JPH09266351A - Alingan semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an AlInGaN semiconductor light emitting element which has an reduced impedance. SOLUTION: Sequentially grown on a sapphire face substrate 1 are a p-GaN low-temperature buffer layer 2, p-GaN buffer layer 3, p-In0.1 Ga0.9 N buffer layer 4, a cladding layer, a p-Al0.15 Ga0.85 N cladding layer 5, a p-GaN light guiding layer 6, an active layer 7, an n-GaN light guiding layer 8, an n-Al0.15 Ga0.85 N cladding layer 9 and an n-GaN cap layer 10. The grown structure is subjected to a plasma CVD process to form an SiN film 14 over its entire surface, subjected to photolithographic and etching processes to remove unnecessary parts except for an light emitting region therefrom, and then subjected to a reactive ion beam etching(RIBE) process using chlorine ions to remove an epitaxial layer other than the light emitting region until the p-GaN buffer layer 3 is exposed. The SiN film 14 is formed there in with a stripe-shaped window 12 for current injection, formed thereon with Ti/Al/Au layers as an n-side electrode 13 which covers the stripe window 12, and then an exposed area of the p-GaN buffer layer is deposited and annealed in a nitrogen atmosphere to form Ni/Au layers as a p-side ohmic electrode 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a semiconductor light emitting device, and more particularly, a light emitting diode (LED).
And an Al _x In _y Ga _1-xy N based semiconductor light emitting device including a semiconductor laser.

[0002]

2. Description of the Related Art AlInGaN-based LEDs and semiconductor lasers have hitherto attracted attention as short-wavelength light sources below 500 nm. This material has extremely excellent characteristics as a high-intensity LED in the blue / green wavelength range (Reference (1) Jpn.J.Appl.Phys.
vol.34, No.7A, pp.L797-799 (1995)), is being put to practical use as a light source for traffic lights and outdoor display devices. As a semiconductor laser, a pulse oscillation of 417 nm has recently been reported at room temperature (Reference (2) Jpn.J.App1.Phys.vol35, No.1B, p).
p.L74-76 (1996)).

In the AlInGaN type semiconductor laser described in the above-mentioned document (2), since the contact resistance between the p-type semiconductor layer and the electrode is very high, the operating voltage during pulse driving becomes as high as several tens of volts, and the element is oscillated during oscillation. The power input is 10 compared to normal devices
Since it is about twice as high, there is a drawback that the element heats up and distortion during modulation increases. Therefore, reduction of the impedance of the element has been an issue.

Further, as an application of the above AlInGaN type semiconductor laser, since a light spot having a diameter much smaller than that of the 630 nm semiconductor laser which is currently realized can be obtained by shortening the wavelength, it is applicable to high density optical disk memory. Most expected. For this purpose, it is essential to realize a single-mode laser that can obtain a stable light beam, and in the short wavelength range of 360-500 nm expected for AlInGaN system, a built-in optical waveguide for transverse mode stabilization is required. The stripe width needs to be a narrow stripe of about 2 μm or less.

[0005]

However, the element having the conventional structure disclosed in the above-mentioned document has a structure in which the n-type semiconductor layer is first laminated on the substrate and then the p-type semiconductor layer is laminated. , When a narrow stripe is provided, p
The contact area between the type semiconductor layer and the electrode is narrowed, and the impedance is further increased. Further, when a narrow stripe is formed in the p-type semiconductor layer, the high resistivity of the p-type semiconductor itself also causes an increase in impedance.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an AlInGaN-based semiconductor light emitting device having a reduced impedance.

[0007]

In a semiconductor light emitting device of the present invention, a plurality of semiconductor layers including at least a p-type cladding layer, an active layer and an n-type cladding layer and an insulating film are provided on at least a part of a substrate. N-stripe current injection windows for single mode oscillation are formed in the insulating film, and n is formed on the insulating film so as to cover the current injection windows.
In an Al _x In _y Ga _1-xy N (0 ≦ x, y ≦ 1) -based semiconductor light emitting device in which a side electrode is formed and a p-side electrode is formed on the p-type cladding layer side, the p _- side electrode is The area in contact with the semiconductor layer is larger than the area of the current injection window.

That is, unlike the prior art, a p-type semiconductor layer is first grown on the substrate side, and then an n-type semiconductor layer is grown to pn.
By adopting the structure of forming the junction, the n-type semiconductor layer is used in the portion where the stripe structure of the element is formed, that is, in the portion where the area is small, and the p-type semiconductor layer having high resistivity and high contact resistance with the electrode is formed. It is characterized in that the impedance of the element is lowered by widening the area and widening the contact area with the p-side electrode.

[0009]

The semiconductor light emitting device of the present invention has the p-type on the substrate.
Since the structure in which the p-type semiconductor layer is grown first and then the n-type semiconductor layer is grown, the contact area between the p-side semiconductor and the electrode can be widened in the light emitting device having the stripe structure, and the ridge structure can be formed. In the case of a light emitting element having
The area of the p-type semiconductor layer can be increased. As a result, the impedance of the element can be reduced, the operating voltage can be reduced, and high efficiency and high output can be realized. Further, it is possible to improve the modulation frequency during modulation and reduce modulation distortion. Therefore, it is possible to realize high speed and high quality of a hard copy output system for printing, photographs, medical images and the like using these light sources.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view of a semiconductor laser according to the first embodiment of the present invention. Sapphire c-plane substrate 1
P-GaN low temperature buffer layer 2, using MOCVD method,
p-GaN buffer layer 3 (Mg-doped, 5 μm), p-In _0.1 Ga
_0.9 N buffer layer 4 (Mg-doped, 0.1 μm), p-Al _0.15 Ga
_0.85 N cladding layer 5 (Mg-doped, 0.5 μm), p-GaN optical guide layer 6 (Mg-doped, 0.1 μm), undoped active layer 7, n-
GaN optical guide layer 8 (Si-doped, 0.1 μm), n-Al _0.15 Ga
_{A 0.85} N cladding layer 9 (Si-doped, 0.5 μm) and an n-GaN cap layer 10 (Si-doped, 0.3 μm) are sequentially grown. The active layer 7 is an undoped Al _0.04 Ga _0.96 N barrier layer (0.01 μm).
m), an undoped In _0.2 Ga _0.8 N quantum well layer (3 nm) and an undoped Al _0.04 Ga _0.96 N barrier layer (0.01 μm).

After that, the p-type impurities are activated by heat treatment in a nitrogen gas atmosphere.

Next, after the SiN film 14 is formed on the entire surface by plasma CVD, unnecessary portions other than the light emitting region are removed by photolithography and etching.

After this, RlBE (re
The epitaxial layer other than the light emitting region is removed by etching by active ion beam etching until the p-GaN buffer layer 3 is exposed. At this time, the cavity end face of the laser is formed.

After forming a stripe-shaped window 12 (width 10 μm) for current injection in the SiN film 14, Ti / Al / Ti / Au is used as an n-side electrode 13 so as to cover the stripe window 12 and p-GaN. Ni / Au is vapor-deposited on the exposed portion of the buffer layer 3 as the p-side electrode 11 and annealed in nitrogen to form an ohmic electrode.

FIG. 2 is a schematic sectional view of a semiconductor laser having a ridge optical waveguide structure according to a second embodiment of the present invention. Using the MOCVD method on the sapphire c-plane substrate 1,
p-GaN low temperature buffer layer 2, p-GaN buffer layer 3 (Mg-doped, 5 μm), p-In _0.1 Ga _0.9 N buffer layer 4 (Mg-doped,
0.1 μm), p-Al _0.15 Ga _0.85 N cladding layer 5 (Mg-doped,
0.5 μm), p-GaN optical guide layer 6 (Mg-doped, 0.1 μm),
Undoped active layer 27, n-GaN optical guide layer 8 (Si-doped,
0.1 μm), n-Al _0.15 Ga _0.85 N cladding layer 9 (Si-doped,
0.5 μm), and n-GaN cap layer 10 (Si-doped, 0.3 μm) is grown. The active layer 27 is composed of undoped Al _0.04 Ga _0.96 N barrier layer (0.01 μm), undoped In _0.2 Ga _0.8 N quantum well layer (3 nm) 4 layers / undoped In _0.1 Ga _0.9 N barrier layer (5 nm) 3
Layered multi-quantum well structure and undoped Al _0.04 Ga
_0.96 N barrier layer (0.01 μm).

After that, the p-type impurities are activated by heat treatment in a nitrogen gas atmosphere.

Next, by photolithography and etching, a ridge stripe having a width of about 2.2 μm is formed by leaving the n-Al _0.15 Ga _0.85 N cladding layer 9 from the n-GaN optical guide layer 8 to 0.1 μm in thickness. At this time, as shown in the schematic view (FIG. 3) of the vicinity of the end face of the ridge viewed from the upper part of the element, the region corresponding to the end face to be formed later by etching has a wide width of 20 μm. A solid line 40 shows the shape of the ridge etching, and a wavy line 41 shows the shape / positional relationship of the end face forming etching. As shown in the figure, the reason for widening the ridge width near the laser end face is to reduce the adverse effect on the flatness of the ridge-shaped end face (J.Quantum Electronics vol.27, pp.1319-133.
1 (1991)). Next, after the SiN film 14 is formed on the entire surface by plasma CVD, the SiN film 14 is removed by photolithography and etching to remove unnecessary portions other than the light emitting region.

After that, the epitaxial layer other than the light emitting region is etched away by RlBE using chlorine ions until the p-GaN buffer layer 3 is exposed. At this time, the cavity end face of the laser is formed.

After this, as in the first embodiment, Si is used.
After forming the striped window 12 for current injection in the N film 14,
Ti / Al / Ti / Au as n-side electrode 13 and Ni / A as p-side electrode 11
Each u is vapor-deposited and annealed in nitrogen to form an ohmic electrode.

In the above two embodiments, the contact width of the n-side electrode on the n-GaN cap layer 10 on the upper portion of the stripe is 2-10.
μm, but p formed on the p-GaN buffer layer 3
The contact area of the side electrode 11 with the semiconductor layer can be made 10 to 100 times wider than that of the n-side electrode by increasing the width of the entire chip. Therefore, even when the contact resistivity of the p-type semiconductor layer is higher than that of the n-type semiconductor layer by one or two orders of magnitude, it is possible to prevent deterioration of device performance. In addition, p which becomes a current path
-If the resistance of the GaN buffer layer 3 becomes a problem, the resistance can be lowered by further increasing the thickness.

That is, the present invention is to reduce the impedance of the device mainly by the properties and constituent factors of the n-type cap layer and the p-type buffer layer.

Therefore, as the layer structure of the semiconductor laser, various generally conceivable structures such as a double hetero structure not using quantum wells can be adopted other than the above-mentioned embodiment.

As the substrate, any material other than sapphire such as a material having a spinel structure (for example, AlMg ₂ O ₄ ) can be used as the insulating material. Further, when the substrate 21 made of a conductive material such as SiC is used instead of an insulating material such as sapphire to form the element structure as shown in FIGS. 4 and 5, a semiconductor layer having a small contact area with the electrode is formed. n
Since the p-side electrode 11 can be formed in a large area and the p-side electrode 11 can make a large area in contact with the p-type semiconductor layer, the resistance can be reduced.

In the above-mentioned embodiment, the laser end face is formed by RlBE using chlorine ions, but it may be formed by a usual cleavage or optical polishing method.

Although the semiconductor laser device has been described above, it is needless to say that it is also effective when it is used as an edge emitting LED with the same structure. Also in the normal LED structure as described in the above-mentioned document (1), the narrower the upper electrode of the light emitting section is, the smaller the area for blocking light is, and the light extraction efficiency is increased, so that the n-type is formed on the p-type layer. It is advantageous to use the structure of the present invention in which a layer is formed because the resistance can be reduced. Further, in the LED, the larger the current spread immediately below the upper electrode is, the more uniform light emission can be obtained. Therefore, it is more advantageous to use the n-type layer on the upper part to reduce the resistance.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a half-body light emitting device according to a first embodiment of the invention.

FIG. 2 is a schematic sectional view of a semiconductor light emitting device according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a relationship between a ridge stripe and an end face formation position in the semiconductor light emitting device according to the second embodiment of the present invention shown in FIG.

FIG. 4 is a schematic sectional view of a semiconductor light emitting device according to another embodiment of the present invention.

FIG. 5 is a schematic sectional view of a semiconductor light emitting device according to another embodiment of the present invention.

[Explanation of symbols] 1 sapphire substrate 2 p-GaN low temperature buffer layer 3 p-GaN buffer layer 4 p-In _0.1 Ga _0.9 N buffer layer 5 p-Al _0.15 Ga _0.85 N clad layer 6 p-GaN optical guide layer 7 undoped Active layer 8 n-GaN optical guide layer 9 n-Al _0.15 Ga _0.85 N cladding layer 10 n-GaN cap layer 11, 13 electrode 14 SiN film

Claims (1)

[Claims] 1. A plurality of semiconductor layers including at least a p-type clad layer, an active layer and an n-type clad layer and an insulating film are laminated in this order on at least a part of a substrate, and single mode oscillation is performed on the insulating film. To form a narrow stripe current injection window, an n-side electrode is formed on the insulating film so as to cover the current injection window, and a p-side electrode is formed on the p-type cladding layer side. _x In _y Ga _1-xy N (0≤x, y≤
1) A system semiconductor light emitting device, wherein an area where the p-side electrode is in contact with the semiconductor layer is larger than an area of the current injection window.