Selective Doping Technique Research Articles

(Invited) Breakdown Improvement of Mg-Diffused Current Blocking Layer in Ga2O3

The path towards an all-planar highly efficient vertical Ga2O3 transistor requires the construction of a buried gate barrier junction to circumvent the pre-mature breakdown near the gate often seen in lateral structures. An effective selective doping technique is necessary to achieve this. By taking advantage of the high diffusivity of dopants and defects in Ga2O3, we propose the use of diffusion doping as a rapid and non-invasive technique to explore the possibility of an effective current blocking layer (CBL) in vertical Ga2O3 transistors. Unlike ion implantation, diffusion doping does not require an 1100°C annealing for the repair of crystal damage. Thus, the desired Mg doping profile can be maintained by the end of device fabrication, which is the key to achieving a high blocking voltage with Mg-doped CBL. In addition, diffusion doping can easily form a much deeper dope junction and be very useful for high-voltage and super-junction devices.Recently, we have demonstrated the first Ga2O3 vertical-diffused-barrier field-effect transistor (or VDBFET) utilizing a Mg-diffusion doped CBL with a spin-on-glass source. The transistor exhibited excellent FET behavior with decent saturation, enhancement-mode operation, and an on/off ratio of more than 109. However, the breakdown voltage is measured to be only 72V most likely due to the punch-through of the Mg-diffused CBL. This is likely caused by a lower-than-expected Mg doping rendering an inefficient electron blocking. In addition, SIMS analysis indicated the existence of Mg-H complex that deactivated the Mg. Thus, the effective Mg doping is even lower than its chemical concentration. Here we will discuss a new strategy to resolve this problem and showcase the characteristics of the improved CBL with a higher breakdown. This development paves the way for the development of high-voltage Ga2O3 VDBFETs.

Fabrication of lateral diamond MOSFET with buried pn-junctions by diamond surface planarization based on carbon solid solution into nickel

New fabrication processes for buried p+-type diamond using etching techniques based on the solid-solution reaction of carbon with nickel were proposed and demonstrated. Specifically, an inversion-channel diamond metal-oxide-semiconductor field-effect transistors (MOSFETs) with source and drain regions buried in the body were fabricated, and their operation were confirmed. An etching process using etching techniques based on the solid-solution reaction of carbon with nickel was applied to realize trench formation and planarization after the growth of a p+-type diamond. The fabricated MOSFET exhibited drain current density equivalent to that of conventional MOSFET with source and drain p+-type regions deposited as islands on an n-type body, and ideal field-effect transistor characteristics with linear and saturation regions, and the drain current density was controlled by the gate voltage. However, the surface protrusion structure owing to the incomplete planarization process limited the device characteristics. The proposed fabrication processes for buried layers are expected to function as an important selective doping technique for diamond electronic devices such as ion implantation.

Substitutional diffusion of Mg into GaN from GaN/Mg mixture

We evaluated Mg-diffusion into GaN from GaN/Mg mixture. The diffusion depth of Mg increased with diffusion temperature from 1100 °C to 1300 °C, whereas the Mg concentration remained constant at 2–3 × 1018 cm−3 independent of temperature. The estimated activation energy for Mg diffusion was 2.8 eV, from which the substitutional diffusion mechanism was predicted. Mg-diffused GaN samples showed p-type conductivity with a maximum hole mobility of 27.7 cm2 V−1 s−1, suggesting that substitutional diffusion contributes to Mg activation. This diffusion technique can be used to easily form p-type GaN and has potential as a p-type selective doping technique.

Broadband Visible−Near Infrared Two‐Dimensional WSe2/In2Se3 Photodetector for Underwater Optical Communications

AbstractP–n junctions based on 2D materials can be achieved using a selective doping technique, while such a method is challenged by the complex fabrication process. Here, a facile van der Waals (vdWs) structured p–n heterojunction is demonstrated by simply transferring an n‐type multilayer α‐In2Se3 (direct bandgap) on a p‐type ultra‐thin WSe2 nanosheet. The vdWs stacked photodetector with an improved type‐II band alignment not only realizes a broadband spectral response from visible to near infrared (405–905 nm), but also operates well with a diode‐like behavior. This behavior is further confirmed by the high‐resolution scanning photocurrent mapping. As a result, the as‐fabricated device exhibits a short response time (<120 µs) and a high responsivity of 1.84 A W−1 under 520 nm laser illumination. Accordingly, an underwater optical communication system based on the WSe2/α‐In2Se3 p‐n heterojunction photodetector is demonstrated, which is promising for next‐generation high‐performance and low‐power detection applications.

Lateral monolayer MoS2 homojunction devices prepared by nitrogen plasma doping

Monolayer MoS2 possesses good electron mobility, structural flexibility and a direct band gap, enabling it to be a promising candidate for flexible and wearable optoelectronic devices. In this article, the lateral monolayer MoS2 homojunctions were prepared by a nitrogen plasma selective doping technique. The monolayer MoS2 thin films were synthesized by chemical vapor deposition and characterized by photoluminescence, atom force microscope and Raman spectroscopy. The electronic and photoelectric properties of the lateral pn and npn homojunctions were discussed. The results showed that the rectifying ratio of the pn homojunction diode is ∼103. As a photodetector of pn homojunction, the optical responsivity is up to 48.5 A W−1, the external quantum efficiency is 11 301%, the detectivity is ∼109 Jones and the response time is 20 ms with the laser of 532 nm and the reverse bias voltage of 10 V. As a bipolar junction transistor of npn homojunction, the amplification coefficient reached ∼102. A controllable plasma doping technique, compatible with traditional CMOS process, is utilized to realize the monolayer MoS2 based pn and npn homojunctions, and it propels the potential applications of 2D materials in the electronic, optoelectronic devices and circuits.

Homogeneous 2D MoTe2 CMOS Inverters and p-n Junctions Formed by Laser-Irradiation-Induced p-Type Doping.

Among all typical transition-metal dichalcogenides (TMDs), the bandgap of α-MoTe2 is smallest and is close to that of conventional 3D Si. The properties of α-MoTe2 make it a favorable candidate for future electronic devices. Even though there are a few reports regarding fabrication of complementary metal-oxide-semiconductor (CMOS) inverters or p-n junction by controlling the charge-carrier polarity of TMDs, the fabrication process is complicated. Here, a straightforward selective doping technique is demonstrated to fabricate a 2D p-n junction diode and CMOS inverter on a single α-MoTe2 nanoflake. The n-doped channel of a single α-MoTe2 nanoflake is selectively converted to a p-doped region via laser-irradiation-induced MoOx doping. The homogeneous 2D MoTe2 CMOS inverter has a high DC voltage gain of 28, desirable noise margin (NMH = 0.52 VDD , NML = 0.40 VDD ), and an AC gain of 4 at 10 kHz. The results show that the doping technique by laser scan can be potentially used for future larger-scale MoTe2 CMOS circuits.

Tuning the optical and electrical properties of MoS2 by selective Ag photo-reduction

Two-dimensional transition metal dichalcogenides have demonstrated potential for advanced electrical and optoelectronic applications. For these applications, it is necessary to modify their electrical or optoelectronic properties. Doping is one of the most prevalent techniques to modify the band structure of semiconductor materials. Herein, we report the p-type doping effect on few-layer and multi-layer MoS2 that are selectively decorated with Ag nanoparticles via laser-assisted direct photoexcitation of MoS2 exposed in AgNO3 solution. This method can control the doping level by varying the duration of the laser irradiation, which is confirmed by the observed gradual rise of MoS2 device channel resistance and photoluminescence spectra enhancement. This study demonstrated a simple, controllable, and selective doping technique using laser-assisted photo-reduction.

Two-Dimensional MoTe­2 PN Diode and CMOS Inverter By Atomic Layer Deposition-Induced Hydrogen Doping

Recently, 2D transition metal dichalcogenides(TMDs) MoTe2 has shown outstanding properties for future electronic devices. Such TMD structures without surface dangling bonds make the 2D MoTe2 more favorable candidate than conventional 3D Si in a few nanometer scale. The band gap of thin MoTe2 appears close to that of Si and quite smaller than those of other typical TMD semiconductors. Even though there have been a few attempts to control charge carrier polarity of MoTe2, functional devices such as complementary metal–oxide–semiconductor (CMOS) inverter have not been reported. Here we demonstrate a 2D CMOS inverter in a single MoTe2 nanosheet by straightforward selective doping technique. In a single MoTe2 flake, initially p-doped channel was selectively converted to n-doped region with high electron mobility of 18 cm2/Vs by atomic layer deposition-induced H-doping. Our ultrathin CMOS inverter exhibited a high DC voltage gain of 29, AC gain of 18 at 1 kHz, and a low static power consumption of a few nW. Our results show a great potential of MoTe2 for future electronic devices based on 2D semiconducting materials Figure 1

Homogeneous 2D MoTe2 p-n Junctions and CMOS Inverters formed by Atomic-Layer-Deposition-Induced Doping.

Recently, α-MoTe2 , a 2D transition-metal dichalcogenide (TMD), has shown outstanding properties, aiming at future electronic devices. Such TMD structures without surface dangling bonds make the 2D α-MoTe2 a more favorable candidate than conventional 3D Si on the scale of a few nanometers. The bandgap of thin α-MoTe2 appears close to that of Si and is quite smaller than those of other typical TMD semiconductors. Even though there have been a few attempts to control the charge-carrier polarity of MoTe2 , functional devices such as p-n junction or complementary metal-oxide-semiconductor (CMOS) inverters have not been reported. Here, we demonstrate a 2D CMOS inverter and p-n junction diode in a single α-MoTe2 nanosheet by a straightforward selective doping technique. In a single α-MoTe2 flake, an initially p-doped channel is selectively converted to an n-doped region with high electron mobility of 18 cm2 V-1 s-1 by atomic-layer-deposition-induced H-doping. The ultrathin CMOS inverter exhibits a high DC voltage gain of 29, an AC gain of 18 at 1 kHz, and a low static power consumption of a few nanowatts. The results show a great potential of α-MoTe2 for future electronic devices based on 2D semiconducting materials.

High-aspect-ratio Neural Electrode Array Fabrication using Thermomigration Process

Abstract A novel fabrication process for a high-aspect-ratio recording and stimulation intracortical neural microelectrode array is described. Using a combination of dicing and KOH wet-etching, microspikes are formed on the surface of a n -type (100), 4 mm thick, silicon wafer. Deep 3 mm cuts are performed in order to produce sharped tip pillars of high-aspect-ratio (0.2x0.2x3 mm). Thermomigration is employed as a selective doping technique performing electrically insulated pillars due to the pn back biased junctions formed between each pair of n -type substrate and p + migrated trails. Gold is deposited over the spikes in order to have a good ionic interface with the neural tissue, while the remaining surface is passivated with a biocompatible layer of cyanoacrylate. The final result is a deep penetrating electrode array with potential new applications in neuroprosthetics’ research field.

Selective doping of silicon by rapid thermal and laser assisted processes

The selective doping technique, made by the combination of spin-on dopant (SOD) source deposition, rapid thermal annealing (RTA) and laser treatments is proposed as an innovative process for large area devices, like silicon solar cells. Rapid thermal diffusion (RTD) is first carried out from phosphorus SOD layers to form a lightly doped junction followed by pulsed laser irradiation to induce overdoping in selectively chosen regions. Here we present extensive study on the dependence of selective doping efficiency through different working variables, such as dopant source dilution, diffusion temperature and time for RTPs, and power and translation velocity for lasers. Electrical and structural characterizations have been performed by using several techniques: SIMS, stripping-Hall, four-point probe resistivity, SEM and TEM analysis. The combined use of these processes has been applied to the realization of selective emitter structures for silicon solar cells.

Beta Silicon Carbide Pn Junction Diodes

AbstractBeta silicon carbide (3C-SiC) diodes have been fabricated using ion implantation as the selective doping technique. Previous work on 3C-SiC diodes have exhibited properties such as low reverse breakdown voltages and high ideality factors. Also, 6H and 4H SiC diodes have been reported. This paper studies a different procedure to produce better 3C-SiC diodes for use in the electronics industry. Current versus voltage, capacitance versus voltage and temperature versus voltage tests were conducted on the devices.Isolation between devices is a prominent concern when building integrated circuits. Proton bombardment is the preferred planar process for forming isolation regions in gallium arsenide (GaAs) due to the lack of a stable native oxide. Hydrogen and boron in GaAs have exhibited good electrical isolation between devices. This paper investigates using proton bombardment to form isolation regions in 3C-SiC. Cubic SiC samples are implanted with a variety of implant doses, ranging from 1 × 1014 to 1 × 1015 ions / cm2 , and implant energies ranging from 150 to 300 keV. Hall measurement tests were performed to study the characteristics of the implanted material.

New selective doping technique for boron using a HBO2 source and a thin oxide mask

Selective adsorption of HBO2 on Si(100) partially covered with thin (≲1 nm) oxide is observed using a Si molecular-beam epitaxy system. The thin oxide is formed by local oxidation by a ArF excimer laser or wet chemical treatment. A selective adsorption rate of more than 20 is observed at 700 °C. After the adsorption, the oxide can be sublimated at 800 °C annealing in ultrahigh vacuum without boron desorption. These phenomena can be applied to selective shallow doping without photoresist.

Selective doping of N-type ZnSe layers with chlorine grown by molecular beam epitaxy

N-type ZnSe with electron concentration up to 3 × 1020 cm−3 and low resistivity down to 1 × 10−4 ohm-cm, has been grown using a selective doping technique with chlorine during molecular beam epitaxy. The photoluminescence evaluation shows that the selectively doped ZnSe layers are superior to uniformly doped ones, especially for the case of high-concentration chlorine doping. The in-depth profile of chlorine concentration in a selectively doped sample was measured with secondary-ion mass spectroscopy (SIMS). The SIMS analysis shows only slight diffusion of the incorporated chlorine atoms even in highly doped samples.