Semiconductor laser diode

A semiconductor laser diode capable of improving reliability and mass-productivity is disclosed. The semiconductor laser diode comprises a first clad layer; a first optical guide layer disposed on the first clad layer; an active layer disposed on the first optical guide layer; a second optical guide layer disposed on the active layer; and a second clad layer disposed on the second optical guide layer, having a greater band gap energy than the second optical guide layer, the band gap energy decreasing as being farther from the second optical guide layer.

This application claims the benefit of the Korean Patent Application No. 10-2007-0053882, filed on Jun. 1, 2007, which is hereby incorporated by reference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor laser diode, and more particularly, to a semiconductor laser diode capable of improving reliability and mass productivity of the product.

2. Discussion of the Related Art

Recently, in accordance with the spread of optical recording and reproducing devices such as a DVD, demand for a semiconductor laser diode (LD), that is, the essential part of the optical recording and reproducing device is being radically increased. Especially, since the technology achieving a high density DVD or a Blue-ray disc having capacity of tens of gigabytes is commercialized, researches have been actively performed into the nitride semiconductor LD of about 405 nm wavelength.

However, further advancement is required because there are still technical limits to guarantee reliability and yield of the nitride semiconductor LD.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a semiconductor laser diode that substantially obviates one or more problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a semiconductor laser diode capable of omitting a dedicated electron barrier layer, by using a structure capable of serving as both the electron barrier layer and a clad layer.

To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a semiconductor laser diode comprises a first clad layer; a first optical guide layer on the first clad layer; an active layer on the first optical guide layer; a second optical guide layer on the active layer; and a second clad layer on the second optical guide layer, having a greater band gap energy than the second optical guide layer, the band gap energy decreasing as being farther from the second optical guide layer.

In another aspect of the present invention, a semiconductor laser diode comprises a first clad layer; a first optical guide layer on the first clad layer; an active layer on the first optical guide layer; a second optical guide layer on the active layer; and a second clad layer on the second optical guide layer, comprising a nitride semiconductor layer containing Al, wherein the Al decreases as being farther from the second optical guide layer.

In yet another aspect of the present invention, a semiconductor laser diode, comprises a first electrode; a conductive substrate on the first electrode; a semiconductor layer having a multi-layer structure, being disposed on the conductive substrate; a clad layer on the semiconductor layer, having a greater energy band gap than an adjacent layer of the semiconductor layer, the energy band gap of the clad layer being decreased as being farther from the semiconductor layer; and a second electrode on the clad layer.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may, however, be embodied in many alternate forms and should not be construed as limited to the embodiments set forth herein. Accordingly, while the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims.

In the following description, the same reference numbers will be used throughout the drawings to refer to the same or like parts. In the drawings, layers and regions are excessively enlarged to be clearly seen and explained.

It will be understood that when an element such as a layer, region or substrate is referred to as being “on” another element, the element may be disposed directly on another element or an interposing element may exist between them. It will also be understood that if part of an element, such as a surface, is referred to as “inner,” it is farther from the outside of the device than other parts of the element.

Those terms are used to refer to other directions in addition to the directions illustrated in the drawings. Furthermore, the terms “directly” herein means “without any interposing element between other two said elements.” Finally, when “and/or” is used, this refers to any combination, that is, all possible combinations comprising one or more of the mentioned items.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms.

First Embodiment

The thin film structure of a nitride semiconductor laser diode is grown on a substrate through single crystal growth. As shown inFIG. 1, a thin film structure20of a semiconductor comprises an n-type clad layer21, an n-type optical guide layer22, an active layer23, a p-type optical guide layer24, and a p-type clad layer25which are disposed on a conductive substrate10in the listed order.

An upper side of the p-type clad layer25includes a ridge structure26, and a dielectric layer30having an opening corresponding to the upper part of the ridge structure26is disposed on the upper side of the p-type clad layer25.

On an upper side of the dielectric layer30, a p-type electrode40is formed in contact with the p-type clad layer25through the opening of the dielectric layer30. An n-type electrode50is disposed on a lower side of the conductive substrate10.

In addition, an electronic barrier layer (EBL)27may be interposed between the active layer23and the p-type clad layer25.

An n-type electrode layer28may be formed between the conductive substrate10and the n-type clad layer21. Also, a p-type electrode layer29may be further formed between the upper part of the ridge structure26of the p-type clad layer25and the p-type electrode40.

An energy band gap related to the above-described diode structure is illustrated by a band diagram ofFIG. 2.

When electric power is applied in the diode structure, electrons move from the n-type clad layer21toward the p-type clad layer25whereas holes move in the opposite direction. Therefore, the holes may be recombined with the electrons by being restricted in the active layer23, thereby achieving light emission.

Here, when relatively lighter electrons are passing through the active layer23, the EBL27obstructs passage of the electrons which did not perform the recombination, accordingly improving the efficiency of the diode.

However, when such an EBL structure is dedicatedly provided, the whole thin film structure is complicated and this may hinder growth of the thin film. Furthermore, since the EBL is in the vicinity of the active layer, Mg, which is a p-type dopant, and Al, which is one of components of the EBL, may be diffused toward the active layer in case of a longtime or high-temperature operation of the diode. As a result, reliability of the diode would be deteriorated.

In addition, considering properties of an optical mode, an optical confinement factor may be deteriorated by an AlGaN EBL having a low refraction index, or an ideal Gaussian distribution of the optical mode may be distorted.

Second Embodiment

FIG. 3shows another embodiment of the semiconductor laser diode. As shown in the drawing, the semiconductor laser diode comprises a conductive substrate100and a semiconductor thin film structure200disposed on the substrate100. The semiconductor thin film structure200may comprise a GaN-based semiconductor layer.

The semiconductor thin film structure200comprises an n-type clad layer210, an n-type optical guide layer220, an active layer230, a p-type optical guide layer240, and a p-type clad layer250which are sequentially disposed on the conductive substrate100.

An upper side of the p-type clad layer250includes a ridge structure251, and a dielectric layer300having an opening corresponding to the upper part of the ridge structure251is disposed on the upper side of the p-type clad layer250.

On an upper side of the dielectric layer300, a p-type electrode400is formed in contact with the p-type clad layer250through the opening of the dielectric layer300. In addition, an n-type electrode500is disposed on a lower side of the conductive substrate100.

An n-type electrode layer260may be formed between the conductive substrate100and the n-type clad layer210. Also, a p-type electrode layer270may be further formed between the upper part of the ridge structure251of the p-type clad layer250and the p-type electrode400.

An energy band gap regarding the above-described diode structure is illustrated by a band diagram ofFIG. 4.

According to the embodiment shown inFIG. 3andFIG. 4, the p-type optical guide layer240is disposed on the active layer230, and the p-type clad layer250that functions as the electron barrier is disposed on the p-type optical guide layer240.

In this case, that is, when the p-type clad layer250also functioning as the electron barrier is on the p-type optical guide layer240, an EBL such as layer27inFIG. 1can be omitted. This case is illustrated by a band diagram ofFIG. 5.

The p-type clad layer250has a greater energy band gap than the p-type optical guide layer240. As shown inFIG. 6andFIG. 7, the p-type clad layer250may be structured so that the energy band gap decreases as being farther from the p-type optical guide layer240. Here, the band gap of the p-type clad layer250can be decreased up to the band gap of the p-type optical guide layer240.

FIG. 6andFIG. 7are band diagrams of the p-type clad layer250. Referring toFIG. 6, the band gap is relatively great near the p-type optical guide layer240and decreases as being farther from the p-type optical guide layer240in a stepwise manner.

Also, as shown inFIG. 7, the band gap of the p-type clad layer250may decrease as being farther from the p-type optical guide layer240in a gradual manner.

The semiconductor layer may comprise a nitride semiconductor (AlxInyGa1-x-yN, 0≦x, y≦1). In this case, the p-type clad layer250may also be implemented by a nitride semiconductor.

Thus, the p-type clad layer250may contain Al. Here, the Al exists most at a contacting surface with the p-type optical guide layer240and gradually decreases as being farther from the p-type optical guide layer240.

Although the band gap is increased according to increase of the Al existing at the contacting surface between the p-type clad layer250and the p-type optical guide layer240, it is preferred that the Al occupies about 10˜30% of the total components of the nitride semiconductor in consideration of a lattice constant difference and lattice coupling.

Also, the p-type clad layer250may comprise a superlattice layer as shown inFIG. 8. In this case, the whole band gap may be determined by an average band gap of the superlattice layer.

As described above, the band structure of the p-type clad layer250is capable of effectively restricting the passage of electrons to the active layer230without requiring a dedicated EBL. Accordingly, the efficiency of recombination between the electrons and the holes is improved, thereby enhancing a light emitting efficiency.

Since the laser structure can be simplified by omitting the EBL, growth of the semiconductor thin film can be performed more efficiently. Also, the dopants such as Mg and Al can be prevented from diffusing, thereby improving reliability of the product.

Furthermore, when the above structure is applied, the thin film structure of the laser diode can be simplified. Therefore, growth of the thin film is facilitated while improving the mass-productivity.