Abstract:A semiconductor thin film with high
carrier mobility was fabricated
on a flexible film. During the solid-phase crystallization process
of the densified amorphous Ge layer, the interfacial reaction with
the GeO
x
underlayer is controlled by the
GeO
x
thickness (0–300 nm) and the
growth temperature (375–450 °C). The appropriate amount
of oxygen diffusion from GeO
x
to Ge produces
large Ge grains (up to 13 μm in diameter) with high crystal
quality. The use of a high heat-resistant polyimide film allows postann… Show more
“…Considering that PA did not change significantly (Fig. 3 d), the decrease in p due to PA was responsible for the increase in μ due to the decease of the impurity scattering 15 , 36 . Figure 3 Electrical properties of the Ge layers as a function of T d before and after PA. ( a ) p and ( b ) μ , which were averaged over four measurements for each sample.…”
Section: Resultsmentioning
confidence: 93%
“…We discovered that temperature control during the deposition of amorphous precursors can significantly modulate the grain size in the solid-phase crystallization (SPC) process of Ge films 35 . Ge thin films with large grain sizes have a reduced p of 1 × 10 17 cm −3 , which is the lowest level for poly-Ge thin films 36 , and also enabled n-type conduction control by impurity doping 37 , 38 . The carrier mobility reached the highest values (690 and 370 cm 2 V –1 s –1 for holes and electrons, respectively) for poly-Ge films, even on a flexible plastic substrate 36 , 39 .…”
Section: Introductionmentioning
confidence: 99%
“…Ge thin films with large grain sizes have a reduced p of 1 × 10 17 cm −3 , which is the lowest level for poly-Ge thin films 36 , and also enabled n-type conduction control by impurity doping 37 , 38 . The carrier mobility reached the highest values (690 and 370 cm 2 V –1 s –1 for holes and electrons, respectively) for poly-Ge films, even on a flexible plastic substrate 36 , 39 . In addition, Sn doping in Ge passivated the acceptor defects and reduced its p to the order of 10 16 cm –3 39 , 40 .…”
Polycrystalline Ge thin films have recently attracted renewed attention as a material for various electronic and optical devices. However, the difficulty in the Fermi level control of polycrystalline Ge films owing to their high density of defect-induced acceptors has limited their application in the aforementioned devices. Here, we experimentally estimated the origin of acceptor defects by significantly modulating the crystallinity and electrical properties of polycrystalline Ge layers and investigating their correlation. Our proposed linear regression analysis method, which is based on deriving the acceptor levels and their densities from the temperature dependence of the hole concentration, revealed the presence of two different acceptor levels. A systematic analysis of the effects of grain size and post annealing on the hole concentration suggests that deep acceptor levels (53–103 meV) could be attributed to dangling bonds located at grain boundaries, whereas shallow acceptor levels (< 15 meV) could be attributed to vacancies in grains. Thus, this study proposed a machine learning-based simulation method that can be widely applied in the analysis of physical properties, and can provide insights into the understanding and control of acceptor defects in polycrystalline Ge thin films.
“…Considering that PA did not change significantly (Fig. 3 d), the decrease in p due to PA was responsible for the increase in μ due to the decease of the impurity scattering 15 , 36 . Figure 3 Electrical properties of the Ge layers as a function of T d before and after PA. ( a ) p and ( b ) μ , which were averaged over four measurements for each sample.…”
Section: Resultsmentioning
confidence: 93%
“…We discovered that temperature control during the deposition of amorphous precursors can significantly modulate the grain size in the solid-phase crystallization (SPC) process of Ge films 35 . Ge thin films with large grain sizes have a reduced p of 1 × 10 17 cm −3 , which is the lowest level for poly-Ge thin films 36 , and also enabled n-type conduction control by impurity doping 37 , 38 . The carrier mobility reached the highest values (690 and 370 cm 2 V –1 s –1 for holes and electrons, respectively) for poly-Ge films, even on a flexible plastic substrate 36 , 39 .…”
Section: Introductionmentioning
confidence: 99%
“…Ge thin films with large grain sizes have a reduced p of 1 × 10 17 cm −3 , which is the lowest level for poly-Ge thin films 36 , and also enabled n-type conduction control by impurity doping 37 , 38 . The carrier mobility reached the highest values (690 and 370 cm 2 V –1 s –1 for holes and electrons, respectively) for poly-Ge films, even on a flexible plastic substrate 36 , 39 . In addition, Sn doping in Ge passivated the acceptor defects and reduced its p to the order of 10 16 cm –3 39 , 40 .…”
Polycrystalline Ge thin films have recently attracted renewed attention as a material for various electronic and optical devices. However, the difficulty in the Fermi level control of polycrystalline Ge films owing to their high density of defect-induced acceptors has limited their application in the aforementioned devices. Here, we experimentally estimated the origin of acceptor defects by significantly modulating the crystallinity and electrical properties of polycrystalline Ge layers and investigating their correlation. Our proposed linear regression analysis method, which is based on deriving the acceptor levels and their densities from the temperature dependence of the hole concentration, revealed the presence of two different acceptor levels. A systematic analysis of the effects of grain size and post annealing on the hole concentration suggests that deep acceptor levels (53–103 meV) could be attributed to dangling bonds located at grain boundaries, whereas shallow acceptor levels (< 15 meV) could be attributed to vacancies in grains. Thus, this study proposed a machine learning-based simulation method that can be widely applied in the analysis of physical properties, and can provide insights into the understanding and control of acceptor defects in polycrystalline Ge thin films.
“…Ga and P doping reduced the carrier mobility of the Ge 1−x Si x and Ge 1−y Sn y layers in all compositions, which is due to the high concentration doping promoting impurity scattering of carriers. 46 Figure 2c shows that, for both n-and p-type, the electrical conductivity σ reached 400 S cm −1 , reflecting high carrier concentration and mobility. demonstrates that, for both n-and p-type, the absolute value of Seebeck coefficient S depended on x and y.…”
Group
IV materials are promising candidates for highly reliable
and human-friendly thin-film thermoelectric generators, used for micro-energy
harvesting. In this study, we investigated the synthesis and thermoelectric
applications of a Ge-based ternary alloy thin film, Ge1–x–y
Si
x
Sn
y
. The solid-phase crystallization
of the highly densified amorphous precursors allowed the formation
of high-quality polycrystalline Ge1–x–y
Si
x
Sn
y
layers on an insulating substrate. The small
compositions of Si and Sn in Ge1–x–y
Si
x
Sn
y
(x < 0.15 and y <
0.05) lowered the thermal conductivity (3.1 W m–1 K–1) owing to the alloy scattering of phonons,
while maintaining a high carrier mobility (approximately 200 cm2 V–1 s–1). The solid-phase
diffusion of Ga and P allowed us to control the carrier concentration
to the order of 1019 cm–3 for holes and
1018 cm–3 for electrons. For both p-
and n-type Ge1–x–y
Si
x
Sn
y
, the power factor peaked at x = 0.06 and y = 0.02, reaching 1160 μW m–1 K–2 for p-type and 2040 μW m–1 K–2 for n-type. The resulting dimensionless figure
of merits (0.12 for p-type and 0.20 for n-type) are higher than those
of most environmentally friendly thermoelectric thin films. These
results indicate that group IV alloys are promising candidates for
high-performance, reliable thin-film thermoelectric generators.
“…Low-temperature crystallization of thin amorphous semiconductor films is in high demand for fabrication of "flexible electronics" devices. Recently, germanium thin films with a record-high hole mobility were obtained on flexible plastic using post-growth annealing at relatively low temperature of 500 o C [1]. However, for using inexpensive plastic flexible substrates, it is necessary to reduce their heating to temperatures below 120 o C. Pulsed laser annealing appears to be the only suitable technique for crystallization of amorphous semiconductor films without overheating substrates [2,3].…”
We report on single-short laser crystallization of Ge/Si multilayer stacks consisting of alternating amorphous nanosized films of silicon and germanium using near- and mid-infrared femtosecond and picosecond laser pulses. The phase composition of the irradiated stacks was investigated by the Raman scattering technique. Several non-ablative regimes of crystallization were found, from partial crystallization of germanium without intermixing the Ge/Si layers to complete intermixing of the layers with formation of GexSi1-x solid alloys. The roles of one- and two-photon absorption, thermal and non-thermal (ultrafast) melting processes, and laser-induced stresses in selective pico- and femtosecond laser annealing are analysed based on theoretical estimations and comparison with experimental data. It is concluded that, due to a mismatch of the thermal expansion coefficients between the adjacent stack layers, efficient explosive solid-phase crystallization of the Ge layers is possible at relatively low temperatures, well below the melting point. The possibility of ultrafast non-thermal phase transition in germanium in the studied regimes is also discussed.
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