Nonpolar Planes Research Articles

Heterogeneous Nucleation Regulation Amends Unfavorable Crystallization Orientation and Defect Features of Antimony Selenosulfide Film for High‐Efficient Planar Solar Cells

AbstractAntimony selenosulfide (Sb2(S,Se)3) has obtained widespread concern for photovoltaic applications as a light absorber due to superior photoelectric features. Accordingly, various deposition technologies have been developed in recent years, especially hydrothermal deposition method, which has achieved a great success. However, device performances are limited with severe carrier recombination, relating to the quality of absorber and interfaces. Herein, bulk and interface defects are simultaneously suppressed by regulating heterogeneous nucleation kinetics with barium dibromide (BaBr2) introduction. In details, the Br adsorbs and dopes on the polar planes of cadmium sulfide (CdS) buffer layer, promoting the exposure of nonpolar planes of CdS, which facilitates the favorable growth of [hk1]‐Sb2(S,Se)3 films possessing superior crystallinity and small interface defects. Additionally, the Se/S ratio is increased due to the replacement of Se by Br, causing a downshift of the Fermi levels with a benign band alignment and a shallow‐level defect. Moreover, Ba2+ is located at grain boundaries by coordination with S and Se ions, passivating grain boundary defects. Consequently, the efficiency is increased from 7.70 % to 10.12 %. This work opens an avenue towards regulating the heterogeneous nucleation kinetics of Sb2(S,Se)3 film deposited via hydrothermal deposition approach to optimize its crystalline orientation and defect features.

Heterogeneous Nucleation Regulation Amends Unfavorable Crystallization Orientation and Defect Features of Antimony Selenosulfide Film for High-Efficient Planar Solar Cells.

Antimony selenosulfide (Sb2(S,Se)3) has obtained widespread concern for photovoltaic applications as a light absorber due to superior photoelectric features. Accordingly, various deposition technologies have been developed in recent years, especially hydrothermal deposition method, which has achieved a great success. However, device performances are limited with severe carrier recombination, relating to the quality of absorber and interfaces. Herein, bulk and interface defects are simultaneously suppressed by regulating heterogeneous nucleation kinetics with barium dibromide (BaBr2) introduction. In details, the Br adsorbs and dopes on the polar planes of cadmium sulfide (CdS) buffer layer, promoting the exposure of nonpolar planes of CdS, which facilitates the favorable growth of [hk1]-Sb2(S,Se)3 films possessing superior crystallinity and small interface defects. Additionally, the Se/S ratio is increased due to the replacement of Se by Br, causing a downshift of the Fermi levels with a benign band alignment and a shallow-level defect. Moreover, Ba2+ is located at grain boundaries by coordination with S and Se ions, passivating grain boundary defects. Consequently, the efficiency is increased from 7.70 % to 10.12 %. This work opens an avenue towards regulating the heterogeneous nucleation kinetics of Sb2(S,Se)3 film deposited via hydrothermal deposition approach to optimize its crystalline orientation and defect features.

Improving optical and electrical stabilities of fluorine-doped tin oxide films in sweat solutions with O2 addition in plasma

Abstract Recently, the use of wearable smart devices has significantly increased; however, sweat can corrode the outer-layer films, thereby decreasing their transmittance, conductivity, and overall functionality. In this study, fluorine-doped tin oxide (FTO) films for wearable smart devices were prepared via magnetron sputtering. The effects and mechanism of O2 gas flow in plasma on the properties of the fabricated films were investigated. Minor changes were observed in the film morphologies, with the preferred orientations shifting from polar (101) to nonpolar (110) and standard positions. As the O2 flow rate increased from 0 to 2 sccm, the transmittance of the film within the visible spectrum increased from 83% to 89%, with sheet resistance values in the order of 102–106 Ω·sq–1. Following immersion in an acidic sweat solution, the film without O2 peeled off, whereas several corrosion pits were observed in the films with 1 or 2 sccm O2. Conversely, following immersion in an alkaline sweat solution, several pits were observed in the films without O2, while the other films exhibited excellent corrosion resistance. The transmittance of the films immersed in different solutions did not significantly differ. Notably, the sheet resistances of the films treated with 1 sccm O2 met the industrial requirement of 3000 Ω. Moreover, the coexistence of polar and nonpolar planes provided transparency and conductive stability to the FTO films treated with 1 sccm O2. Our study aimed to not only enhance the transmittance and sweat-corrosion resistance but maintain the conductivity of the outer screen layer of a wearable smart electronic device.

The determination of WSe2/GaN heterojunction band offsets in the semipolar (11–22) and nonpolar (11–20) planes by x-ray photoelectron spectroscopy

Wurtzite structured GaN has a severe polarization effect in the c (0001) plane, compared to which the polarization effect is small in the semipolar (11–22) plane, and there is no polarization effect in the nonpolar (11–20) plane GaN. To investigate the influence of the polarization effect on the band bending at the heterojunction interface, we fabricated tungsten diselenide (WSe2)/(0001) GaN, WSe2/(11–22) GaN, and WSe2/(11–20) GaN heterojunctions. We measured the heterojunction valence band offsets (VBOs) by x-ray photoelectron spectroscopy. The VBOs of the three WSe2/GaN heterojunctions were measured to be 2.43 ± 0.15, 2.51 ± 0.15, and 2.23 ± 0.15 eV, and the conduction band offsets were calculated to be 1.11 ± 0.15, 1.19 ± 0.15, and 0.91 ± 0.15 eV, showing the type II energy band alignment of the three heterojunctions. The results demonstrate that WSe2/(11–22) GaN-faced heterojunction band bending is the largest. This provides theoretical insights for two-dimensional WSe2 and three-dimensional semipolar (11–22) GaN and nonpolar (11–20) GaN heterojunction device preparation.

Cost-effective superhydrophobic ZnO films with adjustable wetting behaviors deposited via solution precursor plasma spray process

In this work, ZnO films featuring hierarchical micron−/nanometer-sized structures were deposited for adjusting wettability by a simple solution precursor plasma spray (SPPS) process using cost-effective zinc acetate solution. The effects of solution flow rate on the surface microstructures, surface roughness, crystalline orientation, and wetting behaviors of the films were investigated comprehensively. The results showed that high solution flow rate facilitated the formation of apparent hierarchical surface structures featuring more uniformly-distributed micron-sized protrusions and higher surface roughness. The increase of solution flow rate also promoted the crystalline growth along the non-polar (100) plane. With the solution flow rate increasing from 10 ml/min to 40 ml/min, the synergy of the surface structures and crystalline growth orientation resulted in a sharp decrease of the surface energy of the films from ~74.4 mJ/m2 to ~12.6 mJ/m2 and a dramatic elevation of water contact angles from ~130° to ~155°. The wetting states of different films were elucidated by correlating the wetting behaviors with the surface structures. The SPPS-deposited ZnO films showed high adhesion to water droplets, similar to the wetting behaviors of the petal effect, which could be used as a “mechanical hand” for non-loss microdroplet transfer. The work shows that SPPS represents a promising method to deposit cost-effective superhydrophobic films with adjustable wetting behaviors.

Large scale fabrication of GaN nanorods template and characterization of MOCVD grown InGaN/GaN quantum wells on [formula omitted] plane of GaN nanorods

Gallium nitride (GaN) based low-dimensional optoelectronic devices offer distinct advantages over bulk counterparts owing to enhanced surface-to-volume ratio and better strain management. Among these devices, InGaN/GaN multi-quantum wells (MQWs) based on nanostructured GaN have garnered attention due to tunable bandgap along with reduced size for its possible integration into display technology. However, to mitigate the effects of polarization induced by polar planes of GaN, such as quantum confined stark effect, researchers are exploring the growth of MQWs on non-polar planes as a practical approach to improve emission characteristics and device performance. In this work, we present the fabrication of GaN nanorods (NRs) using a two-step etching method, followed by the growth of core-shell InGaN/GaN MQWs on the exposed non-polar {101‾0} sidewalls of GaN NRs. Our metrological studies confirmed the successful growth of InGaN/GaN MQWs on the non-polar sidewalls of strain-relaxed core GaN NRs. Furthermore, power-dependent luminescence study showed emission characteristics with absence of polarization-induced effects. Cathodoluminescence study validated the emission characteristics of InGaN/GaN MQWs grown on the exposed sidewalls of the GaN NRs.

GaN micro- and nanostructures selectively grown on profiled sapphire substrates using PA-MBE without lithography

Purpose: Development of technology for the formation of ordered arrays of nanocolumns (NCs) of GaN microcrystals using plasma-activated molecular beam epitaxy from nitrogen (PA-MBE) on profiled sapphire substrates (SPS) of large diameter with a micro-cone profile. The proposed method eliminates the use of low-performance and expensive nanolithography methods. The article is aimed at a deeper understanding of the processes that determine the growth kinetics of III-N nanocolumns using PA MBE on patterned sapphire substrates with multiple orientations of various non-polar and polar planes. A new technological process for the fabrication of GaN NCs using PA-MPE is proposed, which ensures selectivity of their growth at the tops of PPS micro-cones and suppresses growth on the semipolar planes of these substrates. GaN NCs and microcrystals were grown using PA-MBE on commercially available PPS. A technology has been developed for the formation of discharged arrays of GaN nanocolumns without the use of lithographic procedures. Modes have been established that allow the formation of microcrystals and NCs with different diameters: from 30 nm to several microns. A diagram of the growth of GaN by the PA MBE method on PPS has been constructed, demonstrating the boundaries of the technological regimes for the formation of GaN NCs and microcrystals with different surface topography

Melamine-Assisted Thermal Activation Method for Vacancy-Rich ZnO: Calcination Effects on Microstructure and Photocatalytic Properties.

Defect engineering is considered an effective method to adjust the photocatalytic properties of materials. In this work, we synthesized the vacancy-rich ZnO rods with (100) planes via the melamine-assisted thermal activation method. A high concentration of oxygen vacancies was successfully introduced into non-polar oriented ZnO rods by calcination. The effect of oxygen vacancy on the photocatalytic properties of non-polar-oriented ZnO rods was investigated. Raman and XPS spectra revealed the formation of oxygen vacancies in the ZnO. The results showed that the growth habit and defects in ZnO can be controlled by changing the ratio of ZnO to melamine. The higher ratio of ZnO to melamine led to more amounts of (100) planes and oxygen vacancies in ZnO, and it reached the highest when the ratio was 1.2:1. When the ratio was 1.2:1, ZnO exhibited a high methyl orange degradation rate (95.8%). The differences in oxygen vacancy concentration and non-polar planes were responsible for the improvement in photocatalytic performance. ZnO exhibited good stability and regeneration capacity. After recycling four times, the degradation rate was still at 92%. Using the same method, vacancy-rich α-Fe2O3 was obtained. This work could offer a new and simple strategy for designing a photocatalyst with oxygen vacancies.

Preferential crystal orientation etching of GaN nanopillars in Cl2 plasma

The ability to fabricate organized, dense arrays of GaN nanostructures with high aspect ratios is of great interest for improving light extraction and absorption in optoelectronic devices, such as light-emitting diodes (LEDs) and Lasers.However, achieving this requires a patterning method that allows for the fabrication of GaN nanostructures with a controlled final shape and specific crystallographic facets. Our study shows that a top-down approach combining lithography and Cl2-based plasma etching processes offers the possibility of anisotropically transferring a pattern while revealing smooth nonpolar facets.Although GaN etching in Cl2 is driven by ion-enhanced chemical etching mechanisms, the chemical component is very strong, and Cl2 plasma leads to preferential crystallographic orientation etching of GaN. The mechanisms that drive facet formation are very similar to those involved in wet KOH etching. The etching ability of a specific crystallographic plane by chlorine atoms depends on the planar density and the N dangling bonds present on the plane. Predictably, GaN crystallographic planes will be etched in Cl2 plasmas as follows: a-type semipolar > m-type semipolar planes > a nonpolar plane > m polar planes > c polar planes. Crystallographic etching usually reveals the slowest etching planes, meaning the m-planes. However, consistently with the wet mechanisms, our study shows that the final revealed plane in Cl2 plasma will strongly depend on the surface curvature: in concave surfaces, fast-etch facets persist, while in convex surfaces, slow-etch facets persist. Consequently, Cl2 plasma etching of pillars (convex surfaces) will result in a-type facets, while etching of holes (concave surfaces) result in m-type facets.

Comparative Analysis of the GaN Nonpolar Plane Morphology by Wet Treatment and Its Effect on Electrical Properties in Trench MOSFET

The morphological characteristics of the GaN nonpolar sidewalls with different crystal plane orientations were studied under various TMAH wet treatment conditions, and the effect of different morphological features on device carrier mobility was modeled and analyzed. After TMAH wet treatment, the morphology of the a-plane sidewall presents multiplied zigzag triangular prisms along the [0001] direction, which consist of two adjacent m-plane and c-plane on top. While along the [112̅0] direction, the m-plane sidewall is represented by thin, striped prisms with three m-plane and a c-plane on the side. The density and size of sidewall prisms were studied by varying the solution temperature and immersion period. The prism density decreases linearly as the solution temperature rises. With increased immersion time, both a-plane and m-plane sidewalls show smaller prism sizes. Vertical GaN trench MOSFET with nonpolar a- and m-plane sidewall channels were fabricated and characterized. By properly treated in TMAH solution, transistors with an a-plane sidewall conduction channel exhibit higher current density, from 241 to 423 A cm-2@VDS = 10 V, VGS = 20 V, and higher mobility, from 2.9 to 2.0 cm2 (V s)-1, compared to those of m-plane sidewall devices. The temperature dependence on mobility is also discussed, and a modeling analysis for the difference in carrier mobility is then performed.

Origin and Mechanism of Anisotropic Piezoelectric Generation on the ZnO(101̅0) Crystal Plane

The experimental observation of pressure-induced structural changes is crucial for establishing the correct piezoelectric mechanism. Here, we show the in-plane anisotropic piezoelectric generation behavior on a ZnO non-polar (101̅0) crystal plane. The piezoelectric and rectification effects are found in the [0001] polar direction on the (101̅0) crystal facet. Neither effect was observed in the [12̅10] non-polar direction perpendicular to the [0001] direction. The piezoelectric generation and rectification properties can be reduced and vanished under pressure in the [0001] direction. The spontaneous polarization in the [0001] direction is evidenced to be the origin of piezoelectric effect. Pressure-induced structural change of ZnO is observed for the first time. In the piezoelectric effect, the applied stress causes the polar structure of ZnO to change into a non-polar structure, and the piezoelectric current is generated. This novel piezoelectric model will overturn the existing piezoelectric theory and piezoelectric generation mechanism and contribute to comprehending the crystal orientation-dependent piezoelectric properties and the development of new high-performance piezoelectric materials and devices.

Nonpolar Growth of GaN Films on Polar Sapphire Substrate Using Pulsed Laser Deposition: Investigation of Substrate Temperature Variation on the Quality of Films

The growth of GaN films along nonpolar crystallographic planes, especially s‐plane, on c‐Al2O3 substrate using pulsed laser deposition (PLD) is reported. The role of substrate temperature variation on the structural and morphological properties along this plane is investigated using different techniques. The degree of crystallinity, surface roughness, etc. associated with films are observed to depend strongly on deposition conditions, for example, substrate temperature kept during deposition. Micro‐Raman investigations reveal the presence of an unexpected phonon mode, E1(LO), in the spectra for films deposited at high temperature where prominent crystal growth is observed. The presence of the particular phonon mode observed herewith is due to the nonpolar growth of GaN crystals as well as high density of defects and/or plasmon coupling present in the films. Strong near‐band‐edge emission in the photoluminescence spectra for all specimens shows moderate optical properties of the films. Elemental analysis using X‐ray photoelectron spectra technique confirms the formation of GaN phase for all specimens.

High-Performance Colloidal Quantum Dot Photodiodes via Suppressing Interface Defects.

PbS colloidal quantum dot (CQD) infrared photodiodes have attracted wide attention due to the prospect of developing cost-effective infrared imaging technology. Presently, ZnO films are widely used as the electron transport layer (ETL) of PbS CQDs infrared photodiodes. However, ZnO-based devices still suffer from the problems of large dark current and low repeatability, which are caused by the low crystallinity and sensitive surface of ZnO films. Here, we effectively optimized the device performance of PbS CQDs infrared photodiode via diminishing the influence of adsorbed H2O at the ZnO/PbS CQDs interface. The polar (002) ZnO crystal plane showed much higher adsorption energy of H2O molecules compared with other nonpolar planes, which could reduce the interface defects induced by detrimentally adsorbed H2O. Based on the sputtering method, we obtained the [002]-oriented and high-crystallinity ZnO ETL and effectively suppressed the adsorption of detrimental H2O molecules. The prepared PbS CQDs infrared photodiode with the sputtered ZnO ETL demonstrated lower dark current density, higher external quantum efficiency, and faster photoresponse compared with the sol-gel ZnO device. Simulation results further unveiled the relationship between interface defects and device dark current. Finally, a high-performance sputtered ZnO/PbS CQDs device was obtained with a specific detectivity of 2.15 × 1012 Jones at -3 dB bandwidth (94.6 kHz).

Superlattice-Induced Variations in Morphological and Emission Properties of GaInN/GaN Multiquantum Nanowire-Based Micro-LEDs.

Core-shell GaInN/GaN multiquantum shell (MQS) nanowires (NWs) are gaining great attention for high-efficiency micro-light-emitting diodes (micro-LEDs) owing to the minimized etching region on their sidewall, nonpolar or semipolar emission planes, and ultralow density of dislocations. In this study, we evaluated the changes in NW morphologies and the corresponding device properties induced by GaInN/GaN superlattice (SL) structures. The cathodoluminescence intensities of the samples with 20 and 40 pairs of SLs were about 2.2 and 3.4 times higher, respectively, than that of the sample without SLs. The high-resolution scanning transmission electron microscopy (STEM) inspection confirmed that the high growth temperature of SLs prevented growth in the semipolar plane region close to the n-GaN core. A similar phenomenon was also observed for the GaN quantum barriers of the semipolar MQS region under a high growth temperature of 810 °C. This phenomenon was ascribed to the passivation of the semipolar plane surface by hydrogen atoms and the high probability of decomposition through NH3 or N-H-related bonds. Although no clear SL grew on the semipolar plane near the n-core region, the top area of the nonpolar plane SL was expected to adequately suppress the point defects propagating from the n-GaN core to the semipolar plane MQS. The electroluminescence (EL) spectra and light output curves demonstrated a clear enhancement of more than 3-folds compared to the fabricated micro-LEDs without SL structures, which was associated with the improved crystalline quality of the MQS and enlarged area of the semipolar planes. Moreover, by increasing the growth time of GaN quantum barriers, the EL emission intensity of the micro-LED devices exhibited a 4-fold improvement owing to the reduced carrier overflow in the thickened GaN barriers on the semipolar (11̅01) planes. Thus, the results verified the possibility of realizing highly efficient NW-based micro-LEDs by optimizing the NW morphology using SL structures.

Transition in the preferred orientation of RF sputtered ZnO/Si thin films by thermal annealing: Structural, morphological, and optical characteristics

Polycrystalline ZnO thin films having preferential growth along the polar (002) plane are prepared on Si (111) substrate using RF sputtering technique. A gradual build-up of the semipolar (103) plane with the dominant (002) polar plane of 400–700 °C annealed films is revealed by the Glancing incidence angle X-Ray diffraction (GXRD) pattern. However, a change in preferred orientation from polar (002) to semi-polar (103) and non-polar (100) planes is observed with further annealing in the temperature range 800–1200 °C. This occurs due to an increase in the mobility of adatoms due to annealing which encourages diffusion across grain boundaries and competitive growth among planes leading to the growth of (103) plane. This structural deviation of film from (002) plane to (103) plane leads to the change in surface morphology of annealed films around 800 °C as depicted in Field Emission Scanning Electron Microscopy (FESEM) images. The observed changes in surface morphology of films are further correlated with the variation in optical band gap values and diffuse reflectance spectra. The low reflectance values of the samples represent their anti-reflection property which makes ZnO/Si thin film a conceivable applicant in optoelectronics.

Epitaxial Growth and Characteristics of Nonpolar a-Plane InGaN Films with Blue-Green-Red Emission and Entire In Content Range

Nonpolar () plane In x Ga1−x N epilayers comprising the entire In content (x) range were successfully grown on nanoscale GaN islands by metal-organic chemical vapor deposition. The structural and optical properties were studied intensively. It was found that the surface morphology was gradually smoothed when x increased from 0.06 to 0.33, even though the crystalline quality was gradually declined, which was accompanied by the appearance of phase separation in the In x Ga1−x N layer. Photoluminescence wavelengths of 478 and 674 nm for blue and red light were achieved for x varied from 0.06 to 0.33. Furthermore, the corresponding average lifetime (τ 1/e ) of carriers for the nonpolar InGaN film was decreased from 406 ps to 267 ps, indicating that a high-speed modulation bandwidth can be expected for nonpolar InGaN-based light-emitting diodes. Moreover, the bowing coefficient (b) of the () plane InGaN was determined to be 1.91 eV for the bandgap energy as a function of x.

Crystallographic Effects of GaN Nanostructures in Photoelectrochemical Reaction.

Tuning the surface structure of the photoelectrode provides one of the most effective ways to address the critical challenges in artificial photosynthesis, such as efficiency, stability, and product selectivity, for which gallium nitride (GaN) nanowires have shown great promise. In the GaN wurtzite crystal structure, polar, semipolar, and nonpolar planes coexist and exhibit very different structural, electronic, and chemical properties. Here, through a comprehensive study of the photoelectrochemical performance of GaN photocathodes in the form of films and nanowires with controlled surface polarities we show that significant photoelectrochemical activity can be observed when the nonpolar surfaces are exposed in the electrolyte, whereas little or no activity is measured from the GaN polar c-plane surfaces. The atomic origin of this fundamental difference is further revealed through density functional theory calculations. This study provides guideline on crystal facet engineering of metal-nitride photo(electro)catalysts for a broad range of artificial photosynthesis chemical reactions.

Decreased Fast Time Scale Spectral Diffusion of a Nonpolar InGaN Quantum Dot

Spectral diffusion can lead to considerable broadening of the line width of nitride quantum dots. Here, InGaN quantum dots grown on a nonpolar plane were shown to exhibit a decreased spectral diffusion rate compared to polar nitride dots. A robust intensity correlation method was used to measure the spectral diffusion rate of six quantum dots. A maximum spectral diffusion time of 1170 ± 50 ns was found. An increase of the rate with increasing power was observed. The decreased internal field leads to a lifetime for the nonpolar dots that is shorter than that for polar dots; the important ratio of spectral diffusion time to lifetime is more favorable for nonpolar quantum dots, thereby increasing the chances of generating indistinguishable photons.

Effects of AlN substrate orientation on crystalline quality of wurtzite GaN films investigated via molecular dynamics

Molecular dynamics (MD) simulation was applied to investigate the deposition process of gallium nitride (GaN) films on aluminum nitride (AlN) substrates, in which the effects of different crystallographic orientations and growth temperatures of AlN substrates were investigated. Furthermore, evolution of the surface morphologies, the dislocations, the crystalline structures and the atomic stress were discussed in detail. It could be indicated that the deposited heteroepitaxial GaN films were consisted of zinc blende and wurtzite crystal structures with obvious dislocations when deposited on the polar plane of the AlN substrate. The dislocation density varied in a similar trend as the crystal structure changes. On the other hand, there is no misfit dislocations in the GaN films when deposition on the semi-polar and non-polar planes of the AlN substrate. According to the simulation results, the epitaxial GaN films deposited on the non-polar a-plane of the AlN substrates could be of higher crystalline quality under the same growth conditions.

Challenges and Advancement of Blue III-Nitride Vertical-Cavity Surface-Emitting Lasers

Since the first demonstration of (Al, In, Ga)N-based blue vertical-cavity surface-emitting lasers (VCSELs) in 2008, the maximum output power (Pmax) and threshold current density (Jth) has been improved significantly after a decade of technology advancements. This article reviewed the key challenges for the realization of VCSELs with III-nitride materials, such as inherent polarization effects, difficulties in distributed Bragg’s reflectors (DBR) fabrication for a resonant cavity, and the anti-guiding effect due to the deposited dielectrics current aperture. The significant tensile strain between AlN and GaN hampered the intuitive cavity design with two epitaxial DBRs from arsenide-based VCSELs. Therefore, many alternative cavity structures and processing technologies were developed; for example, lattice-matched AlInN/GaN DBR, nano-porous DBR, or double dielectric DBRs via various overgrowth or film transfer processing strategies. The anti-guiding effect was overcome by integrating a fully planar or slightly convex DBR as one of the reflectors. Special designs to limit the emission polarization in a circular aperture were also summarized. Growing VCSELs on low-symmetry non-polar and semipolar planes discriminates the optical gain along different crystal orientations. A deliberately designed high-contrast grating could differentiate the reflectivity between the transverse-electric field and transverse-magnetic field, which restricts the lasing mode to be the one with the higher reflectivity. In the future, the III-nitride based VCSEL shall keep advancing in total power, applicable spectral region, and ultra-low threshold pumping density with the novel device structure design and processing technologies.