Semiconductor Nanomembranes Research Articles

P-GaAs/n-Ga2O3 heterojunction diode with breakdown voltage of ∼800 V

As an attractive next generation ultrawide bandgap material, Ga2O3 has been demonstrated to be capable of high voltage operation. However, the lack of shallow p-type dopant in Ga2O3 leads to difficulties in developing Ga2O3 based bipolar devices. The semiconductor grafting technology, by bonding a single crystalline p-type semiconductor nanomembrane (NM) to n-Ga2O3 to from abrupt heterojunction, offers a way to expand the application of Ga2O3 in bipolar areas. In this Letter, we report a p-GaAs/(001)-Ga2O3 heterojunction diode fabricated using semiconductor grafting technology. The single crystalline GaAs NM was prepared and transferred onto a Ga2O3 substrate, showing good integrity. Diodes of a mesa diameter of 25 μm were fabricated, showing a high breakdown voltage of ∼800 V, a power figure of merit of 126.5 MW/cm2, and a calculated 1D peak electric field of 1.60 MV/cm. The turn on voltage of the diode was determined to be around 1.91 V with an on–off ratio to be 6 × 106 at −4/4 V and the specific on resistance to be 5.06 mΩ cm2. The ideality factor was extracted to be approximately 1.34, indicating reasonable interface quality. The interfacial defects and the self-passivation effects of Ga2O3 are discussed, and the theoretical band diagram was analyzed for the p-GaAs/n-Ga2O3 heterojunction. By managing the peak electric field with suitable edge termination techniques, higher breakdown voltage can be expected. In addition, by taking advantage of the InGaAsP alloy system, a wide variety of GaAs-Ga2O3 based high voltage HBT can be further developed.

Self-Rolled-Up Ultrathin Single-Crystalline Silicon Nanomembranes for On-Chip Tubular Polarization Photodetectors.

Freestanding single-crystalline nanomembranes and their assembly have broad application potential in photodetectors for integrated chips. However, the release and self-assembly process of single-crystalline semiconductor nanomembranes still remains a great challenge in on-chip processing and functional integration, and photodetectors based on nanomembrane always suffer from limited absorption of nanoscale thickness. Here, a non-destructive releasing and rolling process is employed to prepare tubular photodetectors based on freestanding single-crystalline Si nanomembranes. Spontaneous release and self-assembly are achieved by residual strain introduced by lattice mismatch at the epitaxial interface of Si and Ge, and the intrinsic stress and strain distributions in self-rolled-up Si nanomembranes are analyzed experimentally and computationally. The advantages of light trapping and wide-angle optical coupling are realized by tubular geometry. This Si microtube device achieves reliable Ohmic contact and exhibits a photoresponsivity of over 330mA W-1 , a response time of 370 µs, and a light incident detection angle range of over 120°. Furthermore, the microtubular structure shows a distinct polarization angle-dependent light absorption, with a dichroic ratio of 1.24 achieved at 940nm. The proposed Si-based microtubes provide new possibilities for the construction of multifunctional chips for integrated circuit ecosystems in the More than Moore era.

Synthesis and Characteristics of Transferrable Single‐Crystalline AlN Nanomembranes

AbstractSingle‐crystalline inorganic semiconductor nanomembranes (NMs) have attracted great attention over the last decade, which poses great advantages to complex device integration. Applications in heterogeneous electronics and flexible electronics have been demonstrated with various semiconductor nanomembranes. Single‐crystalline aluminum nitride (AlN), as an ultrawide‐bandgap semiconductor with great potential in applications such as high‐power electronics has not been demonstrated in its NM forms. This very first report demonstrates the creation, transfer‐printing, and characteristics of the high‐quality single‐crystalline AlN NMs. This work successfully transfers the AlN NMs onto various foreign substrates. The crystalline quality of the NMs has been characterized by a broad range of techniques before and after the transfer‐printing and no degradation in crystal quality has been observed. Interestingly, a partial relaxation of the tensile stress has been observed when comparing the original as‐grown AlN epi and the transferred AlN NMs. In addition, the transferred AlN NMs exhibits the presence of piezoelectricity at the nanoscale, as confirmed by piezoelectric force microscopy. This work also comments on the advantages and the challenges of the approach. Potentially, the novel approach opens a viable path for the development of the AlN‐based heterogeneous integration and future novel electronics and optoelectronics.

Recent advances in single crystal narrow band-gap semiconductor nanomembranes and their flexible optoelectronic device applications: Ge, GeSn, InGaAs, and 2D materials

Flexible optoelectronics have attracted much attention in recent years for their potential applications in healthcare and wearable devices.

Correction: Recent advances in single crystal narrow band-gap semiconductor nanomembranes and their flexible optoelectronic device applications: Ge, GeSn, InGaAs, and 2D materials

Correction for ‘Recent advances in single crystal narrow band-gap semiconductor nanomembranes and their flexible optoelectronic device applications: Ge, GeSn, InGaAs, and 2D materials’ by Shu An et al., J. Mater. Chem. C, 2023, 11, 2430–2448, https://doi.org/10.1039/d2tc05041b.

Wide bandgap semiconductor nanomembranes as a long-term biointerface for flexible, implanted neuromodulator

Electrical neuron stimulation holds promise for treating chronic neurological disorders, including spinal cord injury, epilepsy, and Parkinson's disease. The implementation of ultrathin, flexible electrodes that can offer noninvasive attachment to soft neural tissues is a breakthrough for timely, continuous, programable, and spatial stimulations. With strict flexibility requirements in neural implanted stimulations, the use of conventional thick and bulky packages is no longer applicable, posing major technical issues such as short device lifetime and long-term stability. We introduce herein a concept of long-lived flexible neural electrodes using silicon carbide (SiC) nanomembranes as a faradic interface and thermal oxide thin films as an electrical barrier layer. The SiC nanomembranes were developed using a chemical vapor deposition (CVD) process at the wafer level, and thermal oxide was grown using a high-quality wet oxidation technique. The proposed material developments are highly scalable and compatible with MEMS technologies, facilitating the mass production of long-lived implanted bioelectrodes. Our experimental results showed excellent stability of the SiC/silicon dioxide (SiO2) bioelectronic system that can potentially last for several decades with well-maintained electronic properties in biofluid environments. We demonstrated the capability of the proposed material system for peripheral nerve stimulation in an animal model, showing muscle contraction responses comparable to those of a standard non-implanted nerve stimulation device. The design concept, scalable fabrication approach, and multimodal functionalities of SiC/SiO2 flexible electronics offer an exciting possibility for fundamental neuroscience studies, as well as for neural stimulation-based therapies.

Low contact-resistivity and high-uniformity Ni/Au ohmic contacts on Si nanomembranes grafted to Si substrates via low-temperature rapid thermal annealing

Grafted lattice-mismatched semiconductor heterostructures have the potential to simultaneously achieve low on-resistance and high breakdown performance. These novel semiconductor devices are typically fabricated by grafting single-crystal semiconductor nanomembrane (NM) layers onto a foreign substrate. The optimal temperature for grafting often prevents the use of high temperatures to achieve optimal ohmic contacts. Herein, we present a method to form low temperature Ni/Au ohmic contacts for the anode electrode to a p + Si NM that is grafted to a Si substrate. Ohmic contact resistivity (ρc) and its device-to-device uniformity are characterized against different annealing temperatures and are also compared against contact resistivity of p + SOI structure. Low resistivity ohmic contacts (ρc = 5.92 × 10-6 Ω cm2) and high uniformity were achieved on grafted NM structure. Demonstration of low ρc for NM-transferred layers via a low-temperature metallization scheme achieves an important step towards further developing high performance lattice-mismatched heterostructure-based devices.

Lift-off of GaN-based LED membranes from Si substrate through electrochemical etching

Semiconductor nano-membranes provide a new way to develop optical devices with better performance. Herein, we report a fabrication method of GaN-based LED membranes with a complete device structure including contact metals from Si substrate by using electrochemical etching of highly conductive AlN/Si interface, which is often naturally formed in GaN-on-Si materials. Photoluminescence and Raman scattering spectra show that the internal stress after the lift-off was effectively lightened with 1.45 GPa. Electrical measurement results show that both the leakage current and series resistance were largely decreased, and strong and uniform electroluminescence further proved the well-preserved whole structure.

Investigation of effective stress imposed on flexible single-crystalline semiconductor nanomembrane electronics under bending conditions

Flexible electronics have gained attention with their unique ability to withstand stress deformations. However, stress makes significant impact on the electrical performance of the flexible devices. It is commonly believed that the stress imposed on the flexible device is only related to the bending curvature. Our study shows that the actual stress imposed on the device is not only related to the bending radius but also closely related to the device dimension. In this study, the effective stress of the device layer as well as the stress distributions are investigated, with the fundamental flexible diodes as representative examples. Flexible single-crystalline silicon [Formula: see text]-[Formula: see text]-[Formula: see text] diodes are fabricated and measured under different bending curvature conditions. Then the dominant affecting factor of the flexible diodes with bending stress is extracted. 3D finite-element method (3D-FEM) stress distribution modeling is also employed to analyze the stress distributions and demonstrate that the effective stress of the device layer is closely and proportionally related to the device dimension. Furthermore, theoretical calculations are conducted to verify the FEM results and quantitatively show the relation between the stress and the dimension of the flexible devices. The analysis provides a guideline in the design of flexible electronics under bending conditions.

Strain-Induced Lateral Heterostructures in Patterned Semiconductor Nanomembranes for Micro- and Optoelectronics

Strain-Induced Lateral Heterostructures in Patterned Semiconductor Nanomembranes for Micro- and Optoelectronics

Theoretical Analysis of Strain‐Optoelectronic Properties in Externally Deformed Ge/GeSi Quantum Well Nanomembranes via Neutral Plane Modulation

For indirect‐bandgap germanium (Ge), strain‐engineering provides a controllable means to transform Ge into direct‐bandgap material with strongly enhanced light emission efficiency. Flexible electronics offer a powerful platform for introducing external strain into semiconductor nanomembranes (NMs) through deformation with flexible substrates. So far, the Ge/GexSi1−x alloy quantum well (QW) NMs have not been sufficiently investigated to comprehend how the external deformation tunes the wavelength and light‐emitting properties. Herein, a theoretical model based on the elasticity theory and k·p method is established to analyze the strain‐optoelectronic properties of the externally deformed Ge/GexSi1−x QW NMs via neutral plane (NP) modulation in both embedded and sticked form. Calculated results reveal that the elastic strain is linearly distributed, inducing tilt of the band edge similar to the electric field. Considering the fracture limit of the material, the NP layout determines the critical bending curvature that the NM can achieve. Large tunable range of wavelength Δλ of 1615 nm and enhanced transverse electric (TE)/transverse magnetic (TM) peak gain of 949/3778 cm−1 are predicted for r = 1000 nm (the distance between NP and QW) under the bending limit. Further calculations conclude that larger r allow for smaller bending curvature to achieve wider range of wavelength and more enhanced optical gain.

Single-Cell Response to the Rigidity of Semiconductor Nanomembranes on Compliant Substrates.

Single-crystalline semiconductor nanomembranes (NMs) bonded to compliant substrates are increasingly used for biomedical research and in health care. Nevertheless, there is a limited understanding of how individual cells sense the unique mechanical properties of these substrates and adjust their behavior in response to them. In this work, we performed proliferation assays, cytoskeleton analysis, and focal adhesion (FA) studies for NIH-3T3 fibroblasts on 220 and 20 nm single-crystalline Si on polydimethylsiloxane (PDMS) substrates with an elastic modulus of ∼31 kPa. We also characterized cell response on bulk Si as a reference. Our in vitro studies show that varying the thickness of the NM between 20 and 220 nm affects the proliferation rate of the cells, their cytoskeleton, fiber organization, spread area, and degree of FA. For example, cultured cells on 220 nm Si/PMDS exhibit the same response as on bulk Si, that is, they are well-spread with a pentagonal (or dendritic) shape and show a good organization of stress fibers and FAs. On the other hand, the cells on 20 nm Si/PDMS are spherical, with fiber organization and FAs in undetectable levels. We explained the results of our in vitro studies through a shear-lag mechanical model. The calculated FA-substrate contact stiffnesses for fibroblasts on bulk Si and 220 nm Si/PDMS closely match, and they are significantly higher than the stiffness of the integrin clutches and the plaque. Conversely, focal contacts with 20 nm Si/PDMS have comparable lateral compliance to adhesion-mediating intracellular organisms. In conclusion, our work relies on recent advances in NM technology to fill a critical knowledge gap about how individual cells sense and react to the mechanical properties of NM-based substrates. Our findings will have a major impact on the design of flexible electronic materials for applications in biomedical science and health care.

Metal oxide semiconductor nanomembrane-based soft unnoticeable multifunctional electronics for wearable human-machine interfaces.

Wearable human-machine interfaces (HMIs) are an important class of devices that enable human and machine interaction and teaming. Recent advances in electronics, materials, and mechanical designs have offered avenues toward wearable HMI devices. However, existing wearable HMI devices are uncomfortable to use and restrict the human body's motion, show slow response times, or are challenging to realize with multiple functions. Here, we report sol-gel-on-polymer-processed indium zinc oxide semiconductor nanomembrane-based ultrathin stretchable electronics with advantages of multifunctionality, simple manufacturing, imperceptible wearing, and robust interfacing. Multifunctional wearable HMI devices range from resistive random-access memory for data storage to field-effect transistors for interfacing and switching circuits, to various sensors for health and body motion sensing, and to microheaters for temperature delivery. The HMI devices can be not only seamlessly worn by humans but also implemented as prosthetic skin for robotics, which offer intelligent feedback, resulting in a closed-loop HMI system.

Nanomeshed Si nanomembranes

One of the main challenges in stretchable electronics is to achieve high-performance stretchable semiconductors. Here, we introduce an innovative concept of nanomeshed semiconductor nanomembrane which can be regarded almost as intrinsically stretchable to conventional microelectronic layouts. By making a silicon film into homogeneous nanomeshes with spring-like nano traces, we demonstrated a high electron mobility of 50 cm2/V·s, and moderate stretchability with a one-time strain of 25% and cyclic strain of 14% after stretching for 1000 cycles, further improvable with optimized nanomesh designs. A simple analytic model covering both fractional material and trace sidewall surfaces well predicted the transport properties of the normally on silicon nanomesh transistors, enabling future design and optimizations. Besides potential applications in stretchable electronics, this semiconductor nanomesh concept provides a new platform for materials engineering and is expected to yield a new family of stretchable inorganic materials having tunable electronic and optoelectronic properties with customized nanostructures.

Ultrawide strain-tuning of light emission from InGaAs nanomembranes

Single-crystal semiconductor nanomembranes provide unique opportunities for basic studies and device applications of strain engineering by virtue of mechanical properties analogous to those of flexible polymeric materials. Here, we investigate the radiative properties of nanomembranes based on InGaAs (one of the standard active materials for infrared diode lasers) under external mechanical stress. Photoluminescence measurements show that, by varying the applied stress, the InGaAs bandgap energy can be red-shifted by over 250 nm, leading to efficient strain-tunable light emission across the same spectral range. These mechanically stressed nanomembranes could therefore form the basis for actively tunable semiconductor lasers featuring ultrawide tunability of the output wavelength.

Carrier-mediated optomechanical forces in semiconductor nanomembranes with coupled quantum wells

In the majority of optomechanical experiments, the interaction between light and mechanical motion is mediated by radiation pressure, which arises from momentum transfer of reflecting photons. This is an inherently weak interaction, and optically generated carriers in semiconductors have been predicted to be the mediator of different and potentially much stronger forces. Here we demonstrate optomechanical forces induced by electron-hole pairs in coupled quantum wells embedded into a free-free nanomembrane. We identify contributions from the deformation-potential and piezoelectric coupling and observe optically driven motion about three orders of magnitude larger than expected from radiation pressure. The amplitude and phase of the driven oscillations are controlled by an applied electric field, which tunes the carrier lifetime to match the mechanical period. Our work opens perspectives for not only enhancing the optomechanical interaction in a range of experiments, but also for interfacing mechanical objects with complex macroscopic quantum objects, such as excitonic condensates.

Semiconductor Nanomembrane Materials for High-Performance Soft Electronic Devices.

The development of methods to synthesize and physically manipulate extremely thin, single-crystalline inorganic semiconductor materials, so-called nanomembranes, has led to an almost explosive growth of research worldwide into uniquely enabled opportunities for their use in new "soft" and other unconventional form factors for high-performance electronics. The unique properties that nanomembranes afford, such as their flexibility and lightweight characteristics, allow them to be integrated into electronic and optoelectronic devices that, in turn, adopt these unique attributes. For example, nanomembrane devices are able to make conformal contact to curvilinear surfaces and manipulate strain to induce the self-assembly of various 3D nano/micro device architectures. Further, thin semiconductor materials (e.g., Si-nanomembranes, transition metal dichalcogenides, and phosphorene) are subject to the impacts of quantum and other size-dependent effects that in turn enable the manipulation of their bandgaps and the properties of electronic and optoelectronic devices fabricated from them. In this Perspective, nanomembrane synthesis techniques and exemplary applications of their use are examined. We specifically describe nanomembrane chemistry exploiting high-performance materials, along with precise/high-throughput techniques for their manipulation that exemplify their growing capacities to shape outcomes in technology. Prominent challenges in the chemistry of these materials are presented along with future directions that might guide the development of next generation nanomembrane-based devices.

(Invited) Toward High Frequency and High Power Flexible Electronics

Radio frequency (RF) devices have been widely used for commercial wireless communication and military electronics. With the rapid development of wireless communication and radar technology, RF transistors for higher frequency and higher power applications are in demand. Meanwhile, the emerging market of wearable devices and internet of things (IoT) require electronic systems including RF parts to be in flexible or bendable form. Conventional semiconductors for flexible electronics like oxide semiconductors, and amorphous/poly Si and organic semiconductors cannot meet the requirement of wireless communication at the GHz range due to their low electron mobility (0.1 ~ 10 m2/V∙s). To fabricate high frequency flexible transistors, single crystal semiconductor nanomembranes have attracted great attention due to their high electron mobility (>100 m2/V∙s). Our group has reported GHz thin film Si MOSFET with an fT of 1.9 GHz and a maximum oscillation frequency (fmax ) of 3.1 GHz by transferring Si nanomembrane from a silicon-on-insulator wafer to a flexible plastic substrate. To further improve the performance of flexible RF Si MOSFETs, different device structures have been investigated. A strained Si nanomembrane channel has been demonstrated to enhance electron mobility. Flexible Si MOSFET with strained channel has shown an fT of 5.1 GHz and fmax of 15.1 GHz. Gate trench Si MOSFETs using nanoimprint technology has been successfully fabricated. By reducing the gate trench to 100 nm, the transistor shows an fT of 5 GHz and fmax of 38 GHz. Besides Si, we have also fabricated GaAs-based thin film heterojunction bipolar transistors (HBTs) for flexible RF electronics due to the high electron mobility of GaAs. We have successfully demonstrated thin film GaAs HBTs on biodegradable cellulose nanofibril (CNF) substrates by the transfer printing technique. HBTs on CNF substrate show an fT of 37.5 GHz and fmax of 6.9 GHz, facilitating use in GHz range applications. The reported flexible RF transistors based on Si and GaAs thin film have shown the capability of working at the GHz range. However, due to a small bandgap and low breakdown field, they are not suitable for high power applications at high frequency. GaN has been rapidly developed for high-frequency and high-power applications due to its large bandgap, high breakdown field, high electron mobility, and high electron saturation velocity of two dimensional electron gas (2DEG). Several flexible AlGaN/GaN HEMTs have been fabricated by the transfer printing AlGaN/GaN thin film to flexible substrate. Our group have reported flexible RF AlGaN/GaN HEMT on PET substrate with an fT of 60 GHz and fmax of 115 GHz. A layer of 3.5 µm intrinsic single crystalline GaN thin film was used as the heat spreading layer for the HEMT due to large thermal conductivity of single crystalline GaN. The HEMT can successfully work under 0.5 W, which indicates the potential use of AlGaN/GaN HEMTs in high-frequency and high-power flexible electronics. We further combined flexible RF AlGaN/GaN HEMTs with environmental friendly green flexible substrates to fabricate flexible green RF electronics for high-power applications. We successfully fabricated a 500 µm × 500 µm AlGaN/GaN HEMT on biodegradable CNF substrate using the transfer printing technique. The HEMT can achieve an fT and fmax of 40 GHz and 79 GHz, respectively, and work under 0.3 W on CNF substrate. To further exploit the application of flexible green RF AlGaN/GaN HEMTs, we fabricated a flexible RF power amplifier based on the HEMT. The RF power amplifier was fabricated by combining the flexible HEMT and impedance matching network consisting of a spiral inductor and metal-insulator-metal (MIM) capacitor on a temporary Si substrate with a PMMA sacrificial layer. After dissolving the PMMA sacrificial layer, the entire RF power amplifier (~10 µm thick) was transfer printed on a CNF substrate. The RF power amplifier on CNF substrate shows a small signal gain of ~6 dB from 5 GHz to 6 GHz. The RF power performance measurement shows it can deliver an RF power of ~10 mW with peak power added efficiency (PAE) of 4% at 5.5 GHz. The recent progress of flexible RF AlGaN/GaN HEMTs and RF power amplifiers will significantly advance the development of flexible electronics for high-frequency and high-power applications.

Rolled-up SnO2 nanomembranes: A new platform for efficient gas sensors

Metal oxide semiconductor (MOS) nanomembranes hold a great potential for electronic devices. In this work, tubular SnO2 nanomembranes were fabricated by the rolled-up technology and investigated as the sensing element for chemiresistive gas sensors. Due to the high accessibility to both surfaces of nanomembranes and the large amount of adsorbed oxygen species, the sensor based on SnO2 nanomembranes displayed high and fast response for selective detection of acetone, as well as good repeatability, stability and low detection limit of ppb-level. The very good sensing performances derived from the tubular nanomembrane structure suggests a new platform that can be used for chemical gas sensors. This work will drive the integration of tubular MOS nanomembranes into a real microsensor based on the lab-in-tube concept.

High-performance flexible waveguide-integrated photodetectors

Mechanically flexible photonic devices are essential building blocks for novel bio-integrated optoelectronic systems, wearable sensors, and flexible consumer electronics. Here we describe the design and experimental demonstration of high-performance flexible semiconductor nanomembrane photodetectors integrated with single-mode chalcogenide glass waveguides. Through a combination of a waveguide-integrated architecture to enhance light–matter interactions and mechanical engineering of multilayer configurations to suppress strains, the detector devices exhibit record optical and mechanical performance. The devices feature a noise equivalent power as low as 0.02 pW·Hz1/2, a linear dynamic range exceeding 70 dB, and a 3-dB bandwidth of 1.4 GHz, all measured at 1530 nm wavelength. The devices withstand 1000 bending cycles at a submillimeter radius without degradation in their optoelectronic responses. These metrics represent significant improvements over state-of-the-art flexible photodetectors.