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In this study, significant improvements in the characteristics of the InAs quantum-dot surface-emitting distributed feedback lasers using indium tin oxide as a cladding material covered by two types of newly designed metal contacts were achieved. Laser characteristics at room temperature including I–V curves, L–I curves, near-field patterns, and lasing spectra are analyzed and discussed. We adopted a metal grating and a metal strip as p-type electrodes to improve the current distribution of the devices. Uniform laser emission in the near-field was observed. Moreover, substantial reductions in the ohmic resistance of 9.35 Ω and a low-threshold current density of 0.28 kA/cm2 were both achieved under continuous-wave operation, leading to the prospect of high-performance surface emitting distributed feedback.

In this study, GaN-based photonic quasi-crystal surface emitting lasers (PQCSELs) operated at different Γ band-edge modes were fabricated and investigated. The photonic quasi-crystal patterns were defined by utilizing electron-beam lithography and inductively coupled plasma etching. Distinctive higher order Γ band-edge lasing modes were identified in the GaN PQCSELs. The threshold energy density and lasing wavelength for the S3 band-edge mode were 4.6 mJ/cm2 and 394.2 nm, respectively. The decreasing tendency of the threshold energy of PQCSEL was observed while the designed lasing mode moved from the higher Γ band to the lower Γ band. Numerical results showed that the S3 mode had the lower threshold and the threshold gain would be largely varied by tuning the ratio of air hole radius/lattice constant ( r / a ). Based on calculations and experiments, PQCSELs show the opportunity to realize lower threshold lasers than typical PC laser for specific value of r / a and appropriate higher order band-edge modes.

Nanolasers with an ultracompact footprint can provide high-intensity coherent light, which can be potentially applied to high-capacity signal processing, biosensing, and subwavelength imaging. Among various nanolasers, those with cavities surrounded by metals have been shown to have superior light emission properties because of the surface plasmon effect that provides enhanced field confinement capability and enables exotic light-matter interaction. In this study, we demonstrated a robust ultraviolet ZnO nanolaser that can operate at room temperature by using silver to dramatically shrink the mode volume. The nanolaser shows several distinct features including an extremely small mode volume, a large Purcell factor, and a slow group velocity, which ensures strong interaction with the exciton in the nanowire.

Three types of ZnO-based nanocomposites were fabricated consisting of 80-nm Au nanoparticles (NPs), a graphene layer, and ZnO nanorods (NRs). To investigate interactions between the ZnO NRs and Au nanoparticle, multiple material analysis techniques including field-emission scanning electron microscopy (FESEM), surface contact angle measurements, secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopic characterizations were performed. Results indicate that incorporating a graphene layer could block the interaction between the ZnO NRs and the Au NPs. Furthermore, the Raman signal of the Au NPs could be enhanced by inserting a graphene layer on top of the ZnO NRs. Investigation of these graphene-incorporated nanocomposites would be helpful to future studies of the physical properties and Raman analysis of the ZnO-based nanostructure design.

We report on GaN-based vertical-cavity surface emitting lasers (VCSELs) capable of high temperature operation. The structures of VCSELs include double dielectric distributed Bragg reflectors and bonded to a silicon substrate with a p-side-down configuration, allowing a better heat dissipation. The temperature dependent lasing characteristics of VCSELs can sustain to 350K.

The crystal structure of a-plane GaN/ZnO heterostructures on r-plane sapphire was investigated by using the XRD and TEM measurment. It was found the formation of (220) ZnGa2O4 and crystal orientation of semipolar (10$\bar 1$3) GaN at GaN/ZnO interface. The epitaxial relation of normal surface direction are the sapphire (1$\bar 1$02) // a-GaN (11$\bar 2$0) and ZnGa2O4 (220) // semi-polar GaN (10$\bar 1$$\bar 3$). Beside, the emission peak energy of ZnO appears shift about 60 meV in the GaN/ZnO/GaN heterostructures due to the re-crystallization of ZnO layer with Ga or N atom and the formation of the localized state.

In this work, we report on electrically pumped III-N microcavity (MC) light emitters incorporating oxide confinement apertures. The utilized SiO2 aperture can provide a planar ITO design with a higher index contrast (~1) over other previously reported approaches. The fabricated MC light emitter with a 15-μm-aperture shows a turn-on voltage of 3.3 V, which is comparable to conventional light emitting diodes (LEDs), showing a good electrical property of the proposed structure. A uniform light output profile within the emission aperture suggesting the good capability of current spreading and current confinement of ITO and SiO2 aperture, respectively. Although the quality factor (Q) of fabricated MC is not high enough to achieve lasing action (~500), a superlinear emission can still be reached under a high current injection density (2.83 kA/cm2) at 77 K through the exciton-exciton scattering, indicating the high potential of this structure for realizing excitonic vertical-cavity surface-emitting laser (VCSEL) action or even polariton laser after fabrication optimization.

We reported an easy fabrication method to realize ZnO-based microcavities with various cavity shapes by focused ion beam (FIB) milling. The optical characteristics of different shaped microcavities have been systematically carried out and analyzed. Through comprehensive studies of cathodoluminescence and photoluminescence spectra, the whispering gallery mode (WGM) was observed in different shaped microcavities. Up further increasing excitation, the lasing action was dominated by these WGMs and matched very well to the simulated results. Our experiment shows that ZnO microcavities with different shapes can be made with high quality by FIB milling for specific applications of microlight sources and optical devices.

Unlike conventional photon lasing, in which the threshold is limited by the population inversion of the electron-hole plasma, the exciton lasing generated by exciton-exciton scattering and the polariton lasing generated by dynamical condensates have received considerable attention in recent years because of the sub-Mott density and low-threshold operation. This paper presents a novel approach to generate both exciton and polariton lasing in a strongly coupled microcavity (MC) and determine the critical driving requirements for simultaneously triggering these two lasing operation in temperature

In this paper, a high quality ultraviolet light-emitting diodes (UV-LEDs) at 375 nm was developed using a heavy Si-doping technique with metal organic chemical vapor deposition. By using high-resolution X-ray diffraction, the full width at half-maximum of the rocking curve shows that the GaN film inserting a heavily Si-doped GaN layer (Si-HDL) had high crystalline quality. From the transmission electron microscopy image, the threading dislocation density was decreased after inserting a Si-HDL between undoped and n-doped GaN layers by nanoscale epitaxial lateral overgrowth. As a result, a much smaller reverse current and a higher light output were achieved. The improvement of light output at an injection current of 20 mA was enhanced by 40%. Therefore, we can use an in-situ nano pattern without complex photolithography and etching process and improve the internal quantum efficiency of UV-LEDs.

We fabricated and measured GaN-based resonant cavity light-emitting diodes with a 30 nm thick Indium tin oxide (ITO) thin film as a transparent contact layer. Four different ITO structures on p-type GaN samples were deposited by sputter and e-gun, and the corresponding device performance was compared. Each of these four samples has been annealed by its optimal parameters. The ITO thin film deposited by sputter demonstrated better electrical characteristics, surface morphology, specific contact resistance, and the overall device light output compared to those of the e-gun samples. Between the two sputtered ITO types, the hybrid type shows higher roll-over current density of 14 kA/cm2, and the output power is increased from 15 to 39 μ W. From statistical data of the 2-D light intensity under the same current, we saw the lateral current spreading of the pure crystalline ITO by sputter is worst. The hybrid type, which combines the crystalline and amorphous ITO, has the best overall performance when we consider all the electrical, optical, and metrology measurements. From these results, we believe the 30 nm thick hybrid ITO thin film has the best potential to be applied in light emitting devices such as light-emitting diodes, laser diodes, etc.

This paper reviews the fabrication technology and performance characteristics of current-injected GaN-based vertical-cavity surface-emitting lasers (VCSELs) with hybrid distributed Bragg reflectors (DBRs). The GaN-based VCSEL consists of a ten-pair Ta2O5/SiO2 top DBR, a 7 λ-thick optical cavity embedded with 10 InGaN/GaN multiquantum wells, and a 29-pair AlN/GaN bottom DBR. Lasing action is observed under continuous-wave operation at room temperature. The laser characteristics, such as temperature-dependent laser threshold current, emission wavelength, and spontaneous emission coupling factors, have been measured and discussed.

Non-polar (a-plane) InGaN-GaN multiple quantum wells (MQWs) on the GaN nanorod epitaxially lateral overgrowth templates with different nanorod height have been fabricated. The average in-plane strain in the InGaN MQWs has been determined from 2.73 × 10-2 to 2.58 × 10-2 while the nanorod height in templates increases from 0 to 1.7 μm. The polarization ratio of the emission from InGaN MQWs varies from 85 % to 53 % along with the increase of the GaN nanorod height. The reduction of polarization ratio has been attributed to the partial strain relaxation within the epitaxial structures as a result of growth on the GaN nanorod templates and the micro-size air-voids observed in the nanorod templates.

A-plane InGaN/GaN multiple-quantum wells (MQWs) were grown on a series of nanorod epitaxial lateral overgrowth (NRELOG) templates with varied nanorod depth. Optical properties of these samples were investigated by excitation power and temperature-dependent photoluminescence (PL). Due to the absence of quantum-confined Stark effect, the negligible PL emission peak shift and nearly identical power index for all samples were observed. In contrast to the as-grown MQWs, the thermal activation energy and internal quantum efficiency of NRELOG MQWs exhibit 1.6-fold and 4-fold increases, respectively, which are attributed to the improvement of crystal quality by NRELOG. Furthermore, the Shockley-Read-Hall nonradiative coefficient, determined from the fits of power-dependent PL quantum efficiency, is also apparently reduced while MQWs are grown on NRELOG GaN template. The results show the feasibility to fabricate high radiative efficiency a-plane devices via NRELOG.

We presented a study of high-performance GaN-based light emitting diodes (LEDs) using a GaN nanopillars (NPs) structure grown on sapphire substrate by integrating RF-plasma molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). Nanoscale air voids were clearly observed at the interface between GaN NPs and the overgrown GaN layer by cross-sectional scanning electron microscopy. It can increase the light-extraction efficiency due to additional light scattering. The transmission electron microscopy images suggest the air voids between GaN NPs introduced during nanoscale epitaxial lateral overgrowth of GaN can suppress the threading dislocation density. Moreover, Raman spectrum demonstrated that the strain of the GaN layer grown on GaN NPs was effectively eliminated, resulting in the reduction of quantum-confined Stark effect in InGaN/GaN quantum wells. Consequently, the LEDs fabricated on the GaN NPs template exhibit smaller electroluminescent peak wavelength blue shift and great enhancement of the light output (70% at 20 mA) compared with the conventional LEDs.

We present a study of high quality (1 1 ¯ 0 1) GaN films and the InGaN/GaN multiple quantum wells (MQWs) using epitaxial lateral overgrowth (ELO) technique by atmospheric pressure metal organic chemical vapor deposition (MOCVD). The smooth coalescence of the stripes and surface morphology was measured by scanning electron microscope (SEM) and atomic force microscopy (AFM). Due to reduction in internal electric field, semipolar InGaN/GaN MQWs have higher radiative recombination rate from time-resolved photoluminescence (TRPL) measurement. In addition, from degree of polarization (DOP) measurement, we observed higher polarization ratio attributed to the induced anisotropic compressive strain.

The influence of the LT-GaN nucleation layer on the quality of the GaN template was investigated by the study of the surface morphology of the nucleation layer, and of the crystalline and optical properties of the subsequently grown a -plane GaN template. Both X-ray diffraction and photoluminescence results reveal that better crystalline and optical quality could be obtained using thinner nucleation layer thickness and higher V/III ratio, leading to brighter near band edge luminescence as compared to films grown on lower V/III ratio nucleation layer. Our experiments indicate that reduction in the density of nucleation layer islands can effectively improve the crystalline quality of a -plane GaN template, and the V/III ratio of nucleation layer is a more dominant growth parameter to improve the crystalline and optical quality at the same time. The optimized growth parameters for the nucleation layer in our study are thickness of 10 nm and V/III ratio of 9000.

The crystal quality of a -plane GaN films was improved by using epitaxial lateral overgrowth on nano-rod GaN template. The scanning electron microscope images showed the fully coalesced regrowth process completed within only 2 μm thickness. The a -plane GaN films grown on nano-rod template showed superior surface quality and less surface pits. The on-axis and off-axis FWHMs of X-ray rocking curves decreased with the increase in the etching depth of the nano-rod template. TEM analysis revealed that the dislocation density was reduced to around 1.2×10 9 cm −2 by the nano-rod epitaxial lateral overgrowth. In addition, the photoluminescence intensity of the a -plane GaN was enhanced significantly. These results demonstrated the opportunity of achieving a -plane GaN films with high crystal quality via nano-rod epitaxial lateral overgrowth.

In this paper, gallium-nitride (GaN)-based light-emitting diodes (LEDs) with nano-hole patterned sapphire (NHPSS) by nano-imprint lithography are fabricated and investigated. At an injection current of 20 mA, the LED with NHPSS increased the light output power of the InGaN/GaN multiple quantum well LEDs by a factor of 1.33, and the wall-plug efficiency is 30% higher at 20 mA indicating that the LED with NHPSS had larger light extraction efficiency. In addition, by examining the radiation patterns, the LED with NHPSS shows stronger light extraction with a wider view angle. These results offer promising potential to enhance the light output powers of commercial light-emitting devices using the technique of nano-imprint lithography.

The mechanisms of the excitation power dependent internal quantum efficiency in InGaN/GaN multiple quantum wells (MQWs) LEDs grown on the planar and the patterned sapphire substrates (PSS) at temperature of 15 and 300 K were investigated. From observation the tendency of emission peak energy and carrier lifetime variation in MQWs with different excitation power for both LED samples, we conclude the internal quantum efficiency would increase as coulomb screening effect dominates at lower carrier injection stage and decrease due to the band-filling effect at higher density stage. At room temperature, the majority of the initial injected carriers would be first consumed by the thermal activated nonradiative centers that hinder the further achievement of high-efficiency LED devices. Experimentally, the internal quantum efficiency of the LED grown on the PSS is ~70% and that of the LED grown on the planar sapphire substrate is ~62%. For the LED grown on the PSS, the observed higher internal quantum efficiency is due to the larger activation energy Therefore, the reduction of dislocation defects and the prevention of injected carriers escaping from extended states would be a promising prospective for InGaN/GaN MQWs LEDs to achieve high internal quantum efficiency.

A high-quality AlN/GaN distributed Bragg-reflectors (DBR) was successfully grown on sapphire substrate by low-pressure metal-organic chemical vapor deposition using ultra-thin AlN/GaN superlattice insertion layers (SLILs). The reflectivity of AlN/GaN DBR with ultra-thin AlN/GaN SLIL was measured and achieved blue peak reflectivity of 99.4% at 462 nm. The effect of ultra-thin AlN/GaN superlattice insertion layer was examined in detail by transmission electron microscopy, and indicated that the crack of AlN/GaN DBR can be suppress by inserting AlN/GaN SLIL. For electronic properties, the turn on voltage is about 4.1 V and CW laser action of vertical-cavity surface-emitting laser (VCSEL) was achieved at a threshold injection current of 1.4 mA at 77 K, with an emission wavelength of 462 nm.

Theoretical analysis for InGaP/AlGaInP laser diodes with different ridge waveguide structures is performed to investigate the lateral mode behavior using advanced device simulation. The internal physical mechanisms including temperature-induced changes in the refractive index profile, spatial hole burning effect, lateral carrier distribution, and gain profile variation with increasing input current are discussed by theoretical calculation to analyze the effects of different ridge structures on the lateral mode behavior of 660-nm AlGaInP laser diodes. The simulation results show that the use of narrow and shallow ridge geometry is the approach to obtaining single mode operation. Furthermore, it is found that the different values of the ridge height cause the lateral carrier distribution within the active region to be varied, which is also an important factor in determining the emergence of the first order lateral mode in addition to the geometry-dependent waveguide cutoff condition.

This paper reviews the fabrication technology and performance characteristics of optically pumped and electrically pumped GaN-based vertical-cavity surface-emitting lasers (VCSELs). The lasing action of optically pumped hybrid GaN-based VCSELs has been observed at room temperature due to the employment of high-quality and high-reflectivity AlN/GaN-based distributed Bragg reflectors in the VCSEL structure. Based on the device structure of the optically pumped hybrid GaN-based VCSELs, we further achieved the lasing action of electrically pumped GaN-based VCSELs under continuous-wave operation at 77 K. The laser has a threshold injection current of 1.4 mA and emits a blue wavelength at 462 nm together with a narrow linewidth of about 0.15 nm. The laser beam has a divergence angle of about 11.7deg with a polarization ratio of 80%. A very strong spontaneous coupling efficiency of 7.5 times 10-2 was measured.

High-reflectivity ultraviolet distributed Bragg reflectors (DBRs), based on AlN/AlGaN quarter-wave layers, have been designed and grown on 2 in (0 0 0 1) sapphire substrates by metalorganic chemical vapor deposition. The growth of 20-pair AlN/Al0.23Ga0.77N DBR shows no observable cracks in the structure and achieves peak reflectivity of 90% at 367 nm together with a stop-band width of 24 nm. Furthermore, the growth of 34-pair AlN/Al0.23Ga0.77N DBR shows partial cracks from optical microscopy images. According to the room-temperature photoluminescence measurement, the emission spectrum of 34-pair AlN/Al0.23Ga0.77N DBR is broader than that of 20-pair AlN/Al0.23Ga0.77N DBR, which could be due to strain inhomogeneity generated by cracks. Despite the crystal quality problem, the peak reflectivity of 34-pair AlN/Al0.23Ga0.77N DBR could still achieve 97% at 358 nm and the stop-band width is 16 nm.

High-quality GaN layer was successfully grown on a SiO 2 nanorod-array patterned sapphire substrate (NAPSS) using metal-organic chemical vapor deposition by a nanoscaled epitaxial lateral overgrowth (NELO) method. From tunneling electron microscope images, well coalescence and turned dislocations are parallel to the surface direction were clearly observed. The Raman shift measurement shows the residual stress in GaN was greatly reduced from 1.359 to 0.652 GPa when compared to a GaN on flat sapphire substrate. Also, a high-efficiency GaN-based light-emitting diodes (LEDs) were demonstrated on the NELO NAPSS GaN, the respective output power and external quantum efficiency of the NELO NAPSS LEDs were estimated to be 22 mW and 40.2% at an injection current of 20 mA, showing an enhancement factor of 52% over conventional LEDs. The significant improvement resulted from both the enhanced light extraction assisted by the NAPSS, and the reduced dislocation densities using the NELO method.

Theoretical analysis for different active layer structures is performed to minimize the laser threshold current of the ultraviolet GaN/AlGaN multiple-quantum-well laser diodes by using advanced device simulation. The simulation results show that the lower threshold current can be obtained when the number of quantum wells is two or three and the aluminum composition in the barrier layer is about 10%-12%. This result is attributed to several different effects including electron leakage current, nonuniform carrier distribution, interface charge density induced by spontaneous and piezoelectric polarization, and optical confinement factor. These internal physical mechanisms are investigated by theoretical calculation to analyze the effects of quantum-well number and different aluminum compositions in barrier layer on laser threshold properties. Furthermore, the effect of quantum-well thickness is discussed as well. It is found that the optimal quantum-well thickness is about 3 nm due to the balance of the advantages of a large confinement factor against the disadvantages of significant quantum-confined Stark effect (QCSE).

The optical properties of a GaN-based vertical-cavity surface-emitting laser (VCSEL) with two dielectric distributed Bragg reflectors were investigated under optically pumped operation. The laser emits blue-violet light at a wavelength of 414 nm at room temperature with a high spontaneous emission coupling factor (� -factor) of 2 � 10 � 2 and a linewidth of 0.25 nm. The optical gain was determined by the Hakki–Paoli method by measuring the photoluminescence spectra below threshold conditions. At room temperature, an optical gain of 2900 cm � 1 was obtained under threshold condition. The linewidth enhancement factor (� -factor) is estimated from the ratio of the wavelength and gain derivation with respect to the carrier density, and the � -factor at room temperature is estimated to be 2.8. Strong exciton-photon coupling in the microcavity was observed at room temperature. A 9 meV Rabi splitting with 60% peak-to-valley contrast was determined from the photoluminescence measurements. Emission spectra showing the evolution of anticrossing behavior were also observed. [DOI: 10.1143/JJAP.47.6655]

Indium nitride (InN) epilayers have been successfully grown on Si (111) substrates with low-temperature (450°C) grown InN and high-temperature (1050°C) grown AlN (InN∕AlN) double-buffer layers by atmospheric-pressure metal-organic chemical vapor deposition (AP-MOCVD). X-ray diffraction characterizations indicated that highly (0001)-oriented hexagonal InN was grown on Si (111) substrate. Photoluminescence (PL) analyses performed at room temperature showed a strong emission at 0.72eV with a full width at half maximum of 121meV. Excitation intensity dependent measurements demonstrated the PL mechanism to be the band-to-band transition. Time-resolved PL could be fitted by a single exponential exhibiting an ordered film and a recombination lifetime of around 0.85ns. In particular, transmission electron microscopy characterizations indicated that the use of AlN first buffer is very important to achieve a structurally uniform (0001)-oriented InN epilayer on Si (111) by AP-MOCVD.

InGaP/AlGaInP 660-nm resonant-cavity light-emitting diodes (RCLEDs) with stable temperature characteristics have been achieved by extending the resonant cavity length from one optical wavelength (1 lambda) to three optical wavelengths (3 lambda) and tripling the number of quantum wells. When the operation temperature increases from 25degC to 95degC, the degree of power variation at 20 mA is reduced from -2.1 dB to -0.6 dB for the conventional 1- lambda cavity RCLEDs and 3- lambda cavity RCLEDs, respectively. In order to interpret the temperature-dependent experimental results, advanced device simulation is applied to model the RCLEDs with different cavity designs. According to the numerical simulation results, we deduce that the stable temperature-dependent output performance should originate from the reduction of electron leakage current and thermally enhanced hole transport for the 3- lambda cavity AlGaInP RCLEDs.

The GaN-based thin-film vertical-injection LEDs (VLEDs) with GaN nano-cone structures are fabricated and presented. Under the process conditions of fixed Cl 2 /Ar flow rate of 10/25 sccm and ICP/bias power of 200/200 W, the GaN nano-cone structures are self-assembly formed with variable density of 1.5 × 10 7 to 1.4 × 10 9 cm −2 and variable depth of 0.56–1.34 μm when varying the ICP chamber pressure. At a driving current of 350 mA and with chip size of 1 mm × 1 mm, the light output power of our thin-film LED with a specific GaN nano-cone structure reaches 224 mW which is enhanced by 160% when compared with the output power of conventional VLED. In addition, the corresponding light radiation pattern shows much higher light intensity due to the strong light scattering effect by the formed nano-cone structure.

We have developed a simple method to fabricate nanoscale masks by using self-assembly Ni clusters formed through a rapid thermal annealing (RTA) process. The density and dimensions of the Ni nano-masks could be precisely controlled. The nano-masks were successfully applied to GaN-based light-emitting diodes (LEDs) with nano-roughened surface, GaN nanorods, and GaN-based nanorod LEDs to enhance light output power or change structure properties. The GaN-based LED with nano-roughened surface by Ni nano-masks and excimer laser etching has increased 55% light output at 20 mA when compared to that without the nano-roughened process. The GaN nanorods fabricated by the Ni nano-masks and ICP-RIE dry etching showed 3.5 times over the as-grown sample in photoluminescence (PL) intensity. The GaN-based nanorod LEDs assisted by photo-enhanced chemical (PEC) wet oxidation process were also demonstrated. The electroluminescence (EL) intensity of the GaN-based nanorod LED with PEC was about 1.76 times that of the as-grown LED. The fabrication, structure properties, physical features, and the optical and electrical properties of the fabricated devices will be discussed.

This study reports on the reduction of dislocations in the GaN grown on the stripe-patterned r-plane sapphire substrates via metal-organic chemical vapor deposition (MOCVD). The stripes oriented along the sapphire [1 1 2¯ 0] direction with asymmetrical side faces were fabricated by lithographic and wet-etching processes. The two etching sides of sapphire-striped mesa are {0 0 0 1} and {1 1¯ 0 1} faces. GaN grown on both etching facets exhibits different epitaxial relationships with the sapphire substrate. The GaN grown from the {0 0 0 1} side face of the sapphire mesa contains a low-dislocation density in the order of 107 cm−2. The interfacial regions between the GaN and patterned sapphire substrate are also studied to clarify the behavior of GaN epitaxial growth on the inclined sapphire faces and defect-reduction mechanism.

In 2 Se 3 films were deposited on the p + -Si(1 1 1) substrates by metal-organic chemical vapor deposition (MOCVD) for the first time at temperatures higher than 500 °C. Trimethyl indium (TMI) and H 2 Se were used as the source reactants with the flow ratio of [H 2 Se]/[TMI] being maintained at 6.7. The growth temperature was varied from 350 to 650 °C. Powder X-ray diffraction analyses revealed that the In 2 Se 3 film grown is polycrystalline and has a wurtzite structure when the growth temperature is below 450 °C. Instead, a rhombohedral structure began to appear when the growth temperature is above 450 °C. Besides, SEM observations indicated a surface morphology of columnar structure for all films grown. Optical properties were examined by photoluminescence (PL) measurements. It was found that by conducting the growth at 550 °C a strong PL emission at around 2.14 eV was observed at 20 K. The luminescence mechanism was found to be dominated by the free excitons based on the temperature-dependent PL spectra from 20 to 120 K. However, bound exciton emissions were also observed or even became the dominant band when the films were grown at temperatures lower than 500 °C. Otherwise, the intensity of the 2.14 eV peak reduced greatly when the growth temperature was higher than 550 °C. Power-dependent PL measurements with excitation power varying from 0.1 to 100 mW confirm the luminescent mechanism and the material quality of the film grown at 550 °C. It is concluded that single-phase γ-In 2 Se 3 films can be achieved at temperatures lower than 450 °C; however, good-quality In 2 Se 3 films with the simultaneous appearance of γ- and β-phase structures can be grown at around 550 °C.

We report the synthesis of the In 2 O 3 nanostructures grown at different growth temperatures by using the thermal evaporation method. The gold nanoparticles were used as the catalyst and were dispersed on the silicon wafer to facilitate the growth of In 2 O 3 nanostructures. The nanostructures of the In 2 O 3 were characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The photoluminescence study reveals that In 2 O 3 nanostructures could emit different luminescence peaks in the range of 400–600 nm with broad bands by adjusting different growth temperatures. The coverage of the wavelength tuning in the emission peaks of the In 2 O 3 nanostructures could be beneficial for possible applications in white light illumination through manipulating the ratio of each wavelength component.

Ultraviolet nonpolar InGaN/GaN light-emitting diodes grown on trench epitaxial lateral overgrowth (TELOG) a -plane GaN template by metalorganic chemical vapor deposition were fabricated. Two emission peaks at 373 and 443 nm are observed from each fabricated device. The double emission peaks feature is identified by cathodoluminescence images, which show that the ultraviolet peak is emitted from the low-defect density wings on the TELOG and the blue peak is emitted from the TELOG-coalesced seed areas due to different incorporation of indium. The L–I–V diagram revealed that there are leakage current pathways due to the many threading dislocations in seed regions, and that the output power reached 0.2 mW at 140 mA. Two electroluminescence (EL) peaks are observed simultaneously when the driving current is below 50 mA. However, the EL peak at 373 nm dominates when current is above 50 mA. In addition, the degree of polarization of the ultraviolet peak was measured and found to be 28.7%.

We report the synthesis of the In2O3 nanoloquat grown at different oxygen flow rates by using the thermal evaporation method. The gold nanoparticles were used as the catalyst and were dispersed on the silicon wafer to facilitate the growth of In2O3 nanoloquats. The nanostructures of the In2O3 nanoloquats were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The photoluminescence (PL) study reveals that In2O3 nanoloquats could emit different luminescence peaks in the range of 500–600 nm with broad bands by adjusting different oxygen flow rates. The coverage of the wavelength tuning in the emission peaks of the In2O3 nanoloquats could be beneficial for possible applications in white light illumination through manipulating the ratio of each wavelength component. © 2007 Published by Elsevier B.V.

Self-assembled inverted hexagonal pyramids with GaN:Mg and InGaN/GaN multi-quantum-well (MQW) structures were formed through photoelectrochemical wet etching. The formation mechanism of the inverted hexagonal pyramid consisted with a lateral etching process of the InGaN/GaN active layer, bottom-up etching process from N-face GaN direction, and anisotropic etching process. The photoluminescence (PL) intensity of GaN:Mg peak was enhanced in this inverted hexagonal pyramid caused by the quantum confinement effect of this nano-structure. These inverted hexagonal pyramids, consisting of the p-type GaN:Mg, nano-disk InGaN/GaN active layer, and n-type GaN:Si layer, are suitable for nano-scale optoelectronic devices.

Effects of built-in polarization and carrier overflow on InGaN quantum-well lasers with a ternary AlGaN or a quaternary AlInGaN electronic blocking layer (EBL) have been numerically investigated by employing an advanced device-simulation program. The simulation results indicate that the characteristics of InGaN quantum-well lasers can be improved by using the quaternary AlInGaN EBL. When the aluminum and indium compositions in the AlInGaN EBL are appropriately designed, the built-in charge density at the interface between the InGaN barrier and the AlInGaN EBL can be reduced. Under this circumstance, the electron leakage current and the laser threshold current can obviously be decreased as compared with the laser structure with a conventional AlGaN EBL when the built-in polarization is taken into account in the calculation. Furthermore, the AlInGaN EBL also gives a higher refractive index than the AlGaN EBL, which is a benefit for a higher quantum-well optical confinement factor in laser operations.

We report a chemical-wet-etching patterned-sapphire-substrate (CWE-PSS) that simultaneously enhances internal quantum efficiency and light extraction efficiency of gallium nitride based light-emitting-diode (LED). According to transmission electron microscopy (TEM) images, the threading dislocations penetrating into active region was dramatically reduced in the CWE-PSS structure compared to the planar sapphire substrate, i.e. enhancement of internal quantum efficiency. And according to the measurement of angular dependent diffraction power, CWE-PSS also serves as a diffraction grating which diffracts guided light into escaping cones, further improving light extraction efficiency of LED device.

The cone-shaped-sidewall InGaN-based light-emitting diodes (LEDs) with higher light extraction efficiency were fabricated through the photoelectrochemical (PEC) process. The process procedures were consisted with the PEC selective wet oxidation on n-type GaN without p-type GaN layer, removing Ga2O3 layer, crystallographic wet etching process, and forming cone-shaped sidewall structure. The stable crystallographic etching planes were formed as the p-type GaN { } planes and n-type GaN { } planes with a 27{degree sign} included angle. The InGaN/GaN multi-quantum-well (MQW) layers were located at the cone's tip nano-structure in mesa-edge region, and the micro-photoluminescence spectrums had the blue shift phenomenon from 457.8nm to 450.8nm caused by the quantum confinement effect and particle compress strain released.

We review the fabrication technology and performance characteristics of optically pumped GaN-based vertical cavity surface emitting lasers (VCSELs). Two types of VCSELs with different microcavity structures are described. First type of VCSEL has a hybrid microcavity structure that consists of an epitaxially grown AlN/GaN distributed Bragg reflector (DBR), a GaN active layer with InGaN/GaN multiple quantum wells (MQWs), and a Ta2O5/SiO2 dielectric DBR. Second type of VCSEL has a dielectric DBR microcavity structure that has a similar InGaN/GaN MQWs active layer sandwiched in two dielectric DBRs formed by Ta2O5/SiO2 and TiO2/SiO2. Both types of VCSELs achieved laser action under optical pumping at room temperature with emission wavelength of 448 and 414 nm for hybrid DBR VCSEL and dielectric DBR VCSEL, respectively. Both lasers showed narrow emission linewidth with high degree of polarization and large spontaneous emission coupling factors of about 10-2. In addition, a high characteristic temperature of over 240 K was measured, and a distinct spatially inhomogeneous emission pattern was observed.

In this study, we grew non-polar a-plane GaN thin films on r-plane sapphire using a series of growth conditions by metal-organic chemical vapor deposition. The results showed that high temperature and low-pressure conditions benefited two-dimension growth could lead to a fully coalesced a-plane GaN layer with a very smooth surface. The best surface morphology with an excellent mean roughness of 10.5 A was obtained. The different thickness AlN as a nucleation layer and the different δ/β ratio were also considered. The results revealed that the surface morphology would get worse when the thickness of nucleation layer and δ/β ratio were away from the values of optimal condition. The observation of transmission electronic microscopy shown the lowest density of threading dislocations was 1.85×1010/cm2. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report the growth over 2 inch sapphire substrates of hybrid nitride-based microcavities using one crack-free highly reflective AIN/GaN distributed Bragg reflectors (DBRs) incorporated with AIN/GaN superlattice (SL) insertion layers and Ta 2 O 5 /SiO 2 DBRs. The optical cavity is formed by a 5λ cavity consisting of n-type GaN, 10 pairs multiple quantum wells and p-type GaN sandwiched by AIN/GaN and Ta 2 O 5 /SiΟ 2 DBRs. Reflectivity and photoluminescence measurements were carried out on these structures. A 29 periods AIN/GaN DBR incorporated with six AIN/GaN superlattice insertion layers showed no observable cracks and achieved a peak reflectivity of 99.4% and a stopband of 21 nm. Based on these high quality DBRs, the cavity mode is clearly resolved with a linewidth of 2.6 nm. These results demonstrate that the AIN/GaN system is very promising for the achievement of strong light-matter interaction and the fabrication of nitride-based vertical cavity surface emitting lasers.

This paper reviews our recent progress of GaN-based high brightness light-emitting diodes (LEDs). Firstly, by adopting chemical wet etching patterned sapphire substrates in GaN-based LEDs, not only could increase the extraction quantum efficiency, but also improve the internal quantum efficiency. Secondly, we present a high light-extraction 465-nm GaN-based vertical light-emitting diode structure with double diffuse surfaces. The external quantum efficiency was demonstrated to be about 40%. The high performance LED was achieved mainly due to the strong guided-light scattering efficiency while employing double diffuse surfaces

AlGaInP-based resonant-cavity light-emitting diodes (RCLEDs) with high power and high speed have been fabricated. In this study, the RCLEDs were designed with different light-output aperture sizes 84, 60, and 40 µm, for different applications on plastic optical fibers. Small-signal modulation bandwidths as high as 310 MHz at a forward current of 20 mA and an output power as high as 1.5 mW can be achieved for devices with 40 µm apertures. The devices with 84 µm apertures had an output power of more than 3.5 mW at a driving current of 20 mA and a maximum efficiency of over 12% with an epoxy-encapsulated package. The devices with 40 µm apertures satisfied with the IEEE 1394b s400 standard. Furthermore, the devices showed stable coupling efficiency for various currents and output powers at different ambience temperatures. In addition, the lifetime of devices is over 1300 h, and the power decay is less than 0.5 dB at 85 °C for a 40 mA driving current.

We propose a method of realizing strong ultraviolet emission from InGaN/AlGaN multiple quantum wells (MQWs) grown by a multi-step process. During growth of the quantum well layer, only trimethylindium (TMIn) and ammonia were introduced into the reactor, followed by a growth interruption treatment before growth of AlGaN barriers. The growth temperature of QWs dominates the photoluminescence (PL) emission peak position and surface morphologies of the films. It was found that the PL spectra of the samples with MQWs grown at 685 °C showed a strong UV emission at 380 nm. The correlation between surface structures and optical characteristics was studied by cathodoluminescence microscopy. The electroluminescence spectra under various injection currents showed a weak carrier localization effect induced by a quantum-confined Stark effect in the MQW.