Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2001-04-10
2003-03-18
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S045013
Reexamination Certificate
active
06535536
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a semiconductor laser element and, in particular, to a semiconductor laser element having a semiconductor layer including an active layer formed a GaN layer.
2. Description of the Related Art
In the field of manufacturing a high-density optical disc memory or printing using a photosensitive material, a semiconductor laser of 400 nm band having a micro-spot is expected to oscillate a fundamental transverse mode by a highly reliable Gaussian beam.
Disclosed in Jpn. J. Appl. Phys., Vol. 37, pp. L1020, issued in 1998 is “InGaN/GaN/AlGaN-Based Laser Diodes Grown GaN Substrates with a Fundamental Transverse Mode” by Nakamura et al. This is formed as follows: a GaN layer is formed on a sapphire substrate and then the thick GaN film formed by the use of selective growth by using SiO
2
as a mask is removed to make a GaN substrate, and on the GaN substrate are formed an n-GaN buffer layer, an n-InGaN crack preventing layer, an n-AlGaN/GaN modulation doped superlattice clad layer, an n-GaN optical waveguide layer, an n-InGaN/InGaN multiple quantum well active layer, a p-AlGaN carrier block layer, a p-GaN optical waveguide layer, a p-AlGaN/GaN modulation doped superlattice clad layer, and a p-GaN contact layer. However, in this case, a refractive index guiding type structure is formed by forming a ridge structure of about 2 &mgr;m and this semiconductor laser can produce only the fundamental transverse mode oscillation, at most, of about 30 mW because it is very difficult to control the depth of etching. Further, although a try to reduce an element resistance is made by the use of the modulation doped superlattice clad layer, the element resistance is not sufficiently reduced and hence the reliability of the element is observed to be degraded by the joule heat generated when the element is operated.
As described above, the above-mentioned structure presents a problem that a single mode laser having a small contact area with a contact layer is affected in a practical use by heat generation because the element resistance is large.
SUMMARY OF THE INVENTION
The invention has been made in view of the above problem, and it is an object of the invention to provide a semiconductor laser element producing a Gaussian beam of high quality having high reliability to a high power by reducing an element resistance and preventing the effect of heat generation.
A first semiconductor laser element in accordance with the invention is composed of a GaN layer and at least a lower clad layer, a lower optical waveguide layer, an active layer, an upper optical waveguide layer, an upper clad layer, and a GaN contact layer all of which are laminated on the GaN layer in this order, is provided with a current injection window above the active layer, and is further composed of a first AlGaN composition gradient layer which is formed between the GaN layer and the lower clad layer so that a band gap thereof continuously changes from the GaN layer to the lower clad layer and a second AlGaN composition gradient layer which is formed between the upper clad layer and the GaN contact layer so that a band gap thereof continuously changes from the upper clad layer to the GaN contact layer.
Further, the first semiconductor laser element in accordance with the invention may be composed of a third AlGaN composition gradient layer which is formed between the lower clad layer and the lower optical waveguide layer so that a band gap thereof continuously changes from the lower clad layer to the lower optical waveguide layer and a fourth AlGaN composition gradient layer which is formed between the upper optical waveguide layer and the upper clad layer and so that a band gap thereof continuously changes from the upper optical waveguide layer to the upper clad layer.
It is desirable that the above-mentioned first semiconductor laser element in accordance with the invention has an equivalent refractive index difference which is not less than 0.002 and not more than 0.01 in the case where a stripe width is not less than 1 &mgr;m and not more than 2.5 &mgr;m and that it has an equivalent refractive index difference which is not less than 0.002 and not more than 0.015 in the case where a stripe width is not less than 2.5 &mgr;m.
The second semiconductor laser element in accordance with the invention is composed of a GaN layer and at least a lower clad layer, a lower optical waveguide layer, an active layer, an upper optical waveguide layer, an upper clad layer, and a GaN contact layer all of which are laminated on the GaN layer in this order, is provided with a current injection window having a predetermined stripe width above the active layer, and is further composed of the first AlGaN/GaN quantum well gradient layer which is formed between the GaN layer and the lower clad layer and which has an energy gap larger than the GaN layer and smaller than the lower clad layer and/or the second AlGaN/GaN quantum well gradient layer which is formed between the upper clad layer and the GaN contact layer and which has an energy gap larger than the upper clad layer and smaller than the GaN contact layer.
Here the term, “the energy gap” refers to a substantial energy gap, and the term “the energy gap in the quantum well gradient layer” refers to a substantial energy gap obtained in consideration of a tunnel effect.
That is, in the second semiconductor laser element in accordance with the invention, a difference in the energy gap between the neighboring layers is reduced by providing the AlGaN/GaN quantum well gradient layer having an energy gap of intermediate magnitude between the energy gaps of the upper and lower layers, the upper and lower layers being the GaN layer and the lower clad layer and/or the contact layer and the upper clad layer.
Here, the quantum well gradient layer is composed of at least one quantum well layer and a pair of barrier layers sandwiching the quantum well layer. The quantum well gradient layer may be a single quantum well gradient layer having an energy gap connected stepwise to the energy gaps of the upper and lower layers, or may include multiple quantum well gradient layers. Also, in the case of the multiple quantum well gradient layers, the respective multiple layers may be constituted so that the energy gaps of the respective multiple layers continuously change and connect the energy gap between the upper and lower layers.
It is desirable that the second semiconductor laser element in accordance with the invention is further composed of the third AlGaN/GaN quantum well gradient layer which is formed between the lower clad layer and the lower optical waveguide layer and which has a band gap smaller than the lower clad layer and larger than the optical waveguide layer, and/or the fourth AlGaN/GaN quantum well gradient layer which is formed between the upper optical waveguide layer and the upper clad layer and which has a band gap smaller than the upper clad layer and larger than the upper optical waveguide layer.
Also in this case, as described above, the respective quantum well gradient layers may be a single quantum well gradient layer or may include multiple quantum well gradient layers. Also, in the case of the multiple quantum well gradient layers, the respective multiple layers may be constituted so that the energy gaps of the respective multiple layers change in a stepwise or continuous manner.
Of the barrier layers and the quantum layers constituting the respective quantum well gradient layers, only the barrier layers may be doped with impurities or both of the barrier layers and the quantum layers may be doped with impurities.
It is desirable in the second semiconductor laser element in accordance with the invention that the above-mentioned stripe width is not less than 1 &mgr;m and not more than 2.5 &mgr;m and that an equivalent refractive index difference is not less than 0.002 and not more than 0.01 or that the above-mentioned stripe width is not less than 2.5 &mgr;m and that an equivalent refractive index difference is not le
Fukunaga Toshiaki
Matsumoto Kenji
Wada Mitsugu
Ip Paul
Nguyen Tuan N
LandOfFree
Semiconductor laser element does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor laser element, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor laser element will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3048632