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To improve the performance of optoelectronic devices, a high performance wide angle SiO2/Ti3O5 Distributed Bragg Reflector (DBR) mirror was designed and fabricated on double polished sapphire substrate. 17-pairs gradually varied DBR structure was applied in order to acquire a broad stopband reflectivity over 95% from 400 nm to 800 nm, covering the whole visible light region. The DBR mirrors deposited at the backside of optoelectronics devices are also demonstrated to remain a high reflectivity at wide incident angles, which improves the emission efficiency of LEDs and light absorption efficiency of InGaN/GaN photoelectrochemical cell (PEC).

A strong coupling effect often occurs between a metal and semiconductor, so micro/nano-lasers based on surface plasmons can break through the optical diffraction limit and realize unprecedented linear and nonlinear enhancement of optical processes. Hence, metal–insulator–semiconductor (M–I–S) structures based on perovskite materials were explored to design optoelectronic devices. Herein, we constructed an Ag/SiO2/CsPbBr3 hybrid structure to generate surface plasmon coupled emission between the metal and CsPbBr3 perovskite. Combined with experimental characterization and COMSOL Multiphysics software simulations, the best enhancement for CsPbBr3 radiative recombination efficiencies can be achieved with a 10 nm-thickness of the SiO2 layer and 80 nm-thickness of the Ag metal film, further verified by optimizing the thickness of the SiO2 layer above the Ag metal film. In this state, the laser threshold can be as low as 0.138 μW with a quality (Q) factor of up to 3907 under optical pumping, which demonstrate a significant step toward practical applications in biological technology, chemical identification, and optical interconnections of information transmission.

Semi-polar micro-LEDs have gain increasing interests due to the advantages of polarization control and quantum efficiency improvement. In this work, a novel semi-polar (20–21)-plane micro-LEDs array has been designed and manufactured. In comparison with c-plane micro-LEDs, semi-polar micro-LEDs indicate better electrical and optical performance. The relative EQE of semi-polar micro-LEDs remains at 62% under the injected current density of 775.6 A/cm2, which indicates a reduced efficiency droop due to less polarization in MQWs. It has been further proved by a significant reduction of 55% in emission peak blue-shift under the injected current density from 11.1 A/cm2 to 775.6 A/cm2. In addition, the carrier recombination dynamics and spatial light distribution of semi-polar micro-LEDs with different pixel sizes have been studied. Fast recombination lifetime in smaller size semi-polar micro-LEDs indicates a promising way to be used as a high modulation bandwidth light source. Stable and uniform light distribution in a wider range of spatial azimuths further supports for the semi-polar micro-LEDs as a strong candidate for the applications of high-resolution display and high-speed visible light communication.

Current-voltage ( I-V ) characteristics of AlGaN ultraviolet light-emitting diodes (UV-LEDs) under the temperatures ranging from 50 K to 300 K are analyzed. The abnormal diode characteristics of UV-LEDs below the turn-on voltage indicate the existence of space-charge-limited (SCL) current transport in the presence of deep trap states, which induce a non-linear current leakage effect. The SCL current is gradually overwhelmed by Ohmic leakage as the temperature increases, which is mainly due to the thermally generated carrier concentration and traps deactivation. A modified three-diode circuit model is suggested with an additional series resistor and diode to emulate the forward-bias I-V characteristics of UV-LEDs. An excellent fit to the I-V curves of UV-LEDs is achieved, which illustrates the impact of deep trap states on the electrical characteristics of UV-LEDs.

Tunneling field-effect transistors (TFETs) based on two-dimensional (2D) materials are expected to break the physical limits of Moore's Law and extend them to the sub-10 nm scope. We systematically study the performance limits of sub-10 nm (6.4-9.6 nm) monolayer (ML) AsP TFETs by means of ab initio quantum transport calculation. With optimized doping, ML AsP TFETs show excellent performance in the armchair transport direction, which is satisfied the requirements of the International Technology Roadmap for Semiconductors (ITRS) and the International Roadmap for Devices and Systems (IRDS 2028 projection) for high-performance (HP) applications in the next ten years in terms of on-state current, delay time, and power consumption per wide power. More encouragingly, ML AsP TFET can still meet the goal of ITRS for low-power (LP) applications even if the gate length is scaled down to 8.7 nm. The on-state current of our proposed AsP TFET is superior to that of TFETs based on InAs, arsenene, antimonene, bismuthene, etc at approximate nodes, making it highly competitive in two-dimensional material semiconductor devices.

Hybrid white light emitting diodes (LEDs) have been developed utilizing micro-LEDs radiatively pumping down-conversion phosphor materials. The cyan InGaN/GaN multiple quantum wells LEDs with 95 μm in square are fabricated into 4 × 4 pixels as one unit in 4 in wafer by photolithography and inductively coupled plasma etching techniques. The relatively low turn on voltage and low leakage of cyan micro-LEDs indicate good electrical performance. A significant reduction in the efficiency droop characteristics of cyan micro-LED has been observed in comparison with that of standard green LED. Finally, based on a systemic optimization for white emission indexes, high-quality hybrid white light emission has been demonstrated by the combination of blue and cyan micro-LEDs with two types of phosphors, which have a high color rendering index up to 87 at the correlated color temperatures of 6500 K. It also demonstrates a way to adjust the color component by modifying the output power of cyan micro-LED in hybrid LED, showing a promising candidate in a large range of applications including micro-displays, bioinstrumentation, photolithography, and lab-on-chip systems in the future.

Plasmonic nanolaser as a new type of ultra-small laser, has gain wide interests due to its breaking diffraction limit of light and fast carrier dynamics characters. Normally, the main problem that need to be solved for plasmonic nanolaser is high loss induced by optical and ohmic losses, which leads to the low quality factor. In this work, InGaN/GaN nanoplate plasmonic nanolaser with large interface area were designed and fabricated, where the overlap between SPs and excitons can be enhanced. The lasing threshold is calculated to be ~6.36 kW/cm2, where the full width at half maximum (FWHM) drops from 27 to 4 nm. And the fast decay time at 502 nm (sharp peak of stimulated lasing) is estimated to be 0.42 ns. Enhanced lasing characters are mainly attributed to the strong confinement of electromagnetic wave in the low refractive index material, which improve the near field coupling between SPs and excitons. Such plasmonic laser should be useful in data storage applications, biological application, light communication, especially for optoelectronic devices integrated into a system on a chip.

Microwave plasma chemical vapor deposition (MPCVD) has been developed as a popular method to grow artificial single crystal diamonds with high crystal quality due to its feasibility and economical effectivity. However, the surface roughness and defects will lead to the generation of cracks in the growth process and significant degradation of the crystal quality of epitaxial CVD diamond. Although optimized growth parameters and subsequent chemico-mechanical polishing (CMP) could improve the surface morphology of CVD diamond layer for device fabrication, more investigations need to be done. In this study, nano-sized patterns were prepared by self-assembled Ni mask and inductively coupled plasma (ICP) etching method on diamond seed, and the height of nanorods were optimized for high quality single crystal diamond growth. According to the Microscope imaging, Raman spectroscopy, photoluminescence (PL) mapping and X-ray diffraction measurements, the influence of diamond nucleation on nanorod structures has been evaluated. The results demonstrate that the surface morphology and crystal quality of CVD diamond layer can be improved by the nano-sized patterned diamond seed, indicating a promising method for diamond-based device fabrication.

Incubation and shape transition are considered as two essential processes for nucleating of self-assembly InGaN nanocolumns (NCs) in traditional way. We propose a new approach for nuclei forming directly by in-situ annealing and ion irradiating the InGaN template during growing process. The nanoislands, considered as the nuclei of NCs, were formed by a combinational effect of thermal and ion etching (TIE), which made the gaps of the V-pits deeper and wider. On account of the decomposition of InGaN during TIE process, more nitride-rich amorphous alloys would intent to accumulate in the corroded V-pits. The amorphous alloys played a key role to promote the following growth from 2D regime into Volmer-Weber growth regime so that the NC morphology took place, rather than a compact film. As growth continued, the subsequently epitaxial InGaN alloys on the annealed NC nuclei were suffered in biaxial compressive stress for losing part of indium content from the NC nuclei during the TIE process. Strain relaxation, accompanied by thread dislocations, came up and made the lattice planes misoriented, which prevented the NCs from coalescence into a compact film at later period of growing.

III-Nitride semiconductor materials are considered as promising candidates for photoelectrodes (PEs) due to their adjustable direct band gap covering a very broad spectral range. In this study, InGaN/GaN based p–i–n photoelectrodes have been fabricated and nano-sized surface roughening process has been applied. The photocurrent gets 2.5 times enhancement and the incident photon conversion efficiency (IPCE) is improved to be ∼30% at the wavelength of 400 nm. In addition, the turn-on voltages of InGaN/GaN-based PEs have been effectively reduced from +0.8 V down to about −0.4 V (vs. reversible hydrogen potential, RHE). Such improvements are mainly attributed to reduced dislocation density, increased surface area, and optimized build-in electrical field. These findings give innovative insight to improve photoelectrochemical devices for hydrogen generation.

InGaN/GaN single nanorod (NR) light-emitting diodes (LEDs) have successfully been fabricated by nanoimprint lithography and focused ion beam-induced deposition. The current–voltage characteristics of single NR LEDs show low leakage current of $2\times 10^{\mathrm {-12}}$ A at a reverse bias of −5 V and turn-ON voltage of $\sim 3.8$ V. Linear polarization-oriented parallel to the $c$ -axis with a degree of $\sim 50$ % was discovered from the electroluminescence emission of single NR LEDs.

Hybrid white micro-pillar structure light emitting diodes (LEDs) have been manufacture utilizing blue micro-LEDs arrays integrated with 580 nm CIS ((CuInS2-ZnS)/ZnS) core/shell quantum dots. The fabricated hybrid white micro-LEDs have good electrical properties, which are manifested in relatively low turn-on voltage and reverse leakage current. High-quality hybrid white light emission has been demonstrated by the hybrid white micro-LEDs after a systemic optimization, in which the corresponding color coordinates are calculated to be (0.3303, 0.3501) and the calculated color temperature is 5596 K. This result indicates an effective way to achieve high-performance white LEDs and shows great promise in a large range of applications in the future including micro-displays, bioinstrumentation and visible light communication.

Plasmonic nanolasers based on wide bandgap semiconductors are presently attracting immense research interests due to the breaking in light diffraction limit and subwavelength mode operation with fast dynamics. However, these plasmonic nanolasers have so far been mostly realized in the visible light ranges, or most are still under optical excitation pumping. In this work, III-nitride-based plasmonic nanolasers emitting from the green to the deep-ultraviolet (UV) region by energetic electron beam injection are reported, and a threshold as low as 8 kW cm-2 is achieved. A fast decay time as short as 123 ps is collected, indicating a strong coupling between excitons and surface plasmon. Both the spatial and temporal coherences are observed, which provide a solid evidence for exciton-plasmon coupled polariton lasing. Consequently, the achievements in III-nitride-based plasmonic nanolaser devices represent a significant step toward practical applications for biological technology, computing systems, and on-chip optical communication.

The correlation between surface structural and luminescence properties of InGaN epi-layers grown by metal organic chemical vapour deposition has been investigated. Ring-shaped regions with high In-content are observed around V-pits by spatial resolved cathodoluminescence and energy dispersive X-ray spectroscopy. These ring-shaped regions are found to form a potential energy well with depth about 300 meV with respect to the ordinary regions, which can attract carriers and suppress non-radiative recombination. The causes of the formation of high-In-content region are discussed. This localised characteristic of carriers is supported further by power and temperature dependent photoluminescence results. The understanding of the spatially emission characteristics might be helpful to improving the internal quantum efficiency of InGaN/GaN light emitting diodes (LEDs).

The AlGaN-based deep ultraviolet light-emitting diodes (UV LEDs) with specific design of staggered AlGaN quantum wells are investigated numerically. The proposed UV LEDs with Al 0.45 Ga 0.55 N–Al 0.5 Ga 0.5 N–Al 0.45 Ga 0.55 N and Al 0.5 Ga 0.5 N–Al 0.45 Ga 0.55 N–Al 0.5 Ga 0.5 N staggered quantum well layers exhibit significant improvement for the light output power and carrier injection efficiency compared with the conventional AlGaN UV LED. The enhanced performance of the designed LEDs is explained by the simulated distribution of carrier concentration, radiative recombination rate and wave function overlap in the quantum wells.

Thin film solar cells (TFSC) are the most potential for development of new and renewable clean energy. The large-scale production and application of TFSC can ease the energy crisis and protect the environment for human. However, buffer layer is a critical layer, which determines the performance of TFSC. This paper reviews the preparation, mechanisms, deposition systems, and development of ZnS thin-film buffer layers and points out that CBD-ZnS thin film is the best buffer layer material taking place of CdS.

In the last two decades, remarkable progress has been achieved in the field of optoelectronic devices based on III-nitride semiconductors. In terms of photonics applications in the visible-UV spectral range, III-nitrides are one of the most promising materials. For instance, emerging gallium nitride (GaN)-based micro-light-emitting diode (LED) technology for high-resolution display, and UV photo-detection for environmental monitoring, health, and medical applications. In this work, hybrid micro/nano-LEDs with integration of II-VI quantum dots by means of lithography and nano-imprinting patterning techniques are demonstrated, and high-performance red/green/blue and white emissions are achieved. Consequently, plasmonic nanolasers are designed and fabricated using a metal-oxide-semiconductor structure, where strong surface plasmon polariton coupling leads to the efficient lasing with a low excitation threshold from the visible to UV tunable spectral range. Furthermore, performance-improved AlGaN UV solar-blind avalanche photodiodes (APDs) with a separate absorption and multiplication structure by polarization engineering are reported. These APDs deliver a record-high avalanche gain of up to 1.6 × 105 . These newest advances in nano/micro-LEDs, nanolasers, and APDs can shed light on the emerging capabilities of III-nitride in cutting-edge applications.

GaN-based micro light emitting diodes (micro-LEDs) on silicon (Si) substrates with 40 μm in diameter are developed utilizing standard photolithography and inductively coupled plasma etching techniques. From current-voltage curves, the relatively low turn-on voltage of 2.8 V and low reverse leakage current in the order of 10 −8 A/cm 2 indicate good electrical characteristics. As the injection current increases, the electroluminescence emission wavelength hardly shifts at around 433 nm, and the relative external quantum efficiency slightly decays, because the impact of quantum-confined Stark effect is not serious in violet-blue micro-LEDs. Since GaN-LEDs are cost effective on large-area Si and suitable for substrate transfer or vertical device structures, the fabricated micro-LEDs on Si should have promising applications in the fields of high-resolution display and optical communication.

The photoelectrodes based on III-nitride semiconductors with high energy conversion efficiency especially for those self-driven ones are greatly desirable for hydrogen generation. In this study, highly ordered InGaN/GaN multiple-quantum-well nanorod-based photoelectrodes have been fabricated by a soft UV-curing nano-imprint lithography and a top-down etching technique, which improve the incident photon conversion efficiency (IPCE) from 16% (planar structure) to 42% (@ wavelength = 400 nm). More significantly, the turn-on voltage is reduced low to −0.6 V, which indicates the possibility of achieving self-driven. Furthermore, SiO2/Si3N4 dielectric distributed Bragg reflectors are employed to further improve the IPCE up to 60%. And the photocurrent (@ 1.1 V) is enhanced from 0.37 mA/cm2 (original planar structure) to 1.5 mA/cm2. These improvements may accelerate the possible applications for hydrogen generation with high energy-efficiency.

A series of highly ordered c-plane InGaN/GaN elliptic nanorod (NR) arrays were fabricated by our developed soft UV-curing nanoimprint lithography on a wafer. The photoluminescence (PL) integral intensities of NR samples show a remarkable enhancement by a factor of up to two orders of magnitude compared with their corresponding as-grown samples at room temperature. The radiative recombination in NR samples is found to be greatly enhanced due to not only the suppressed non-radiative recombination but also the strain relaxation and optical waveguide effects. It is demonstrated that elliptic NR arrays improve the light extraction greatly and have polarized emission, both of which possibly result from the broken structure symmetry. Green NR light-emitting diodes have been finally realized, with good current-voltage performance and uniform luminescence.

Highly ordered AlxGa1−xN nanorods with varied aluminum alloy compositions (0.18 ≤ x ≤ 0.8) are fabricated with nanoimprint lithography and top-down dry etching techniques. And the structural properties and morphology are obtained by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Compared with as-grown AlGaN samples, nanorod samples reveal outstanding optical performance on account of strain releasing and light extraction enhancement. Through Raman scattering and cathodeluminescence measurements, it has been observed clear red-shifts of E2h modes and near band edge emission (NBE) peaks of AlGaN nanorods compared to the planar ones, indicating the residual strain releasing after nano-fabrication. The integrated intensities of NBE peaks of AlGaN nanorods manifest light emission enhancement up to 2.7 at deep-UV range. Finite-difference time-domain (FDTD) simulations have been adopted to investigate the light extraction and far-field distribution of such structures, it turned out that ordered nanorod array can enhance the TM polarized emission extraction 2–7 folds compared to the planar structure. The optical regulation in nanorod arrays should take the responsibility for the observed optical enhancements, which is proved by the far-field distribution of light, thus it can improve the performance of ultraviolet LEDs.

GaN nanorods with a period of 400 nm and diameter of 200 nm, and nano-gratings with a period of 400 nm and gap width of 100 nm are fabricated on wafers by a soft UV-curing nanoimprint lithography. These nanostructures show high periodicity and good morphology. The photoluminescence (PL) spectra exhibit that the integral PL intensity of GaN nanorods is enhanced as much as 2.5 times, compared to that of as-grown GaN films. According to finite-difference time-domain simulations and cathodoluminescence mappings, it is concluded that the enhancement for nanorods is due to the improvements of both spontaneous emission rate and light extraction efficiency caused by periodic GaN structures on the surface. By identifying the Raman shift of E1(TO) and E2(H) modes of GaN films with nano-gratings and nanorods, the normal-plane strain e(zz) is determined. The PL emission energy is found to be proportional to the e(zz), whose linear proportionality factor is calculated to be -27 meV GPa(-1).

Blue InGaN/GaN nanohole light-emitting diodes have been fabricated by soft UV-curing nanoimprint lithography, filling with CdSe/ZnS core/shell nanocrystals (NCs) as color conversion mediums. The excitonic recombination dynamics of hybrid nanohole light-emitting diodes were investigated by time-resolved photoluminescence, observing a significant reduction in the decay lifetime of excitons as a result of an efficient non-radiative resonant energy transfer, which leads to the improvement of color conversion and efficiency droop in these hybrid nanohole light-emitting diodes compared to hybrid nanocrystals/standard planar light-emitting diodes. The color-conversion efficiency and effective quantum yield of hybrid nanohole light-emitting diodes were nearly twice as much as those of hybrid standard light-emitting diodes. A model on the excitonic recombination process was proposed to explore this situation, explaining the advantages of non-radiative resonant energy transfer that avoiding energy loss associated with the intermediate light emission and conversion steps and transferring energy non-radiatively and resonantly to NCs with a higher quantum yield. The efficiency droop of hybrid nanohole light-emitting diodes was validly suppressed compared to the bare ones, even better than that of hybrid standard light-emitting diodes. It mainly results from the extraction of excess carrier concentrations in InGaN/GaN multiple quantum wells via the rapid non-radiative resonant energy transfer process under the higher injection condition, revealing a great potential to realize efficient white light emitters in the future.

Highly ordered c-plane InGaN/GaN elliptic nanorod (NR) and nano-grating (NG) arrays were fabricated by our developed soft UV-curing nanoimprint lithography on a wafer. The polarized photoluminescence emission from these elliptic NR and NG arrays has been investigated both theoretically and experimentally. Considerable in-plane optical anisotropy, with a polarization ratio of 15% and 71% and a peak shift of 5.2 meV and 28.1 meV, was discovered from these c-plane InGaN/GaN elliptic NR and NG arrays, respectively. The k·p perturbation theory was adopted to explore this situation, simulating the transitions from conduction subbands to valence subbands and their corresponding optical momentum matrix elements at/around Γ point under the in-plane asymmetric strain. The good agreements of observed and simulated results demonstrate that the in-plane strain asymmetry is the essential cause of the optical polarization in this case, revealing the great potential to utilize strain effect to control the polarization of...

Through investigating the temperature dependent current-voltage (T-I-V) properties of GaN based blue and green LEDs in this study, we propose an asymmetric tunneling model to understand the leakage current below turn-on voltage (V < 3.2 V): At the forward bias within 1.5 V ∼ 2.1 V (region 1), the leakage current is main attributed to electrons tunneling from the conduction band of n-type GaN layer to the valence band of p-type GaN layer via defect states in space-charge region (SCR); While, at the forward bias within 2 V ∼ 2.4 V (region 2), heavy holes tunneling gradually becomes dominant at low temperature (T < 200K) as long as they can overcome the energy barrier height. The tunneling barrier for heavy holes is estimated to be lower than that for electrons, indicating the heavy holes might only tunnel to the defect states. This asymmetric tunneling model shows a novel carrier transport process, which provides better understanding of the leakage characteristics and is vital for future device improvements.

Surface-plasmon (SP) coupled red light emitting InGaN/GaN multiple quantum well (MQW) structure is fabricated and investigated. The centre wavelength of 5-period InGaN/GaN MQW structure is about 620 nm. The intensity of photoluminescence (PL) for InGaN QW with naked Ag nano-structures (NS) is only slightly increased due to the oxidation of Ag NS as compared to that for the InGaN QW. However, InGaN QW with Ag NS/SiO2 structure can evidently enhance the emission efficiency due to the elimination of surface oxide layer of Ag NS. With increasing the laser excitation power, the PL intensity is enhanced by 25%–53% as compared to that for the SiO2 coating InGaN QW. The steady-state electric field distribution obtained by the three-dimensional finite-difference time-domain method is different for both structures. The proportion of the field distributed in the Ag NS for the GaN/Ag NS/SiO2 structure is smaller as compared to that for the GaN/naked Ag NS structure. As a result, the energy loss of localized SP modes ...

InGaN/GaN light-emitting diode structures with Al-coated GaN nanorods were fabricated by using soft ultraviolet nanoimprint lithography. The intensity of light emission was found to be greatly enhanced due to the strong near-fields confined at the interface of Al/GaN and extended to the multiple quantum wells (MQWs) active region. The dynamics of carrier recombination and plasmon-enhanced Raman scattering were also investigated, providing a progressive view on the effective energy transfer between MQWs and surface plasmons.

A significant enhancement in solar hydrogen generation efficiency has been achieved by inductive coupled etching (ICP) surface roughening treatment using nano-sized nickel mask. As much as 7 times improvement of photocurrent is demonstrated in comparison with a planar one fabricated from the same parent wafer. Under identical illumination conditions in HBr solution, the incident photon conversion efficiency (IPCE) shows an enhancement with a factor of 3, which even exceed 54% at 400 nm wavelength. We believe the enhancement is attributed to several facts including improvement in absorption, reacting area, carrier localization and carrier lifetime.

The spontaneous emission (SE) of InGaN/GaN quantum well (QW) structure with silver(Ag) coated on the n-GaN layer has been investigated by using six-by-six K-P method taking into account the electron-hole band structures, the photon density of states of surface plasmon polariton (SPP), and the evanescent fields of SPP. The SE into SPP mode can be remarkably enhanced due to the increase of electron-hole pairs near the Ag by modulating the InGaN/GaN QW structure or increasing the carrier injection. However, the ratio between the total SE rates into SPP mode and free space will approach to saturation or slightly decrease for the optimized structures with various distances between Ag film and QW layer at a high injection carrier density. Furthermore, the Ga-face QW structure has a higher SE rate than the N-face QW structure due to the overlap region of electron-hole pairs nearer to the Ag film.