1. Field of the Invention
The present invention relates to a light emitting device array and, more particularly, to a light emitting device array having a plurality of hexagonal pyramid light emitting structures formed by selective growth.
2. Description of the Related Art
Recently, researches have been actively conducted on semiconductor light emitting devices as a new light source that can replace filament-based light bulbs and fluorescent lamps. In particular, the researches on light emitting diodes (LEDs) using nitride compound semiconductors such as GaN have been gaining attention. Without a suitably compatible substrate, however, nitride crystals tend to have many crystal defects.
To remedy such problems, there has been suggested a method providing a high quality nitride light emitting device by forming hexagonal pyramid-shaped light emitting structures by selective growth.
FIG. 1 is a sectional view illustrating a conventional hexagonal pyramid shaped light emitting device.
As shown in FIG. 1, a dielectric layer 14 having a window W is formed on a first conductivity lower nitride semiconductor layer 12a formed on a sapphire substrate 11. A first conductivity upper nitride semiconductor layer 12b, an active layer 15, and a second conductivity nitride semiconductor layer 16 are grown in the window W by a lateral growth process utilizing the dielectric layer 14. At this time, the nitride semiconductor layers 12b, 15 and 16 are grown in the window W to form a hexagonal pyramid shaped light emitting structure. One of a transparent conductive thin film 17 and an electrode 19 is fanned on the second conductivity nitride semiconductor layer 16 of the hexagonal pyramid light emitting structure, and a part of the dielectric layer is etched to expose a surface of the first conductivity lower nitride semiconductor layer 12a and form another electrode 18 of different polarity.
It has been reported that a large number of defects, growing in a horizontal direction, in the nitride single crystals obtained by the selective growth, are blocked or change direction in the process of lateral growth, thus rarely affecting the active layer. Also, since the effect of lattice mismatch between the nitride single crystals and a substrate is insignificant, the crystal growth defects may be decreased.
In such an LED structure, a hexagonal pyramid structure has a substantial light emission area enlarged by the inclined side surfaces thereof and the piezoelectric field effect may also be mitigated by the crystal growth direction.
In addition, in order to obtain superior luminance, the hexagonal pyramid light emission structure shown in FIG. 1 is provided in a plurality arranged in an array. For optimal space utilization, the windows of the hexagonal pyramid light emitting devices are disposed in a triangular arrangement. However, as shown in FIG. 2, in an equilateral triangular arrangement of windows, even if the hexagonal pyramid light emission structures 20 are grown to occupy a maximum area, a great number of wasted areas A, which cannot be utilized as the light emission area, remain.
Therefore, there is a need for an arrangement of hexagonal pyramid light emission structures in order to minimize the waste of space and maximize the light emission area of a light emitting device.