-Ga2O3 for high power LED, the output power can be increased by more than 5 times

-Ga2O3 not only can be used for power components, but also can be used for LED chips, a variety of sensor components and imaging components, etc., a wide range of applications. Among them, the use of GaN semiconductor chip LED chip is the most promising use. It is particularly worth mentioning that -Ga2O3 has the characteristics of high power LED which is suitable for large drive current.

GaN based LED chip is widely used in blue, violet and ultraviolet light wavelength shorter LED. Among them, the blue LED chip is an important part of the white LED. GaN based blue LED chips are now manufactured on sapphire substrates.

Compared with the sapphire substrate, the transmittance of ultraviolet and visible light is 80%, and the resistivity is about -Ga2O3, which is about 0.005 cm, and has good conductivity.

The higher the transmittance is, the easier it is to extract the light emitted from the light-emitting layer of the LED chip, which is expected to improve the output power and luminous efficiency. Furthermore, the vertical structure of the anode and the cathode can be formed on the surface and the back surface of the LED chip due to the high conductivity. The sapphire substrate is insulated, so the transverse configuration of the anode and cathode is adopted.

The vertical structure can not only reduce the component resistance and thermal resistance, but also make the current distribution uniformity. Because of the smaller component resistance and thermal resistance, the less heat output of the LED chip, so it is suitable for the situation of large drive current.

The vertical structure is easy to make the current distribution uniformity, so even if the flow of large current, LED chip is not easy to damage. In addition, the current flowing through the LED chip, but also reduce the phenomenon of uneven lighting. As a result, compared with the common sapphire substrate, the output power of the -Ga2O3 substrate can be estimated to be more than 10 times.

SiC substrate can also realize vertical structure, but its cost is higher. The use of beta -Ga2O3, then it is expected to lower the cost of manufacturing substrates.

There are also some problems in the component characteristics of SiC substrate. The blue light absorption characteristics of SiC substrate are in inverse proportion to the resistance. To suppress the absorption of blue light, the resistance will become larger. So there is a limit to the reduction of component resistance.

Optical output power of 5 times the market products

Although the GaN based LED chip using the beta -Ga2O3 substrate is currently under development, some results have been obtained. For example, Japan's information and Communications Research Institute (NICT) of the research team produced a light-emitting wavelength of 300 m square LED element 450nm. The element is based on the N type Ga2O3 substrate, and the MOCVD method is used to form the active layer of the N type GaN layer, the InGaN/GaN multiple quantum well, and the P type GaN layer through the buffer layer (Figure A-1). The N type electrode is formed on the substrate side, and the Ag type p electrode is formed on the other side of the Ti/Au electrode.

The product in the drive current for the light output power of 1200mA is 170mW (Figure A-2). Compared with the commercially available 300 m square lateral structure blue LED chip, can achieve more than 5 times the optical output power. Moreover, by improving the light emitting layer and light extraction structure, the optical output power can be increased by 2 times.

In addition, NICT's team has also developed a device to reduce the resistance of the use of beta -Ga2O3 substrate LED chip. The chip size is 300 m square, when the driving current is 200mA, the operating voltage is only 3.3V (Figure A-3). The size of the running structure of the product in the driving current of 200mA, the operating voltage up to 4.7V. Due to the low operating voltage, it is possible to reduce the amount of heat generated when driving at high current.

Thermal resistance below 1/10

In addition, the trial produced LED chip thermal resistance is very low. By applying the LED chip to the lower side of the P package, the thermal resistance can be suppressed (Figure A-1). The use of AuSn as a part of the metal solid crystal, and LED chip size of 1mm square, it is estimated that the active layer to the total thermal resistance of joining metal at 0.1 DEG /W below, only the transverse structure of the same size, the products sold to 1/100 1/10.

And the current distribution of the LED chip is very uniform. In order to investigate the current distribution, the team examined the in-plane temperature distribution inside the 1mm square LED chip. The results show that even if the component temperature rises 70 degrees, the maximum temperature difference in the surface is only about 7.

As mentioned above, the LED chip using the beta -Ga2O3 substrate is ideal for high current applications. In this substrate for LED products, NICT's research team is to launch the product within 2012 years as the goal, to promote the development of practical direction.