JPH02310975A - Superilluminescent diode - Google Patents

Abstract

PURPOSE:To fully prevent light from returning from an edge side to a light emission section and to fully restrain FP mode oscillation by forming a bending guide active layer which guides light following a linear active layer to a direction which is different from that on an extension axis of the active layer. CONSTITUTION:A linear active layer 14 is formed vertically to a cleavage edge side 21 which becomes a take-out surface of light, and bent at an active layer 15 of a bending guide following the active layer 14 at a radius of curvature R which allows to guide most of light emitted at the linear active layer 14. In a part wherein light is absorbed while being guided, the longer the bending guide active layer 15 is, the more it effects in a state that non-excitation or reverse-bias is applied. In this case, bending loss is extremely little at the radius of curvature R of 3mm or more, and most light is guided and escaped. Effect to restrain FP mode oscillation becomes larger by forming an AR film to the edge side 21 for taking out of light.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a superluminescent diode capable of emitting incoherent light with large intensity and small radiation angle, which is useful as a light source for optical discs, optical disks, etc. It is.

[Conventional technology]

Generally, in a light emitting device that attempts to extract high-output incoherent light from the end face of the active layer, it is important to suppress laser oscillation due to Fabry-Perot (FP) mode. Methods have been implemented to reduce the reflectance of light at the end faces of the active layer, such as forming the active layer, diagonally etching the end faces, and burying the end faces. However, it is difficult to sufficiently suppress FP mode oscillation using only the AR coat. Furthermore, when suppressing the FP mode by obliquely etching the end face, burying the end face, or using a combination of these, the difference in refractive index at the end face is extremely large, and the reflectance reaches about 1% compared to when the valve is open. In particular, as the active layer becomes thicker, this effect becomes greater and the reflectance also increases, so there is a drawback that it is difficult to suppress the F'P mode using these means alone.

FIG. 3 shows a schematic diagram of a buried type superluminescent diode in which a non-excitation region 10 is formed in combination with a conventional end face buried region 11. In FIG. 3, 9 is a current injection region, 10 is a non-excitation region, and 11 is an end face buried region, and an element is formed from these three regions.

Further, an AR coating film 13 is formed on the light extraction surface of this element. Here, the active li3 of the non-excited region 10
Since the width of the active layer 3 in the current injection region 9 is the same as that of the active layer 3, carriers are excited in the non-excited region 10 due to the light guide effect, which reduces the absorption coefficient.
In order to suppress the odd mode, it is necessary to have a length equal to or longer than the current injection region 9, and there is a drawback that the non-excitation region 10 must be made long. In Fig. 3, 1 is an n-type substrate, 2 is an n-type light guide layer, 4 is a p-type rad layer, 5 is a p-type electrode layer, and 6 and T are p-type and n-type current constrictors, respectively. 8 is a p-type ohmic electrode, and 12 is an n-type ohmic electrode.

Further, FIG. 4 shows a plan view of a buried type superluminescent diode in which a non-excited region is formed, which solves the drawbacks of the device shown in FIG. 3 to some extent. The feature of this device is that the valve open end face and the axis directions of the active layers of the current injection region 9 and the non-excitation region 10 are deviated from perpendicular, and both end faces are difficult to become a co-imager in laser oscillation. At this time, the greater the deviation from the perpendicularity of the axial direction of the active layer with respect to both end faces, the greater the effect of suppressing FP mode oscillation, but when considering the coupling with the optical fiber when extracting incoherent light, This has the disadvantage that the coupling efficiency deteriorates due to the large axis misalignment.

[Problem to be solved by the invention]

In the above-mentioned conventional structural element, the light guide layer 2 is formed adjacent to the active layer 3 in order to increase the light extraction efficiency, especially as shown in the structural diagram of FIG. In this case, the effective absorption coefficient in the non-current injection region decreases and F
There is a problem in that P odd mode laser oscillation is likely to occur.

In view of the above points, the present invention has been made to solve the problems of the conventional elements.The purpose of the present invention is to sufficiently suppress FP mode oscillation even if the element length is short, and to It is an object of the present invention to provide a superluminescent diode that can obtain high-output incoherent light without reducing the coupling efficiency.

[Means to solve the problem]

To achieve this objective, the superluminescent diode according to the invention follows a linear active layer and directs light in a direction different from the extension axis of this active layer to effectively suppress the FP odd mode. Rather than guiding, an active layer is formed, and the light that is emitted at the current injection part and then directed in the opposite direction to the light extraction direction is reflected from the end face using the direction of total reflection at the end face. It is characterized by preventing light from returning in the light extraction direction and suppressing FP mode oscillation.

[Effect]

Therefore, in the present invention, the element length can be shortened by forming an active layer following a linear active layer to guide light in nine directions different from the extension axis of the active layer. In addition to being able to sufficiently suppress KFP mode oscillation, high-output incoherent light can be obtained without reducing the coupling efficiency with the optical fiber.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 shows a diagram of the principle of the device of the present invention. 1st
In the figure, a linear active layer 14 is formed perpendicularly to the valve open end surface 21 that serves as a light extraction surface, and the active layer 15 with 9 guides has a linear active layer 14 that follows this active layer 14. It is formed by bending it with a curvature R that allows it to emit light and guide most of the subsequent light.

In an element with such a configuration, the linear active layer 14 emits light, and the light that travels toward the curve 9 guide active layer 15 is caused by the curved portion of the guide in the active layer 15. , a portion (2) that is guided by the end face 221 and reflected by the end face, and a portion (2) that is absorbed while being guided.

At this time, the amount of light leaking in the portion (2) is determined by the curvature of the guide and the difference in refractive index between the active layer and the buried layer in the guide structure.The smaller the curvature and the larger the difference in refractive index, the less light leaks. Then, since the leaked light spreads in the buried layer and is reflected at the end face, the amount of light that returns to the linear active layer 14 and the tip of the tab and recombines is small.

Furthermore, the light guided to the end face 22 at the portion (2) is reflected by the end face and can be emitted in a direction that does not couple with the current injection portion at all. In this case, for most of the ■-v group semiconductors that make up the device, the angle of incidence and the angle of reflection are θ
Then, if θ>16 degrees or more, total reflection will occur.

Further, in the state where the wave guide active layer 15 is not excited or reverse biased in the part (3), the longer the bending is, the greater the effect is. In this case, when the radius of curvature R is 3w or more, the bending loss is extremely small, and most of the light can be guided and released.

Further, by forming an AR film on the light extraction end face 21, the effect of suppressing the FP mode detection loss is further increased.

On the other hand, the light emitted by the active layer 15 of the curved guide and directed toward the linear active layer 14 and the end face is guided to the end face by the leaking part ■' in the curved guide active layer 15 due to the bending of the guide. The part ■′ that is reflected between the edges and
The light reaches the linear active layer 14 and is output from the light extraction surface 21. Part of this
leads to an increase in incoherent light output.

That is, in the superluminescent diode of the present invention, current is also injected into the non-excited region so that light generated in the current injection region where the active layer is linear is not absorbed in the non-excited region. (9) By injecting current even in the non-excited region of the conventional device, stimulated emission is caused within a range that is not overlooked, and the device structure is designed to promote an increase in optical output.

Therefore, by injecting current into regions other than the linear active layer, the overall device length can be shortened.

Next, an embodiment of the present invention will be described with reference to FIG. It should be noted that this embodiment is merely an illustration, and it goes without saying that various changes and improvements may be made without departing from the spirit of the present invention.

FIG. 2 shows an embodiment of the present invention using InP/Ga1nAsP based materials. In order to obtain the superluminescent diode of the present invention, the liquid phase growth method (L
PE) and vapor phase epitaxy (VPE, MO-CVO) or molecular beam epitaxy (MBE), etc., n-type InP
An a-type GaInAsP light guide layer (λ: 1.
1μm composition)2. Non-doped QaInAaP active layer (λ
:1.3μm composition)3. p-type InP cladding layer 4. A P-type QaInAmP electrode layer (λ: 1.1 μm composition) 5 is grown. Next, a thin film of p-type GaInAsP or SIN is deposited by RF bipolar sputtering or CVO method.
It is formed between the entire surfaces of the electrode layer 5. Thereafter, the active layer is embedded using a photoetching technique, and the linear active layer 14 is formed into stripes along the (110) direction with a width of 4 to 5 μm, a length of 400 μm, and a curved shape.
5, the active layer 14 is wrinkled in the axial direction with curvature R#0.5 and Rkq 1.5, and the current injection region 9 is striped in such a way that the length of the guide active layer 15 is 200 μm and 400 μm, respectively. Then, using this 8101 stripe thin film or SiN stripe thin film as a mask, apply a 4% bromine methanol solution! The layers 75, 4, and 3.2 are etched until they reach the substrate 1 to form an inverted mesa-shaped stack.

Next, as a second growth, a p-type InP layer 6. and n-type InP
Buried growth for current confinement of layer 1 was performed.

On the upper surface of the wafer obtained in this way, Au-Zn was evaporated and p
A type ohmic electrode 8 is formed on the entire surface, and the Au
-G.-Ni was deposited to form an n-type ohmic electrode 12 on the entire surface. In this way, the structure of each layer of the obtained nine elements is as follows in the state shown in FIG. 2, and each crystal layer matches the lattice constant of InP.

1:8n doped n-type InP substrate, thickness 80 μm, carrier density 3×10 “on-”, IPD5X I
O' cm - 2 m n-type GaInAsP light guide layer, thickness 0.2 μm.

Sn doped, carrier density 5X I Q"crn-"3
: n-type GaInAsP active layer, thickness 0.2-0.3μ
m.

Non-doped 4: P-type InP crystal layer, thickness 1.5 μm, Zn doped.

Carrier density 5x101? crn-” 5: p-type GaInAiP electrode layer, thickness 0.7 μm, Zn
Doped, 16:p-type InP current confinement layer with carrier density 5X 10'', thickness -1.5 μm, Zn
Dope, carrier density IXIQl? z-”7: n-type I
'nP current confinement layer, thickness -1.5 μm, Sn-doped, carrier density 1x10"m-" This device has a curvature R! = fO, 5g element has an element length of 600
The element with μm2 curvature R'=, 1.6- has an element length of 800 μm.
.

Divide the pellets into pellets with a constant width of 400 μm, mount them on a heat sink with AuSn solder, and apply a current.

The optical output characteristics at a wavelength of 1.3 μm were measured at 25°C.
In continuous operation, the optical output increased without loss as the current was injected, and an incoherent optical output of 3 mW at 200 mA could be obtained. No difference in properties due to difference in curvature R was observed. Compared to conventional elements,
By forming the guide active layer 15, the light is guided in a direction different from the extension axis of the active layer 14, which is straight between the arm opening plane, and by utilizing the axis misalignment at the end face, the end face Since we were able to efficiently prevent light from returning to the light emitting part, the overall element length was reduced to about 1/2 or less than the conventional element for an element with a curvature R of 0.5 m. It was possible to sufficiently suppress FP mode oscillation.

The radius of curvature R is 2.5 mm or more, and the loss due to the curve 9 is negligible.
! =! 1.6 van has 9 songs lost”=, Q, l
dB, R# 0.5 tm, the loss of the curve is -1 dB or less υ, and most of the light is guided while undergoing loss in the active layer 15 of the curve υ guide. Also, the incident angle of the light at the end face is set at θ=16 so that the light that reaches the end face is totally reflected.
The length of the song 9 guide active layer 15 is equal to or greater than 20°.
0 μm (curvature R”q 0.5 m) and 400 μm
(curvature R' = 1.6 ms) was determined and carried out.

Although the present invention has been described with reference to an example using an n-type InP substrate, the effect is the same even if a p-type InP substrate is used, and in that case, the n-type region and the p-type region may be replaced in each structure. . t7'h, In this example, the BH type buried keepsake photodiode is described.
, or a similar effect can be obtained with a type such as vSP.

Further, in the above embodiment, InP-Ga with a wavelength of 1.3 μm
Although an InAsP-based semiconductor has been described, it is clear that the method of the present invention can also be applied to incoherent light-emitting elements using other wavelength ranges and semiconductors different from this example (GaAs-GaAt artificial type, etc.).

Furthermore, as the buried structure, not only the method of burying with a ①-V group single crystal epitaxial layer, but also the structure of burying a mesa structure containing an active region with an organic material such as polyimide, a low melting point glass, etc. are also useful. In these cases, the difference in refractive index between the active part and the buried part is large, so even if the curvature of the guide part is large, the loss is small, and the light is effectively guided to the end face in the non-excited part and the light is completely absorbed at a large incident angle. It can be configured so that it is not reflected and returned to the active area.

Further, in the formation of the υ guide active layer 15, arcs of circles with curvatures of 0.5- and 1.6 tm were used in this embodiment, but the same effect can be obtained with polygons other than arcs. It is clear that

9. In the above embodiment, the entire surface electrode was described, but each linear active layer 141 uses the υ guide active layer 15 as a divided electrode, and the curved guide active layer 15 is de-excited or reverse biased like in the conventional element. Incoherent light can be obtained even if .

〔Effect of the invention〕

As described above, according to the present invention, a linear active layer is formed with a curve that guides light in a direction different from the extension axis of the active layer. It was possible to sufficiently prevent the return of light from the end face to the light emitting part, and it was possible to sufficiently suppress the loss of FP mode detection. This suppressing effect of FP mode oscillation is caused by the light absorption effect in the non-current injection part and the guiding of light in a direction completely different from the extension axis direction of the light emitting part when the bending guide active layer is non-excited. It has two features: high efficiency (FP mode oscillation can be suppressed, so the overall element length can be shortened).

As a result, the efficiency of wafer utilization is high, and the productivity of devices is improved.

[Brief explanation of drawings]

Fig. 1 is a rounded plan view explaining the present invention in detail, Fig. 2 (-), (b) and (,) are plan views showing one embodiment of the present invention, A-A' of the light guide layer. 3(a), (b) and (,) are plan views showing structural examples of conventional light emitting diodes, a sectional view in the stripe direction and a sectional view of the light emitting part, and FIG. 4 is a sectional view of the light emitting part. FIG. 7 is a plan view showing another conventional example. 1... n-type InP substrate, 2... n-type GaInA
sP optical guide layer, 3@...non-doped G&InAsP
Active layer, 4@11Sllp type InP cladding layer, 5...
・P-type GaInAsP electrode layer, 6... p-type InP
Current narrow 9 layers, T... n-type InP current narrow... n-type ohmic electrode, 14, 116 linear active layer, 15...
...Active layer of curved guide.

Claims (3)

[Claims] (1) In a waveguide superluminescent diode made of a compound semiconductor in which an active layer is sandwiched above and below by materials of a p-type region and an n-type region, which have a larger band gap energy and a lower refractive index than the active layer. A superluminescent diode comprising a linear active layer and, following the active layer, an active layer that guides light in a direction different from the axis of extension of the active layer. (2) The superluminescent diode according to claim 1, wherein the electrode for current injection is a full-surface electrode. (3) The superluminescent diode according to claim 2, wherein the electrode is divided into two or more parts, and current can be injected into each electrode.