due to the lack of inversion symmetry in wurtzite crystals, is obtained with the $k$-dependent spin-orbit term in the Hamiltonian, often neglected in the literature. All the energy bands display a Rashba-like spin texture for the in-plane spin expectation value. We also provide the density of states and the carrier density as functions of the Fermi energy. Alternatively, we show an analytical description of the conduction band, valid close to $Γ$ point. The same fitting procedure is applied to the 6$\times$6 valence band Hamiltonian. However, we find that the most reliable approach is the 8$\times$8 k.p Hamiltonian for both compounds. The k.p Hamiltonians and parameter sets that we develop in this paper provide a reliable theoretical framework that can be easily applied to investigate electronic, transport, optical, and spin properties of InAs- and InP-based nanostructures.
We study band alignment in wurtzite-zincblende polytype InAs heterostructured nanowires using temperature dependent resonance Raman measurements. Nanowires having two different wurtzite fractions are investigated. Using visible excitation wavelengths in resonance Raman measurements, we probe the electronic band alignment of these semiconductor nanowires near a high symmetry point of the Brillouin zone (E$_{1}$ gap). The strain in the crystal structure, as revealed from the shift of the phonon mode, explains the observed band alignment at the wurtzite-zincblende interface. Our experimental resu…
We use polarized photocurrent spectroscopy in a nanowire device to investigate the band structure of hexagonal Wurtzite InAs. Signatures of optical transitions between four valence bands and two conduction bands are observed which are consistent with the symmetries expected from group theory. The ground state transition energy identified from photocurrent spectra is seen to be consistent with photoluminescence emitted from a cluster of nanowires from the same growth substrate. From the energies of the observed bands we determine the spin orbit and crystal field energies in Wurtzite InAs. This …
Using ab initio methods based on the density functional theory, we investigate the segregation and formation energies for various dopants (Si, Be, Zn, Sn), commonly used to obtain p- or ntype conductivity in GaAs and InAs nanowires. The distribution of Au and O atoms, which may be unintentionally incorporated during the wire growth, is also studied. The calculations performed for nanowires of zinc blende and wurtzite structure show that the distribution of most of the impurities depends on the crystal structure of the wires. For example, it is shown that the same growth conditions can lead to …
We employ first-principles techniques tailored to properly describe semiconductors (modified Becke-Johnson potential added to the exchange-correlation functional), to obtain the electronic band structures of both the zinc-blende and wurtzite phases of GaAs, GaSb, InAs, and InSb. We extract the spin-orbit fields for the relevant valence and conduction bands at zone center, by fitting the spin-splittings resulting from the lack of space inversion symmetry of these bulk crystal structures, to known functional forms---third-order polynomials. We also determine the orientations of the spin-orbit ve…
Most III-V semiconductors, which acquire the zinc-blende phase as bulk materials, adopt the metastable wurtzite phase when grown in the form of nanowires. These are new semiconductors with new optical properties, in particular, a different electronic band gap when compared with that grown in the zinc-blende phase. The electronic gap of wurtzite InAs at the Gamma-point of the Brillouin zone (E0 gap) has been recently measured, E0 = 0.46 eV at low temperature. The electronic gap at the A point of the Brillouin zone (equivalent to the L point in the zinc-blende structure, E1) has also been obtain…
We report a detailed ab initio study of two superlattice heterostructures, one component of which is a unit cell of CuPt ordered InSb_(0.5)As_(0.5). This alloy part of the heterostructures is a topological semimetal. The other component of each system is a semiconductor, zincblende-InSb, and wurtzite-InAs. Both heterostructures are semiconductors. Our theoretical analysis predicts that the variation in the thickness of the InSb layer in InSb/InSb_(0.5)As_(0.5) heterostructure renders altered band gaps with different characteristics (i.e. direct or indirect). The study holds promise for fabrica…
The pressure dependent phonon modes of predominant wurtzite InAs nanowires has been investigated in a diamond anvil cell under hydrostatic pressure up to 58 GPa. The TO and LO at Gamma point and other optical phonon frequencies increase linearly while the LO TO splitting decreases with pressure. The recorded Raman modes have been used to determine the mode Gruneisen parameters and also the value of Borns transverse effective charge. The calculated Borns transverse effective charge exhibits a linear reduction with increasing pressure implying an increase in covalency of nanowires under compress…
We report on growth of Te-doped self-catalyzed InAs nanowires by molecular beam epitaxy on silicon (111) substrates. Changes in the wire morphology, i.e. a decrease in length and an increase in diameter have been observed with rising doping level. Crystal structure analysis based on transmission electron microscopy as well as X-ray diffraction reveals an enhancement of the zinc blende/(wurtzite+zinc blende) segment ratio if Te is provided during the growth process. Furthermore, electrical two-point measurements show that increased Te-doping causes a gain in conductivity. Two comparable growth …
While non-nitride III-V semiconductors typically have a zincblende structure, they may also form wurtzite crystals under pressure or when grown as nanowhiskers. This makes electronic structure calculation difficult since the band structures of wurtzite III-V semiconductors are poorly characterized. We have calculated the electronic band structure for nine III-V semiconductors in the wurtzite phase using transferable empirical pseudopotentials including spin-orbit coupling. We find that all the materials have direct gaps. Our results differ significantly from earlier {\it ab initio} calculation…
The asymmetric peak at 212 - 218 cm-1 occurring in InAs micro-nano wires is investigated using spatially resolved Raman spectroscopy (SRRS) of uniform, bent and long tapered MNWs grown on a Si (001) substrate. It is attributed to superposition of E2h phonon (wurtzite : WZ) and TO phonon (zinc blende : ZB) of InAs. Polarized and wavelength dependent SRRS establishes the presence of WZ and ZB phases in these MNWs. However, formation of WZ phase for larger diameter InAs MNWs is not commensurate with existing growth mapping studies, which needs to be understood further. Study of several of these M…
We present a comprehensive study of the optical properties of InAs/InP self-assembled quantum dots (QDs) using an empirical pseudopotential method and configuration interaction treatment of the many-particle effects. The results are compared to those of InAs/GaAs QDs. The main results are: (i) The alignment of emission lines of neutral exciton, charged exciton and biexciton in InAs/InP QDs is quite different from that in InAs/GaAs QDs. (ii) The hidden correlation in InAs/InP QDs is 0.7 - 0.9 meV, smaller than that in InAs/GaAs QDs. (iii) The radiative lifetimes of neutral exciton, charged exci…
Optical properties of semiconductors can exhibit strong polarization dependence due to crystalline anisotropy. A number of recent experiments have shown that the photoluminescence intensity in free standing nanowires is polarization dependent. One contribution to this effect is the anisotropy of the dielectric function due to the fact that most nanowires crystalize in the wurtzite form. While little is known experimentally about the band structures wurtzite phase III-V semiconductors, we have previously predicted the bulk band structure of nine III-V semiconductors in wurtzite phase.Here, we p…
We report electrical characterization of quantum dots formed by introducing pairs of thin wurtzite (WZ) segments in zinc blende (ZB) InAs nanowires. Regular Coulomb oscillations are observed over a wide gate voltage span, indicating that WZ segments create significant barriers for electron transport. We find a direct correlation of transport properties with quantum dot length and corresponding growth time of the enclosed ZB segment. The correlation is made possible by using a method to extract lengths of nanowire crystal phase segments directly from scanning electron microscopy images, and wit…
Optical vibration modes of InP nanowires in the wurtzite phase were investigated by Raman scattering spectroscopy. The wires were grown along the [0001] axis by the vapor-liquid-solid method. The A1(TO), E2h and E1(TO) phonon modes of the wurtzite symmetry were identified by using light linearly polarized along different directions in backscattering configuration. Additionally, forbidden longitudinal optical modes have also been observed. Furthermore, by applying an extended 11-parameter rigid-ion model the complete dispersion relations of InP in the wurtzite phase have been calculated, showin…
By using a C3v symmetric (111) surface as a growth substrate, we are able to achieve high structural symmetry in self-assembled quantum dots, which are suitable for use as quantum-entangled photon emitters. Here we report on the wavelength controllability of InAs dots on InP(111)A, which we realized by tuning the ternary alloy composition of In(Al,Ga)As barriers that were lattice-matched to InP. We changed the peak emission wavelength systematically from 1.3 to 1.7 micrometer by barrier band gap tuning. The observed spectral shift agreed with the result of numerical simulations that assumed a …
A virtual substrate for high quality InAs epitaxial layer has been attained via metalorganic vapor-phase epitaxy growth of Sb-assisted InxGa1-xAs metamorphic buffers, following a convex compositional continuous gradient of the In content from x = 53 % to 100 %. The use of trimethylantimony (or its decomposition products) as a surfactant has been found to crucially enable the control over the defect formation during the relaxation process. Moreover, an investigation of the wafer offcut-dependence of the defect formation and surface morphology has enabled the achievement of a reliably uniform gr…
The optical properties of single InAsP/InP quantum dots are investigated by spectrally-resolved and time-resolved photoluminescence measurements as a function of excitation power. In the short-wavelength region (below 1.45 $μ$m), the spectra display sharp distinct peaks resulting from the discrete electron-hole states in the dots, while in the long-wavelength range (above 1.45 $μ$m), these sharp peaks lie on a broad spectral background. In both regions, cascade emission observed by time-resolved photoluminescence confirms that the quantum dots possess discrete exciton and multi-exciton states.…
We report findings from several ab-initio, self-consistent calculations of electronic and transport properties of wurtzite aluminum nitride. Our calculations utilized a local density approximation (LDA) potential and the linear combination of Gaussian orbitals (LCGO). Unlike some other density functional theory (DFT) calculations, we employed the Bagayoko, Zhao, and Williams' method, enhanced by Ekuma and Franklin (BZW-EF). The BZW-EF method verifiably leads to the minima of the occupied energies; these minima, the low laying unoccupied energies, and related wave functions provide the most var…
We have performed a detailed study of the lattice distortions of InP wurtzite nanowires containing an axial screw dislocation. Eshelby predicted that this kind of system should show a crystal rotation due to the dislocation induced torque. We have measured the twisting rate and the dislocation Burgers vector on individual wires, revealing that nanowires with a 10-nm radius have a twist up to 100% larger than estimated from elasticity theory. The strain induced by the deformation has a Mexican-hat-like geometry, which may create a tube-like potential well for carriers.
Metastable wurtzite crystal phases of semiconductors comprise enormous potential for high-performance electro-optical devices, owed to their extended tunable direct band gap range. However, synthesizing these materials in good quality and beyond nanowire size constraints has remained elusive. In this work, the epitaxy of wurtzite InP microdisks and related geometries on insulator for optical applications is explored. This is achieved by an elaborate combination of selective area growth of fins and a zipper-induced epitaxial lateral overgrowth, which enables co-integration of diversely shaped c…
The electronic band structure of complex nanostructured semiconductors has a considerable effect on the final electronic and optical properties of the material and, ultimately, on the functionality of the devices incorporating them. Valence electron energy-loss spectroscopy (VEELS) in the transmission electron microscope (TEM) provides the possibility of measuring this property of semiconductors with high spatial resolution. However, it still represents a challenge for narrow-bandgap semiconductors, since an electron beam with low energy spread is required. Here we demonstrate that by means of…
InAs-based two-dimensional electron systems grown on lattice mismatched InP substrates offer a robust platform for the pursuit of topologically protected quantum computing. We investigated strained composite quantum wells of In$_{0.75}$Ga$_{0.25}$As/InAs/In$_{0.75}$Ga$_{0.25}$As with In$_{0.75}$Al$_{0.25}$As barriers. By optimizing the widths of the In$_{0.75}$Ga$_{0.25}$As layers, the In$_{0.75}$Al$_{0.25}$As barrier, and the InAs quantum well we demonstrate mobility in excess of $1 \times 10^{6}\,$cm$^{2}/$Vs. Mobility vs. density data indicates that scattering is dominated by a residual thr…
Nanowire (NW)-based opto-electronic devices require certain engineering in the NW geometry to realize polarized-dependent light sources and photodetectors. We present a growth procedure to produce InAs/InP quantum dot-nanowires (QD-NWs) with an elongated top-view cross-section relying on the vapor-liquid-solid method using molecular beam epitaxy. By interrupting the rotation of the sample during the radial growth sequence of the InP shell, hexagonal asymmetric (HA) NWs with long/short cross-section axes were obtained instead of the usual symmetrical shape. Polarization-resolved photoluminescen…
We report on the systematic investigation of the optical properties of a selectively grown quantum dot gain material assisted by block-copolymer lithography for potential applications in active optical devices operating in the wavelength range around 1.55 um and above. We investigated a new type of diblock copolymer PS-b-PDMS (polystyrene-block-polydimethylsiloxane) for the fabrication of silicon oxycarbide hard mask for selective area epitaxy of InAs/InP quantum dots. An array of InAs/InP quantum dots was selectively grown via droplet epitaxy. Our detailed investigation of the quantum dot car…
The combination of core/shell geometry and band gap engineering in nanowire heterostructures can be employed to realize systems with novel transport and optical properties. Here, we report on the growth of InAs/InP/GaAsSb core-dual-shell nanowires by catalyst-free chemical beam epitaxy on Si(111) substrates. Detailed morphological, structural, and compositional analyses of the nanowires as a function of growth parameters were carried out by scanning and transmission electron microscopy and by energy-dispersive X-ray spectroscopy. Furthermore, by combining the scanning transmission electron mic…
The quasiparticle band structures of four polytypes 3C, 6H, 4H, and 2H of GaP, GaAs, GaSb, InP, InAs, and InSb are computed with high accuracy including spin-orbit interaction applying a recently developed approximate calculation scheme, the LDA-1/2 method. The results are used to derive band offsets $ΔE_c$ and $ΔE_v$ for the conduction and valence bands between two polytypes. The alignment of the band structures is based on the branch-point energy $E_{\rm BP}$ for each polytype. The aligned electronic structures are used to explain properties of heterocrystalline but homomaterial junctions. T…
Semiconductor Rashba nanowires are quasi-one dimensional systems that have large spin-orbit (SO) coupling arising from a broken inversion symmetry due to an external electric field. There exist parametrized multiband models that can describe accurately this effect. However, simplified single band models are highly desirable to study geometries of recent experimental interest, since they may allow to incorporate the effects of the low dimensionality and the nanowire electrostatic environment at a reduced computational cost. Commonly used conduction band approximations, valid for bulk materials,…
Stable partial dislocation complexes in GaN as charge carrier lifetime modifiers for terahertz device applications by molecular dynamics and first-principle simulations
V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine（乌克兰国家科学院V.拉什卡廖夫半导体物理研究所）；Educational Scientific Institute of High Technologies, Taras Shevchenko National University of Kyiv（基辅塔拉斯舍甫琴科国立大学高等技术教育科学研究所）；National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”（乌克兰国立伊戈尔·西科尔斯基基辅理工学院）；University of Rome “Tor Vergata”（罗马托维尔加塔大学）
Crystal-phase low-dimensional structures offer great potential for the implementation of photonic devices of interest for quantum information processing. In this context, unveiling the fundamental parameters of the crystal phase structure is of much relevance for several applications. Here, we report on the anisotropy of the g-factor tensor and diamagnetic coefficient in wurtzite/zincblende (WZ/ZB) crystal-phase quantum dots (QDs) realized in single InP nanowires. The WZ and ZB alternating axial sections in the NWs are identified by high-angle annular dark-field scanning transmission electron …
