Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure
Reexamination Certificate
2002-12-31
2004-11-02
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
C257S052000, C257S049000, C257S615000, C438S022000, C438S046000, C438S604000
Reexamination Certificate
active
06812496
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser device using a group III nitride semiconductor.
2. Description of the Prior Art
In general, group III nitride semiconductors of the formula In
x
Ga
y
Al
z
N (where 0≦x≦1, 0≦y≦1, 0≦z≦1, and x+y+z=1) have wide energy band gaps and high thermal stability, and their band gap widths can be controlled through the adjustment of their composition. For these reasons, their application is being developed in a variety of semiconductor devices such as light-emitting devices and high-temperature devices.
As light-emitting devices, light-emitting diodes (LEDs) that emit light having luminous intensity of the order of a few candelas in a wavelength range of blue to green have already been put to practical use, and laser diodes (LDs) are in the process of being developed for practical use. With respect to laser diodes, from the early stages of their development, the feasibility of using a comparatively easily available insulating substrate, such as sapphire, has been studied.
However, in a device using a sapphire substrate, crystal distortion resulting from a large lattice mismatch between the substrate and the epitaxial layer (about 14% between the sapphire C plane and the GaN crystal) and high-density dislocation defects (10
8
to 10
10
cm
−2
) introduced into the epitaxial layer have undesirable effects on the device's characteristics such as its working life. Moreover, where sapphire is used as the substrate of a semiconductor laser device, since the substrate and the epitaxial layer have different cleavage planes, it is difficult to obtain satisfactory end surfaces when the end surfaces of the optical resonant cavity are formed by a method relying on cleavage, a common way of forming them.
Attempts have been made to avoid these problems by using as the substrate a material other than sapphire, for example SiC or the like. This, however, does not fundamentally improve the problems associated with the size and availability of the substrate, lattice mismatch, etc.
From the viewpoint of resolving the lattice mismatch between the substrate and the epitaxial layer, reducing crystal defects, and obtaining a satisfactory crystal, the inventors of the present inventions have been developing devices using as their substrate GaN, which, like their epitaxial layer, is a group III nitride semiconductor.
As a result, it is now possible to greatly improve the characteristics of nitride semiconductor laser devices. However, the use of a GaN substrate does not always result in a satisfactory nitride semiconductor laser device. Specifically, it has been found out that, in some such devices, their operation current gradually increases, or their characteristics rapidly deteriorate. Through an intensive study in search of the causes, the inventors of the present invention have found out that there are several methods of producing a GaN substrate, each producing a substrate different in structure and quality, and that the resulting differences affect the layered structure formed on the substrate, greatly influencing the characteristics of a nitride semiconductor laser device.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a nitride semiconductor laser device using a group III nitride semiconductor also as a substrate wherein the structure of the device is optimized to suit the substrate actually used in order to achieve excellent operation characteristics and a long laser oscillation life.
To achieve the above object, according to one aspect of the present invention, in a semiconductor laser device comprising a substrate of a group III nitride semiconductor, a layered structure of a group III nitride semiconductor formed on the top surface of the substrate, and an electrode formed on the top surface of the layered structure, the substrate has a dislocation-concentrated region extending from the bottom surface to the top surface thereof and a low-dislocation region constituting the remaining portion thereof other than the dislocation-concentrated region, the layered structure has a stripe-shaped laser optical waveguide region located right above the low-dislocation region of the substrate, and the electrode is located right above the low-dislocation region of the substrate.
This semiconductor laser device has a substrate of a group III nitride semiconductor, in which a dislocation-concentrated region extends so as to vertically penetrate it. However, a laser optical waveguide region included in a layered structure of a group III nitride semiconductor is located not above the dislocation-concentrated region but above a low-dislocation region, i.e. the portion of the substrate other than the dislocation-concentrated region. Thus, even if the dislocation-concentrated region influences the structured layer and causes defects in a portion thereof above the dislocation-concentrated region, the laser optical waveguide region, located away from those defects, offers satisfactory characteristics.
Moreover, an electrode formed on the top surface of the layered structure is also located not above the dislocation-concentrated region but above the low-dislocation region. Thus, even if the defects in the portion above the dislocation-concentrated region reach the top surface of the layered structure and are exposed, the electrode is located away from those defects. This prevents current from flowing through the dislocation-concentrated region of the substrate and through a possibly defect-ridden portion of the layered structure above it, and thus helps alleviate the deterioration of the laser optical waveguide region resulting from an increase in the operation current.
According to another aspect of the present invention, in a semiconductor laser device comprising a substrate of a group III nitride semiconductor, a layered structure of a group III nitride semiconductor formed on the top surface of the substrate, and an electrode formed on the bottom surface of the substrate, the substrate has a dislocation-concentrated region extending from the bottom surface to the top surface thereof and a low-dislocation region constituting the remaining portion thereof other than the dislocation-concentrated region, the layered structure has a stripe-shaped laser optical waveguide region located right above the low-dislocation region of the substrate, and the electrode is located right below the low-dislocation region of the substrate.
This semiconductor laser device, too, has a dislocation-concentrated region extending in a substrate so as to vertically penetrate it. However, a laser optical waveguide region is located not above the dislocation-concentrated region but above a low-dislocation region. Thus, even if defects arise in a portion of the layered structured above the dislocation-concentrated region, the laser optical waveguide region, located away from those defects, offers satisfactory characteristics. On the bottom surface of the substrate, the lower end of the dislocation-concentrated region is exposed. However, since an electrode formed on the bottom surface of the substrate is located not below the dislocation-concentrated region but below the low-dislocation region, and is thus located away from where the dislocation-concentrated region is exposed. This prevents current from flowing through the dislocation-concentrated region, and thus helps alleviate the deterioration of the laser optical waveguide region resulting from an increase in the operation current.
According to still another aspect of the present invention, in a semiconductor laser device comprising a substrate of a group III nitride semiconductor and a layered structure of a group III nitride semiconductor formed on the top surface of the substrate, the substrate has a dislocation-concentrated region extending from the bottom surface to the top surface thereof and a low-dislocation region constituting the remaining portion thereof other than the dislocation-concentrated region, th
Ito Shigetoshi
Motoki Kensaku
Takatani Kunihiro
Taneya Mototaka
Yuasa Takayuki
LandOfFree
Group III nitride semiconductor laser device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Group III nitride semiconductor laser device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Group III nitride semiconductor laser device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3329615