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The effect of AlGaN interlayer (IL) in bottom quantum barriers on efficiency enhancement of the InGaN green light-emitting diodes (LEDs) on patterned silicon substrate has been investigated. Significantly, the LEDs with AlGaN IL show high emission efficiency at low current and the maximum wall-plug efficiency is 58% at 7.5 mA (17 mW). This is attributed to the effect of AlGaN IL on carrier distribution and screening dislocations due to its higher bandgap, based on LEDs structure with V-shaped pits. Consequently the ameliorated properties of LEDs with AlGaN IL provide a good choice for LEDs operating at low current density.

In this study, the influence of InGaN/GaN superlattices (SLs) preparing layer and InGaN/GaN blue multiple quantum wells (BMQWs) preparing layer on the performance of InGaN-based green LED on patterned silicon substrate is investigated. Experimental results show that compared to BMQWs, the use of SLs in preparing layer allows us to better improve the crystalline quality of active region, trigger the formation and enlargement of V-shape pits at dislocations as well as to facilitate the vertical carrier injection and promote lateral current distribution, which in general leads to the reduced leakage currents, lower operating voltages and enhanced quantum efficiency/wall-plug efficiency.

Incorporating high-speed camera technology, an experimental system of high-speed digital image correlation is established and extended to blasting research. Based on the model experiment, the effects of the filling medium and the decoupling coefficient on stress evolution in decoupled charge blasting are studied. Different filling media are found to have a significant effect on the transmission of blasting energy. Compared with coupled charge blasting, decoupled charge blasting with air as the filling medium reduces the blasting stress peak in the specimens; while within a certain decoupling coefficient range, the decoupled charge blasting with plasticine as the filling medium increases the blasting stress peak in specimens. The blasting stress attenuation index in specimens exhibits the trend of an initial increase and then a decrease with increasing decoupling coefficient, where the decoupling coefficient corresponding to the maximum stress attenuation index is determined by the filling medium. In addition, the numerical simulation results show that, in decoupled charge blasting, the filling medium greatly reduces the pressure at the borehole wall. With increasing decoupling coefficient, the pressure at the borehole wall attenuates with a mild degree of attenuation.

In hard rock deep-hole blasting excavation, blastholes are rarely utilized due to the clamping effect of the lower rock, which affects excavation progress and restricts the development and application of deep-hole blasting technology. Cut blasting is a key to improving excavation speed. In this paper, a new cutting method designating the two-step cutting technology was presented. The blasthole was divided into upper and lower sections without changing the blasthole layout. The upper section was detonated first, creating sufficient free surface for the lower section, which was detonated secondly. This created a larger cavity and improved blasthole utilization. Results showed good blasting effects for two-step cutting technology through theoretical analysis and engineering applications. The blasthole utilization rate was 96.1% when the upper and lower specific charge ratio = 0.78. This paper provides a good reference for resolving the low blasthole utilization problem in deep-hole blasting of vertical shafts within a hard rock.

The blasting stress wave and blasting gas generated by explosive blasting are the two main motive powers of rock fragmentation. An experimental method based on water jet test is used to study the energy distribution ratio of blasting stress wave and blasting gas; the utilization efficiency of blasting energy under different borehole constraint conditions is also analyzed. It proves that the blasting stress wave does not cause the water jet, and the blasting gas is the only power of the water column jet. The results show that the energy of the blasting gas and blasting stress wave respectively account for about 64% and 36% of the total energy generated by the explosion of lead azide. The utilization efficiency of the blasting gas energy under strong, medium, and weak constraint conditions is 100%, 80%, and 52%, respectively. The borehole constraint condition is crucial for the effective utilization of blasting energy.

Laboratory experiments were performed using a digital laser dynamic caustics experimental system to study the blasting damage effect of joints on medium. The distance between the joint and the borehole was the only variable in this experiment. Research showed that: It is found that the ability of cracks to propagate through a joint is significantly affected by the angle of the crack. When the angle between the crack and the joint increases to 25.1 °, the crack cannot pass through the joint. The increase in the distance between the joint and the borehole can reduce the damage caused to the medium. When the distance between the joint and the borehole is 60mm, the joint does not show significant effect on the dynamic crack propagation. The joint promotes the damage of the medium between the borehole and the joint and inhibits the damage of the medium beyond the joint. With an increase in the distance between the joint and the borehole, the reflected stress wave gradually weakens, and the influence of reflected stress wave on v and Kd I gradually decreases.

Indium gallium nitride (InGaN)-based light-emitting diodes (LEDs) are considered a promising candidate for red-green-blue (RGB) micro displays. Currently, the blue and green LEDs are efficient, while the red ones are inefficient for such applications. This paper reports our work of creating efficient InGaN-based orange and red LEDs on silicon(111) substrates at low current density. Based on the structure of InGaN yellow LEDs, by simply reducing the growth temperature of all the yellow quantum wells (QWs), we obtained 599 nm orange LEDs with peak wall-plug efficiency (WPE) of 18.1% at 2 A / cm 2 . An optimized QW structure was proposed that changed two of the nine yellow QWs to orange ones. Compared with the sample containing nine orange QWs, the sample with two orange QWs and seven yellow QWs showed similar emission spectra but a much higher peak WPE up to 24.0% at 0.8 A / cm 2 with a wavelength of 608 nm. The improvement of peak WPE can be attributed to the improved QW quality and the reduced active recombination volume. Subsequently, a series of efficient InGaN-based orange and red LEDs was demonstrated. With further development, the InGaN-based red LEDs are believed to be attainable and can be used in micro LED displays.

Inhomogeneous electroluminescence (EL) of InGaN green LEDs grown on mesh-patterned Si (111) substrate had been investigated. Sample with n-AlGaN inserted between the pre-strained layers and the first quantum well showed the inhomogeneous EL in the low current density range. Near-field EL emission intensity distribution images depicted that inhomogeneity in the form of premature turn-on at the periphery of the LED chip, results in stronger emission intensity at the edges. This premature turn-on effect significantly reduces the luminous efficacy and higher ideality factor value due to locally current crowding effect. Raman measurement and fluorescence microscopy results indicated that the partially relaxed in-plane stress at the edge of the window region acts as a parasitic diode with a smaller energy band gap, which is a source of edge emission. Numerical simulations showd that the tilted triangular n-AlGaN functions like a forward-biased Schottky diode, which not only impedes carrier transport, but also contributes a certain ideality factor.

Relationship between the external quantum efficiency (EQE) curves and the dominant non-radiative recombination mechanisms of InGaN green LEDs grown on silicon substrates were investigated. Through the analysis of the ABC+ f ( n ) model, the significant drop in EQE at low current levels is due to an increasingly defect-related Shockley-Read-Hall (SRH) recombination. Under extremely low current densities, the defect traps can even become the dominant channel for the leakage current through the tunneling process, thereby reducing the efficiency of carrier injection into the active region. These observations were further supported by the carrier lifetime measurement. However, this fails to explain the droop in EQE at high current densities, especially when SRH recombination has been saturated. Our results show that carrier leakage has becomes dominant at high current density when Auger recombination has been less impossible. Reduced carrier leakage may lead to increased carrier injection efficiency, which in turn alleviates EQE droop.

The effects of the preparation layer grown under different conditions, which is an InGaN/GaN SLs structure inserted between the n-GaN layer and the MQWs, on the performance of green-yellow LED have been investigated. In this paper, the quality of InGaN/GaN multiple quantum wells (MQWs) and the optoelectronic properties of LED have been focused on. According to the experimental results, when the growth temperature of GaN barriers in SLs was increased, the interface between InGaN layers and GaN layers became more abrupt, and the indium distribution in the quantum wells became more uniform. In consequence, the forward voltage was reduced, the external quantum efficiency (EQE) was improved. By decreasing the growth rate of the high temperature barriers, the indium uniformity became even better, forward voltage was reduced again and EQE was further improved.

The effect of AlGaN interlayer in quantum barrier on the electroluminescence characteristics of GaN-based green light emitting diodes (LEDs) grown on silicon substrate was investigated. The results show that AlGaN interlayer is beneficial to improve the luminous efficiency of LED devices and restrain the phase separation of InGaN. The former is ascribed to the inserted AlGaN layers can play a key role in determining the carrier distribution and screening dislocations in the active region, and the latter is attributed to the increased compressive stress in the quantum well. However, when the electrical stress aging tests were performed at a current density of 100 A/cm2, LED devices with AlGaN interlayers are more likely to induce the generation/proliferation of defects in the active region under the effect of electrical stress, resulting in the reduced light output power at low current density.

Low-temperature GaN cap layer was designed after quantum wells for the V-pits contained InGaN-based green light-emitting diodes (LEDs). It is found that the LEDs performances are greatly improved with thicker cap layer. The indium distribution in InGaN/GaN multiple quantum wells (MQWs) becomes more homogeneous. The quality of interface between quantum well and quantum barrier (QB) is promoted, and the carrier confinement effect is enhanced. Thereby the external quantum efficiency (EQE) increases at high current density. However, the sample with a relative thicker cap layer exhibits the lower EQE at low current density, which is attributed to the more defects at the upper interface of QWs, and the increased probability of carriers meeting at these non-radiative recombination centers. Meanwhile, only the major emission peak emitted from c-plane MQWs can be observed in the electroluminescence spectrum of 100 K, and other emission peaks are hardly visible, which indicates that the sample with thicker cap has better carrier transport performance.

Hole transport in InGaN/GaN multiple quantum wells (MQWs) LEDs has been proposed to be insufficient due to relatively large effective mass and low mobility. Here, for the first time, we have direct observed hole overflow from MQWs and enter into InGaN/GaN superlattices (SLs) layer in V-pits-containing GaN-based green LEDs at room temperature. To suppress the hole leakage, an n-AlGaN hole blocking layer (HBL) is inserted between SLs layer and MQWs. The experimental show an interesting and baffling result is that the HBL-containing sample not only exhibits severe hole leakage in high current density range, but also has higher external quantum efficiency (EQE). Numerical simulation reveals that the HBL can change the transportation path of carriers, forcing more electrons injecting from c-plane into the MQWs instead of from V-pit sidewalls. This will increase the carrier concentration in the MQWs, and eventually lead to higher EQE. Meanwhile, less electrons transported through V-pit allowed more holes injecting into deeper layers via V-pit sidewalls, and electroluminescence emission from the SLs layer became stronger when HBL was inserted.

The impact of the V-pits covering layer (VCL) position on the optoelectronic performance of InGaN-based green light-emitting diodes (LEDs) was investigated. It is found that earlier covering of V-pits will hinder the hole injection via the sidewall of V-pits, and then result in less quantum wells (QWs) participating in radioluminescence. The current-voltage characteristics show that the LEDs with earlier covering of V-pits have higher operating voltage at room temperature, and a more dramatic voltage rise with the reduction of temperature. Meanwhile, more manifested emission peaks for sidewall QWs and deeper QWs near to n-type layer was observed in the sample with earlier coveing of V-pits at cryogenic temperatures, for the reason that the holes being injected via V-pits sidewall have higher kinetic energy and could transport to deeper QWs.

Realization of efficient yellow-light-emitting diodes (LEDs) has always been a challenge in solid-state lighting. Great effort has been made, but only slight advancements have occurred in the past few decades. After comprehensive work on InGaN-based yellow LEDs on Si substrate, we successfully made a breakthrough and pushed the wall-plug efficiency of 565-nm-yellow LEDs to 24.3% at 20 A/cm2 and 33.7% at 3 A/cm2. The success of yellow LEDs can be credited to the improved material quality and reduced compressive strain of InGaN quantum wells by a prestrained layer and substrate, as well as enhanced hole injection by a 3D pn junction with V-pits.

Will the blue light at night in lamp and screen destroy East Asians? How to avoid it? Along the axis of light-melatonin-reproduction, this paper summarized a theoretical model related to the influence of modern lighting and display on human reproduction from literature and then finds out six possible proofs for this model from the history of humans' exposures to light at night. Although these proofs may all have some loopholes, the four standards for healthy light ray at night proposed by this paper only imitate the nature, namely they are tenable even without these proofs. This paper also have measured the proportion of blue light in various light sources, and have evaluated their influences on reproduction; meanwhile, this paper also has proposed concrete solutions and even has developed relevant LED lamps; At last, some suggestions and warnings were offered.

We report on the crystallographic tilting of AlN/GaN layers grown on Si (111) substrates with different miscut angles toward [110] direction. The inclination angle of the Si (111), AlN (002) and GaN (002) planes to the sample surface was measured by high resolution X-ray diffraction. We found that the tilt angles of the AlN and GaN layers with respect to the Si (111) plane are significantly larger than that predicted by the classical Nagai model. We proposed that in-plane mismatch played an important role in the tilt epitaxy of AlN/GaN layers on miscut Si (111) substrate.

A GaN light emitting diodes (LED) wafer was coated with Pt, Au, Al and In. The photoluminescence (PL) excited from wafer back shows that Pt and Au coating can quench the PL while In and Al can increase the PL intensity by eight times and make the wavelength red shift. When connected to the Pt with a wire, indium can also quench the PL. The potential difference between any two kinds of the metals was measured and the PL intensity from each coated area showed a remarkable pertinence to the coating metal potentials. A built-in potential barrier model is proposed to explain results.

The annealing effect on the optical properties of ZnO epilayers was reported. The ZnO thin films were grown using metal organic chemical vapor deposition method, and annealed in atmosphere at 850 °C for different time periods. Double-crystal X-ray diffraction showed that, after annealing, the density of the edge-dislocations decreased dramatically upon annealing, however, the screw-dislocations were not affected significantly. Strong green photoluminescence was observed in the annealed ZnO films while the as-grown films showed only near band edge emission. The deterioration of the optical properties in the annealed film, however, only occurred near the film surface in a very thin layer.

Epitaxial ZnO thin films have been grown on 2-in diameter Si(1 1 1) substrates by atmospheric-pressure metalorganic chemical vapor deposition. An initial Al layer with a thickness of 10 A was deposited in order to protect the Si surface from oxidation. The structural property was characterized using a double-crystal X-ray diffractometer, and the photoluminescence spectra were measured using the excitation of 325 nm line of a He–Cd laser. The minimum full-width at half-maximum (FWHM) of the diffraction peak of ZnO(0 0 2) is 0.35° and 0.16° for the ω and ω - 2 θ scans, respectively. Free-exciton emission with a shoulder at the bound-exciton peak was observed at 10 K. Microscopic images show cracks for the sample of 3.0 μm thickness, and the crack density is about 7.6×10 2 /cm −1 . The maximum area of a crack-free triangular region is bout 1756 μm 2 .

A thin AlN buffer layer was used to grow ZnO thin film on Si(1 1 1) substrate by atmospheric pressure MOCVD to protect the substrate from being oxidized and to eliminate the mismatch between the epilayer and the substrate. Double crystal X-ray diffraction results indicate that high-crystallinity ZnO film has been obtained. The full-width of half-maximum (FWHM) of ZnO (0 0 0 2) and ZnO ( 1 0 1 ¯ 2 ) ω-rocking curve peaks are 460″ and 1105″, respectively. The crack density Of ZnO surface is 20 strip/cm by optical microscope graph determination. In situ laser reflectance trace shows that a quasi-two-dimension growth mode was obtained when the film growth rate is up to 4.3 μm/h. Free exciton emission and bound exciton emission accompanied by their longitudinal optical phonon replicas can be observed from the photoluminescence spectrum at 10 K.

GaN green LED was grown on Si (111) substrate by MOCVD. To enhance the quality of InGaN/GaN MQWs, same-temperature (ST) GaN protection layers with different thickness of 8 Å, 15 Å, and 30 Å were induced after the InGaN quantum wells (QWs) layer. Results show that a relative thicker cap layer is benefit to get InGaN QWs with higher In percent at fixed well temperature and obtain better QW/QB interface. As the cap thickness increases, the indium distribution becomes homogeneous as verified by fluorescence microscope (FLM). The interface of MQWs turns to be abrupt from XRD analysis. The intensity of photoluminescence (PL) spectrum is increased and the FWHM becomes narrow.

GaN-based blue light emitting diodes (LEDs) have undergone great development in recent years, but the improvement of green LEDs is still in progress. Currently, the external quantum efficiency (EQE) of GaN-based green LEDs is typically 30%, which is much lower than that of top-level blue LEDs. The current challenge with regard to GaN-based green LEDs is to grow a high quality InGaN quantum well (QW) with low strain. Many techniques of improving efficiency are discussed, such as inserting AlGaN between the QW and the barrier, employing prestrained layers beneath the QW and growing semipolar QW. The recent progress of GaN-based green LEDs on Si substrate is also reported: high efficiency, high power green LEDs on Si substrate with 45.2% IQE at 35 A/cm2, and the relevant techniques are detailed.

After nearly ten years of exploration, our team firstly had a breakthrough in the technologies of materials growth and thin film chip manufacturing for high efficiency GaN based blue LED on silicon substrate in the world. The internal quantum efficiency and extraction efficiency of the vertical structure blue LED chips reached 80%. These LED chips have been realized mass production, and been successfully used in street lamps, miners lamp, down light, bulb light, flashlight and display imaging etc. In this paper, the related key technologies are comprehensive and systematically introduced. Selective-Area-Growth and Maskless-Micro-Epitaxial-Lateral-Overgrowth technologies were invented, by which a high crystalline quality GaN film was achieved with an only 100 nm AlN buffer layer. A set of systemic technologies were invented for manufacturing vertical thin film structure LED on silicon substrate, included high reflectance low resistance P type ohmic contact electrode, high stability low resistance N type electrode ohmic contact, surface roughening, complementary electrode, releasing residual tensile stress of GaN film technologies etc. At 350 mA (35 A/cm2), the light output power of blue LED (450 nm) on silicon is 657 mW, and external quantum efficiency of it is 68.1%.

The roles of V-shaped pits on the improvement of quantum efficiency in InGaN/GaN multiple quantum well (MQW) light-emitting diodes are investigated by numerical simulation. The simulation results show that V-shaped pits cannot only screen dislocations, but also play an important role on promoting hole injection into the MQWs. It is revealed that the injection of holes into the MQW via the sidewalls of the V-shaped pits is easier than via the flat region, due to the lower polarization charge densities in the sidewall structure with lower In concentration and {10–11}-oriented semi-polar facets.

InGaN/GaN multi-quantum well (MQW) light emitting diodes with heavily Mg doped and unintentionally doped (UID) low-temperature Al0.2Ga0.8N electron blocking layer (EBL) were investigated. Broad short-wavelength electroluminescence peak, which has strong relative intensity to the main emission, was found in the UID-EBL sample at cryogenic temperatures. Study suggests that the broad peak is emitted by the sidewall MQWs. This result indicates that the electroluminescence of sidewall MQWs, in which the carrier density is high enough, can be detected at cryogenic temperatures. The lineshape variation with current density reveals detailed information on the process of carrier injection into the sidewall MQWs.

Crack free GaN films were grown on 1200×1200μm2 patterned Si (111) substrates and 36 light emitting diodes (LEDs) were fabricated in each pattern unit. Spatial distribution of the tensile stress in the pattern units and its influence on the LED performance are studied by micro-Raman and electroluminescence (EL). The Raman shift of the GaN E2 mode shows that the tensile stress is the maximum at the center, partially relaxed at the edge, and further relaxed at the corner. With the stress relaxation, the EL wavelength has a significant blue shift and the luminous intensity shows a great enhancement.

Little attention was paid to the effect of oxygen vacancy configuration, although it is well known that oxygen vacancy plays a key role in determining the electrical and optical properties of VO2. By means of different heat treatments, the oxygen vacancy configuration in VO1.965 nanometer ceramic is controlled and its behavior is investigated in detail. It is found that VO1.965 ceramic aged at 60°C for a day displays a new first order phase transformation at about 30°C, which is associated with the oxygen vacancy distribution. An explanation based on the symmetry conforming principle is tentatively presented.