Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With reflector – opaque mask – or optical element integral...
Reexamination Certificate
2001-12-27
2003-05-27
Tran, Minh Loan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With reflector, opaque mask, or optical element integral...
C257S099000, C257S103000, C257S096000, C257S094000, C257S022000, C257S014000
Reexamination Certificate
active
06570191
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improvements of a surface-light-emitting device including a light-generating layer and a light resonator constituted by two multi-film reflecting layers between which the light-emitting layer is interposed.
2. Discussion of Related Art
There is known a surface-light-emitting device including a semiconductor substrate and a plurality of semiconductor layers which are grown on the semiconductor substrate. The semiconductor layers comprise a light-generating layer (active portion), and a light resonator constituted by two multi-film reflecting layers (DBR: distributed-Bragg reflectors) which are located on the opposite sides of the light-generating layer, to reflect a light generated by the light-generating layer. The semiconductor layers further comprise an outermost semiconductor layer which is located on one of the opposite sides of a laminar semiconductor structure consisting of the above-indicated semiconductor layers, which one side is remote from the substrate. The outermost semiconductor layer has a light-emitting surface from which the light generated by the light-generating layer and resonated by the light resonator is emitted. Examples of such a surface-light-emitting device include a resonant-cavity light-emitting diode and a surface-light-emitting laser.
JP-A-2000-299492 discloses a light-emitting diode of quantum-well type, as an example of the surface-light-emitting device. This light-emitting diode includes a plurality of semiconductor layers laminated on a substrate. The semiconductor layers comprise a light-generating layer of a quantum-well structure having a thickness not larger than the wavelength (100 Å, i.e., 10 nm) of the electron wave, and a light resonator consisting of two reflecting layers which are located on the respective opposite sides of the light-generating layer and which reflect a light generated by the light-generating layer. By applying an electric current between a pair of electrodes formed on the respective opposite surfaces of a laminar semiconductor structure consisting of the semiconductor layers, the light generated by the light-generating layer is emitted from one of the opposite surfaces of the laminar semiconductor structure which is remote from the substrate. In the light-emitting diode disclosed in the above-identified publication, an electron wave within the light-generating layer and an optical wave within the light resonator are coupled together, so that the light-generating layer generates a light only in a resonance mode. This phenomenon so-called “a cavity QED effect” permits the emitted light to have a high degree of directivity and a narrow line width, and prevents total reflection of the light by the crystal surface, assuring an advantage of a high degree of external quantum efficiency.
A known surface-light-emitting device as described above includes, for instance, an n-GaAs semiconductor substrate, and a first multi-film reflecting layer, a light-generating layer and a second multi-film reflecting layer which are successively grown on the substrate. The first multi-film reflecting layer consists of a multiplicity of n-(Al)GaAs/Al(Ga)As films superposed on each other such that the (Al)GaAs films and the Al(Ga)As films are alternately arranged. The ratios of the elements indicated in the parentheses are suitably selected, and may be zero. The second multi-film reflecting layer consists of a multiplicity of p-(Al)GaAs/Al(Ga)As films superposed on each other such that the (Al)GaAs films and the Al(Ga)As films are alternately arranged. The parentheses have the same meaning as described just above. Where the wavelength of the light to be emitted from the surface-light-emitting device is as short as about six hundred and some tens of nanometers (nm), the concentrations of Al of the (Al)GaAs films must be made relatively high in order to reduce the light absorptance. However, an increase in the Al concentration undesirably reduces or substantially zeros the refractive index at the boundaries of the alternately arranged films, leading to difficulty in obtaining a sufficiently high degree of reflectivity of the multi-film reflecting layers. Another problem encountered in the known surface-light-emitting device relates to a change of a gas used to form the first multi-film reflecting layer (formed on the side of the substrate) and the light-generating layer (active portion of the device). Described in detail, epitaxial growth of the AlGaInP/GaInP light-generating layer on the first multi-film reflecting layer is initiated by changing the gas from arsine AsH
3
which has been used for growing the As-based material of the first multi-film reflecting layer, to phosphine PH
3
to be used for the epitaxial growth of the light-generating layer on the first reflecting layer. However, this arsine-to-phosphine change of the gas takes a relatively long time, causing an increased surface roughness of the first reflecting layer, and oxidization of Al, making it difficult to form a high-quality active portion on the first reflecting layer, that is, the light-generating layer having a high quality on the first reflecting layer.
On the other hand, it has been proposed to form the first and second (n- and p-) multi-film reflecting layers consisting of (Al)GaInP/Al(Ga)InP films. The reflecting layers according to this proposal exhibit a high degree of reflectivity even where the light to be emitted has a considerably short wavelength. In addition, the epitaxial growth of the AlGaInP/GaInP light-generating layer on the first reflecting layer does not require a change from arsine AsH
3
to phosphine PH
3
, before the epitaxial growth of the light-generating layer on the first reflecting layer. Accordingly, the light-generating layer serving as the active portion of the surface-light-emitting device can be advantageously given a high degree of crystallinity. However, the use of the p-(Al)GaInP/Al(Ga)InP second multi-film reflecting layer gives rise to a relatively large degree of carrier blockage, and an accordingly high electric resistance, and results in reduced enclosure of electrons, so that the operating efficiency of the surface-light-emitting device is deteriorated where the device is designed to emit a light having a relatively short wavelength. Another problem arises from the use of the (Al)GaInP/Al(Ga)InP films for the first and second (n- and p-) multi-film reflecting layers, where a mesa structure is formed by selective etching effected on the laminar semiconductor structure grown on the semiconductor substrate. That is, it is extremely difficult to practice a wet-etching process to form the mesa structure. Although the application of the wet-etching process is not impossible, the yield ratio in the production of the surface-light-emitting device is considerably low where the wet-etching process is used to form the mesa structure. In addition, the difficulty to form the mesa structure by the wet-etching process leads to difficulty to form a current-blocking region by subjecting the peripheral portion of the mesa structure to an oxidizing treatment.
SUMMARY OF THE INVENTION
The present invention was made in view of the prior art described above. It is therefore a principal object of the present invention to provide a surface-light-emitting device which includes multi-film reflecting layers having a high degree of reflectivity with respect to a relatively short wavelength of light, and a light-generating layer having a high degree of crystallinity, and which has a low electric resistance and exhibits a high operating efficiency. It is an optional object of this invention to provide a surface-light-emitting device including a laminar semiconductor structure which is formed on a semiconductor substrate and which has a mesa structure formed by wet-etching and having a current-blocking region formed by an oxidizing treatment.
The principal object indicated above may be achieved according to the principle of the present invention, which provides a surfac
Hirotani Masumi
Mizuno Yoshiyuki
Sale Terence Edward
Tu Chuan-Cheng
Daido Steel Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tran Minh Loan
Tran Tan
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