JPH09266352A - Semiconductor light emitting device - Google Patents

Abstract

(57) Abstract: Impedance is reduced in a semiconductor light emitting device. An n-GaN low temperature buffer layer 2, an n-GaN buffer layer 3, an n-InGaN buffer layer 4, n are formed on a sapphire substrate 1.
-AlGaN clad layer 5, n-GaN light guide layer 6, active layer 7, p-GaN light guide layer 8, p-AlGaN clad layer 9 partially having a ridge stripe portion, ridge stripe p-
A GaN lower cap layer 10 is laminated, and a SiN film 11 is formed on a portion of the p-AlGaN cladding layer 9 other than the ridge stripe. Further, after growing the p-GaN upper cap layer 12 on the SiN film 11 and the p-GaN lower cap layer 10, the epitaxial layer other than the portion including the light emitting region is formed by n-GaN buffer layer by RIBE using chlorine ions. Etch away until 3 is exposed. After this, Ti / A is deposited on the n-GaN buffer layer 3.
l / Ti / Au n-side electrode 14 and Ni on top cap layer 12
/ Au p side electrode 13 is vacuum-deposited and annealed in nitrogen to form an ohmic electrode.

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 to a semiconductor light emitting device including a light emitting diode (LED) and 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, in the device having the conventional structure disclosed in the above document, the n-type semiconductor layer is first laminated on the substrate and then the p-type semiconductor layer is laminated. If a narrow stripe is provided,
The contact area between the p-type semiconductor layer and the p-side electrode is narrowed, and the impedance is further increased.

As described above, in a semiconductor light emitting device in which the p-type semiconductor layer has a large resistivity and the contact resistance with the p-side electrode is large, it is desired to reduce the impedance of the device.

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

[0008]

A semiconductor light emitting device of the present invention comprises a substrate, at least an n-type clad layer, an active layer, and a p-type layer.
The semiconductor layers of the mold clad layer are laminated in this order,
In a semiconductor light emitting device, a stripe portion that defines a light emitting region is formed in a part of the mold cladding layer, a p-type cap layer is formed on the stripe portion, and a p-side electrode is formed on the p-type cap layer. The p-type cap layer includes a stripe-shaped lower cap layer stacked on the stripe portion and an upper cap layer formed on the lower cap layer and having an area larger than that of the lower cap layer. The contact area between the p-side electrode and the p-type upper cap layer is larger than the contact area between the lower cap layer and the upper cap layer.

That is, the present invention reduces the impedance of the element by increasing the contact area between the p-type semiconductor layer having a large contact resistance with the electrode and the p-side electrode.

The upper cap layer may include a portion laminated on the lower cap layer and an overhang portion protruding from the lower cap layer.

Further, the projecting portion may be formed on an insulating film formed on a portion of the p-type clad layer excluding the stripe portion.

The above structure has Al _x In _y Ga _1-xy N (0≤x, y≤
It can be used for 1) type semiconductor light emitting devices.

[0013]

According to the semiconductor light emitting device of the present invention, by increasing the contact area between the p-type semiconductor layer and the p-side electrode, the impedance can be reduced as compared with the conventional device structure. As a result, the operating voltage can be reduced, and a semiconductor light emitting device having a stable transverse mode can be provided.

Therefore, the speedup of the hard copy output system for printing, photographs, medical images, etc., using these light sources,
Higher quality or higher performance of high-density optical memory can be realized.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a semiconductor light emitting device 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. N-GaN low temperature buffer layer 2, nG is formed on the sapphire c-plane substrate 1 by MOCVD method.
aN buffer layer 3 (Si-doped, 5 μm), n-In _0.1 Ga _0.9 N
Buffer layer 4 (Si-doped, 0.1 μm), n-Al _0.15 Ga _0.85 N
Cladding layer 5 (Si-doped, 0.5 μm), n-GaN optical guide layer 6 (Si-doped, 0.1 μm), undoped active layer 7, p-GaN
Optical guide layer 8 (Mg-doped, 0.1 μm), p-Al _0.15 Ga _0.85 N
A clad layer 9 (Mg-doped, 0.5 μm) and a p-GaN lower cap layer 10 (Mg-doped, 0.2 μm) are grown. Active layer 7
Is a three-layer structure of an undoped Al _0.04 Ga _0.96 N barrier layer (0.01 μm), 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).

Next, a ridge stripe having a width of about 2.2 μm is formed by p-Al _0.15 Ga _0.85 N by photolithography and etching.
The clad layer 9 is formed so that the remaining thickness is 0.1 μm.

Next, a SiN film 11 is formed on the entire surface by plasma CVD, and then unnecessary portions on the ridge are removed by photolithography and etching.

Thereafter, p- is formed by the second MOCVD growth.
A GaN upper cap layer 12 (Mg-doped) is grown. Then, the p-type impurities are activated by heat treatment in a nitrogen gas atmosphere.

After this, RIBE (rea
The epitaxial layer other than the portion including the light emitting region is etched away by ctive ion beam etching) until the n-GaN buffer layer 3 is exposed. At this time, it is possible to form the laser cavity end face by etching, but in that case, the ridge width is expanded to 10 μm or more at the part corresponding to the end face, and there is no adverse effect on the flatness of the ridge shape end face. It is desirable to reduce the amount (J. Quantum Electronics vol.
27, pp. 1319-1331 (1991)). When forming the resonator end face by cleavage, it is not necessary to widen the ridge width of the end face.

After that, an n-side electrode is formed on the n-GaN buffer layer 3.
Ti / Al / Ti / Au as 14 and Ni / Au as the p-side electrode 13 on the upper cap layer 12 are vacuum deposited and annealed in nitrogen to form an ohmic electrode.

Although sapphire, which is an insulating material, is used as the substrate in the above-described embodiment, a semiconductor laser according to the second embodiment shown in FIG. 2 is produced using a conductive substrate 101 such as SiC. It is also possible. In this case, n-
It is not necessary to expose the GaN buffer layer 3 by etching, and the n-side electrode is formed on the lower surface of the substrate 101.

FIG. 3 shows a schematic sectional view of a semiconductor laser according to a third embodiment of the present invention. Various structures can be adopted for the structure below the active layer including the type of substrate. Therefore, the structure is the same as that of the first embodiment shown in FIG. 1, and only the structure above the p-GaN optical guide layer 8 is shown. . In this embodiment,
In the second MOCVD growth, the p-GaN lower cap layer 10 is p-doped on the p-GaN lower cap layer 10 by selective growth that is difficult to stack on the insulating film 211.
-The GaN upper cap layer 212 is selectively grown to form the p-side electrode 21.
The contact area with 3 was increased.

A schematic sectional view of a semiconductor laser according to the fourth embodiment of the present invention is shown in FIG. The ridge waveguide type lateral mode control is the same as that of the above-described embodiment, except that both sides of the ridge are etched into a groove shape 314 having a width of about 5 μm, and the SiO ₂ insulating film 311 is formed into a coating type shadow spin layer. It was formed by using a coat and heat treatment, and had a shape in which the groove 314 was embedded. On top of this, the p-GaN upper cap layer 31 is formed similarly to the embodiment of FIGS.
2 was grown to increase the contact area with the p-side electrode 313. In the structure of the embodiment of FIG. 4, the SiO ₂ insulating film is removed by wet etching while applying ultrasonic waves, and at this time, the GaN lower cap layer 310 having poor crystallinity is used.
The semiconductor laser of the fifth embodiment shown in FIG. 5 may be produced by removing the portion other than the epitaxial layer near the upper portion by lift-off.

The effect of the present invention is obtained by forming a ridge, forming an insulating film layer, and growing the GaN upper cap layer for the second time. Therefore, as the layer structure of the semiconductor laser, various generally conceivable structures such as a multiple well structure and a double hetero structure not using quantum wells can be adopted in addition to the above-described embodiment. Sapphire or Si as substrate
Substances with a spinel structure other than C (eg AlMg ₂ O ₄ )
Etc. can be used.

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.

Further, the structure of the present invention is a semiconductor light emitting device which is formed from an n-type semiconductor layer on a substrate and has a p-type semiconductor layer on the side of the current injection window, and the resistivity of the p-type semiconductor layer and the electrode A material having a high contact resistivity is effective in a semiconductor light emitting device having any composition.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a semiconductor laser according to a first embodiment of the present invention.

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

FIG. 3 is a schematic sectional view of a semiconductor laser according to a third embodiment of the present invention.

FIG. 4 is a schematic sectional view of a semiconductor laser according to a fourth embodiment of the present invention.

FIG. 5 is a schematic sectional view of a semiconductor laser according to a fifth embodiment of the present invention.

[Explanation of symbols]

1 Sapphire c-plane substrate 2 n-GaN low temperature buffer layer 3 n-GaN buffer layer 4 n-In _0.1 Ga _0.9 N buffer layer 5 n-Al _0.15 Ga _0.85 N clad layer 6 n-GaN optical guide layer 7 undoped active layer 8 p-GaN optical guide layer 9 p-Al _0.15 Ga _0.85 N clad layer 10 p-GaN lower cap layer 11 SiN film 12 p-GaN optical guide layer 13,14 Electrode

Claims (4)

[Claims] 1. A substrate having at least an n-type cladding layer,
The semiconductor layers of the active layer and the p-type clad layer are laminated in this order, a stripe portion that defines a light emitting region is formed in a part of the p-type clad layer, and a p-type cap layer is formed on the stripe portion. In a semiconductor light emitting device having a p-side electrode formed on a p-type cap layer, the p-type cap layer is formed on a stripe-shaped lower cap layer laminated on the stripe portion, and on the lower cap layer. And an upper cap layer having an area larger than that of the lower cap layer, the p-side electrode and the p-side electrode.
A semiconductor light emitting device, wherein a contact area with the upper mold cap layer is larger than a contact area between a lower cap layer and an upper cap layer. 2. The semiconductor light emitting device according to claim 1, wherein the upper cap layer includes a portion laminated on the lower cap layer and an overhang portion protruding from the lower cap layer. . 3. The semiconductor according to claim 1, wherein the projecting portion is formed on an insulating film formed on a portion of the p-type clad layer excluding the stripe portion. Light emitting element. 4. The n-type cladding layer, the active layer, the p-type cladding layer and the p-type cap layer are made of Al _x In _y Ga _1-xy N (0 ≦ x,
4. The semiconductor light emitting device according to claim 1, wherein the semiconductor layer is a y ≦ 1) type semiconductor layer.