Jinchai Li

Xiamen University | XMU · Department of Physics

This study presents broadband ultraviolet photodetectors (BUV PDs) based on Ga2O3/GaN core-shell micro-nanorod arrays with excellent performance. Micro-Nanoarchitectonics of Ga2O3/GaN core-shell rod arrays were fabricated with high-temperature oxidization of GaN micro-nanorod arrays. The PD based on the microrod arrays exhibited an ultrahigh respon...

The controlled growth of single-crystalline (InxGa1-x)2O3-based materials with high indium contents is still a big challenge due to the large solid-phase miscibility gap, unclear growth mechanism, and the lack of...

Quantum states and arrangement of valence levels determine most of the electronic and optical properties of semiconductors. Since the crystal field split-off hole (CH) band is the top valence band in high-Al-content AlGaN, TM-polarized optical anisotropy has become the limiting factor for efficient deep-ultraviolet (DUV) light emission. Additional...

A systematic study was carried out for strain-induced microscale compositional pulling effect on the structural and optical properties of high Al content AlGaN multiple quantum wells (MQWs). Investigations reveal that a large tensile strain is introduced during the epitaxial growth of AlGaN MQWs, due to the grain boundary formation, coalescence and...

Here we report a comprehensive numerical study for the operating behavior and physical mechanism of nitride micro-light-emitting-diode (micro-LED) at low current density. Analysis for the polarization effect shows that micro-LED suffers a severer quantum-confined Stark effect at low current density, which poses challenges for improving efficiency a...

The impact of multi quantum wells (MQWs) structure on the homogeneity of spontaneous luminescence and quantum efficiency of the high power InGaN blue laser diode (LD) is numerically investigated. The structure with 2QWs in the active region is found to be the optimal choice for the high power InGaN LD. Accordingly, the edge emitting LD structure is...

As demonstrated during the COVID-19 pandemic, advanced deep ultraviolet (DUV) light sources (200–280 nm), such as AlGaN-based light-emitting diodes (LEDs) show excellence in preventing virus transmission, which further reveals their wide applications from biological, environmental, industrial to medical. However, the relatively low external quantum...

The polycrystal Ga2O3 on GaN was realized by high‐temperature oxidization of the GaN films with oxidation time 1h and 10h, and the metal‐semiconductor‐metal photodetectors based on the Ga2O3/GaN heterostructure were fabricated by using Ti and Au metal electrodes. A comparative study of different electrodes and oxidation time on the performance of u...

Far-UVC light with emission wavelengths between 207 nm and 222 nm has shown significant potential for killing pathogens without damaging exposed human tissues and can be an alternative for safe sterilization. This work first reports on different compressively strained (AlN) 8 /(GaN) 2 nanorods constructing by strain engineering digitally alloyed Ga...

AlGaN has attracted considerable interest for ultraviolet (UV) applications. With the development of UV optoelectronic devices, abnormal carrier confinement behaviour has been observed for c-plane-oriented AlGaN quantum wells (QWs) with high Al content. Because of the dispersive crystal field split-off hole band (CH band) composed of p z orbitals,...

Two types of high‐voltage flip chip deep ultraviolet light emitting diodes (HV‐FC DUV‐LEDs) are constructed with 2 × 2 and 3 × 3 cells, respectively, in which each single cell is fabricated with inclined sidewalls covered by SiO2/Al. The simulation results suggest that the structure with inclined sidewalls is much favorable to extract the transvers...

The effects of ultrathin AlN insertion layers on the strain status, as well as optical properties of AlGaN multiple quantum wells (MQWs), were studied. A large stress variation of about -1.46 GPa can be achieved by introducing two ultrathin AlN layers at each interface between the quantum well and the barrier, thereby resulting in the fact that the...

The authors report on growth and characterization of semipolar (112¯2) GaN films improved by an in situ SiNx pretreatment of m‐sapphire substrate surface. Formation of SiNx and Ga‐rich surface at the initial growth stages is evidenced by X‐ray photoelectron spectroscopy. With the SiNx pretreatment, the GaN nucleated island density decreases due to...

In this paper, the optical properties of GaN-based green light emitting diode (LED) are investigated and the internal quantum efficiency (IQE) values are measured by temperature dependent photoluminescence (TDPL) and power dependent photoluminescence (PDPL) methods. The "S-shaped” shift of peak wavelength measured at different temperature disappear...

A series of InN films were grown on GaN-on-sapphire template with H2 pulse flow by metal organic vapor phase epitaxy. The scanning electron microscopy and atomic force microscopy observations demonstrate that the smooth surface has been achieved. The X-ray diffraction and Raman spectra measurements indicate that InN layers experience stronger accom...

The quantum efficiency of deep UV light emitting diodes (LED) drops dramatically with the increasing of Al content. Understanding the emission mechanism of high Al-content AlGaN multiple quantum wells (MQW) is the one of the most important objects for improving the quantum efficiency of deep UV LED. In this work, high Al-content AlGaN MQW structure...

We report the modified pulse growth method together with an alternating introduction of larger-radius impurity (Mg) for the quality improvement and misfit strain release of an AlN epitaxial layer by the metal–organic chemical vapour deposition (MOCVD) method. Various pulse growth methods were employed to control the migration of Al atoms on the sub...

A novel multidimensional Mg-doped superlattice (SL) is proposed to enhance vertical hole conductivity in conventional Mg-doped AlGaN SL which generally suffers from large potential barrier for holes. Electronic structure calculations within the first-principle theoretical framework indicate that the densities of states (DOS) of the valence band nea...

Asymmetric light reflectance associated with localized surface plasmons excited in metal nanoparticles on a quartz substrate is observed and analyzed. This phenomenon is explained by the superposition of two waves, the wave reflected by the air/quartz interface and that reflected by the metal nanoparticles, and the resulting interference effects. F...

Ultra-short-period (AlN)m/(GaN)n superlattices with tunable well and barrier atomic layer numbers were grown by metal-organic vapour phase epitaxy, and employed to demonstrate narrowband deep ultraviolet photodetectors. High-resolution transmission electron microscopy and x-ray reciprocal space mapping confirm that superlattices containing well-def...

High internal efficiency and high temperature stability ultraviolet (UV) light-emitting diodes (LEDs) at 308 nm were achieved using high density (2.5 × 10(9) cm(-2)) GaN/AlN quantum dots (QDs) grown by MOVPE. Photoluminescence shows the characteristic behaviors of QDs: nearly constant linewidth and emission energy, and linear dependence of the inte...

The electronic properties of GaN/AlN quantum wells are engineered by Si doped in different positions with the aid of the first-principle calculations. The local potential where the dopant located is dragged down as a result of negative center induced by the Si atom, leading to a different shift of the potential, and further affects the band bending...

We report localised-surface-plasmon (LSP) enhanced deep-ultraviolet light-emitting diodes (deep-UV LEDs) using Al nanoparticles for LSP coupling. Polygonal Al nanoparticles were fabricated on the top surfaces of the deep-UV LEDs using the oblique-angle deposition method. Both the top- and bottom-emission electroluminescence of deep-UV LEDs with 279...

According to first-principles calculations, the solubility of Mg as a substitute for Ga or Al in Al x Ga1 – x N bulk is limited by large, positive formation enthalpies. In contrast to the bulk case, the formation enthalpies become negative on Al x Ga1 – x N surface. In addition, the N-rich growth atmosphere can also be favorable to Mg incorporation...

The method of In bilayer pre-deposition and penetrated nitridation had been proposed, which had been proven to have many advantages theoretically. To study the growth behavior of this method experimentally, various pulse times of trimethylindium supply were used to get the optimal indium bilayer controlling by metalorganic vapour phase epitaxy. The...

Growing AlN layers remains a significant challenge because it is subject to a large volume fraction of grain boundaries. In this study, the nature and formation of the AlN growth mechanism is examined by ab initio simulations and experimental demonstration. The calculated formation enthalpies of the constituent elements, including the Al/N atom, Al...

Dense and atomically flat AlN film with root-mean-square roughness value of 0.32 nm was grown on sapphire substrate at a relatively lower temperature by using a three-step epitaxy technique. On the basis of this AlN template, AlGaN-based multiple quantum wells (MQWs) with atomically flat hetero-interfaces were epitaxially grown to suppress nonradia...

The effect of direct metal coating on the photoluminescence (PL) properties of ZnO nanorods (NRs) has been investigated in detail in this work. The direct coating of Ag nanoparticles (NPs) induces remarkable enhancement of the surface exciton (SX) emissions from the ZnO NRs. Meanwhile, the charge transfer process between ZnO and Ag also leads to no...

We report the development of complete structural AlGaN-based deep-ultraviolet light-emitting diodes with an aluminum thin layer for increasing light extraction efficiency. A 217% enhancement in peak photoluminescence intensity at 294 nm is observed. Cathodoluminescence measurement demonstrates that the internal quantum efficiency of the deep-UV LED...

Graded-composition multiple quantum barriers (GQB) were designed and incorporated in c-plane InGaN/GaN light-emitting diodes (LEDs) grown on c-plane sapphire substrate to improve hole transport and efficiency droop. The simulation of GQB LED design predicts enhancement of the hole transport in the active region at both low and high current densitie...

A graded-composition electron blocking layer (GEBL) with aluminum composition increasing along [ 0001] direction was designed for c-plane GaN-based light-emitting diodes (LEDs). The simulation results demonstrated that such GEBL can effectively enhance the capability of hole transportation across the EBL as well as the electron confinement. Consequ...

We had demonstrated several novel methods to improve efficiency droop behavior in GaN-based light-emitting diodes (LEDs). LEDs with different kinds of insertion layers (ILs) between the multiple quantum wells (MQWs) layer and n-GaN layer were investigated. By using low-temperature (LT, 780°C) n-GaN as IL, the efficiency droop behavior can be allevi...

Internal quantum efficiency (IQE) of InGaN/GaN UV LEDs with patterned sapphire substrates (PSS) was investigated using electroluminescence (EL) and photoluminescence (PL) methods. The physical mechanisms that affect temperature-dependent EL efficiency as a function of injected carrier density were deduced. In order to reduce the density of non-radi...

A graded-composition electron blocking layer (GEBL) with aluminum composition increasing along the [0001] direction was designed for c-plane InGaN/GaN light-emitting diodes (LEDs) by employing the band-engineering. The simulation results demonstrated that such GEBL can effectively enhance the capability of hole transportation across the EBL as well...

InGaN/GaN LED with graded-thickness MQWs has superior hole and radiative recombination distribution by simulation modeling, and electroluminescence spectrum reveals additional emission from the narrower wells. Output power and efficiency droop behavior are both improved.

We have studied the characteristics of efficiency droop in GaN-based light emitting diodes (LEDs) with different kinds of insertion layers (ILs) between the multiple quantum wells (MQWs) layer and n-GaN layer. By using low-temperature (LT) (780 °C) n-GaN as IL, the efficiency droop behavior can be alleviated from 54% in reference LED to 36% from th...

InGaN/GaN light-emitting diodes (LEDs) with graded-thickness multiple quantum wells (GQW) was designed and grown by metal-organic chemical vapor deposition. The GQW structure, in which the well-thickness increases along [0001] direction, was found to have superior hole distribution as well as radiative recombination distribution by performing simul...

Nonpolar (a-plane) GaN nanorod arrays with embedded InxGa1−xN/GaN (x = 0.09, 0.14, 0.24, and 0.30) multiple quantum wells (MQWs) grown on r-plane sapphire have been fabricated successfully by self-assembled Ni nanomasks and subsequent inductively coupled plasma reactive-ion etching. After nanorod fabrications, the polarization ratio of the emission...

Electronic structures of N-doped and undoped Mg0.25Zn0.75O/ZnO superlattices (SLs) were investigated by using a first-principles calculation. The partial charge density profiles show that electron and hole states are separated into ZnO and N-doped Mg0.25Zn0.75O layers. This property is further confirmed by the calculations of layer-projected densit...

The non-polar a-plane AlxGa1−xN alloys on GaN epitaxial layer with different Al compositions (0≤x≤0.2) were grown on r-plane (1 1¯ 0 2) sapphire substrates by using low-pressure metalorganic chemical vapor deposition (MOCVD) and the Al composition x were estimated from the X-ray diffraction measurements. According to the result of asymmetric X-ray...

A nanoscale non-contact electrical measurement has been developed based on Auger electron spectroscopy. This approach used the specialty of an Auger electron, which is self-generated and free from external influences, to overcome the technical limitations of conventional measurements. The detection of the intrinsic local charge and internal electri...

The internal electric field is modified by using Mg- and Si- δ -codoped Al _x Ga _1-x N / Al _y Ga _1-y N superlattices (SLs). The first-principles simulation results show that the internal electric field in SL has been significantly intensified due to the charge transferring from Si-doped interface to Mg-dop...

We designed Mg-doped InGaN/GaN quantum well (QW), strained ultrathin InN/GaN QWs, and Mg and Si δ-doped AlGaN/GaN superlattices (SLs) by using first-principles simulations. The designed structures were grown by metal–organic vapor phase epitaxy (MOVPE) on high-quality thick GaN using an interruption technique. The injection-current-dependent electr...

Distinct GaN islands of triangular base were formed during the annealing processes of GaN nucleation layers grown on Si-rich SiNx nanoislands patterned sapphire substrates due to enhanced diffusion and regrowth anisotropy. Subsequent high temperature growth of GaN epilayers on the nucleation layers resulted in island coarsening and shape variations...

A detailed study of emission mechanism is performed in undoped and Mg-doped InGaN/GaN multiple quantum wells (MQWs) by means of injection-current- and temperature-dependent electroluminescence measurements. Two emission peaks corresponding to the recombination in InGaN quantum well are observed at high injection-current level in both MQWs. Accordin...

The linear electro-optic (Pockels) effect of wurtzite gallium nitride (GaN) films and six-period GaN/Al x Ga 1-x N superlattices with different quantum structures were demonstrated by a polarization-maintaining fiber-optical Mach-Zehnder interferometer system with an incident light wavelength of 1.55µm. The samples were prepared on (0001) sapphire...

The electronic structures of Mg modulation-doped and undoped Al _0.5 Ga _0.5 N / Ga N superlattices (SLs) are investigated by using first-principles density function theory. The layer-projected densities of states indicate that the band alignment is changed from type I to type II and the band bending due to polarization is reduc...

Six-period 4 nm GaN/10 nm AlxGa1−xN superlattices with different Al mole fractions x were prepared on (0001) sapphire substrates by low-temperature metal-organic chemical vapor deposition. The linear electro-optic (Pockels) effect was studied by a polarization-maintaining fiber-optical Mach-Zehnder interferometer system with an incident light wavel...

Wafers with normal light-emitting diode structure were grown by metal organic chemical vapor deposition system. The pressure and temperature were varied during growth of buffer layer in order to grow different types of epilayers. The cathodoluminescence results show that the interface distortion of quantum well plays an important role in radiant ef...

The ab initio 'mixed-basis + norm conserving non-local pseudopotential' method 'was performed on calculating the electronic structures of four Mg-Si or Mg-O codoped configurations in wurtzite GaN. The results show that dense states generate around the valence band edges after codoping. The top of valance band split widely and shift up towards the c...