Crystal Phases in III--V Nanowires: From Random Toward Engineered Polytypism

Caroff, Philippe; Bolinsson, Jessica; Johansson, Jonas

doi:10.1109/jstqe.2010.2070790

Cited by 177 publications

(220 citation statements)

References 143 publications

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“…It has been observed that the III-V semiconductors can often adopt a different crystal phase than in bulk when grown as NWs. For instance, GaP, GaAs, InP and InAs were found to change their crystal phase from ZB in bulk to WZ in Au-catalyzed NWs grown by MOVPE [62,106]. In the case of Au-catalyzed MBE, the GaAs NWs usually adopt the WZ phase [64,97,107], whereas the self-catalyzed GaAs NWs are usually ZB [108][109][110].…”

Section: Extended Defectsmentioning

confidence: 99%

“…However in other reports, it has been argued that the sequence should be repeated at least for four bilayers, i.e. CACA and ABCA before they can be considered as WZ and ZB segments, respectively [106]. Nevertheless, these structural defects or the mixed ZB-WZ structures can be unwanted as they have reported to influence the optical and transport properties of the NWs [43,122].…”

Section: Extended Defectsmentioning

confidence: 99%

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Position-Controlled Uniform GaAs Nanowires on Silicon using Nanoimprint Lithography

et al. 2014

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This thesis deals with the growth of GaAs nanowires (NWs) by molecular beam epitaxy (MBE) using vapor-liquid-solid method on various substrates including GaAs(111)B, Si(111) and graphene. The growth of the NWs on GaAs substrates was carried out by Au-catalyzed technique, whereas the growths on Si and graphene substrates were carried out using self-catalyzed technique that has been the main focus of this thesis. The long-term goal of this work was to produce p-n radial junction GaAs NWs for solar cell applications.Necessary conditions were established for obtaining vertical self-catalyzed GaAs NWs on Si(111), which is reproducible from run-to-run. One of the major issues in these NWs grown by both Au-and self-catalyzed techniques is their crystal structure. The Au-catalyzed GaAs NWs usually adopt a wurtzite (WZ) crystal phase, whereas the self-catalyzed NWs a zinc blende (ZB) phase. However, in both the cases the NWs contain stacking faults, rotational twins or/and a mixed crystal phase. The ZB and WZ phases show different optical properties, and one phase might be favored over other for certain applications. Therefore the crystal phase was controlled within single NWs by tuning the V/III ratio and introducing GaAsSb inserts. The change of the crystal phases was correlated with the change in the contact angle of the Ga droplet.Since the discovery of graphene, an ultra-thin two-dimensional material, the research on graphene has become an active field in recent years due to its remarkable properties including excellent electrical and thermal conductivities, mechanical strength and flexibility, and optical transparency. By growing the semiconductor NWs on graphene, a completely new hybrid system can be envisioned where the unique properties of both NWs and graphene can be utilized. Therefore we established a method for the growth of semiconductor NWs on graphene by demonstrating epitaxial growth of vertical GaAs and InAs NWs on different graphitic substrates.Core-shell heterostructure, doping, optical properties, and position controlled growth of self-catalyzed GaAs NWs were investigated. Growth of GaAs/GaAsSb coreshell NWs where the Sb content was tuned from about 10% -70% was studied. The effect of growth temperature and the Sb flux on the morphology of GaAsSb shell was investigated. In addition, by utilizing the core-shell geometry where the shell copies the crystal phase of the core, WZ phase of GaAsSb was demonstrated. Successful p-type doping of GaAs core using Be as dopant, and n-type doping of GaAs shell using Si and Te as dopants were achieved. To investigate the optical properties, GaAs/AlGaAs coreshell NWs were grown with different V/III ratios during the core growth. The NWs grown with high V/III ratio, despite containing a higher density of twinned ZB and WZ GaAs with SFs, were found to have superior optical quality as compared to the NWs grown with low V/III ratio that contain pure ZB GaAs. The observed V/III ratio dependent optical quality was correlated to the intrinsic defects such as As vac...

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Section: Extended Defectsmentioning

confidence: 99%

Section: Extended Defectsmentioning

confidence: 99%

Position-Controlled Uniform GaAs Nanowires on Silicon using Nanoimprint Lithography

et al. 2014

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“…Occasionally, NW segments of hexagonal wurtzite (WZ) structure have been observed to penetrate the ZB structure, as well. In III-V NWs structural defects, such as rotational twins and stacking faults (SFs) along the growth direction of the NWs are often observed, the latter been responsible for the transition between ZB and WZ structures and viceversa [14,15]. High density of these defects in the nanometer scale may induce a variation of the band gap and influence electron transport along the NWs [15].…”

Section: Introductionmentioning

confidence: 99%

Nanostructure and strain properties of core-shell GaAs/AlGaAs nanowires

Kehagias¹,

Florini²,

Kioseoglou³

et al. 2015

Semicond. Sci. Technol.

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GaAs/AlGaAs core-shell nanowires were grown on Si(111) by Ga-assisted molecular beam epitaxy via the vapor-liquid-solid mechanism. High-resolution and scanning transmission electron microscopy observations showed that nanowires were predominantly zinc-blende single crystals of hexagonal shape, grown along the [111] direction. GaAs core nanowires emerged from the Si surface and subsequently, the nanowire growth front advanced by a continuous sequence of (111) rotational twins, while the AlGaAs shell lattice was perfectly aligned with the core lattice. Occasionally, single or multiple stacking faults induced wurtzite structure nanowire pockets. The AlGaAs shell occupied at least half of the nanowire's projected diameter, while the average Al content of the shell, estimated by energy dispersive X-ray analysis, was x = 0.35. Furthermore, molecular dynamics simulations of hexagonal cross-section nanowire slices, under a new parametrization of the Tersoff interatomic potential for AlAs, showed increased atom relaxation at the hexagon vertices of the shell. This, in conjunction with the compressively strained Al 0.35 Ga 0.65 As shell close to the GaAs core, can trigger a kinetic surface mechanism that could drive Al adatoms to accumulate at the relaxed sites of the shell, namely along the diagonals of the shell's hexagon. Moreover, the absence of long-range stresses in the GaAs/Al 0.35 Ga 0.65 As coreshell system may account for a highly stable heterostructure. The latter was consolidated by temperaturedependent photoluminescence spectroscopy.

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“…For example, the values of the effective g-factors are often determined as g = (E + (B) − E − (B))/µ B B, where E ± (B) is the energy of opposite spin projections under a magnetic field B. We have calculated the g factor at B = 1 T switching on and off the spin-orbit term ∆ in Hamiltonian (7). This leads to g factors with enabled (g so ) and suppressed (g 0 ) spin mixing.…”

Section: B Holesmentioning

confidence: 99%

Electrons, holes, and excitons in GaAs polytype quantum dots

Climente

Segarra

Rajadell

et al. 2016

Journal of Applied Physics

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Single and multi-band (Burt-Foreman) k ·p Hamiltonians for GaAs crystal phase quantum dots are developed and used to assess ongoing experimental activity on the role of such factors as quantum confinement, spontaneous polarization, valence band mixing and exciton Coulomb interaction. Spontaneous polarization is found to be a dominating term. Together with the control of dot thickness [Vainorious et al. Nano Lett. 15, 2652] it enables wide exciton wavelength and lifetime tunability. Several new phenomena are predicted for small diameter dots [Loitsch et al. Adv. Mater. 27, 2195], including non-heavy hole ground state, strong hole spin admixture and a type-II to type-I exciton transition, which can be used to improve the absorption strength and reduce the radiative lifetime of GaAs polytypes.

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Crystal Phases in III--V Nanowires: From Random Toward Engineered Polytypism

Cited by 177 publications

References 143 publications

Position-Controlled Uniform GaAs Nanowires on Silicon using Nanoimprint Lithography

Position-Controlled Uniform GaAs Nanowires on Silicon using Nanoimprint Lithography

Nanostructure and strain properties of core-shell GaAs/AlGaAs nanowires

Electrons, holes, and excitons in GaAs polytype quantum dots

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