Abrupt GaP/GaAs Interfaces in Self-Catalyzed Nanowires

Abstract

We achieve the self-catalyzed growth of pure GaP nanowires and GaAs1-xPx/GaAs1-yPy nanowire heterostructures by solid-source molecular beam epitaxy. Consecutive segments of nearly pure GaAs and GaP are fabricated by commuting the group V fluxes. We test different flux switching procedures and measure the corresponding interfacial composition profiles with atomic resolution using high-angle annular dark field scanning transmission electron microscopy. Interface abruptness is drastically improved by switching off all the molecular beam fluxes for a short time at the group V commutation. Finally, we demonstrate that the morphology of the growth front can be either flat or truncated, depending on the growth conditions. The method presented here allows for the facile synthesis of high quality GaP/GaAs axial heterostructures directly on Si (111) wafers.

Growth and Characterization of GaP/GaPAs Nanowire Heterostructures with Controllable Composition

“…As mentioned in previous studies, [25,55] the reservoir effect of the catalyst droplet and residual group-V partial pressure can strongly affect heterointerface abruptness. Thus, group-V fluxes were interrupted at the heterointerfaces prior and after the ND formation by closing both shutters for 5 s to avoid the NW growth in gradient conditions during As and P needle valves adjustment and flux stabilization.…”

“…[53,54] To remove any residual contaminants, the substrate was subsequently degassed under ultra-high vacuum (UHV)-conditions in MBE load lock, buffer, and growth chambers at 200, 400, and 780 C, correspondingly. The latter value was chosen to create the openings and remain the rest of oxide layer to promote the self-catalytic VLS NW growth [55,56] performed at a substrate temperature (T growth ) of 630 C. According to our previous observations, deposition at the same conditions on the thermally de-oxidized Si (111) substrates tends to 2D growth. To form the catalyst droplets, Ga predeposition with an equivalent thickness corresponding to one ML of Ga on Si (111) [8] was performed at T growth .…”

Nanowire growth and sublimation: CdTe quantum dots in ZnTe nanowires

“…1e) is not symmetrical and features a tail towards the NW tip; the Cd content x of Cd x Zn 1−x Te at position z can be fitted with two interfaces separated by a distance d, x(z) = x i (z − d/2) − x i (z + d/2), each interface being broadened by a Gaussian of width σ and an exponential of length τ extending along the growth direction towards the tip. While a more sophisticated model of the interface could be elaborated [6,9], as suggested by the different growth rates of CdTe and ZnTe and the different values of their formation energy, it would require an accurate knowledge of the thermodynamics of Cd, Zn and Te in the gold nanoparticle and this is beyond the scope of the present study. Going on with the simple hypothethis of an exponential tail, the convoluted profile is obtained by a straightforward calculation as Figure 1d shows two examples of such a profile, the one which provides a good fit to the measured EDX profile ( Fig.…”

Measuring and Modeling the Growth Dynamics of Self-Catalyzed GaP Nanowire Arrays

“…[8][9][10] The self-catalyzed MBE growth of GaAs and GaP NWs occurs under very similar growth conditions (substrate temperature, group III and group V fluxes), so that ternary Ga(As,P) NWs can be grown within the full compositional range simply by altering the composition of the group V flux (P/As ratio). 11,12 Besides possible applications, the growth compatibility between different materials is useful for fabricating thin marker layers which may be inserted 2 at regular time intervals to monitor the growth dynamics, as done for InAs(P), 13 In(As,P) 14 or Ga(Al)As 15 NWs. In the particular case of GaP, Ga(As,P) markers have been used to characterize the kinetics of self-catalyzed 12 and Au-catalyzed 16 NWs.…”