Transition region width of nanowire hetero- and pn-junctions grown using vapor–liquid–solid processes

Abstract

The transition region width of nanowire heterojunctions and pn-junctions grown using vapor-liquid-solid (VLS) processes has been modeled. With two constituents or dopants I and II, the achievable width or abruptness of the junctions is attributed to the residual I atom/molecule stored in the liquid droplet at the onset of introducing II to grow the junction, and the stored I atom/molecule consumption into the subsequently grown crystal layers. The model yields satisfactory quantitative fits to a set of available Si-Ge junction data. Moreover, the model provides a satisfactory explanation to the relative junction width or abruptness differences between elemental and compound semiconductor junction cases, as well as a guideline for achieving the most desirable pn-junction widths.PACS 64.75.Jk; 61.46.Km

Strain and Stability of Ultrathin Ge Layers in Si/Ge/Si Axial Heterojunction Nanowires

“…25−28 One way to address this problem is to choose a catalyst with low Si and Ge solubility. 25 Solid catalysts, AlAu 2 29 and AgAu, 30 do indeed improve compositional abruptness in Si/Ge heterointerfaces. By growing nanowires using such catalysts, we now have the opportunity to examine the interfacial structure and quantify the local strain fields in compositionally abrupt Si/Ge interfaces.…”

Direct observation of interface and nanoscale compositional modulation in ternary III-As heterostructure nanowires

“…If we introduce an element which quickly increases the driving force, a smaller amount of the material is absorbed before it reaches its steady state composition and therefore will imply a sharp transition region. 30 This seems to be the case for the InAs/ Ga x In 1Àx As interface region where Ga is introduced. In contrast, the Ga x In 1Àx As/InAs interface is much wider because the In atoms seem to have a smaller driving force towards the solid than Ga, and Ga is expelled from the liquid by solidification into the nanowire, prior to reaching the steady state liquid composition.…”

Peculiarities of axial and radial Ge–Si heterojunction formation in nanowires: Monte Carlo simulation

“…The thickness of these regions corresponds to Si-Ge HJ width. In [31], the concentration in leading and trailing edges was fitted by decay exponential functions as n Ge (z) = n 0 -Aؒexp(-z/α) and n Ge (z) = n 0 + Bؒexp(-z/β), where n 0 = Ge concentration after stabilization, A, B = constant coefficients, z = coordinate along the NW axis, α and β = coefficients characterizing the HJ width. But in [6] it was shown that the trailing edge is approximated by error function more accurately.…”

“…Experimental Si-Ge axial HJs in VLS-grown NWs are not atomically flat [5,6]. The HJ blurriness appeared to be due to principal restrictions of the VLS growth mechanism [31]. Therefore, in recent papers Al-Au with high eutectic temperature [32] was suggested as catalyst.…”