Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1999-03-16
2002-03-12
Davie, James W. (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
C257S015000, C372S046012
Reexamination Certificate
active
06356572
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a semiconductor light emitting device. More particularly, the present invention is useful for a semiconductor laser device. Further, the semiconductor light emitting device according to the present invention is useful for use with optical information processing and optical communication light source.
BACKGROUND OF THE INVENTION
A high output semiconductor laser and a process for forming an element structure thereof for the purpose of a system application of a rewritable optical disk can be seen, for example, in IEEE J. Quantum Electron. 1993, vol. 29, No. 6, pp. 1874-1879, and IEEE Photonics Technol. Lett. 1997, vol. 9, No. 4, pp. 413-415.
On the other hand, it is requested that an injection current (or, an injection amount of a carrier of an electron, a positive hole or the like) to an active layer necessary for oscillation of a laser beam having a fixed intensity be reduced to increase an optical output of a semiconductor laser device. The reduction in a threshold current of the semiconductor laser device is one of techniques to fulfill the aforementioned request.
Further, as a technique for solving a problem of a leakage of a carrier injected into an active layer without contributing to laser oscillation, of a so-called carrier overflow, there is disclosed, in Japanese Patent Laid-Open No. Hei 5-7051, a technique in which a barrier region having a strained super lattice is provided between the active layer and a cladding layer. Further, a technique using a multi quantum barrier (MQB) structure similar to a multi-quantum well structure is disclosed in Japanese Patent Laid-Open No. Hei 6-244509. In these techniques, due to the barrier region or the multi-quantum barrier structure, a carrier which is about to leak from the active layer is returned to the active layer by the barrier region or the multi-quantum barrier structure. The operation of an operating mechanism thereof is performed by a potential barrier formed by the barrier region or the multi-quantum barrier structure. Furthermore, there is disclosed, in Japanese Patent Laid-Open No. Hei 6-334265, the constitution in which the multi-quantum barrier structure is employed as an optical guide layer of a multi-quantum well type active layer in order to adapt the aforementioned techniques to an active layer having the multi-quantum well structure.
SUMMARY OF THE INVENTION
While in the conventional techniques disclosed in above-described references and the like, the process for forming a window structure necessary for attaining a high output in terms of characteristics of elements is mentioned but the process simultaneously concurrently holding a low threshold operation other than the change of the active layer structure is not referred to.
Further, the above-described three Japanese Patent Laid-Opens disclose the technique in which the carrier overflow from the active layer is suppressed in the barrier region of the multi-quantum structure or the super lattice structure to realize the low threshold operation of the semiconductor laser, but do not teach whether or not the aforementioned techniques can be applied to the preparation of an element structure on the substrate having an angle of inclination from a main surface of a crystal. Such a substrate having on its surface the surface inclined from the main crystalline surface as a reference will be hereinafter referred to as “misoriented substrate”. As the main crystalline surface, the miller index surface, for example, (100) surface can be mentioned.
In use of the misoriented substrate, for example, a semiconductor laser of a AlGaInP group has to be introduced in order that the oscillation wavelength is made into 650 nm or less. In the case where a crystal is grown on the misoriented substrate, the grown surface sometimes exhibits the shape which is different from that of the crystal grown on the normal substrate (the surface of the surface orientation (100) in the zinc blend crystalline structure). As an angle of inclination &thgr; is set larger, a trouble of the photoconductive wave caused by the aforesaid shape, a deformation of a near field image and the like also appear. The problem resulting from the misoriented substrate is desired to be solved in terms of the applied field of the zinc blend type crystal.
A first object of the present invention is to secure a low threshold even if a misoriented substrate is used for a crystal growing substrate to constitute a semiconductor light emitting device.
A second object of the present invention is to provide a new construction capable of concurrently holding a low threshold and a high efficiency operation even if a misoriented substrate is used for a crystal growing substrate to constitute a semiconductor light emitting device. The low threshold and the high efficiency operation are useful matters in designing the structure of an active layer for obtaining a high output characteristic in a laser light source for optical information processing and optical communication system.
The present invention is useful particularly for a semiconductor laser device formed on the misoriented substrate, but attains the low threshold high efficiency operation simultaneously with the high output characteristic of the semiconductor laser device, and further realizes a system device using it as a light source. A semiconductor laser element using the misoriented substrate is widely used for a short-wavelength laser device.
The semiconductor light emitting device according to the present invention has the construction in which as a semiconductor substrate, a substrate away from the (100) surface orientation in the range of an inclination angle &thgr;=0°<&thgr;≦54.7° is used, and a semiconductor super lattice period thin film layer is inserted between the misoriented substrate and the active layer region. Further, by making the device described in the following, the quality of a semiconductor crystalline layer provided on the misoriented substrate can be further enhanced, and the element characteristic can be further improved. The present invention can hold simultaneously concurrently the low threshold high efficiency operation of the semiconductor laser element and the high output characteristic by the provision of the means described in detail in the following.
In the substrate away from the (100) surface orientation at the inclination angle &thgr; of 54.7°, the crystalline surface thereof has the maximum inclination angle that can be actually used in the (111) surface. The inclination of the substrate in excess of the above is not practical.
The details of the semiconductor super lattice period thin film layer according to the present invention will be described later.
Prior to entry into the detailed description of the mode for carrying out the present invention, the main operation and effect of the super lattice periodic thin film layer provided in the semiconductor multi-layer particularly according to the present invention will be explained from three aspects.
A first effect is to enable enhancement of flatness of a multi-quantum well construction active layer. By the present invention, it is possible to keep a low threshold of a semiconductor light emitting device having threshold, for example, a semiconductor laser device. A second effect is to enable realization of a low threshold and high efficiency operation of a semiconductor laser device. A third effect is that the super lattice period thin film layer enables performance of a role as a stop layer of diffusion of impurity diffusion in a semiconductor laser device or the like.
A first aspect is a general aspect for a semiconductor device using a misoriented substrate and a semiconductor light emitting device.
A second aspect is useful particularly for a semiconductor laser device.
A third aspect is useful for a semiconductor light emitting device having a window structure in an optical output portion or a semiconductor laser device and is extremely practical.
First, introduction of a super lattice period thin film
Hamada Hiroshi
Hiruma Kenji
Tanaka Toshiaki
Davie James W.
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
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