Light emitting devices, such as light emitting diodes or laser diodes, which use group III-V or II-VI compound semiconductors, are capable of emitting visible and ultraviolet light of various colors such as red, green, and blue owing to development of device materials and thin film growth techniques. These light emitting devices are also capable of emitting white light with high luminous efficacy through use of a fluorescent substance or color combination and have several advantages of low power consumption, semi-permanent lifespan, fast response speed, safety, and environmental friendliness as compared to conventional light sources such as, for example, fluorescent lamps and incandescent lamps.
Accordingly, fields of application sectors of the light emitting devices are expanded up to transmission modules of optical communication means, light emitting diode backlights to replace cold cathode fluorescence Lamps (CCFLs) which serve as backlights of liquid crystal display (LCD) apparatuses, white light emitting diode lighting apparatus to replace fluorescent lamps or incandescent lamps, vehicular headlamps, and traffic lights. Recently, a high-voltage light emitting device to which a plurality of light emitting cells is applied is implemented owing to expansion of the fields of application.
FIG. 1 is a view illustrating a structure of a conventional horizontal high-voltage light emitting device.
According to the conventional light emitting device in FIG. 1, a plurality of light emitting cells 20 may be disposed on a substrate 10. Each light emitting cell 20 includes a first conductive type semiconductor layer 21, an active layer 22, and a second conductive type semiconductor layer 23. A first electrode layer 30 electrically connected to the first conductive type semiconductor layer 21, a second electrode layer 40 disposed on the second conductive type semiconductor layer 23, and a passivation layer 50 protecting the light emitting cells 20 while electrically separating the first electrode layer 30 from the second electrode layer 40 are provided. However, in the case of the conventional horizontal light emitting device for the high voltage as illustrated in FIG. 1, a sapphire (Al2O3) substrate having a thickness of about 100 μm is used such that it is not easy to radiate heat generated when emitting light. Thereby, characteristics of the device are deteriorated.
A flip-chip type light emitting device is used as one of the methods for solving the problem of heat radiation. In the case of the flip-chip type light emitting device, a reflective layer is disposed on the second electrode layer in the structure of the light emitting cell to change a photon path, thereby improving luminance efficiency. However, the emitted light totally reflected by the substrate is absorbed into the light emitting cell, or light extraction is not performed at a space between the light cells such that the amount of light emission extracted upwards is smaller than the amount of light emission generated at the active layer, thereby lowering luminance efficiency. FIG. 2 is a view showing phenomenon of radiation of the flip-chip type light emitting device.