Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – Active layer of indirect band gap semiconductor
Reexamination Certificate
2002-05-24
2004-11-23
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
Active layer of indirect band gap semiconductor
C257S012000, C257S013000, C257S014000, C257S025000, C257S436000
Reexamination Certificate
active
06822266
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light-emitting device for use in optical transmissions, displays and so forth.
In recent years, semiconductor light-emitting devices have been widely used for optical communications, information display panels and so forth. In these cases, it is important for the semiconductor light-emitting device to have high light-emitting efficiency. Furthermore, a fast response speed is critical for a semiconductor light-emitting device in optical communications. Semiconductor light-emitting devices having these properties have been increasingly developed in recent years.
A common plane emission-type Light-Emitting Diode (LED) does not have a favorable high-speed response property and is limited to about 100-200 Mbps. Accordingly, a semiconductor light-emitting device, called a resonant cavity-type LED, is being developed. This resonant cavity-type LED is a semiconductor light-emitting device in which a light-emitting layer is positioned at an antinode of a standing wave generated by a resonator formed by two mirrors to control spontaneously emitted light. This achieves a high-speed response with a high degree of efficiency. In particular, a Plastic Optical Fiber (POF) has recently been used for communications over a relatively short distance. A resonant cavity-type LED using an AlGaInP semiconductor material as a light-emitting layer is being developed that enables highly efficient light emission at 650 nm, which is within a low-loss wavelength range of this POF.
However, the aforementioned conventional resonant cavity-type LED has the following problems. The optical output of the resonant cavity-type LED depends on a gain at a resonance wavelength of the aforementioned resonator. The gain thus corresponds to the intensity of a light-emitting spectrum in the light-emitting layer. Therefore, when a peak of the light-emitting spectrum coincides with the resonance wavelength, the optical output is maximized. The optical output decreases as the resonance wavelength is displaced from the peak of the light-emitting spectrum.
The resonance wavelength barely changes even when the temperature changes. However, the emission wavelength from the light-emitting layer largely depends on temperature. That is, as the temperature falls, the emission wavelength becomes shorter. As the temperature rises, the emission wavelength becomes longer. Therefore, the optical output from the resonant cavity-type LED depends on temperature. Furthermore, since the temperature dependence of the optical output from the resonant cavity-type LED is greater than that of a common LED, it is problematic to use the resonant cavity type LED for communications.
Conventionally, to solve the problem of temperature dependence of the optical output from the resonant cavity-type LED, a plurality of quantum well active layers are provided. The well width of each quantum well active layer is changed to increase the gain spectrum width. Consequently, a large gain can be obtained at a resonance wavelength within a wider temperature range.
However, the response speed depends on the number of quantum well layers in the aforementioned resonant cavity-type LED, with independent quantum wells having different widths. Therefore, the response speed is reduced when there are two or more quantum well layers.
Accordingly, an object of the invention is to provide a resonant cavity-type semiconductor light-emitting device having excellent response characteristics and an optical output with little dependence on temperature.
SUMMARY OF THE INVENTION
A first embodiment of the invention provides a semiconductor light-emitting device comprising a resonator having a pair of multilayer reflection films formed on a semiconductor substrate with a predetermined gap therebetween. A quantum well active layer is provided at a position of an antinode of a standing wave generated in the resonator. The quantum well active layer is doped with an impurity.
According to the above constitution, since the quantum well active layer is doped with impurities, a half-value width of a light-emitting spectrum is greater than when the impurities are not doped. The temperature dependence of the optical output is also reduced.
In one embodiment of the semiconductor light-emitting device according to the first aspect of the invention, the quantum well active layer is a single quantum well active layer.
According to this embodiment, since the active layer has a single quantum well structure, a high-speed response can be achieved.
In one embodiment of the semiconductor light-emitting device according to the first aspect of the invention, the impurity is either a p-type impurity or an n-type impurity.
According to this embodiment, the same impurity type used in layers other than the quantum well active layer can be used.
In one embodiment of the semiconductor light-emitting device according to the first aspect of the invention, the concentration of the impurity is 2×10
17
cm
−3
or higher.
According to this embodiment, the half-value width of the light-emitting spectrum is notably increased in comparison to when the impurities are not doped.
In one embodiment of the semiconductor light-emitting device according to the first aspect of the invention, the impurity includes both a p-type impurity and an n-type impurity.
According to this embodiment, the half-value width of the light-emitting spectrum is greater at a lower concentration of the impurities than when an impurity of either one of the conductive types is doped.
In one embodiment of the semiconductor light-emitting device according to the first aspect of the invention, each concentration of the p-type impurity and the n-type impurity is 7×10
16
cm
−3
or higher.
According to this embodiment, the half-value width of the light-emitting spectrum is notably increased compared to when the impurities are not doped.
In one embodiment of the semiconductor light-emitting device according to the first aspect of the invention, the p-type impurity can be any one of Zn, Mg, Be and C. The n-type impurity can be any one of Si, Se and Te.
According to this embodiment, the same impurity type used in layers other than the single quantum well active layer can be used.
A second aspect of the invention provides a semiconductor light-emitting device comprising a resonator having of a pair of multilayer reflection films formed on a semiconductor substrate with a predetermined gap therebetween. A quantum well active layer is provided at a position of an antinode of a standing wave generated in the resonator. The half-value width of the light-emitting spectrum by the quantum well active layer is 25 nm or greater.
According to the above constitution, since the half-value width of the light-emitting spectrum from the single quantum well active layer is 25 nm or greater, the temperature dependence of the optical output can be reduced.
In one embodiment of the semiconductor light-emitting device according to the second aspect of the invention, the quantum well active layer is a single quantum well active layer.
According to this embodiment, a change in optical output within the temperature range of −20° C. to 70° C. can be restricted to 20% or lower.
A third aspect of the invention provides a semiconductor light-emitting device comprising a resonator having of a pair of multilayer reflection films formed on a semiconductor substrate with a predetermined gap therebetween. A single quantum well active layer is provided at a position of an antinode of a standing wave generated in the resonator. The rate of minimum optical output to the maximum optical output in the temperature range of −20° C. to 70° C. is 0.8 or higher.
According to the above constitution, since an optical output temperature change rate in the optical output within the temperature range of −20 to 70° C. is 20% or lower, this light-emitting device can be used as a light-emitting device for optical transmissions.
In one embodiment of the semiconductor light-emitting devic
Kurahashi Takahisa
Murakami Tetsurou
Nakatsu Hiroshi
Ohyama Shouichi
Flynn Nathan J.
Forde Remmon R.
Sharp Kabushiki Kaisha
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