Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2000-08-22
2002-03-19
Davie, James W. (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
C372S046012
Reexamination Certificate
active
06359919
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device using a gallium nitride-based compound semiconductor and a manufacturing technique for the same and, more particularly, to a gallium nitride-based compound semiconductor laser, a method of manufacturing the same, and a method of manufacturing a gallium nitride-based compound semiconductor device.
In recent years, gallium nitride-based compound semiconductors such as GaN, InGaN, GaAlN, and InGaAlN have received a great deal of attention as materials for blue semiconductor lasers. Semiconductor lasers using these materials are designed as short-wavelength lasers and hence can focus beams to small diameters. Owing to this advantage, these lasers are expected to be used as light sources for high-density information processing such as processing in optical disks.
Various structures and manufacturing methods have been proposed for semiconductor lasers of this type. In either of these proposed techniques, a laser having satisfactory characteristics has not been obtained because a gallium nitride-based compound semiconductor layer is difficult to cause crystal growth. That is, even if a gallium nitride-based compound semiconductor layer is formed by crystal growth, a high-quality crystal cannot be obtained. Since the crystal quality is poor, carriers cannot be efficiently injected into the active layer. In addition, in a structure having a striped opening in a current blocking layer, the crystal quality of the regrown layer formed after etching for forming the striped opening deteriorates, resulting in voltage drops at the electrode contacts and the like.
To realize a highly reliable blue semiconductor laser which is used for optical disks and the like and operates at a low threshold and a low voltage, it is important to efficiently inject carriers into the active layer and suppress voltage drops at the electrode contacts and the like. However, with the prior techniques, these requirements cannot be satisfied.
According to a semiconductor laser using a gallium nitride-based compound semiconductor material, it is difficult to cause crystal growth of the material and to obtain a high-quality crystal layer. In addition, the crystal quality of the regrown layer formed after etching for forming a striped opening deteriorates. For these reasons, carriers cannot be efficiently injected into the active layer, and voltage drops occur at the electrode contacts and the like. That is, it is difficult to realize a highly reliable device which is used for optical disks and the like and operates at a low threshold and a low voltage.
That a gallium nitride-based compound semiconductor layer cannot be satisfactorily regrown after it is etched applies to various semiconductor devices using gallium nitride-based compound semiconductors as well as semiconductor lasers.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situations, and has as its object to provide a highly reliable gallium nitride-based compound semiconductor laser which allows efficient injection of carriers into the active layer, can suppress voltage drops at the electrode contacts and the like, is used for optical disks and the like, and operates at a low threshold and a low voltage, and a method of manufacturing the same.
It is another object of the present invention to provide a method of manufacturing a gallium nitride-based compound semiconductor device, in which a gallium nitride-based compound semiconductor can be properly regrown once it is etched, thereby contributing to an improvement in the characteristics of various semiconductor devices.
According to a first aspect of the present invention, there is provided a gallium nitride-based compound semiconductor laser comprising:
an active layer having a cyclic structure formed by cyclically stacking not less than two types of semiconductor layers;
first and second cladding layers of first and second conductivity types formed to sandwich the active layer so as to form a double-heterojunction structure;
first and second electrodes connected to the first and second cladding layers;
a current blocking layer formed between the second electrode and the second cladding layer and having a striped opening portion for constricting a current for the double-heterojunction structure; and
a current injection layer formed between the second electrode and the current blocking layer and in the opening portion and having an area larger than that of the opening portion,
wherein each of the first and second cladding layers, the current blocking layer, the current injection layer consists essentially of a material represented by the following composition formula:
In
x
Ga
y
Al
z
N
where x+y+z=1, and 0≦x, y, z≦1, and
when a thickness of the current blocking layer is represented by TA, and a distance between the current blocking layer and the active layer is represented by TB, a condition of TB<TA is satisfied.
According to a second aspect of the present invention, there is provided a gallium nitride-based compound semiconductor laser comprising:
an active layer having a cyclic structure formed by cyclically stacking not less than two types of semiconductor layers;
first and second cladding layers of first and second conductivity types formed to sandwich the active layer so as to form a double-heterojunction structure;
first and second electrodes connected to the first and second cladding layers;
a current blocking layer formed between the second electrode and the second cladding layer and having a striped opening portion for constricting a current for the double-heterojunction structure; and
a current injection layer formed between the second electrode and the current blocking layer and in the opening portion and having an area larger than that of the opening portion,
wherein each of the first and second cladding layers, the current blocking layer, the current injection layer consists essentially of a material represented by the following composition formula:
In
x
Ga
y
Al
z
N
where x+y+z=1, and 0≦x, y, z≦1, and
when a thickness of the current blocking layer is represented by TA, and a thickness of the current injection layer excluding a portion in the opening portion is represented by TC, a condition of TC<TA is satisfied.
Acdording to a third aspect of the present invention, there is provided a gallium nitride-based compound semiconductor laser comprising:
an active layer having a cyclic structure formed by cyclically stacking not less than two types of semiconductor layers;
first and second cladding layers of first and second conductivity types formed to sandwich the active layer so as to form a double-heterojunction structure;
first and second electrodes connected to the first and second cladding layers;
a current blocking layer formed between the second electrode and the second cladding layer and having a striped opening portion for constricting a current for the double-heterojunction structure; and
a current injection layer formed between the second electrode and the current blocking layer and in the opening portion and having an area larger than that of the opening portion,
wherein each of the first and second cladding layers, the current blocking layer, the current injection layer consists essentially of a material represented by the following composition formula:
In
x
Ga
y
Al
z
N
where x+y+z=1, and 0≦x, y, z≦1, and
when a distance between the current blocking layer and the active layer is represented by TB, and a thickness of the current injection layer excluding a portion in the opening portion is represented by TC, a condition of TB<TC is satisfied.
According to a fourth aspect of the present invention, there is provided a gallium nitride-based compound semiconductor laser comprising:
an active layer having a cyclic structure formed by cyclically stacking not less than two types of semiconductor layers;
first and second cladding layers of first and second conductivity ty
Fujimoto Hidetoshi
Hatakoshi Gen-ichi
Ishikawa Masayuki
Nishio Johji
Nunoue Shin-ya
Davie James W.
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Zahn Jeffrey
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