J.F. Zhang

Liverpool John Moores University | LJMU · Electrical Electronic Engineering Research Centre

In this work, a novel normally-off p-channel AlGaN/GaN/AlGaN Metal-Semiconductor field effect transistor (MESFET) with threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> ) of -0.7 V is demonstrated. The state-of-the-art breakdown voltage of -198 V and breakdown electric field...

Solar‐blind ultraviolet (UV) photodetectors based on p‐organic/n‐Ga 2 O 3 hybrid heterojunctions have attracted extensive attention recently. Herein, the multifunctional solar‐blind photodetector based on p‐type poly[ N ‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT)/n‐type amorphous Ga 2 O 3 (a‐Ga 2...

In this work, an improved method of metal-organic chemical vapor deposition was utilized to grow high-quality AlPN/GaN heterostructures. The characteristics of AlPN those are essential to achieving high linearity in the resulting devices were then investigated. High linearity AlPN/GaN high electron mobility transistors (HEMTs) with flatter transcon...

In this work, we demonstrated the enhancement mode (E-mode) β-Ga2O3 metal–oxide–semiconductor field-effect transistor (MOSFET) by introducing a hybrid floating gate (HFG) structure. This E-mode Ga2O3 MOSFET featured the highest VTH of 9.03 V and the highest maximum current ID of 70.0 mA/mm among the reported lateral normally off β-Ga2O3 MOSFETs. Me...

p>Although there has been a large amount of research focusing on the noise performance of GaN HEMTs in L-bands and Ku-bands, few studies have focused specifically on the noise performance at mm-Wave frequencies. In this letter, the fabricated 120 nm MISHEMTs exhibited a low minimum noise figure ( NF _min) of 1.3 dB with an associated gai...

p>Although there has been a large amount of research focusing on the noise performance of GaN HEMTs in L-bands and Ku-bands, few studies have focused specifically on the noise performance at mm-Wave frequencies. In this letter, the fabricated 120 nm MISHEMTs exhibited a low minimum noise figure ( NF _min) of 1.3 dB with an associated gai...

In this letter, we demonstrated β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> lateral Schottky barrier diodes (SBDs) with breakdown voltage (BV) over 10 kV via anode engineering techn...

In this Letter, we demonstrate the Schottky gated p-AlGaN/u-GaN/AlGaN p-channel field-effect transistors (p-FETs) with an extremely low interface state density of 2.5 × 1011 cm−2 eV−1. Benefiting from the high-quality Schottky interface with suppressed interface states, the excellent stability with negligible hysteresis is proved, even after ten se...

A method of indium-tin oxide /Au/ indium-tin oxide (IAI) structure as transparent conductive layer to improve the current spreading and suppress efficiency droop of ultraviolet light-emitting diodes (UV-LEDs) is investigated. The morphology and distribution of Au clusters formed by annealing are investigate by atomic force microscope and scanning e...

Low-dimensional lead-free metal halides have shown considerable potential for visible-blind ultraviolet (UV) photodetectors (PDs) owing to their extraordinary optoelectronic properties. Herein, a high-quality perovskite-like CsAg2I3 thin film was successfully fabricated via the pyridine additive-assisted one-step solution method, and it exhibited a...

In this paper, a method of indium-tin oxide /Graphene /Indium-tin oxide (ITO/Gr/ITO) structure as transparent conductive layer (TCL) to improve the current spreading of ultraviolet light-emitting diodes (UV-LEDs) is reported. The ITO/Gr/ITO structure is obtained by RF magnetron sputtering and wet-transferred. Raman spectroscopy measurement further...

Wide-bandgap (WBG) perovskite solar cells (PSCs) are essential for highly efficient and stable silicon/perovskite tandem solar cells. In this study, we adopted a synthetic strategy with lead thiocyanate (Pb(SCN) 2 ) additive and methylammonium chloride (MACl) posttreatment to enhance the crystallinity and improve the interface of WBG perovskite fil...

Perovskite solar cells (PSCs) are considered as a promising photovoltaic technology due to their high efficiency and low cost. However, their long-term stability, mechanical durability, and environmental risks are still unable to meet practical needs. To overcome these issues, we designed a multifunctional elastomer PPG-mUPy-APDS with abundant hydr...

Perovskite solar cells (PSCs) are considered as a promising photovoltaic technology due to their high efficiency and low cost. However, their long‐term stability, mechanical durability, and environmental risks are still unable to meet practical needs. To overcome these issues, we designed a multifunctional elastomer with abundant hydrogen bonds and...

AlGaN-based ultraviolet-A light-emitting diodes (UVA LEDs) inevitably suffer from current crowding effects at high injection levels due to their lateral device structure, resulting in non-uniform light emission and device overheating. In N-polar UV LEDs, the problem is further exacerbated by increased hole injection efficiency, leading to current c...

Hetero-epitaxial growth of GaN often leads to high density of threading dislocations, which poses a significant challenge to the promotion of the performance of GaN-based devices. In this study, we address this issue by utilizing an Al-ion implantation pretreatment on sapphire substrates, which induces high-quality regularly arranged nucleation and...

The advantages of van der Waals epitaxial nitrides have become a research hot topic. It is worth noting that graphene plays an important role in the research of epitaxial AlN epitaxial layer. In this work, we demonstrate a method to obtain high-quality and low-dislocation AlN epitaxial layer by combining graphene and sputtered AlN as the nucleation...

In this letter, a watt-level C-band monolithic microwave integrated circuits (MMICs) rectifier with lateral gallium nitride (GaN) Schottky barrier diode (SBD) is demonstrated for the first time. The proposed MMIC is fabricated on SiC-based AlGaN/GaN heterojunction material with a circuit dimension of only 2.5 $\times$ 2.1 mm. Benefited from the h...

In this paper, hydrogen terminated metal oxide semiconductor field effect transistors (MOSFETs) having a sub-micron gate length were fabricated on a single crystalline diamond sample using the 300 °C ALD grown Al2O3 as gate dielectric and passivation layer. The device shows a maximum output current density of 942 mA/mm and a lowest on-resistance of...

In this work, the effect of gamma irradiation on the quasi-vertical GaN Schottky barrier diodes (SBDs) with passivation layer was investigated for the first time. The forward I-V characteristic was improved and the reverse leakage was slightly increased after 1Mrad gamma irradiation. Moreover, the annealing process was carried out after the irradia...

Although the certified power conversion efficiency of organic-inorganic perovskite solar cells (PSCs) has reached 25.7%, their thermal and long-term stability is a major challenge due to volatile organic components. This problem has been a major obstacle to their large-scale commercialization. In the last few years, carbon-based all-inorganic perov...

The advent of big data era has put forward higher requirements for electronic nanodevices that have low energy consumption for their application in analog computing with memory and logic circuit to address attendant energy efficiency issues. Here, a miniaturized diode with a reversible switching state based on N-n MoS2 homojunction used a bandgap r...

Degradation and defect evolution in GaN-based UV LEDs under 3 MeV proton irradiation were throughly investigated in this work. Combined with the yellow luminescence band at ∼2.2 eV in photoluminescence spectra with the energy level of E v + 0.16 eV extracted by deep-level transient spectroscopy measurement, an intrinsic C N -related defect with an...

In this work, high-performance high-electron-mobility transistors (HEMTs) with a thin GaN channel and an AlN back barrier were fabricated and investigated in detail. The AlN back barrier HEMTs possess a higher current density and a better linearity than traditional devices. In addition, the off-state leakage current of the AlN back barrier HEMTs is...

The extremely low leakage, fast response, and excellent thermal conductivity of diamond facilitate its potential application in pulse power switching devices. In this study, we investigated the static and transient characteristics of diamond avalanche diodes (DADs) via 2-D device simulation. DAD is based on a Schottky barrier diode (SBD) structure....

SrTiO 3 (STO), a room-temperature paraelectric material in bulk form, has been a rich playground for emergent phenomena for decades. As an emerging material, great attention has been paid to freestanding 2D STO thin films. Recently, the room-temperature ferroelectricity has been unveiled in strained STO thin films; however, it remains an open quest...

In this letter, we demonstrated an AlN/GaN metal-insulator-semiconductor high electron mobility transistor (MISHEMT) on a Si substrate with in-situ SiN as gate dielectric with excellent mm-wave performance at low supply voltages. Benefited from the thin in-situ SiN, a low ohmic contact resistance ${R} _{C}$ of $0.2 \sf {\Omega } \cdot \text {mm}...

The synaptic devices based various electronic materials have been widely investigated to realize functions of artificial information processing with low power consumption. In this work, a novel CVD graphene field-effect transistor is fabricated with ionic liquid gate to study the synaptic behaviors based on the electrical-double-layer mechanism. It...

In this work, we have achieved novel lateral enhancement-mode (E-M) and depletion-mode (D-M) $\beta $ -Ga2O3 metal-oxide-semiconductor junction field-effect- transistors (MOS-JFETs) featuring a low gate leakage current ( $\text{I}_{{\text {G}}}$ ) and a large gate swing. Ascribing to the high-quality SiO2 layer above the P-NiO $_{{{\text {X}}}}$...

In this article, we carry out the parameter shift of quasi-vertical GaN-on-Si Schottky barrier diodes (SBDs) under ON-state stress with a high forward current of 2–4 kA/cm2. Turn-on voltage ${V}_{{\mathrm {\mathbf {on}}}}$ , ON-resistance $R_{ON}$ , reverse leakage current ${I}_{\text {reverse}}$ , Schottky barrier height $\phi $ , and idea...

The model of lateral β-Ga 2 O 3 metal–oxide–semiconductor field-effect transistor (MOSFET) was established using Sentaurus Technology Computer Aided Design software. The gate-to-drain distance of the device was 13.7 μm, and the breakdown voltage was 1135 V. The single event effect simulation model caused by heavy ion irradiation was introduced, and...

A study of 1.7 kV normally-off p-GaN gate high-electron-mobility transistors (HEMTs) on SiC substrates is presented. The fabricated p-GaN HEMT with a gate-drain spacing LGD = 5 µm exhibited a threshold voltage of 1.10 V, a maximum drain current of 235 mA/mm, an ON/OFF ratio of 108, and a breakdown voltage of 440 V. Benefiting from the semi-insulati...

In this article, we demonstrate a novel E-mode HEMT featuring in situ AlN dielectric layer on p-GaN cap layer. Compared with conventional p-GaN gate HEMT, the threshold voltage of in situ AlN/p-GaN gate HEMT shifts from 1.8 to 3.9 V, and the forward gate breakdown voltage is increased from 10.0 to 17.6 V. By considering 10 years’ lifetime at 63% fa...

All-inorganic CsPbBr3 perovskite solar cells (PSCs) have attracted more attentions due to the excellent environmental stability, however, the wide bandgap and relatively poor crystallinity of CsPbBr3 have been the main obstacle to improve their power conversion efficiency (PCE). Herein, we proposed an efficient and simple strategy of precursor addi...

In this study, an enhancement-mode gallium oxide MOSFET with a ferroelectric charge storage gate stack structure is numerically investigated. The device is simulated from the aspects of traps and material parameters, physical models, and voltage sources. The device is found to be optimal in performance when the ferroelectric film thickness is 17 nm...

The radiation effect of swift heavy ions (16MeV 181Ta) on the Au/Ni/-Ga2O3 vertical Schottky barrier diodes(SBDs) were investigated at the fluence of 1×108, 3×108 and 3×109 cm-2. The SBDs were characterized by current density-voltage (J-V) and capacitance-voltage (C-V) measurements. It was found that Schottky barrier height ϕ decreased from 1.11 e...

We report on achieving high conductivity hydrogenated boron (B) and silicon (Si) co-doped diamond with a room-temperature Hall result of a square resistance of 2724 ohm/sq, a sheet hole density of 3.3×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> cm <sup xmlns:mml="http://www.w3.org/1998/...

In this article, we demonstrate high-performance reverse blocking GaN high-electron-mobility transistors (HEMTs) with a recessed-drain structure on AlGaN/GaN/AlGaN double heterostructure. By using a low damage recessed-drain structure, the turn-on voltage ( $\textit{V}_{\text{ON}}\text{)}$ as small as 0.35 V is achieved. Furthermore, owing to enha...

In this paper, the method for growing α-Ga2O3 films on c-plane sapphire substrates using an inexpensive fine-channel mist-CVD face-to-face heating plate was investigated. Because high temperatures can result in reactor deformation, expensive AlN ceramics resistant to deformation are used as the reactor fabrication material in traditional fine-chann...

β-Ga 2 O 3 /graphene heterostructure engineering has been regarded as an effective method to improve the optoelectronic performance of the β-Ga 2 O 3 device. Here, hydrogenation/fluorination covalent functionalized graphene (HC/FC) was employed, and the synergistic effect of covalent functionalization and intrinsic electric field ( E in ) was intro...

Wide‐bandgap inorganic cesium lead halide CsPbIBr2 is a popular optoelectronic material that researchers are interested in because of the character that balances the power conversion efficiency and stability of solar cells. It also has great potential in semitransparent solar cells, indoor photovoltaics, and as a subcell for tandem solar cells. Alt...

This letter reports on the demonstration of recessed-gate ultra-wide bandgap semiconductor Al0.6Ga0.4N MOSFET with Hf0.5Zr0.5O2 (HZO) ferroelectric charge storage dielectric structure. A positive threshold voltage ( $\text{V}_{\text {TH}}$ ) of 3.550 V and maximum gate swing of 15 V is achieved due to the trapped electrons induced by remnant polar...

The solar-blind photodetectors based on amorphous Ga2O3 (a-Ga2O3) are attractive in recent years due to their simple fabrication process and good compatibility with different substrates. Herein, the cost-effective and high-performance thin-film transistor (TFT) type solar-blind photodetector based on a-Ga2O3 was realized successfully at room temper...

The cascode structure was fabricated by combining the H-diamond normally-ON p-FET with the Si normally-OFF p-FET. The cascode shows normally-OFF characteristics with the threshold voltage of $-$ 0.8 V and the maximum transconductance of 344.6 mS/mm. The maximum saturation drain current and minimum ON-resistance are 34.2 mA/mm and 18.74 $\Omega $...

A low ohmic contact resistance ( R c ) is a challenge for an AlGaN/GaN heterostructure with a high Al-composition barrier, which is highly desired to further push the performance of GaN transistors. In this Letter, an effective ohmic contact technique with an in situ SiN x layer inserted between the conventional Ti/Al/Ni/Au metal stack and the III-...

Van der Waals heterostructure based on 2D materials is a promising technology for high-performance optoelectronic devices because of its tunable bandgaps and optical properties. However, photodetectors with a low dark current and a fast response speed commonly lose their photoresponsivity. The recovery current induced by the Schottky barrier height...

In this article, we experimentally study the instability of the key electrical characteristic for the fabricated ${\beta }$ -Ga2O3 MOSFET under positive bias stress (PBS) and negative bias stress (NBS), such as threshold voltage ( ${V}_{{\mathrm {TH}}}$ ), ON-resistance ( ${R}_{{\mathrm {on}}}$ ), subthreshold slope (SS), and hysteresis. An ion...

All‐inorganic perovskite CsPbBr3 has drawn a lot of interest as an active layer applied in photovoltaics due to its outstanding stability in ambient air. However, the procedure of preparing high‐quality CsPbBr3 films still remains a serious challenge because of the tedious process and toxic solvent. Herein, a solvent engineering method that involve...

Metallic antiferromagnets are demonstrated to show an unconventional spin Hall effect (SHE) and the inverse spin Hall effect (ISHE), which are very promising for Néel-vector detection. However, the ISHE is absent in insulating antiferromagnets, as it does not conduct charge current. Here, we report our observation of the anomalous ISHE at the inter...

A $\beta $ -Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> MOSFET is fabricated and its threshold voltage $({V}_{\mathrm{TH}})$ instability mechanisms are experimentally investigated...

Low‐temperature, ambient processing of high‐quality CsPbBr3 films is demanded for scalable production of efficient, low‐cost carbon‐electrode perovskite solar cells (PSCs). Herein, we demonstrate a crystal orientation engineering strategy of PbBr2 precursor film to accelerate its reaction with CsBr precursor during two‐step sequential deposition of...

CsPbI3 perovskite solar cells (PSCs) are becoming desirable for their outstanding performance and thermal stability, while their inferior tolerance to moisture restricts further advances. Herein, CsPbBr3 pieces are introduced onto TiO2 electron transport layer (ETL) before CsPbI3 film deposition, which can act as nucleation seeds to assist crystal...

In this study, we investigate heavy ion irradiation effects on commercial 650 V p-GaN normally-off HEMTs. Ge and Cl ions are used to irradiate the GaN devices in the experiments. Ge and Cl ion beam irradiation have little impact on the output characteristics of GaN devices. After heavy ion irradiation, the leakage currents between source and drain...

Recently, Ga2O3 has attracted widespread attention from domestic and foreign research scholars due to its large bandgap and high breakdown electric field. And it has huge application prospects in many fields such as optoelectronic devices, transistors, and high-power devices. Different from the traditional expensive and complex methods such as PLD,...

High-quality AlGaN/GaN/AlN heterostructures with thin GaN channel and thick AlN buffer layer were grown by metal organic chemical vapor deposition (MOCVD) on SiC substrate. By analyzing growth modes of GaN films on AlN buffer layers with different thicknesses, it is revealed that film-forming point of GaN grown on AlN buffer increases with the incr...

The introduction of an in situ C-doped GaN layer in green light-emitting diodes (LEDs) is successfully realized by optimizing the temperature of the GaN growth process. The C-doped GaN film acts as a current spreading layer for green LEDs, allowing for a more uniform current distribution and consequently an increase in luminous efficiency. At the s...

β-Ga2O3 films were grown on AlN templates by metal organic chemical vapor deposition (MOCVD), and the properties of the β-Ga2O3/AlN heterostructures were investigated in detail. The β-Ga2O3/AlN heterostructure with abrupt interface was observed by the high resolution transmission electron microscope with high angle annular dark field. The refactor...

Ultra-wide bandgap semiconductor Ga2O3 based electronic devices are expected to perform beyond wide bandgap counterparts GaN and SiC. However, the reported power figure-of-merit hardly can exceed, which is far below the projected Ga2O3 material limit. Major obstacles are high breakdown voltage requires low doping material and PN junction terminatio...

In this article, a novel device structure of an enhancement-mode (E-mode) Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> MOSFET is proposed based on the combination of the p-NiO/n-Ga <su...