Patent Grant
7483463
This application claims the benefit of Korean Patent Application No. 10-2006-0012602, filed on Feb. 9, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Disclosure
The present disclosure relates to a ridge-waveguide semiconductor laser diode (LD), and more particularly, to a ridge-waveguide semiconductor LD configured such that a current is laterally injected through side surfaces of a ridge portion.
2. Description of the Related Art
Semiconductor laser diodes (LDs) are widely used for transmitting, recording, and reading data in communication devices, such as optical communication devices, or in electronic devices, such as compact disk players (CDPs) or digital video disk players (DVDPs).
As the use of the semiconductor LDs has increased, semiconductor LDs having a low critical current value and a ridge portion that suppresses multiple transverse mode oscillation have been developed. The ridge portion is formed by upwardly protruding a p-type cladding layer and a p-type contact layer, and a current (holes) is vertically injected down into the ridge portion. However, the vertical current injection has a drawback in that high power is consumed and heat is generated due to the high resistance of a region doped with an impurity, such as magnesium (Mg), when the current (holes) passes through p-type semiconductor layers including the p type cladding layer and a p-type waveguide layer.
The present invention may provide a ridge-waveguide semiconductor laser diode with an improved current injection structure.
According to an aspect of the present invention, there may be provided a ridge-waveguide semiconductor laser diode comprising: a substrate; a lower multi-semiconductor layer formed on the substrate; an active layer formed on the lower multi-semiconductor layer; an upper multi-semiconductor layer having a ridge portion and formed on the active layer; and an upper electrode formed on the upper multi-semiconductor layer, wherein the upper electrode covers at least one side surface of the ridge portion.
The above and other features and advantages of the present invention are illustrated in detailed exemplary embodiments thereof with reference to the attached drawings in which:
The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.
Referring to
The upper multi-semiconductor layer 160 may be divided into first through third regions R1, R2, and R3.
The first region R1 has a ridge portion 165 protruding in a stripe shape from a central part of the upper multi-semiconductor layer 160. The ridge portion 165 may protrude vertically or may be inclined to have a trapezoidal cross-section.
The upper multi-semiconductor layer 160 includes an upper waveguide layer 170 and an upper cladding layer 180. A part of the upper waveguide layer 170 and the upper cladding layer 180 are formed on the ridge portion 165.
An electron blocking layer 171 may be formed in the upper waveguide layer 170. The energy level of the electron blocking layer 171 is much higher than that of the upper waveguide layer 170 such that the electron blocking layer 171 can prevent electron overflow.
A current spreading layer 175 may be embedded in the upper waveguide layer 170. The current spreading layer 175 is disposed on the ridge portion 165 on the upper waveguide layer 170. The current spreading layer 175 allows an injected current to spread over the entire surface thereof, such that the current can be uniformly injected into the active layer 150.
The upper contact layer 190 and the upper electrode 200 cover at least one side surface 165b of the ridge portion 165, such that the current can be injected through the side surface 165b. In order to inject the current through an upper surface 165a of the ridge portion 165, the upper contact layer 190 and the upper electrode 200 may also be formed to cover the upper surface 165a of the ridge portion 165.
The second and third regions R2 and R3 are formed on parts of the upper waveguide layer 170 outside the ridge portion 165, and insulating layers 205 are formed on the second and third regions R2 and R3. The insulating layers 205 cover both lateral edges of the current spreading layer 175. The insulating layers 205 insulate the upper contact layer 190 from the upper waveguide layer 170 and the current spreading layer 175.
The ridge-waveguide semiconductor LD of the present embodiment may be a GaN-based semiconductor LD. In detail, the ridge-waveguide semiconductor LD may be formed as described hereafter.
The substrate 100 may be formed of sapphire (Al2O3), gallium nitride (GaN), silicon (Si), aluminium nitride (AlN), or silicon carbide (SiC).
The lower contact layer 120 may be formed of n-GaN. The lower cladding layer 130 may be formed of n-AlxGa1-xN (0≦x<1). The lower waveguide layer 140 may be formed of n-InxGa1-xN (0≦x<1). The active layer 150 may be formed of InxGa1-xN (0<x<1) and have a single-quantum well or multi-quantum well structure. The upper waveguide layer 170 may be formed of p-InxGa1-xN (0≦x<1). The electron blocking layer 171 may be formed of a p-AlxGa1-xN (0<x<1) compound semiconductor.
The current spreading layer 175 may have a hetero-junction structure of a p-GaN layer and a p-InGaN layer so that the energy level of the current spreading layer 175 can be much lower than the energy level of the upper waveguide layer 170.
The upper cladding layer 180 may be a single layer formed of p-AlxGa1-xN (0≦x<1) or may have a superlattice structure formed by alternately and repeatedly stacking p-AlxGa1-xN (0≦x<1) layers having different aluminum (Al) composition ratios. For example, the upper cladding layer 180 may have a superlattice structure where a p-Al0.08Ga0.92N layer and a p-GaN layer are repeatedly stacked. The superlattice structure leads to a reduction in both carrier injection resistance and the risk of cracks, and thus the upper cladding layer 180 can be stably crystal-grown and a high optical confinement effect can be maintained.
The upper contact layer 190 improves ohmic contact properties between the upper cladding layer 180 and the upper electrode 200, and may be formed by sequentially stacking p+-GaN/Pd layers on an upper surface 180a and side surfaces 180b of the upper cladding layer 180.
The upper electrode 200 may be made of a highly conductive metallic material, for example, a commonly used electrode material. In detail, the upper electrode 200 may be a single layer formed of Au, Ni, Ti, or Al, or may be a double layer of these materials.
The insulating layers 205 may be formed of an insulting material such as SiO2.
The operation of the ridge-waveguide semiconductor LD according to the present embodiment will now be explained with reference to
Referring to
Also, when the upper cladding layer 180 has a superlattice structure formed by alternately stacking p-AlxGa1-xN (0≦x1) layers having different Al composition ratios, the carriers pass through the upper cladding layer 180 by tunneling or carrier overflow, thereby further reducing the injection resistance.
Moreover, since the upper electrode 200 made of a metallic material with high thermal conductivity covers both the side surfaces 180b as well as the upper surface 180a of the upper cladding layer 180, the ridge-waveguide semiconductor LD of the present embodiment has high heat dissipation capability.
Furthermore, the ridge-waveguide semiconductor LD of the present embodiment can improve the electrical characteristics of a long wavelength semiconductor LD. In general, semiconductor LDs emitting a blue or green laser beam with a long wavelength use a low temperature p-type semiconductor layer. The low temperature p-type semiconductor layer is inferior in terms of electrical characteristics to a high temperature p-type semiconductor layer in that the hole concentration is low and resistance is high in the low temperature p-type semiconductor. The ridge-waveguide semiconductor LD of the present embodiment can improve the electrical characteristics of the long-wavelength semiconductor LD that uses the low temperature semiconductor layer, by improving a current injection mechanism.
The effect of a ridge-waveguide semiconductor LD according to an embodiment of the present invention compared to a conventional ridge-waveguide semiconductor LD will be explained hereafter.
Conventional Ridge-waveguide Semiconductor LD
A conventional ridge-waveguide semiconductor LD having a vertical current injection structure as shown in
A ridge-waveguide semiconductor LD allowing both vertical and lateral injection according to an embodiment of the present invention as shown in
The characteristics of the manufactured two LDs will now be explained with reference to
As described above, the ridge-waveguide semiconductor LD according to the present invention has the following advantages.
First, since a current is injected through both the side surfaces of the ridge portion, injection resistance can be reduced and high operating voltage and power can be achieved.
Second, since the upper electrode made of a metallic material covers both the side surfaces of the ridge portion, efficient heat dissipation can be ensured.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2006-0012602 | Feb 2006 | KR | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4622673 | Tsang | Nov 1986 | A |
| 6356571 | Kiely et al. | Mar 2002 | B1 |
| 6479836 | Suzuki et al. | Nov 2002 | B1 |
| 6614824 | Tsuda et al. | Sep 2003 | B2 |
| 6983003 | Sonobe et al. | Jan 2006 | B2 |
| 20040051107 | Nagahama et al. | Mar 2004 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20060280215 A1 | Dec 2006 | US |
