Recently released OFweek semiconductor lighting Reuters report said the Chinese Academy of Sciences, Chinese researchers have been using the current strain engineering 150mA injected 530nm light emitting diode (LED), light output power increased by 28.9%. The study is a collaborative project between the Institute of Semiconductors of the Chinese Academy of Sciences and the University of Hong Kong.

The strain engineering project has greatly improved the light output of green LEDs

Schematic of the epitaxial material of conventional LED and shallow quantum well (SQW) LEDs (Fig. 1, left). Light intensity-current-voltage (LIV) characteristics of conventional LEDs and SQW LEDs (Figure 2, top right). The EQE and current characteristics of conventional LEDs and SQW LEDs are compared (Figure 3, bottom right).

The light output of the green light-emitting nitrogen semiconductor LED structure tends to be low due to the difficulty in producing the high indium content indium gallium nitride required for longer wave light emission. In addition to material quality challenges, the strain induced by lattice mismatch with pure gallium nitride (GaN) also causes a large piezoelectric effect, thereby generating an electric field that causes electrons and pores to separate, reducing the recombination ratio of photons ( That is, the quantum bound Stark effect, QCSE).

The researchers solved this problem by inserting a layer of low-indium indium nitride (InGaN) before the high indium-emitting layer. It is found through simulation experiments that the low indium content indium nitride (InGaN) layer can weaken the strain electric field in the active light emitting multiple quantum well (MQW) structure.

The epitaxial material of the low indium content indium nitride (InGaN) shallow quantum well (SQW) step is achieved by using metal organic meteorological deposition (MOCVD) techniques on the control plane (0001) sapphire (Fig. 2). The traditional multiple quantum well (MQW) active region consists of 12 3nm In0.3Ga0.7N well periods between 12nm GaN grids, while the shallow quantum well (SQW) structure consists of 12nm nitrides. 12 2 nm In0.1Ga0.9N shallow well + 3 nm In0.3Ga0.7N deep well period composition between (GaN) grids. These materials were then fabricated into 256 μm x 300 μm mesa structure wafers.

A 325 nm nitrogen cadmium laser was used to excite the photoluminescence spectrum of the material at low temperature (85K) and room temperature (298K). One of the effects of shallow quantum wells (SQW) is to reduce the peak-to-full width at half maximum (FWHM) of conventional LED materials from 16.7 nm to 13.1 nm for SQW materials and 80.1 nm for 298K environments at 85K. Dropped to 15.7nm.

The use of shallow quantum well (SQW) structures in this study also increases peak intensity. These results provide a basis for indicating an improvement in the crystal quality of the SQW material. In particular, narrow FWHM means "more consistent indium distribution and less carrier localization" due to reduced strain in the active region. The peak height of the shallow quantum well (SQW) material in the 298K environment is 55.1% at 85K, while the corresponding ratio of the conventional structure is 24.1%. This indicates that the smaller the quantum bound Stark effect (QCSE), the higher the luminescence recombination rate and the internal quantum effect (IQE) that shallow quantum well (SQW) materials can provide.

The electroluminescence phenomenon is measured in an integrating sphere to obtain the light intensity-current-voltage (LIV) result (Fig. 2). The shallow quantum well (SQW) and conventional devices have approximately the same voltage performance, while at 150 mA, the shallow quantum well (SQW) LED (49.3 mW) has a light output that is 28.9% higher than conventional devices (38.4 mW).

Researchers believe that this enhanced characteristic is attributed to the improved coincidence of electron and hole wave functions, thereby increasing the recombination rate of photons. For photoluminescence, this performance has not been improved to the same extent because the bias in electroluminescence enhances the polarized electric field. The external quantum effect (EQE) is 10.2-13.3% higher than conventional LED devices (Figure 3). (Compile: Viki)

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