4 research outputs found
Damage-Free Smooth-Sidewall InGaAs Nanopillar Array by Metal-Assisted Chemical Etching
Producing densely
packed high aspect ratio In<sub>0.53</sub>Ga<sub>0.47</sub>As nanostructures
without surface damage is critical for
beyond Si-CMOS nanoelectronic and optoelectronic devices. However,
conventional dry etching methods are known to produce irreversible
damage to III−V compound semiconductors because of the inherent
high-energy ion-driven process. In this work, we demonstrate the realization of ordered, uniform,
array-based In<sub>0.53</sub>Ga<sub>0.47</sub>As pillars with diameters
as small as 200 nm using the damage-free metal-assisted chemical etching
(MacEtch) technology combined with the post-MacEtch digital etching
smoothing. The etching mechanism of In<i><sub>x</sub></i>Ga<sub>1−<i>x</i></sub>As is explored through the
characterization of pillar morphology and porosity as a function of
etching condition and indium composition. The etching behavior of
In<sub>0.53</sub>Ga<sub>0.47</sub>As, in contrast to higher bandgap
semiconductors (<i>e</i>.<i>g</i>., Si or GaAs),
can be interpreted by a Schottky barrier height model that dictates
the etching mechanism constantly in the mass transport limited regime
because of the low barrier height. A broader impact of this work relates
to the complete elimination of surface roughness or porosity related
defects, which can be prevalent byproducts of MacEtch, by post-MacEtch
digital etching. Side-by-side comparison of the midgap interface state
density and flat-band capacitance hysteresis of both the unprocessed
planar and MacEtched pillar In<sub>0.53</sub>Ga<sub>0.47</sub>As metal-oxide-semiconductor
capacitors further confirms that the surface of the resultant pillars
is as smooth and defect-free as before etching. MacEtch combined with
digital etching offers a simple, room-temperature, and low-cost method
for the formation of high-quality In<sub>0.53</sub>Ga<sub>0.47</sub>As nanostructures that will potentially enable large-volume production
of In<sub>0.53</sub>Ga<sub>0.47</sub>As-based devices including three-dimensional
transistors and high-efficiency infrared photodetectors
Self-Anchored Catalyst Interface Enables Ordered Via Array Formation from Submicrometer to Millimeter Scale for Polycrystalline and Single-Crystalline Silicon
Defying
text definitions of wet etching, metal-assisted chemical etching (MacEtch),
a solution-based, damage-free semiconductor etching method, is directional,
where the metal catalyst film sinks with the semiconductor etching
front, producing 3D semiconductor structures that are complementary
to the metal catalyst film pattern. The same recipe that works perfectly
to produce ordered array of nanostructures for single-crystalline
Si (c-Si) fails completely when applied to polycrystalline Si (poly-Si)
with the same doping type and level. Another long-standing challenge
for MacEtch is the difficulty of uniformly etching across feature
sizes larger than a few micrometers because of the nature of lateral
etching. The issue of interface control between the catalyst and the
semiconductor in both lateral and vertical directions over time and
over distance needs to be systematically addressed. Here, we present
a self-anchored catalyst (SAC) MacEtch method, where a nanoporous catalyst film is used to produce nanowires through the pinholes, which in turn
physically anchor the catalyst film from detouring as it descends.
The systematic vertical etch rate study as a function of porous catalyst
diameter from 200 to 900 nm shows that the SAC-MacEtch not only confines
the etching direction but also enhances the etch rate due to the increased
liquid access path, significantly delaying the onset of the mass-transport-limited
critical diameter compared to nonporous catalyst c-Si counterpart.
With this enhanced mass transport approach, vias on multistacks of
poly-Si/SiO<sub>2</sub> are also formed with excellent vertical registry
through the polystack, even though they are separated by SiO<sub>2</sub> which is readily removed by HF alone with no anisotropy. In addition,
320 μm square through-Si-via (TSV) arrays in 550 μm
thick c-Si are realized. The ability of SAC-MacEtch to etch through
poly/oxide/poly stack as well as more than half millimeter thick silicon
with excellent site specificity for a wide range of feature sizes
has significant implications for 2.5D/3D photonic and electronic device
applications
Enhanced Performance of Ge Photodiodes <i>via</i> Monolithic Antireflection Texturing and α‑Ge Self-Passivation by Inverse Metal-Assisted Chemical Etching
Surface
antireflection micro and nanostructures, normally formed
by conventional reactive ion etching, offer advantages in photovoltaic
and optoelectronic applications, including wider spectral wavelength
ranges and acceptance angles. One challenge in incorporating these
structures into devices is that optimal optical properties do not
always translate into electrical performance due to surface damage,
which significantly increases surface recombination. Here, we present
a simple approach for fabricating antireflection structures, with
self-passivated amorphous Ge (α-Ge) surfaces, on single crystalline
Ge (c-Ge) surface using the inverse metal-assisted chemical etching
technology (I-MacEtch). Vertical Schottky Ge photodiodes fabricated
with surface structures involving arrays of pyramids or periodic nano-indentations
show clear improvements not only in responsivity, due to enhanced
optical absorption, but also in dark current. The dark current reduction
is attributed to the Schottky barrier height increase and self-passivation
effect of the i-MacEtch induced α-Ge layer formed on top of
the c-Ge surface. The results demonstrated in this work show that
MacEtch can be a viable technology for advanced light trapping and
surface engineering in Ge and other semiconductor based optoelectronic
devices
Direct Electrical Probing of Periodic Modulation of Zinc-Dopant Distributions in Planar Gallium Arsenide Nanowires
Selective
lateral epitaxial (SLE) semiconductor nanowires (NWs),
with their perfect in-plane epitaxial alignment, ability to form lateral
complex p–n junctions <i>in situ</i>, and compatibility with planar processing, are a
distinctive platform for next-generation device development. However,
the incorporation and distribution of impurity dopants in these planar
NWs <i>via</i> the vapor−liquid−solid growth mechanism remain relatively unexplored. Here, we present
a detailed study of SLE planar GaAs NWs containing multiple alternating
axial segments doped with Si and Zn impurities by metalorganic chemical
vapor deposition. The dopant profile of the lateral multi-p–n
junction GaAs NWs was imaged simultaneously with nanowire topography
using scanning microwave impedance microscopy and correlated with
infrared scattering-type near-field optical microscopy. Our results
provide unambiguous evidence that Zn dopants in the periodically twinned
and topologically corrugated p-type segments are preferentially segregated
at twin plane boundaries, while Si impurity atoms are uniformly distributed
within the n-type segments of the NWs. These results are further supported
by microwave impedance modulation microscopy. The density functional
theory based modeling shows that the presence of Zn dopant atoms reduces
the formation energy of these twin planes, and the effect becomes
significantly stronger with a slight increase of Zn concentration.
This implies that the twin formation is expected to appear when a
threshold planar concentration of Zn is achieved, making the onset
and twin periodicity dependent on both Zn concentration and nanowire
diameter, in perfect agreement with our experimental observations