JPS6243356B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in buried structure semiconductor lasers.

FIG. 1 shows a conventional InGaAsP/InP buried structure semiconductor laser. FIG. 2 shows an example of the current-optical output characteristics of this type of semiconductor laser. In such a laser, it is important to make the leakage current I _L smaller than the current Ie flowing through the active layer 3 in order to achieve a low threshold and high efficiency. The leakage current I _L flowing on both sides of the active layer 3 flows through the upper cladding layer (p-InP) 4, the buried layer (n-InP) 7, and the current blocking layer (p-InP).
The pnpn structure consisting of InP) 6 and lower cladding layer (n-InP) 2 makes it extremely small. However, when the pnpn structure is turned on, an excessive leakage current I _L flows, so it is necessary to increase the turn-on voltage of the pnpn structure. It is easy to increase this turn-on voltage by adjusting the carrier concentration of each layer appropriately. However, I _G in Figure 1
When a gate current as shown by flows, the turn-on voltage drops extremely due to the thyristor action. Such gate current I _G can be eliminated by aligning the upper boundary between active layer 3 and current blocking layer 6 to eliminate a current path. However, in reality, it is almost impossible to fabricate a structure without a current path for the gate current I _G with good reproducibility due to manufacturing technology. That is, in an actual semiconductor laser, the gate current I _G flows more or less, so as the injection current of the semiconductor laser increases, the gate current I G flows more or less.
As _G increases, the turn-on voltage of the pnpn structure decreases. Then, when the applied voltage applied to the semiconductor laser reaches the turn-on voltage, the pnpn structure turns on and an excessive leakage current I _L flows.
As shown in FIG. 2, the light output is drastically reduced. Therefore,
For an element like the one shown in Figure 2, the maximum output at 30°C is approximately
It was low at around 20mW. Furthermore, the higher the temperature becomes, the smaller the injected current is required to turn on, so the output at high temperatures particularly decreases. In this way, in conventional buried structure semiconductor lasers, when a gate current I _G flows through the pnpn structure, the turn-on voltage decreases and the turn-on occurs with a low injection current, resulting in a low maximum output, especially at high temperatures. It had the disadvantage of

The purpose of the present invention is _to
The object of the present invention is to provide a buried structure semiconductor laser which has a pnpn structure with no drop in turn-on voltage, has a high maximum output, and has a high output even at high temperatures.

According to the present invention, there is provided a semiconductor substrate of a first conductivity type, and a first semiconductor substrate formed on the semiconductor substrate and having a forbidden band width smaller than that of a current blocking layer.
a first conductivity type semiconductor layer, a striped lower cladding layer of the first conductivity type formed on the first semiconductor layer, and a striped lower cladding layer formed on the lower cladding layer. an active layer, a striped upper cladding layer formed on the active layer and having a second conductivity type opposite to the first conductivity type, and a striped upper cladding layer formed on the first semiconductor layer and on both sides of the active layer. second
A buried structure semiconductor laser is obtained which is characterized by comprising a conductivity type current blocking layer and a first conductivity type buried layer formed on the current blocking layer and on both sides of the upper cladding layer.

The present invention will be described in detail below with reference to the drawings.

FIG. 3 is a cross-sectional view of one embodiment of the present invention.
In the figure, 30 is an n-InP substrate, 31 is a buffer layer (n-InP, thickness ~5 μm), and 32 is n-InGaAsP.
layer (thickness ~0.5 μm, λ ~1.25 μm), 33 is the lower cladding layer (n-InP, thickness ~03 μm), 34 is the active layer (non-doped InGaAsP thickness ~0.2 μm), 3
5 is the upper cladding layer (thickness ~ 2.5 μm, p-
36 is a cap layer (p-InGaAsP layer, thickness ~0.7 μm), 37 is a current blocking layer (p-
InP, thickness ~0.5μm), 38 is a buried layer (n-
39 is an n-InGaAsP layer (thickness ~ 1 μm), 40 is a Zn diffusion layer, 41 is SiO ₂
In the film, 42 is a p-electrode, and 43 is an n-electrode. In this embodiment, an upper cladding layer 35, a buried layer 38, a current blocking layer 37, an n-InGaAsP layer 3
2. The pnpn structure consisting of the buffer layer 31 blocks the leakage current _IL . Unlike the conventional pnpn structure, the pnpn structure of this embodiment is characterized by the presence of the n-InGaAsP layer 32. n-InGaAsP layer 32
Therefore, npn which is a part of the above pnpn structure
The gain of transistor 44 can be made very small. That is, the n-InGaAsP layer 32 is a current blocking layer (p-InP) 37 corresponding to the base.
Because it has a narrower bandgap than the 100% bandgap, the emitter injection efficiency becomes very small, and therefore the gain becomes very small.

As described above, since the gain of the npn transistor 44 is very small, the turn-on voltage of the pnpn structure of this embodiment does not decrease even if the gate current I _G shown in the figure flows. Therefore, by setting the carrier concentration in each layer appropriately and increasing the turn-on voltage to about 3 to 4 V, it is possible to prevent the pnpn structure from turning on in the practical injection current range and reduce the leakage current I _L flowing through it to almost zero. You can.

As described above, in this embodiment, since there is almost no reactive current flowing through the pnpn structure, a buried structure semiconductor laser capable of high output and high temperature operation is obtained.

The manufacturing method of the buried structure semiconductor laser of this example will be briefly described. First, a buffer layer 31, an n-InGaAsP layer 32, a lower cladding layer 33, an active layer 34, an upper cladding layer 3 are formed on an n-InP substrate 30.
5. Form the cap layer 36 using liquid phase epitaxial technology or the like. Next, the cap layer 36, the upper cladding layer 35, the active layer 34, and the lower cladding layer 33 are formed into stripes by photoetching using a SiO ₂ film or the like as a mask. Thereafter, a current blocking layer 37, a buried layer 38, and an n-InGaAsP layer 39 are formed again using liquid phase epitaxial technology or the like. During growth, a SiO ₂ film is formed on the cap layer 36 and growth is performed only on both sides of the stripe. Thereafter, a SiO ₂ film 41 is formed using the CVD method and photoetching method, and a Zn diffusion layer 40, a p-electrode 42,
An n-electrode 43 is formed.

Finally, to summarize the features of the present invention, it is possible to obtain a buried structure semiconductor laser with extremely small leakage current and capable of high output and high temperature operation.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a conventional InGaAsP/InP buried structure semiconductor laser. Figure 2 shows the conventional
This is an example of the current-optical output characteristics of an InGaAsP/InP buried structure semiconductor laser. FIG. 3 is a sectional view of an InGaAsP/InP buried structure semiconductor laser according to an embodiment of the present invention. In the figure, 1...n-InP substrate, 2...lower cladding layer, 3...active layer, 4...upper cladding layer, 5: cap layer, 6...current blocking layer, 7...buried layer,
8... n-InGaAsP layer, 9... Zn diffusion layer, 10...
SiO ₂ film, 11...p-side electrode, 12...n-side electrode, 3
0... n-InP substrate, 31... buffer layer, 32...
n-InGaAsP layer, 33...lower cladding layer, 34
...active layer, 35... upper cladding layer, 36... cap layer, 37... current blocking layer, 38... buried layer, 39... n-InGaAsP layer, 40... Zn diffusion layer,
41...SiO ₂ film, 42...p electrode, 43...n electrode,
44...npn transistor.

Claims (1)

[Claims] 1 A semiconductor substrate of a first conductivity type, and a first semiconductor substrate of a first conductivity type formed on the semiconductor substrate and having a band gap smaller than that of the current blocking layer.
a striped lower cladding layer of the first conductivity type formed on the first semiconductor layer, a striped active layer formed on the lower cladding layer, and a striped lower cladding layer of the first conductivity type formed on the first semiconductor layer; a striped upper cladding layer having a second conductivity type opposite to the first conductivity type formed on the active layer; and a second cladding layer formed on the first semiconductor layer and on both sides of the active layer. A buried structure semiconductor laser comprising a conductivity type current blocking layer and a first conductivity type buried layer formed on the current blocking layer and on both sides of the upper cladding layer.