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We reported the combination of micro-pyramid active layers and graphene electrode to realize the phosphor-free InGaN based white light emitting diodes (LEDs). SEM and TEM measurements were used to characterize the structural qualities of the micro pyramid arrays. According to CL and EDX analyses, the two emitting peaks originated from the indium segregation during the MOCVD process. Multilayer graphene was used to simplify the fabrication process for the electrical connection of the micro-pyramid arrays. The wavelength shift of two emitting peaks were both small with the increase of injection currents, indicating the weak QCSE. What was more, the reverse current leakage was also quite low for the phosphor-free InGaN micro-pyramid white light emitting diodes arrays connected by graphene.

In this work, the effects of growth pressure and growth rate on electrical and structural properties of Mg-doped GaN were investigated. It has been shown that enhanced growth rates induced by higher growth pressures may lead to decreased structural and electrical properties of p-type GaN layers. If the growth rate is kept unchanged, higher growth pressures will be beneficial for the quality of Mg-doped GaN due to the enhanced NH3 overpressure.

A study about the achievement of dichromatic white light-emitting diodes (LEDs) was performed. A series of dual wavelength LEDs with different last quantum-well (LQW) structure were fabricated. The bottom seven blue light QWs (close to n-GaN layer) of the four samples were the same. The LQW of sample A was 3 nm, and that of sample B, C and D were 6 nm, a special high In content ultra-thin layer was inserted in the middle of the LQW of sample C and on top of that of sample D. XRD results showed In concentration fluctuation and good interface quality of the four samples. PL measurements showed dual wavelength emitting, the blue light peak position of the four samples were almost the same, sample A with a narrower LQW showed an emission wavelength much shorter than that of sample B, C, D. EL measurement was done at an injection current of 100 mA. Sample A only showed LQW emission due to holes distribution. Because of wider LQW, the emission wavelength of sample B, C and D was longer and peak intensity was weaker. Sample D with insert layer on top of LQW showed strongest yellow light emission with a blue peak. As the injection current increased, sample A showed highest output light power due to narrower LQW. Of the other three samples with wider LQW, sample D showed highest output power. Effective yellow light emission has always been an obstacle to the achievement of dichromatic white LED. Sample D with insert layer close to p-GaN can confine the hole distribution more effectively hence the recombination of holes and electrons was enhanced, the yellow light emission was improved and dichromatic white LED was achieved.

A study on the effect of Mg doping in quantum-well (QW) layers on dual-wavelength light-emitting diodes (LEDs) was performed. A series of dual-wavelength LEDs with different Mg doping conditions were fabricated. According to electroluminescence measurement, as the Mg doping concentration and regions varied, improved hole distribution and bottom-QW emission was achieved. This result is in accord with APSYS simulation. In addition, the sample with Mg doping in all QWs showed the highest output power and smallest efficiency droop. It is concluded that Mg doping in QWs could ameliorate the optical and electrical properties of dual-wavelength LEDs.

A new model consisting of an inhomogeneous porous medium saturated by incompressible fluid is investigated. We focus on the effects of inhomogeneity for the streamline patterns and instabilities of the system. Influences of the 'mean porosity' and gradient of distributions of porosity are also emphasized. The results cannot be obtained by studying the media with constant porosity as carried out by other researchers, and have not been discussed before.

For Al-rich AlGaN which is applied to deep ultraviolet LEDs, improving doping efficiency without cracking problem is one of the most important research issues. Delta-doping technique offers a promising approach. In this study, we report delta-doping experiments in high aluminum content n-AlxGa1-xN (x=0.55) grown by MOCVD and investigate the effect of the growth technique. In the experiment we designed, a uniformly-doped sample (reference sample) and three delta-doping samples with varying delta-doping time (6 s, 15 s, and 30 s) were fabricated on AlN templates. Measured by high-resolution X-ray diffraction (HR-XRD) ω-scan and atomic-force microscope (AFM), samples with delta-doping technique show better crystal quality. Moreover, tested by contactless sheet resistance and Hall-effect test, delta-doping samples exhibit better electrical property with lower sheet resistance, higher carrier mobility, and larger carrier density. When increasing delta-doping time, all properties were gradually improved. These improvements were attributed to SiNx-growth-mask and dislocation-blocking effect induced by delta-doping technique. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

GaN-based LEDs is applied to illumination and visible-light communication. In this study, we research the impact of electron blocking layer (EBL) with different aluminum (Al) contents of 20% and 15% on the modulation bandwidth of high-power LEDs. LEDs with 15% Al in EBL shows higher radiative recombination rate and hole injection efficiency. Moreover, LED with 15% Al in EBL exhibits the modulation bandwidth of 25.5 MHz versus 23.5 MHz for LED with 20% Al at 300 mA. This finding demonstrates the influence of piezoelectric polarization field and low hole injection efficiency caused by EBL on modulation bandwidth of high-power LEDs.

A study about the effect of Mg doping in specified quantum-barrier on dual wavelength light emitting diodes (LEDs) was performed. A series of dual wavelength LEDs with different Mg doping conditions and barrier thickness were fabricated. According to electroluminescence measurement, as Mg doping concentration and barrier thickness varied, improved carrier distribution and bottom QWs emitting was achieved. This result is in accord with APSYS simulation. In addition, the sample with appropriate Mg doping level showed dual wavelength emitting. It is concluded that Mg doping in specified quantum-barrier could improve optical and electrical properties of dual wavelength LEDs.

We study the Raman spectra of Bi4Ge3O12 crystal at different temperatures, as well as its melt. The structure characters of the single crystal, melt and growth solid–liquid boundary layer of BGO are investigated by their high-temperature Raman spectra for the first time. The rule of structure change of BGO crystal with increasing temperature is analysed. The results show that there exists [GeO4] polyhedral structure and Bi ion independently in BGO melt. The bridge bonds Bi–O–Bi and Bi–O–Ge appear in the crystal and at the boundary layer, but disappear in the melt. The structure of the growth solid–liquid boundary layer is similar to that of BGO crystal. In the melt, the long-range order structure of the crystal disappears. The thickness of the growth solid–liquid boundary layer of BGO crystal is about 50 μm.

Abnormal inline defects were caught after nitride spacer etching processes. Detailed MEBES layout checking and inline SEM inspection revealed that such defects always appeared at the boundaries in between PFETs and NFETs regions. The microstructure and chemical composition of the defects were analyzed in detail by various TEM imaging and microanalysis techniques. The results indicated that the defect possessed core-shell structure, with oxide core and nitride shell. Based on the TEM failure analysis results and manufacturing processes, we conclude that the defects originated from PR fencing due to the PR hardening during PFET and NFET LDD/Halo implantation. The oxide core was generated during oxide spacer formation using an ozone-TEOS process, which was responsible for the nitride spacer under-etch issue.

Electron-beam induced radiation damage can give rise to large structural collapse and deformation of low k and ultra low k IMD in semiconductor devices, posing great challenges for failure analysis by electron microscopes. Such radiation damage has been frequently observed during both sample preparation by dual-beam FIB and TEM imaging. To minimize radiation damage, in this work we performed systematic studies on every possible failure analysis step that could introduce radiation damage, i.e., pre-FIB sample preparation, FIB milling, and TEM imaging. Based on these studies, we utilized comprehensive technical solutions to radiation damage by each failure analysis step, i.e., low-dose/low-kV FIB and low-dose TEM techniques. We propose and utilize the low-dose TEM imaging techniques on conventional TEM tools without using low-dose imaging control interface/software. With these new methodologies or techniques, the electron-beam induced radiation damage to ultra low k IMD has been successfully minimized, and the combination of single-beam FIB milling and low-dose TEM imaging techniques can reduce structure collapse and shrinkage to almost zero.

Impact wear tests were carried out in a laboratory simulating the working condition of balls against lining plates in ball mills in order to find the optimal combination of materials for balls and lining plates. The results showed that: (1) for the same plate material with increasing hardness of balls, the wear resistance of plates and the wear system (balls plus plates) increased; (2) for the same ball material with increasing plate hardness, the wear resistance of the balls and the system increased, too. Pilot tests were done in real ball mills in two fire power stations for pulverizing coal. The results were coincident with those obtained in laboratory tests. The optimal mating was high chromium cast iron ball mills working in ball mills lined with medium chromium steel plates.

In this paper, an attempt is made to highlight a new SEM based technique that was used to detect pinholes in the as- deposited/as-grown dielectrics. The fundamental principle governing the technique is discussed. This technique is benchmarked against a well-established fault- isolation technique using the Liquid Crystal. In fact, this technique was found to supplement the Liquid Crystal technique. A case study, discussed in the paper, helps understand the usefulness of the technique especially in detecting defects on as- deposited/as-grown dielectric films.

Copper as a metal of choice for interconnection purposes, needs damascene approach to realize the interconnect formation. This approach needs etch stop layers to form via and trench. Metal and dielectric barriers are also needed to prevent copper from diffusing into the substrate. The integrity and adhesion of all these different layers is a subject of great concern from the yield standpoint. The problem needs more careful attention with porous low k dielectric material. In this paper, some aspects related to the adhesion of the various thin films that form the damascene stack are discussed. Analysis of failures/outliers encountered during routine die pull test is also done. The failure analysis performed on such failures provided a very good insight into the weakness in the dielectric stack, that form the interconnect, in the case of device with copper as back-end metallisation. Techniques to improve the adhesion of various layers and other novel approaches used to improve the process margin are also discussed. Relationship between the die size and stress induced dielectric delamination is also discussed in this paper.

The effect of In codoping effect in GaN:Mg layers were investigated through strain analysis. A hydrostatic lattice expansion is induced by In doping which cannot be simply explained by the size effect of In and Mg dopants. Together with the photoluminescence spectrums, this lattice expansion is a strong evidence for the elimination of nitrogen vacancies. The biaxial strain and edge dislocations are reduced with In doping. A theoretic model of interaction between In atoms and edge dislocations are established to explain this phenomenon.

A new model consisting of a liquid film overlying a saturated and inhomogeneous porous layer is investigated. We concentrate on effects of inhomogeneity on transition of instability modes. Influences of the averaged porosity and the gradient of porosity distribution on the instability behaviors of a liquid-porous layer system are emphasized. The average permeability of the porous layer is a key factor to determine the penetration of convection in the system.