JPS6261386A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To eliminate the large variation in a reactive current due to an inrush current amount by suppressing the current flowing into a buried layer as much as possible by providing an impurity diffused layer. CONSTITUTION:An N-type InP first buried layer 5 is grown on a P-type InP substrate 1, a stripelike groove 10 is formed, and an Zn-diffused layer 8 is formed along the groove 10. A P-type InP buffer layer 2 and the second buried layer 6 as the first layer, a nondoped InGaAsP active layer 3 and the third buried layer 6' as the second layer, and an N-type InP clad layer 4 as the third layer are sequentially laminated and grown. Since the layer 4 and the layer 5 are separated by a reverse conductivity type Zn diffused region 8, a gate current 7-b does not flow, and even if an inrush current 7 is increased, a current blocking layer of a thyristor structure formed of the layers 4, 6, 5, 2 or the substrate 1 is not almost conducted.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a semiconductor laser, and more particularly to a semiconductor laser element having a buried heterostructure.

<Prior art> A buried semiconductor laser device in which the active layer for laser oscillation is surrounded by a semiconductor layer with a lower refractive index and a larger energy gap than the active layer oscillates in a stable transverse mode with a low oscillation threshold current value, and is capable of high-speed modulation. It has advantages such as being able to
It is used as a light source for optical communication systems and measurement systems using optical fibers, making it an extremely important element in industry.

However, in this buried laser element, as the amount of injected current increases, the reactive current that does not pass through the active layer increases rapidly, which results in the total maximum output value being limited. It is also known that this reactive current increases as the temperature rises, and is particularly important for industrially important 1 nGaAsP/
This has become a practical obstacle for lnP-based embedded semiconductor devices.

The cause of the above-mentioned reactive current can be considered as follows. That is, a buried semiconductor laser is mainly manufactured in a structure as shown in FIG. 2 or 3. FIG. 2 shows, for example, an n-type InP buffer layer 2 on an n-type InP substrate 1 and a non-doped InGaA substrate.
After the sP active layer 3 and the p-type InP cladding layer 4 are epitaxially grown in sequence, the entire epitaxially grown layer is etched into a mesa shape using a normal chemical etching method, and a p-type InP buried layer 5 and an n-type InP buried layer 5 are formed on both sides of the epitaxially grown layer. It is made by growing 6-karat gold. FIG. 3 shows, for example, after a p-type InP buried layer 5 and an n-type InP buried layer 6 are sequentially epitaxially grown on an n-type InP substrate 1, a groove is carved using an ordinary chemical etching method, and then an n-type 1fiP layer is formed. Buffer layer 2.1n
A GaAsP active layer 3 and a p-type InP cladding layer 4 are epitaxially grown in the groove. In devices manufactured by either method, laser oscillation depends on the injection current 7 passing through the active layer 3, and the p-n junction formed by the buried layers 5 and 6 on both sides of the active layer 3 is reverse biased. Therefore, when the injection current 7 is small, almost no current flows through this portion. However, as the amount of injected current increases, a considerable amount of current also flows into the buried layers 5 and 6 on both sides of the active layer 3. This is because the gate current 7b flowing from the cladding layer 4 to the buried layer 5 causes the thyristor formed by the cladding layer 4, buried layer 5, and buffer layer 2 (or substrate 1) to conduct (Hiro et al. : Laser Research Vol. 13, p. 156, 1985). In order to reduce the injection current 7b (/i:, the active layer 3 may be provided at the junction surface of the top layer between the lower buried layer 5 and the upper buried layer 6), but current liquid phase epitaxial technology With chemical etching techniques, such precise layer thickness control is not possible, and the reactive currents caused by the above-mentioned causes cannot be prevented.

<Object of the Invention> In view of the above-mentioned problems, the present invention provides a buried semiconductor laser element having a structure in which the current flowing into the buried layer J1 is suppressed as much as possible so that the reactive current does not change significantly depending on the amount of injected current. The entire purpose is to provide.

<Summary of the Invention> In order to achieve the above object, the present invention provides a compound semiconductor substrate having a conductivity type of n-type or a first conductivity type selected as n-type, and a first conductivity type opposite to the first conductivity type. After growing the buried layer, a stripe-shaped trench with a depth reaching the substrate of the first conductivity type is formed, and impurities of the first conductivity type are diffused only from the surface within this trench. Buffer R of the same conductivity type and 4-conductivity type
A multilayer crystal structure for laser oscillation is formed by sequentially epitaxially growing an active layer having a smaller energy gap and higher refractive index than the first buffer layer and a cladding layer of the first conductivity type and the opposite conductivity type.

<Example> Hereinafter, one example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a semiconductor laser device according to one embodiment of the present invention. Figure 4 (A) shows the manufacturing process of this laser element.
(B) Shown in (C). First, for example, n-type (+00) I
The Kn-type InP first buried layer 5 is entirely grown I7 on the nP substrate l, and silicon nitride (S
iNx) film 9 is deposited. Next, a stripe pattern (not shown) of 7 photoresists of @3 μm is formed in the (+10> direction) using photolithography technology, and using this as a mask, the SiNx film 9 is etched with a solution of HF:NH4F"l:40. 4(A).Next, in order to form a constricted current path, this S
Using the iNx film 9 as a mask, a striped groove 10 with a width of 3 μm reaching the InP substrate 1 is formed by etching with concentrated hydrochloric acid as shown in FIG. After that, using the inner wall surface of the groove 10 as a diffusion surface, for example, Zn is diffused to a depth of 0.5 μm,
A Zn diffusion layer 8 is formed along the groove 10 as shown in FIG. 4(C). Note that the width of the groove 100 can be appropriately selected within the range of 1 to 5 μm. After removing the SiNx film 9, a p-InP buffer layer 2 as a first layer, a second buried layer 6,
For the second layer and 17, a non-doped 1nGaAsP active layer 3, a third buried layer 6', and an n-InP cladding N4 as the third layer are successively grown. The buffer 1, layer 2 and active layer 3 are
1410 to become the laser oscillation operating part, and the second
The buried layer 6 and the third buried layer 6' are formed to overlap the first buried layer 5 outside the groove 10. The n-cladding layer 4 (/1gl0) is widely deposited over the entire area inside and outside. On the above multilayer crystal structure, p-side and p-side electrodes (not shown) are connected to the surface of the substrate I and the surface of the cladding layer 4. After forming each, (+10)
A resonator is formed between the folds on the surface.

In the above structure, unlike the semiconductor laser element of the conventional structure shown in FIGS. Since it is separated by the region 8, the gate current 7-1) cannot flow (-). Therefore, the press-in current for laser oscillation is effectively constricted to the striped active layer 3, and Even if the injection current 7 is increased for the purpose of increasing the total output, the current blocking layer of the thyristor structure composed of the cladding layer 4, second buried layer 6, first buried layer 5, buffer layer 2, or substrate 1 remains conductive. There is little to do and it is possible to keep the reactive current very small.

Below, in order to explain this point in more detail, the second
A semiconductor with the structure shown in the figure or Figure 3! , /- The equivalent circuit of the semiconductor laser device is shown in FIG. 5(A), and the equivalent circuit of the semiconductor laser device of this embodiment is shown in FIG. 5(B). The current blocking structure is represented by the equivalent circuit of a thyristor (the circuit inside the broken line) in the first element structure, but in the structure shown in Fig. 5), as the injection current (IT) 7 increases, the gate current (Ic) 7b 12, so that the thyristor conducts and due to its amplifying action, the current 15 is much larger than IG.
flows. Since Is is a reactive current that does not pass through the active layer represented by the diode I)A'''c, in the conventional element represented by this equivalent circuit, as the injection current IT increases, J
The reactive current also increases rapidly. On the other hand, the fifth
In the structure shown in Figure (B), as the injection current IT increases, the reactive current passing through the diode Ds connected in parallel with the active layer increases, but its current is simply proportional to the injection flow rate. Since the thyristor remains non-conductive, the increase in reactive current is extremely small compared to the case of FIG. 5(A). Diode Ds represents a pn junction formed by cladding layer 4 and Zn diffusion region 8. In the above example, since the reactive current was small, high output operation of 70 mW or more was possible at room temperature, and since the influence of heat generation due to the reactive current was small, laser oscillation was possible up to a high temperature of 140° C. or higher.

Although the above embodiments have been described using an n-type substrate as the growth substrate, the same applies even when an n-type substrate is used. The impurities diffusing from the groove lO are C
It is possible to use p-type impurities such as d. Also number 1.
Second. The case where InP is used as the third buried layer has been explained, but these buried layers may be InP, which has a lower refractive index and a smaller energy gap than the active layer.
Other materials such as GaAsP may also be used. The epitaxial growth layer is not limited to InGaAsP/InP-based semiconductor material Vζ, but can also be formed using GaAtAs/GaA.
It is clear that the present invention can also be applied to s-based semiconductor laser devices.

<Effects of the Invention> As explained in detail above, according to the present invention, even if the injection current is increased, the current flowing through the entire current blocking layer is hardly increased, and high output operation can be achieved. A suitable semiconductor laser device can be manufactured using the signal light source and I-. Furthermore, as a result, it is possible to prevent the device from generating heat due to reactive current that does not pass through the active layer, and it is possible to obtain a semiconductor laser device that can be operated at extremely high temperatures.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a semiconductor laser device showing one embodiment of the present invention. FIGS. 2 and 3 are cross-sectional views showing a conventional buried semiconductor laser element. FIG. 4 is an explanatory diagram showing the manufacturing process of one embodiment of the present invention. FIG. 5 is a circuit diagram showing an electrical equivalent circuit of an embedded semiconductor laser element. 1... Substrate , 2... buffer layer, 3... active layer,
4... Cladding layer, 5, 6... Buried layer, 7... Injection' direct current, 8... Diffusion part, 9... Silicon nitride film,
10...Groove. Agent Patent Attorney Aihiko Fuku (and 2 others) No. 1 [12]
I Figure 2 Figure 3 (Al t8) (C) Figure 4 (B) Figure 5

Claims (1)

[Claims] 1. A buried layer having a conductivity type opposite to that of the semiconductor substrate is deposited on a semiconductor substrate for supporting crystal growth, and a striped groove having a depth reaching the semiconductor substrate is provided in the buried layer. an impurity diffusion region formed by diffusion along the inner wall surface of the groove; a buffer layer of the same conductivity type as the first conductivity type laminated in the groove; and a buffer layer having a smaller energy gap and a higher refractive index than the buffer layer. A semiconductor laser device characterized in that a laser oscillation operating section is formed of an active layer and a cladding layer of a conductivity type opposite to the first conductivity type. 2. Claim 1, wherein the semiconductor substrate is (100) InP, and the direction of the striped grooves is the <011> direction.
The semiconductor laser device described in . 3. The semiconductor laser device according to claim 2, wherein the semiconductor substrate is p-type InP, and the impurity diffused along the inner wall surface of the groove is Zn or Cd.