Light-emitting diode (referred to hereinafter as LED) is a main component of the solid body illumination technology. Voltage applied between two electronic terminals of LED induces electric current to flow through p-n junction, and LED emits light owing to emissive recombination of electrons and holes.
The advantages of LED are a long service life, high reliability, as well as a high coefficient of electric energy-to-luminous radiation transformation.
LEDs emitting infra-red, red and green light are made and sold for a long time. Technology for manufacturing LEDs made on the base of III-nitrides and emitting ultra-violet, blue, green and white light has been essentially improved over the last years (see for example U.S. Pat. No. 7,642,108, U.S. Pat. No. 7,335,920, U.S. Pat. No. 7,365,369, U.S. Pat. No. 7,531,841, U.S. Pat. No. 6,614,060). Owing to this LEDs have become more popular and are used in various fields including illumination.
FIG. 1 shows the known prior art III-nitride LED (Hiromitsu Sakai, Takashi Koide, Hiroyuki Suzuki, Machiko Yamaguchi, Shiro Yamasaki, Masayoshi Koike, Hiroshi Amano and Isamu Akasaki, Jpn. J. Appl. Phys. Vol. 34, Part 2, No 11A, pp. L1429, Jan. 11, 1995).
III-nitride LED 100 has a layer structure consisting of a substrate 110, thin buffer layer 120, n-type layer 130 with n-type contact 170 applied (referred to hereinafter as n-contact), p-type layer 150 with p-type contact 160 applied (referred to hereinafter as p-contact), and the active layer 140. In addition, the principal part of LED is an active layer 140 within which generation of light radiation occurs as a result of recombination process of electrons and holes. In usual III-nitride LED, n-type layer 130, p-type layer 150 and active layer 140 have one crystal structure—one crystal phase of III-nitride semiconductor. Usually, this crystal structure corresponds to wurtzite structure. However, an active layer of II-nitride LED 100 can be made from III-nitride semiconductor with chemical composition dissimilar from chemical compositions of n-type layer 130 and p-type layer 150 (Hiromitsu Sakai, Takashi Koide, Hiroyuki Suzuki, Machiko Yamaguchi, Shiro Yamasaki, Masayoshi Koike, Hiroshi Amano and Isamu Akasaki, Jpn. J. Appl. Phys. Vol. 34, Part 2, No 11A, pp. L1429, Jan. 11, 1995). Thus, this III-nitride LED comprises two heteroboundaries between the layers of one crystal phase with dissimilar chemical composition which form a double heterostructure or a quantum well. III-nitride double heterostructure or a quantum well comprises two I type heteroboundaries which form potential wells both for electrons as well as for holes.
The drawback of the structures with I-type heteroboundaries formed from the III-nitride semiconductors of one crystal phase with different chemical composition is that they form potential wells both for electrons and for holes and thus prevent uniform filling of the active layer with holes because their mass in III-nitride semiconductors essentially larger than mass of electrons. In the result, only one well closest to the p-type layer is filled with electrons and holes and emits the larger part of light in the structures with several quantum wells. Density of the carriers in the quantum well closest to the p-type layer becomes high at a large current density and thus LED effectiveness drops because of nonlinear recombination processes such as Auger recombination.
It is clear from the above that effectiveness of light generation by the usual light-emitting semiconductor device (LED) on the base of one crystal phase of III-nitrides is limited at high current densities because of non-homogeneous distribution of holes in the active layer and nonlinear recombination processes.
Thus, the object of the invention is an increasing the effectiveness of luminous radiation by the light-emitting device.
USPTO Backgrounds
USPTO Backgrounds