Influence of growth parameters on In-droplet-assisted growth of InAs nanowires on silicon
Influence of growth parameters on In-droplet-assisted growth of InAs nanowires on silicon
Ezekiel A. Anyebe 0 1
0 Federal University of Agriculture , PMB 2373, Makurdi , Nigeria
1 & Ezekiel A. Anyebe
The influence of growth parameters on the morphology and density of InAs nanowires (NWs) grown on bare Si substrates using Indium (In) droplets as catalyst is investigated. By tuning the growth temperature, V/III flux ratio, and growth rate, the diameter and yield of asgrown NWs were controllably manipulated. It is demonstrated that the In-droplet-assisted growth of InAs NWs can only be realized on bare Si within a relatively narrow growth window of 420-475 C. Below 420 C, NWs' growth is kinetically limited, while the highest yield of vertically aligned NWs was obtained at *450 C. It is shown that In-catalyzed InAs NWs nucleation can only be realized on Si at highly As-rich conditions (V/III flux ratio [50), while the axial growth rate was found to be strongly dependent on the V/III flux ratio. The nucleation and axial growth of In-catalyzed InAs NWs are promoted by a low growth rate, while a high growth rate favors the formation of unwanted parasitic islands.
InAs; Nanowires; Semiconductors; Molecular beam epitaxy
Introduction
Semiconducting nanowires (NWs) have been touted as
promising building blocks for applications in photonics and
electronic devices
(Duan et al. 2003; Tian et al. 2007;
Colinge et al. 2010; Tomioka et al. 2012; Wang et al. 2014)
due to their unique properties including superior light
absorption, enhanced photo-carrier separation, and epitaxial
growth insensitive to lattice mismatch
(Wei et al. 2009)
. In
particular, InAs NWs have garnered enormous research
interest due to its narrow direct band gap (0.35 eV), small
electron effective mass, and high electron mobility of
*30,000 cm2/Vs at 300 K
(Wallart et al. 2005; Ihn and
Song. 2007)
with potential for applications in high-speed
electronics and mid-infrared optoelectronic devices
(Dimakis et al. 2011)
. The monolithic integration of NWs with
Si has recently attracted enormous research interest to
exploit the low-cost and scalability of the well-established Si
platform as well as the fascinating electronic and
optoelectronic properties of NWs. Although, Au is commonly used
for NWs nucleation, its use is accompanied with the
introduction of unwanted impurities and deep level traps
(Allen
et al. 2008)
, which are detrimental to applications in
optoelectronic devices
(Bar-Sadan et al. 2012)
. Consequently,
there is a paradigm shift towards Au-free technologies
including catalyst-free
(Wei et al. 2009; Dimakis et al. 2011;
Hwang et al. 2015)
and droplet-assisted growth (DAG) of
NWs
(Somaschini et al. 2013; Anyebe et al. 2014; Ermez
et al. 2015)
. Whereas catalyst-free growth is Indium (In) free
and requires no catalyst for NWs nucleation, droplet-assisted
growth involves the in situ deposition of group-III element
droplets (mostly Ga or In seeds) on the substrate prior to
growth initiation to function as catalyst for the preferential
nucleation of NWs. DAG growth is not only impurity-free
and compatible with the complementary metal-oxide
semiconductor (CMOS) platform
(Glas et al. 2013)
, it also allows
for the precise control of NWs density
(Somaschini et al.
2013; Anyebe et al. 2014; Ermez et al. 2015)
, which is highly
essential for applications in functional optoelectronic
nanodevices. For instance, the electron mobility
(Ford et al.
2009a, b; Abul Khayer and Lake 2010)
and light absorption
(Krogstrup et al. 2013; Heiss et al. 2014)
, and hence
performance of transistors and solar cells, respectively, have
been shown to be strongly dependent on the NWs diameter.
It is well established that the size and density of NWs can
be controllably manipulated by tuning basic growth
precursors
(Anyebe et al. 2017; Li et al. 2017)
. Various growth
strategies have been employed for the growth parameter
studies of InAs NWs including selective area growth (SAG)
(Mandl et al. 2011; Bjoerk et al. 2012)
, catalyst-free growth
on SiOx-coated substrates
(Hertenberger et al. 2010;
Koblmu¨ ller et al. 2010; Madsen et al. 2011)
, and Au-catalyzed
growth
(Dayeh et al. 2007; Tchernycheva et al. 2007; Babu
and Yoh 2011; Zhang et al. 2016)
. An investigation of the
influence of growth parameters on In-droplet-assisted InAs
NWs grown on Si would unravel the conditions for realizing
optimal NWs with the highest density and aspect ratio as
well as enable for the predictable and reproducible
fabrication of high performance, and impurity-free
nanoelectronic devices compatible with the CMOS technology.
However, despite the significant influence of In-rich
conditions (and in effect the predeposition of In droplets) on the
NWs geometry
(Jung et al. 2014; Zhang et al. 2014)
resulting from strong differences in adatom kinetics
compared to other growth techniques, little is known about the
influence of growth parameters on the morphology an (...truncated)