Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With particular dopant concentration or concentration profile
Reexamination Certificate
2000-01-07
2003-09-02
Tran, Minh Loan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With particular dopant concentration or concentration profile
C257S102000, C257S103000
Reexamination Certificate
active
06614059
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a light-emitting device like a semiconductor laser device, and more particularly relates to a semiconductor light-emitting device for emitting radiation in the ultraviolet to blue regions. The present invention also relates to a method for fabricating the semiconductor light-emitting device and to an optical disk apparatus using the light-emitting device.
In recent years, semiconductor light-emitting devices that can emit radiation at short wavelengths ranging from the ultraviolet to blue regions, or semiconductor laser devices, in particular, have been researched and developed vigorously. This is because such light-emitting devices are expected to further increase the recording density of optical disks or the resolution of laser printers and are applicable to optical measuring instruments, medical equipment, display devices, illuminators and so on.
Examples of semiconductor materials that can emit radiation at such short wavelengths include Group III nitride semiconductors. For instance, a semiconductor laser device with a multiple quantum well active layer, which is a stack of silicon (Si)-doped GaInN/GaInN layers, can oscillate continuously at a wavelength of about 401 nm and at room temperature and can operate for as long as about 3,000 hours under the conditions that the ambient temperature is 20° C. and the output power thereof is 2 mW. See Japanese Journal of Applied Physics, Vol. 36 (1997), pp. 1568-1571, for example.
Group III nitride semiconductor crystals are generally grown by a metalorganic vapor phase epitaxy (MOVPE) process. For example, Japanese Laid-Open Publication No. 6-196757 discloses a method of growing a semiconductor layer of GaInN of excellent crystal quality on a semiconductor layer of GaN by using nitrogen as a carrier gas.
The known method of producing a Group III nitride semiconductor, however, is disadvantageous in that pits are created in the GaInN/GaN multiple quantum well structure thereof (to be an active layer) at as high a density as 10
8
to 10
9
cm
−2
as described in Applied Physics Letters, Vol. 72 (1998), pp. 710-712, for example.
Those pits adversely affect the operation characteristics of a light-emitting device, e.g., raises the threshold value, at which the laser device starts to oscillate, or lowers the reliability thereof. This is because the existence of the pits not only decreases the luminous efficacy, but also causes localized levels by making the composition of In non-uniform, constitutes a source of diffusion of In being grown or results in scattering or absorption loss in an optical waveguide.
To obtain a Group III nitride semiconductor light-emitting device, or semiconductor laser device, in particular, with characteristics practically applicable to an optical disk apparatus, for example, the composition of In within the GaInN well layer thereof should be uniformized. In addition, each multiple quantum well layer should be of uniform quality and be sufficiently planarized.
Moreover, the structure of the device should be modified such that electrons, which are injected from an n-type conductive layer into the quantum well layer, can be injected into the active layer efficiently and uniformly without overflowing into a p-type conductive layer during the operation of the device.
SUMMARY OF THE INVENTION
An object of the present invention is solving the problems of the prior art to suppress the creation of pits in quantum well layer containing indium and nitrogen in a Group III nitride semiconductor light-emitting device and to inject electrons into the quantum well layer more efficiently.
To achieve this object, the present invention takes the following measures:
1) Each barrier layer included in the quantum well layer contains aluminum;
2) The stress vector of each barrier layer is of the opposite sign to that of each well layer;
3) Only one of barrier layers that is in contact with a p-type conductive layer contains aluminum in multiple quantum well layer;
4) In growing the quantum well layer by an MOVPE process, triethylgallium is used as a gallium source.
The present inventors analyzed how inverted hexagonal parallelepiped pits with {1-101} planes as facets are formed at a high density in a GaInN/GaN or GaInN/GaInN multiple quantum well structure in accordance with a conventional fabrication process. As a result, we reached the following conclusions.
To relax a compressive strain induced in a GaInN layer or a strain resulting from localized segregation of In, nuclei of pits are created at more than a critical thickness. In addition, at the growth temperature of the GaInN layer (usually at a growth temperature of about 800° C.), the growth rate for {1-101} planes is lower than that for the (0001) plane in the GaInN layer. Accordingly, as the crystals are growing, the pits are also increasing their sizes. Those pits, which have been created in the GaInN layer, are gradually filled in and the surfaces of the crystals are planarized while an optical guide layer, a cladding layer and so on are grown one upon the other on the GaInN layer at a growth temperature of about 1000° C. This is because the growth rate for the {1-101} planes is higher than that for the (0001) plane in the optical guide layer, etc.
It should be noted that when a zone axis index or a Miller index representing a crystallographic plane orientation is followed by a negative sign, the index following the negative sign is a negative direction index in this specification.
The present inventors examined various methods of suppressing the creation of those pits. As a result, we made the following findings.
Specifically, if the multiple quantum well structure includes an aluminum (Al)-containing barrier layer, then a tensile strain is induced in the barrier layer, and a compressive strain applied to the multiple quantum well structure decreases. Consequently, the critical thickness increases.
In addition, the existence of Al with high electric field intensity in a crystal reduces the diffusion of In, thus suppressing the segregation of In, which strongly tends to segregate locally.
Moreover, the growth rate of the Al-containing semiconductor layer, i.e., an AlGaN layer, for the {1-101} planes is not so different from that for the (0001) plane compared to the GaInN layer. Accordingly, the expansion of pits can be reduced.
Furthermore, if the In mole fraction in the well layer is 0.1 or less, the total thickness of the multiple quantum well structure does not exceed the critical thickness.
Furthermore, if the strain vector of the barrier layer is of the sign opposite to that of well layer, then the total strain applied to the multiple quantum well structure can be reduced, thus increasing the critical thickness.
Also, if triethylgallium (TEG) is used a gallium source in forming the multiple quantum well structure, then the growth rate for the (0001) plane is not so different from that for the {1-101} planes in the quantum well structure.
Accordingly, the expansion of pits can be reduced.
As for a method for injecting electrons more efficiently, we made the following findings.
If the multiple quantum well structure includes a barrier layer with a strain vector of the opposite sign to that of each well layer, then the total strain induced in the multiple quantum well structure can be smaller. Thus, the intensity of a piezoelectric field induced in the multiple quantum well structure decreases. As a result, electrons are injected into the well layers more uniformly.
Alternatively, if only one barrier layer in contact with a p-type conductive layer contains Al and the other barrier layers, which are not in contact with the p-type conductive layer, do not contain Al, then the electrons injected into the well layers do not overflow into the p-type conductive layer. As a result, the electrons can be injected into the well layers more efficiently.
Specifically, a first semiconductor light-emitting device according to the present invention is made of Group I
Ban Yuzaburo
Hasegawa Yoshiaki
Ishibashi Akihiko
Kidoguchi Isao
Suzuki Masakatsu
Dickey Thomas L.
Matsushita Electric - Industrial Co., Ltd.
McDermott & Will & Emery
Tran Minh Loan
LandOfFree
Semiconductor light-emitting device with quantum well 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 light-emitting device with quantum well, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor light-emitting device with quantum well will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3029689