High-quality Ohmic Contacts Research Articles

Transparent (Ni,Au)/ZnO:Al-Based Ohmic Contacts to p-Type GaN as an Insight into the Role of Ni and Au in Standard p-Type GaN Contacts.

In this work, Ni/ZnO:Al and Au/ZnO:Al structures are proposed as efficient ohmic contacts to p-GaN. Through a careful selection of deposition parameters and annealing environment, we not only achieve the formation of high-quality ohmic contacts but also gain insights into the interfacial reactions, enhancing the understanding of conventional Ni/Au contact formation on p-GaN. In particular, the notion that the presence of NiO at the interface is enough for an ohmic contact to form is challenged by showing that in fact it has to be NiO formed at the interface from metallic Ni and additional oxygen. An Au-based ohmic contact is also presented, and its formation mechanism is explained, contrary to popular knowledge that Au does not form an ohmic contact with p-GaN. The obtained contacts are low resistivity, with contact resistances of 4.77 × 10-3 Ω·cm2 and 3.34 × 10-3 Ω·cm2 for Au-based and Ni-based ones, respectively. What is also important is that we show these oxide-based contacts with metallic interlayers give lower series resistances in simplified diode structures than a standard Ni/Au-based contact, making them promising for optoelectronic devices.

Growth and performance of n++ GaN cap layer for HEMTs applications

Apart from providing high-quality ohmic contacts to III-N devices, n++ GaN cap layers can eliminate surface-related current collapse effects in high-electron-mobility transistors (HEMTs). Various metal-organic chemical vapor deposition conditions and n-type doping are tested in GaN growth on sapphire by using triethylgallium as a Ga precursor, replacing more conventional trimethylgallium. Consequently, despite relatively low temperature of the growth at 800 °C to facilitate InAlN barrier capping, optimized growth conditions and SiH4 flow provided free electron concentration of 7.2 × 1019 cm−3 and mobility of 103 cm2/Vs. Moreover, electron concentration in the range of 1020 cm−3 is demonstrated by using flow modulation epitaxy. On the other hand, as calibration growths indicated, excessive SiH4 flow alone can lead to high density of edge dislocations and surface undulations without enhancing free electron concentration. 6 nm (Si: 4.2 × 1019 cm−3) and 8 nm thick (Si: 7.2 × 1019 cm−3) n++ GaN cap is implemented in normally-off n++ GaN/InAlN/AlN/GaN HEMTs grown on Si, with a collapse-free performance for the latter case. By calculating energy band and free carrier concentration profiles of the heterostructures it is shown, that free electrons of a sufficiently thick and doped n++ GaN cap can shield the channel from the unstable surface potential.

Investigation of AlGaN UV emitting tunnel junction LED devices by off-axis electron holography

Here we use off-axis electron holography combined with advanced transmission electron microscopy techniques to understand the opto-electronic properties of AlGaN tunnel junction (TJ)-light-emitting diode (LED) devices for ultraviolet emission. Four identical AlGaN LED devices emitting at 290 nm have been grown by metal–organic chemical vapour deposition. Then Ge doped n-type regions with and without InGaN or GaN interlayers (IL) have been grown by molecular beam epitaxy onto the top Mg doped p-type layer to form a TJ and hence a high quality ohmic metal contact. Off-axis electron holography has then been used to demonstrate a reduction in the width of the TJ from 9.5 to 4.1 nm when an InGaN IL is used. As such we demonstrate that off-axis electron holography can be used to reproducibly measure nm-scale changes in electrostatic potential in highly defected and challenging materials such as AlGaN and that systematic studies of devices can be performed. The LED devices are then characterized using standard opto-electric techniques and the improvements in the performance of the LEDs are correlated with the electron holography results.

Low resistance ohmic contact of multi-metallic Mo/Al/Au stack with ultra-wide bandgap Ga2O3 thin film with post-annealing and its in-depth interface studies for next-generation high-power devices

Ultra-wide band gap materials like β-Ga2O3 is considered as a potential candidate for power devices owing to their high breakdown voltage in contrast to the conventional semiconductors. The performance and the figure-of-merit for power devices critically depend on resistance offered by ohmic contact of metal with ultra-wide gap materials. However, high-quality ohmic contacts with Ga2O3 presents a significant challenge due to Fermi-level pinning and formation of Schottky barriers for the majority of metal contacts. Here, we investigated the electrical characteristics and interfacial reactions of Au/Al/Mo metal stack with β-Ga2O3 thin film at various annealing temperatures to demonstrate the ohmic contact formation mechanism. In-depth surface-sensitive XPS and UPS are employed to study the interface of metallic stack/Ga2O3 thin film. Our results indicate that post-annealing at high temperatures led to the intermixing of the metallic stack and results in the formation of binary intermetallic compounds of Al and Au. The intermetallic compound diffuses into the Ga2O3 layer and resulting in the creation of an oxygen-deficiency near the interface and helping to achieve contact resistance of 7.15 × 10−6 Ω cm2. This study establishes a robust foundation for the expanded utilization of Ga2O3 in power electronics and optoelectronics devices, emphasizing the vital role of interface engineering.

Importance of layer distribution in Ni and Au based ohmic contacts to p-type GaN

In this work, we report on the importance of layer distribution after annealing to form a high quality ohmic contact on p-type GaN, using nickel (Ni) and gold (Au) thin layer association. Both the standard GaN/Ni/Au and its reverse, GaN/Au/Ni on p-type GaN were studied. The Au/Ni stack exhibits the most promising results in this study. While the standard GaN/Ni/Au contact exhibits a quasi-linear current-voltage (I-V) characteristic, its counterpart, GaN/Au/Ni, shows pure ohmic behavior, with a specific contact resistance (ρc) as low as 2.0 × 10−4 Ω.cm2 after rapid thermal annealing (RTA) at 500 °C for 5 min under air ambient, equivalent to the best literature results. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses demonstrate the incomplete inversion of layers during annealing leading to a GaN/Ni/Au/NiO stack that explains why GaN/Ni/Au contact shows inferior electrical performance. On the other hand, for the GaN/Au/Ni contact annealed in the same conditions, the excellent results can be attributed to both (i) the presence of the gold layer at the interface with GaN, allowing the formation of gallide solid solution (Ga-Au) and (ii) the formation of NiO directly contacted with the p-GaN. Those two mechanisms are known to lead to the formation of good ohmic contact on p-type GaN. These results demonstrate that although GaN/Ni/Au is a standard contact for p-GaN layers, the opposite stack (GaN/Au/Ni) gives the best Ohmic behavior. This is important for achieving the best performance of GaN power diodes or transistors including a p-gate structure.

EFFECT OF RAPID THERMAL ANNEALING TEMPERATURE ON THE ELECTROPHYSICAL PROPERTIES OF THE OHMIC CONTACT OF Ti/Al /Ni METALLIZATION TO THE GaN/AlGaN HETEROSTRUCTURE

Effect of rapid thermal annealing temperature on the electrophysical properties of the ohmic contact of Ti/Al/Ni metallization with layer thicknesses of 20/120/40 nm to the GaN/AlGaN heterostructure with a two-dimensional electron gas on a sapphire substrate has been discovered by transmission line measurement and secondary ion mass spectroscopy methods. Rapid thermal annealing of the samples was carried out in a nitrogen atmosphere at the temperature ranging from 850 to 900 °C for 60 s. It has been discovered that a high-resistance heterostructure layer with a thickness of about 25 nm is located on the initial samples between metallization and the two-dimensional electron gas, which prevents the formation of ohmic contact. After rapid thermal annealing at the temperature of less than 862,5 °C, the metallization components interact with each other and with the heterostructure, which leads to the decrease in the thickness of the high-resistance heterostructure layer to 15–20 nm and to the nonlinearity of the I – V characteristic. At rapid thermal annealing temperatures in the range from 862,5 to 875 °C, the thickness of the high-resistance heterostructure layer decreases to several nanometers due to the interaction of Ti/Al/Ni metallization components with the heterostructure, which promotes the tunneling effect of charge carriers and formation of a high-quality ohmic contact with a resistivity of about 1⸱10 –4 Ohm∙cm 2 . With an increase of the rapid thermal annealing temperature over 875 °C, the interaction of the metallization and heterostructure components occurs throughout the entire depth, the two-dimensional electron gas degrades, and the I – V characteristic of the contact becomes nonlinear. The results obtained can be used in the technology for creating GaN-based products with a two-dimensional electron gas.

Pseudo-vertical Mo/Au Schottky diodes on {113} oriented boron doped homoepitaxial diamond layers

Pseudo-vertical diodes on {113} oriented homoepitaxial boron-doped diamond were successfully fabricated using molybdenum as a metal for both the Schottky and ohmic contacts. After metal deposition, diodes were stabilized by annealing for 20 min at 300 °C and their I-V and C-V characteristics were measured at temperatures from 30 to 180 °C. Results show that Mo forms a very good and stable Schottky contact on {113} oriented homoepitaxial boron-doped diamond. At 180 °C, forward current densities higher than 1kA/cm2 are achieved, while the reverse current density stays unchanged at 10−8 A/cm2. The ideality factor of the diode I-V characteristic drops to 1.23 and the barrier height of the Schottky contact increases to 1.71 eV. This effect is attributed to inhomogeneity in the Schottky barrier. These characteristics are fully comparable with those of the best Schottky diodes fabricated on {100} oriented homoepitaxial boron-doped diamond. Results confirm that the use of {113} oriented homoepitaxial boron-doped diamond for the fabrication of high-temperature power devices is advantageous, as it enables high quality Schottky and ohmic contacts.

One step and in situ synthesis of Ni foam-supported Pt-Ni(OH)2 nanosheets as electrochemical sensor for ammonia–nitrogen detection

In this work, Ni foam-supported Pt-Ni(OH)2 nanosheets (Pt-Ni(OH)2-Ni foam) was designed to construct a novel electrochemical sensor for detection of ammonia–nitrogen in water. Pt-Ni(OH)2-Ni foam was prepared via one step and in situ hydrothermal synthesis in chloroplatinic acid solution and Ni foam acted as Ni source and conductive substrate. The electrochemical measured results indicated that Pt-Ni(OH)2-Ni foam showed excellent catalytic activity to electrooxidation of ammonia due to great synergistic effect between Pt and Ni(OH)2. Furthermore, the constructed electrochemical sensor based on Pt-Ni(OH)2-Ni foam exhibited great detection ability to ammonia–nitrogen with the linear range from 0.05 μM to 600 μM. The limit of detection was 39.2 nM (Sensitivity/Noise = 3). The optimized electron sturcure and high-quality ohmic contact between Pt and Ni(OH)2 were main reasons of great performances of Pt-Ni(OH)2-Ni foam. This work provided a potential sensor for ammonia–nitrogen determination.

In-situ fabrication of carbon cloth-supported polypyrrole-platinum nanosheets for the electrochemical detection of ammonia–nitrogen

In this work, a novel electrochemical sensing platform was designed based on carbon cloth-supported polypyrrole-platinum nanosheets (Pt-PPy-CC) for detection of ammonia–nitrogen in water. The Pt-PPy-CC electrode was synthesized by growing PPy and Pt nanosheets on CC via electrochemical deposition and exhibited great electrocatalytic activity for oxidation reaction of ammonia, further showed great detection ability for ammonia–nitrogen with high sensitivity of 6.67 µA µM−1 and low detection limit of 0.24 µM (sensitivity/noise = 3; S/N = 3). The electrochemical behavior of the sensing platform could be ascribed to the catalytic activity of Pt nanosheets, self-supported structure of electrode and high-quality Ohmic contact between p-type PPy and Pt. This study provided a new strategy to fabricate electrochemical sensor for ammonia–nitrogen.

Effect of cobalt particle deposition on quantum corrections to Drude conductivity in twisted CVD graphene

Graphene applications in electronics require experimental study of the formation of high-quality Ohmic contacts and deeper understanding of electron transport mechanisms at metal/grapheme contacts. We have studied carrier transport in twisted CVD graphene decorated with electrodeposited Co particles forming Ohmic contacts with graphene layers. We have compared layer resistivity as a function of temperature and magnetic field R�(T, B) for as-synthesized and decorated twisted graphene on silicon oxide substrates. Experiments have proven the existence of negative (induction < 1 Tl) and positive (induction > 1 Tl) contributions to magnetoresistance in both specimen types. The R�(T, B) functions have been analyzed based on the theory of 2D quantum interference corrections to Drude conductivity taking into account competition of hopping conductivity mechanism. We show that for the experimental temperature range (2–300 K) and magnetic field range (up to 8 Tl), carrier transport description in test graphene requires taking into account at least three interference contributions to conductivity, i.e., from weak localization, intervalley scattering and pseudospin chirality, as well as graphene buckling induced by thermal fluctuations.

Insight into the Al/N-GaN barrier property to realize high quality n-type Ohmic contact

Controlling the Schottky barrier at the interface between metal and the N-face n-GaN (N-GaN) is greatly vital to realize the high quality Ohmic contact. The effects of different defects on the n-type Schottky properties of Al(111) and N-GaN (Al/N-GaN) interface are studied using first-principles calculations. Our calculated results show that the n-type Schottky barrier height of Al/N-GaN interfaces is reduced by decorating defects like the nitrogen vacancy (VN) and the oxygen dopant at the nitrogen site (ON), and enhanced by introducing the gallium vacancy (VGa) and the ON−VGa complex. We demonstrate that the interface configuration and carrier transport properties play critical roles in controlling the Ohmic characteristics of metal-semiconductor contacts, based on which a schematic diagram for the formation mechanism of the n-type Schottky barrier height is established. Moreover, it is found that introducing donor defects at the Al/N-GaN interface with the ‘short’ Al–N bond results in the thinning of the depletion region and then enhances the tunneling, which is identified to be a better solution for improving the Ohmic contact of GaN-based LEDs. Our theoretical work enriches the fundamental understanding of the contact characteristics of Al/N-GaN and provides an important guide for designing the low-resistance N-GaN and metal contact devices.

An STM – SEM setup for characterizing photon and electron induced effects in single photovoltaic nanowires

Vertical arrays of semiconductor nanowires show great potential for material-efficient and high-performance solar cells. The characterization and correlation between material structure and properties of the individual nanowires are crucial for the continued performance improvement of such devices. In this work, we developed a method with a scanning tunneling microscope (STM) probe inside a scanning electron microscope (SEM) to enable the studies of single photovoltaic nanowires. The STM probe is used to contact individual nanowires in ensembles. We combine the STM-SEM with an in situ light emitting diode (LED) illumination source to study both the electrical and photovoltaic properties of vertical GaAs nanowires with radial p-i-n junctions. We also illustrate that the local charge separation ability within the nanowires can be studied by electron beam induced current (EBIC) measurements. The in situ SEM setup allows the correlation between properties and nanowire structure. The data show that the quality of the electrical contact to the semiconductor nanowire is crucial to be able to investigate the inherent properties of the nanowires. We have established a procedure to make high-quality ohmic contacts to the nanowires with the STM probe. We also show that the effect of mechanical strain on the electrical properties can be investigated by the STM-SEM setup.

(Invited) Exploration of Process Techniques for Ga2O3 Based Electronics

Monoclinic β-phase Ga2O3 has outstanding potential for power electronics, and high quality, large diameter bulk crystals and epitaxial layers of Ga2O3 are already available with a range of controllable n-type doping levels by edge-defined film-fed (EFG) growth using iridium crucibles, by Czochralski or by float zone. The direct energy bandgap of Ga2O3, ∼4.9 eV, yields a very high theoretical breakdown electric field (∼8 MV/cm). For power electronics, the Baliga figure-of-merit proportional carrier mobility, critical electric field and breakdown voltage, is almost four times higher for Ga2O3 than for GaN. Currently, the major limitation for Ga2O3 based device fabrication is the lack of low resistance Ohmic contacts, low damage dry etching process, and thermally stable Schottky contacts. In this work, we report a technique by employing Aluminum Zinc Oxide (AZO) to improve Ohmic contacts on Ga2O3, studies of etch rates and etching induced damages with Cl2/Ar and BCl3/Ar based discharge as well as Ni/Au and Pt/Au Schottky contacts. High quality Ohmic contacts are a prerequisite for any device to deliver low contact resistance at moderate anneal temperatures. Additional contact resistance leads to slower device switching speeds as well as reliability issues due to local contact heating from high contact resistance during device operation. AZO thin films have been widely studied for transparent and flexible device applications such as liquid crystal displays, plasma display panels, electronic paper displays, organic light emitting diode, solar cells, touch panels, gas sensors and other optoelectronics devices. To be used as a contact layer on Ga2O3, a band alignment to ensure a less barrier to electron transport from the contact metal layer via AZO into the Ga2O3.is a prerequisite. The AZO/Ga2O3 heterojunction was realized with a nested gap alignment of band offsets with a valence band offset of 0.61eV ± 0.06eV and a conduction band offset of 0.79 eV ± 0.80 eV determined from x-RayPhotoelectron Spectroscopy (XPS) measurements. This is useful information for Ohmic contact schemes on n-type Ga2O3 devices. A minimum transfer resistance and specific contact resistance of 0.42 Ω-mm and 2.82 ´ 10-5 Ω-cm2 were achieved after a relative low annealing temperature of 400°C. It is essential to generate high resolution pattern transfer processes on semiconductor with wet chemical or dry etching. While numerous wet etchants been reported, these etching processes involve strong acids and elevated temperatures, and the standard positive photoresists will not be able to use as the etching mask. For dry etching, although, the etching rates are generally low, and the resultant oxygen deficient surfaces, standard device patterning and process are compatible with Ga2O3 based device fabrication. Both Cl2/Ar and BCl3/Ar discharges were used to etch high quality bulk Ga2O3 with a Plasma-Therm Inductively Coupled Plasma (ICP) system in this work. The etching is ion-enhanced and leads to a reduction of Schottky barrier height and diode reverse breakdown voltage in diodes fabricated on the etched surfaces depending on the rf and IPC powers. For low rf and ICP power conditions, the reverse breakdown voltage decreased around 6%, while barrier height reduced from 1.2 to 1.01 eV. Under higher power conditions, the reverse breakdown voltage decreased around 35%, and the barrier height was reduced to 0.86 eV. For Schottky diodes, Ni/Au or Pt/Au were used to form Schottky contact on bulk or epitaxial β- Ga2O3. The barrier heights were 1.07 and 1.04 eV for Ni/Au and Pt/Au, respectively, at 25°C. The diode on-state resistances (Ron) decreased with increasing temperature. The temperature coefficient of reverse breakdown voltage (VB), β, was −4 mV/K for Ni/Au and −0.1 mV/K for Pt/Au. The figure-of-merit (VB 2/RON) was above 3 MW/cm2 at 25°C for Ni/Au diodes and was still ∼1 MW/cm2 at 200°C. The reverse recovery times were also measured as a function of temperature and were of the order of 21–28 ns over the range 25–150°C.

Effect of interfacial composition on Ag-based Ohmic contact of GaN-based vertical light emitting diodes

By investigating the effect of a defective interface structure on Ag-based Ohmic contact of GaN-based vertical light-emitting diodes, we found a direct relationship between the interfacial composition and the Schottky barrier height of the Ag(111)/GaN(0001) interface. It was demonstrated that the Schottky barrier height of a defect-free Ag(111)/GaN(0001) interface was 2.221 eV, and it would be dramatically decreased to 0.375 eV with the introduction of one Ni atom and one Ga vacancy at the interface structure. It was found that the tunability of the Schottky barrier height can be attributed to charge accumulations around the interfacial defective regions and an unpinning of the Fermi level, which explains the experimental phenomenon of Ni-assisted annealing improving the p-type Ohmic contact characteristic. Lastly, we propose a new method of using Cu as an assisted metal to realize a novel Ag-based Ohmic contact. These results provide a guideline for the fabrication of high-quality Ag-based Ohmic contact of GaN-based vertical light-emitting diodes.

Study of the characteristics of ohmic contact between metal electrodes and Cu 2 ZnSnS 4 thin films

Selection of ohmic contacts to Cu2ZnSnS4 (CZTS) films is one of the most crucial tasks involved in the fabrication of efficient CZTS devices. In the present work, the formation of ohmic contact with the p-type CZTS films was studied. The p-type CZTS thin films were fabricated by thermal evaporation, followed by the subsequent sulphurisation in the atmosphere of N2 + H2S (5%). Ag, In, Al and Ti were chosen as the metal electrodes of the CZTS-based films. The characteristics of CZTS thin films and the structure of Mo/CZTS/M (M = Ag, In, Al and Ti) were investigated using XRD, Raman, SEM, and EDX, to name but a few. The ohmic contact property of the studied material was tested using an I–V characterisation system. The results showed that Al could form a high-quality ohmic contact with the p-type CZTS films among the metallic electrodes.

A simple non-recessed and Au-free high quality Ohmic contacts on AlGaN/GaN: The case of Ti/Al alloy

In this work, non-recessed and Au-free low resistance Ohmic contacts are investigated on AlGaN/GaN on silicon. Based on Ti/Al bilayers, Circular TLM are fabricated and contact values are extracted varying different parameters such as single and combined annealing temperatures and surface treatment. Alloy formation upon annealing has been monitored by XRD. The results indicated that two phases, Ti3AlN and cubic TiAl3, have been formed upon annealing. Furthermore, the increase of Al thickness (up to 240nm) resulted in a tetragonal TiAl3 phase formation, with a contact resistance degradation. Finally, we have shown that a low contact resistance (1Ωmm) is achievable after clean 1 (Caro's + SC1 + HF) and upon annealing at 500°C for 3min and 800°C for 30s when using 70nm and 180nm of Ti and Al, respectively. In this case, the presence of an additional Ti3AlN (111) phase has been identified and is certainly the origin of the high quality of the Ohmic contact.

Room-temperature, low-impedance and high-sensitivity terahertz direct detector based on bilayer graphene field-effect transistor

We report a room-temperature, low-impedance and high-sensitivity terahertz direct detector based on bilayer graphene field-effect transistor (GFET). Epitaxially grown on silicon carbide, the bilayer graphene had an as-grown carrier mobility of 3000 cm2/Vs. The source/drain contacts were formed on the freshly cleaned graphene sheet to minimize the contact resistance and served also as terahertz antennas. The gate and the dielectric layer underneath with a length of 145 nm and a gap of 203 nm to the source/drain antennas were formed in a self-alignment process. Although the carrier mobility in the GFET was reduced to about 405 cm2/Vs, the high-quality ohmic contacts and the short graphene channel delivered an overall source-drain resistance less than 203 Ω. A voltage responsivity of 30 V/W and a noise-equivalent power of 51 pW/Hz1/2 were estimated in direct detection at 0.33 THz. By using the GFET detector as a two-terminal detector, i.e., with the gate floating, a transmission-type terahertz imaging was demonstrated. Such a low-impedance GFET detector is ready to be matched to a commercial 50-Ω low-noise radio/microwave frequency amplifier allowing for high-speed homodyne detection and heterodyne detection in a quasi-optical configuration.

Effect of surface treatment on the quality of ohmic contacts to single-crystal p-CdTe

In this work, we study the electrical properties of contacts to p-CdTe, formed by different methods. Two types of symmetric structures (Cu–Au/p +/p-CdTe/p +/Au–Cu and Mo–MoO x /p +/p-CdTe/p +/MoO x –Mo) with p + regions, obtained by different surface-treatment methods, are used. In order to determine the optimum conditions for the formation of high-quality ohmic contacts to p-type cadmium telluride, the electrical properties of the symmetric structures are studied. To compare the characteristics of the obtained ohmic electrical contacts, the measurements are conducted under both constant and alternating current over a wide frequency range.

Investigation of Fermi level pinning at semipolar (11–22) p-type GaN surfaces

Schottky barrier height (SBH; ΦB) and their dependence on the work function of metals (ΦM) at semipolar (11–22) p-GaN surfaces were investigated using Schottky diodes fabricated with different metals. The SBH increased with temperature, whereas the ideality factor decreased. This behavior was explained by means of the barrier inhomogeneity model, giving the mean barrier heights of 1.93–2.05eV for different metals. The S-parameter (dΦB/dΦM) was obtained to be 0.04. This small S-parameter implies that the surface Fermi level is nearly perfectly pinned at deep-level states (caused by vacancy-related and/or Mg-induced defects) located at 1.98eV above the valence band. This finding indicates that the surface modification is essentially required for the formation of high-quality ohmic and/or Schottky contacts.

Automatic Release of Silicon Nanowire Arrays with a High Integrity for Flexible Electronic Devices

Automatic release and vertical transferring of silicon/silicon oxide nanowire arrays with a high integrity are demonstrated by an Ag-assisted ammonia etching method. By adding a water steaming step between Ag-assisted HF/H2O2 and ammonia etching to form a SiOx protective layer sheathing Si nanowires, we can tune the composition of the nanowires from SiOx (0 ≤ x ≤ 2) to Si nanowires. Ag plays a key role to the neat and uniform release of Si/SiOx nanowire arrays from Si wafer in the ammonia etching process. The vertical Si nanowire array device, with both sides having high-quality Ohmic contact, can be transferred to arbitrary substrates, especially on a flexible substrate. The method developed here offers a facile method to realize flexible Si nanowire array functional devices.