Structural and optical properties of high quality zinc-blende/wurtzite GaAs nanowire heterostructures

Abstract

The structural and optical properties of three different kinds of GaAs nanowires with 100% zinc-blende structure and with an average of 30% and 70% wurtzite are presented. A variety of shorter and longer segments of zinc-blende or wurtzite crystal phases are observed by transmission electron microscopy in the nanowires. Sharp photoluminescence lines are observed with emission energies tuned from 1.515 eV down to 1.43 eV when the percentage of wurtzite is increased. The downward shift of the emission peaks can be understood by carrier confinement at the interfaces, in quantum wells and in random short period superlattices existent in these nanowires, assuming a staggered band offset between wurtzite and zinc-blende GaAs. The latter is confirmed also by time-resolved measurements. The extremely local nature of these optical transitions is evidenced also by cathodoluminescence measurements. Raman spectroscopy on single wires shows different strain conditions, depending on the wurtzite content which affects also the band alignments. Finally, the occurrence of the two crystallographic phases is discussed in thermodynamic terms.

Raman spectroscopy of wurtzite and zinc-blende GaAs nanowires: Polarization dependence, selection rules, and strain effects

“…The second type of nanowires corresponds to GaAs with 30% wurtzite phase. 51 The results are presented separately in the next two sections.…”

“…50 The samples presented in this paper have been obtained at arsenic pressures between 3 ϫ 10 −6 and 3 ϫ 10 −7 mbar, which represent growth rates, respectively, between 3 and 0.3 m / h. We have shown in the past that a reduction in the growth rate results in an increase in the fraction of wurtzite in the nanowire. 51 The structure of the nanowires was studied by highresolution transmission electron microscopy ͑HRTEM͒ in a Philips/FEI CM 300. Samples were prepared as follows for the transmission electron microscopy ͑TEM͒ measurements.…”

“…51 Representative HRTEM measurements of these nanowires are presented in Fig. 6, where a bright field TEM image is shown.…”

“…The gradient was achieved by gradually changing the arsenic pressure during growth. 51 A representative bright field TEM micrograph of the first 1.5 m of such nanowire is presented in Fig. 10.…”

Population dynamics and dephasing of excitons and electron-hole pairs in polytype wurtzite/zinc-blende InP nanowires

“…Another interesting type of axial heterostructures uses alternating few nm short segments of the same chemical material but different crystal structure as e.g. in wurtzite/zincblende InP [18][19][20] and GaAs 21 NWs revealing a type-II band alignment.…”