Semiconductor luminous elements and semiconductor laser

Details Semiconductor luminous elements and semiconductor laser Semiconductor luminous elements and semiconductor laser

2001-03-08

2004-05-11

Ip, Paul (Department: 2828)

Coherent light generators

Particular active media

Semiconductor

C372S045013, C372S046012

Reexamination Certificate

active

06735230

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a semiconductor light emitting device, such as a semiconductor laser and a light emitting diode, which uses a compound of a Group III element and nitrogen (a Group III nitride type, gallium nitride type compound semiconductor) and is capable of emitting light in the blue area that is required for an optical disk memory having a high storage density and for a high-precision laser beam printer. More specifically, the present invention concerns a semiconductor light emitting device in which a conductive substrate is used as a substrate on which a semiconductor layer having a superior light emitting property is laminated, and electrodes can be taken out from both of the upper and lower surfaces of a chip and is allowed to have a cleavage, and also concerns a semiconductor laser on which such a semiconductor light emitting device and its chip is mounted with a superior heat radiating property.
BACKGROUND OF THE INVENTION
With respect to blue-type semiconductor lasers, for example, Japanese Journal of Applied Physics (Jpn. J. Apply. Phys.) Vol. 35 (1996), pp 74-76, has reported a construction in which a CW oscillation is available in the blue area. As illustrated in
FIG. 19
, hexagonal system Group III nitride compound semiconductors are successively stacked on a sapphire substrate
71
by metal organic chemical vapor deposition (hereinafter, referred to as MOCVD); that is, the following layers are stacked: a GaN buffering layer
72
, an n-type GaN layer
73
, an n-type stress alleviating layer
74
made from In
0.1
Ga
0.9
N, an n-type clad layer
75
made from Al
0.12
Ga
0.88
N, an n-type light guide layer
76
made from GaN, an active layer
77
made of a multiple quantum well structure of an InGaN type compound semiconductor, a p-type light guide layer
78
made from p-type GaN, a p-type first clad layer
79
made from p-type Al
0.2
Ga
0.8
N, a p-type second clad layer
80
made from Al
0.12
Ga
0.88
N and a contact layer
81
made from a p-type GaN. One portion of this semiconductor layers thus stacked is then etched by dry etching, etc. so that, as illustrated in
FIG. 19
, n-type GaN layer
73
is exposed to outside, and an n-side electrode
83
is formed on the surface thereof, and a p-type electrode
82
is formed on the aforementioned contact layer
81
respectively.
Moreover, Japanese Patent Notifying Publication No. 8217/1996 (Tokukouhei 8-8217) discloses a method in which a Ga
a
Al
1−a
N (0<a≦1) serving as a buffering layer is formed, and a gallium nitride type compound semiconductor is stacked thereon.
However, in any of these methods, since the semiconductor layers are stacked on the sapphire substrate, the n-side electrode has to be formed on the n-type layer that has been exposed by etching one portion of the stacked semiconductor layers. Moreover, since the sapphire substrate is very hard, it is very difficult to provide a cleavage; therefore, the laminated layers of the Group III nitride compound semiconductor are again etched by dry etching to form an end face constituting a light resonator.
In the conventional blue-type semiconductor light emitting device, since a sapphire substrate is used as the substrate, it is not possible to form a vertical type element (referred to as a construction in which electrodes are formed on both of the upper and lower surfaces, and hereinafter, the same is true ) having electrodes formed on both of the upper and lower faces of the laminated layer. For this reason, complex manufacturing processes are required, a complex chip bonding process is also required, and it is not possible to provide a cleavage, resulting in a failure in forming a flat end face from the atomic point of view.
Moreover, Patent Publication No. 2677221 discloses a method for laminating a Group III nitride compound semiconductor on a gallium arsenide substrate. In this method, a buffer layer of GaN, etc. is formed at a low temperature of approximately 350 to 530° C. by using a hydride vapor-phase epitaxial method, and a semiconductor laminated portion is then allowed to grow. However, in this method gallium nitride type compound semiconductor such as GaN is directly formed on a GaAs substrate, with the result that in comparison with a GaAs lattice constant of 5.6537 Å, cubic GaN has a lattice constant of approximately 4.5 Å, which is a greatly different value. For this reason, a highly unconformity hetero-epitaxial growth takes place, frequently resulting in a defective stacked layer; therefore, it is difficult to reduce the transition density to an extent necessary to emit laser light, and from the viewpoint of crystalline property, this method is more difficult than the method for laminating a gallium nitride type compound semiconductor layer on a sapphire substrate.
Moreover, another structure has been known in which a gallium nitride type compound semiconductor is stacked on a silicon carbide substrate with an AlN or GaAlN type semiconductor layer being provided as a buffer layer. However, in this structure also, in the same manner as the case where the lamination is made on the sapphire substrate, a hexagonal system gallium nitride type compound semiconductor is laminated at a high temperature, and a hexagonal-system-use silicon carbide substrate is adopted. Therefore, a substrate that is by far more expensive substrate than a sapphire substrate has to be used, and the substrate costs virtually
20
times as expensive as the sapphire substrate, resulting in a failure in putting this method into practical use.
As described above, the conventional blue-color semiconductor laser has the structure in which a Group III nitride compound semiconductor layer is laminated on a sapphire substrate, and sapphire has a thermal conductivity of 0.46 W/(cm·K), which is extremely smaller than that of Si (thermal conductivity 1.7 W/(cm·K)), etc. In the blue color semiconductor laser, since its wavelength is particularly short and since the Group III nitride compound semiconductor layer is inferior in the crystalline property, and tends to generate heat, its heat radiating efficiency gives greatly influences on the property and reliability of the semiconductor laser, as described earlier. For this reason, as shown in Japanese Unexamined Patent Application No. 235729/1995 (Tokukaihei 7-235729) as well as in
FIG. 20
, an upper p-side electrode
82
close to the active layer is die-bonded through a bonding agent
92
such as solder so as to directly contact a sub-mount
90
, with the chip facing down. In this case, as described earlier, the n-side electrode
83
is formed in a concave section, and there is a step difference between the p-side electrode
82
and the n-side electrode
83
; therefore, the die-bonding has to be carried out with solder agent
91
corresponding to the thickness being interpolated in between, or as illustrated in
FIG. 21
, a step difference is formed on the surface of the sub-mount
90
, and the bonding is carried out with the step difference of the LD chip
70
being coincident with this step difference.
As described above, in the blue color LD chip using the conventional Group III nitride compound semiconductor, the Group III nitride compound semiconductor is laminated on the sapphire substrate; therefore, in order to carry out a mounting process so as to increase the heat-radiating efficiency, the die-bonding has to be carried out with thick solder agent
91
being interpolated on the side of the concave n-side electrode
83
, or the mounting has to be carried out with the step difference of the LD chip
70
being coincident with the step difference formed on the surface of the sub-mount
90
. However, in the case of the thick solder agent
91
, it is highly possible that, when the solder agent
91
is fused, solder flows onto the laminated semiconductor layer (on the side wall exposed by etching), causing short-circuiting between the laminated n-type layer and the p-type layer or causing much current leakage. Moreover, in the case when the step difference is formed on

Affiliated with

Also associated with

Rating

Semiconductor luminous elements and semiconductor laser 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 luminous elements and semiconductor laser, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor luminous elements and semiconductor laser will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3265837