Saga University, the use of new materials to produce a successful green LED, easy to reduce costs and improve efficiency"

Was successfully developed by using ZnTe (zinc telluride) as the green LED with luminous wavelength of 550nm. The light output power and input power ratio of 0.1 ~ 0.2%, "luminous efficiency with the same wave band GaP class green LED products" (Saga University assistant professor Tanaka). There is room for further improvement in luminous efficiency, "about 5 to about 10 times" (Tanaka). According to the idea, the green LED will improve efficiency 5 ~ 10 times after the production. In addition to improving efficiency, the cost can be easily reduced to less than GaP class green LED. This time, from the use of ZnTe board to make LED chip to the package are completed by Saga University alone.

At present, the luminous wavelength of GaP class 550nm green LED is applied to the photoelectric billboards, indicator lights, mobile phone keys, such as decorative lighting. In such applications, if the use of class ZnTe green LED, because of its high luminous efficiency, it can achieve the purpose of reducing power consumption and cost. Moreover, the optical output power is also expected to exceed the class GaP green LED, can be expected to become the use of plastic optical fiber (POF) optical communication system. This is because the 550nm band is just a small area of POF transmission loss. Green LED can be used as a display light source, but the class LED ZnTe is not intended for this purpose. The band gap of ZnTe is 2.27eV, which is not suitable for the 520nm band which is easy to expand the color range. 520nm band for the current use of InGaN class green LED. By increasing the efficiency of the manufacturing method, the improvement of the ratio of the optical output power to the input power is due to the improvement of the LED manufacturing method. In the green LED chip, P type ZnTe was used in the bottom plate, and the "n" layer was formed by thermal diffusion method. At the same time, we can optimize the concentration distribution of Al and improve the luminous efficiency by setting the diffusion control layer on the base plate. This is due to the fact that the thermal diffusion is more likely to form a n type layer than the epitaxial growth method known as the MOCVD method and the MBE method, which makes it easier to accurately control the growth of the II group and the ratio of the VI raw material supply. 0.1 ~ 0.2% of the optical output power and input power ratio is in the size of about 400 ~ 500 m square LED chip, the drive current is 10mA, the driving voltage of +3V. In the future, efficiency is expected to further improve. This is because ZnTe is a direct transfer semiconductor, so we can improve the efficiency of the heterojunction. Class GaP and class InGaN green LED are indirect transfer semiconductors. Generally speaking, compared with the indirect migration, the electrons and the positive holes in the direct transfer crystals are easier to combine to improve the luminous efficiency. The prototype for LED homojunctions. By changing it into the same heterojunction as the LED that has been put into operation, the ratio of the light output power to the input power can be estimated to be about 5 to about 10 times. Because the heterojunction is easy to block the carrier, so the luminous efficiency is improved. Material costs and lower manufacturing costs ZnTe class green LED manufacturing costs may be lower than the GaP class green LED. This is because the ZnTe GaP low cost materials, and green ZnTe LED can be used to help reduce the cost of manufacturing method. The cost of making 1 LED devices is only about GaP of class LED (1/4) (Tanaka). With regard to manufacturing methods, the ZnTe substrate was successfully manufactured by using a method called "Bridgman method". The vapor pressure near the melting point of ZnTe is about 1 atmospheric pressure. In principle, the pressure that is suitable for the growth of the crystal is only several atmospheric pressure. With this feature, the structure of the device can be simplified by Bridgman method. However, this method is also facing a problem, that is, compared with other methods known as the "LEK method" ZnTe crystals, the crystallization quality is too low. The reason is that the best growth condition under Bridgman method has not been fully established. Bridgman method is gradually improved, and has been put into operation for the THz substrate ZnTe substrate, "2 times lower crystalline quality" (Tanaka). Specifically, according to the results of the comparison of the half peak width of the X ray rocking curve, the bottom plate made by Bridgman method is 50 seconds, which is about 2 times as much as that of the current product (about 20 seconds). The smaller the value, the better the quality. In the future, Saga University in the product oriented to improve the efficiency of green LED, but also will focus on the production of green laser. In order to make the laser, in order to facilitate the formation of the structure with high efficiency, the method of MOCVD.

Source: Nikkei BP