JPS58207690A - Buried type semiconductor laser - Google Patents

Abstract

PURPOSE:To reduce a reactive current flowing into the circuit other than optical waveguide of the InGaAsP active layer and improve temperature characteristic by employing a P type InP substrate, N type InP current confinement layer, P type InP current blocking layer. CONSTITUTION:Since P type InP substrate 1 is used, an NPN transistor part sandwiches the InGaAsP active layer 5 having small band gap energy, efficiency of implanting electrons which are minor carriers to the P type InP clad layer 4 from the N type InP clad layer 6 is low and a current gain of NPN transistor is low. As a result, a switching voltage of pnpn layer becomes high and a current almost does not flow for a voltage applied during normal operation. As described above, a reactive current flows a little to the area other than the optical waveguide 5C of InGaAsP active layer. Therefore, good linearity of injected current-optical output can be obtained and a high output can also be obtained. Moreover, even when an oscillation threshold current density increases under a high temperature, increment of reactive current is small and good temperature characteristic can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a buried semiconductor laser with excellent temperature characteristics.

The buried semicircular laser has a low oscillation threshold current and can be driven with low power. Stable fundamental transverse mode oscillation can be maintained from several times the oscillation threshold to a high injection current region of several tens of times or more. Since the injected carriers are effectively confined in the active layer optical waveguide, the differential quantum efficiency of the injected current vs. optical output characteristic is high9.
It has excellent characteristics such as In particular, nGaAsP-based embedded semiconductor lasers using InP as a substrate are suitable for the low-loss transmission wavelength range of silica glass-based optical fibers, so they are attracting attention as light sources for long-distance, high-capacity optical fiber communication systems, and are undergoing rapid development. It is progressing.

Several 1nOaAsP buried semiconductor lasers have been reported to date. In the process of epitaxially growing a multilayer film including an active layer on an InP substrate with grooves, the active layer is grown separately in the groove part and the surrounding flat area, and the active layer in the groove part is grown separately. InGaAsP with a structure used as a guiding waveguide that becomes a resonator for laser oscillation
A buried semiconductor laser has an active layer that serves as an optical waveguide.
Because it is formed during the second growth process, it is easier to manufacture than the case where the leading waveguide is formed by mesa etching, and the time that the side surface of the optical waveguide is exposed to the growth atmosphere is shorter and the reliability is higher. ◇An embedded semiconductor laser with such a shape is the buried semiconductor laser reported by Omura et al. in the Journal of Quantum Electronics, Volume QE-17, published in 1981, pages 646 to 650.
Crescent, as reported by Miyoshi and Ishikawa et al. in Electronics Letters, Vol. 17, published in 1981, pp. 465-466. ■Klubuto Substrate type, etc. are available. Both of the buried semiconductor lasers having the above two structures have a small oscillation threshold of about 20 tA at room temperature. However, the temperature characteristics of the oscillation threshold are not necessarily good, and the oscillation threshold Ith is
``The characteristic temperature To of a male expressed as cexp(1τ) is
The TO value reported for AsP semiconductor lasers, etc. is approximately 7.
It is below 0K, about 50K to 60K. Therefore 70
It becomes difficult to operate in high @ ranges such as ℃ or 100℃. The reason for the poor temperature characteristics is considered to be the result of an increase in the reactive current component that flows around the active layer leading wavepath section in high temperature conditions and high current injection conditions.

Therefore, the present invention can be applied to InGaAs with a shape that embeds the conventional trench.
In P-embedded semiconductor lasers, In0aAs has excellent temperature characteristics by suppressing the increase in reactive current components even in high-temperature conditions.
A method for manufacturing a P-embedded semiconductor laser is provided.

In the buried semiconductor laser of the present invention, an n-type InP current confinement layer is formed on a p-type InP substrate, and the n-type I
A V-shaped groove is formed from above the flow confinement layer in nP', and only in the lower part l of the V-shaped groove is the n
An n-type 1nP cladding layer is formed on the p-type InP current blocking layer on the surface side in such a way that the InP current confinement layer is interrupted, and in the V-shaped groove, the n-type 1nP cladding is formed entirely on the In(JaAsP active layer). A multilayer film comprising at least two layers of layers is formed, and a 1n layer is formed separately in the groove.
The structure is such that the GaAsP active layer is a region where radiative recombination occurs.

Next, the present invention will be explained in detail using the drawings.

FIG. 1 is a perspective view of an embedded semiconductor laser showing an embodiment of the present invention. First, to explain the manufacturing process, in the first LPE growth, the (001) plane p-type InP base &
On top of 1, an n-type InP current confinement layer 2 (8n dogg, l x IQ"cm") is placed about 2 am (1
) laminated in thickness. Next, a V groove (to) with a diameter of 2.5 μm and a depth of about 2 μm is formed in the <110> direction using a normal photolinkage technique. ■8 for groove etching
i0s membrane 0) mask and 1Tcll and Hs PO
4 (1'J 7F: Mixed liquid (mixed volume ratio, 5HC/!:1
)bPO4), the sides of the groove are <111>B
The surface is selectively exposed and becomes a mirror state Ic.

Next, Zn expansion was applied to the surface to form a p-type In with a thickness of approximately 05 μm.
A p-current blocking diffusion layer 3 is formed. This past v m
In the lower part of io, the Zn diffusion front is p-type InP.
In order to reach the substrate l, the n-type InP current confinement layer 2 is V
The groove 1o is completely interrupted at the lower part thereof.

In the second LPE growth, the p-type InP cladding layer 4 (
Z-n doped, 1×10111crn1 flat part thickness approximately 05 μm), non-doped InGaAsP active layer 5
Three layers are laminated, including an n-type InP cladding layer 6 (sn-doped, 1×10"cm", thickness of about 2.5 pm at the flat part). The p-type InP cladding layer 4 and the InGaAsP active layer 5 grow separately in the V-groove and the flat part, and a p-type InP cladding layer 4C and an InGaAsP active layer optical waveguide 5C are formed in the V-groove. p-side J@electrode 201 n-type 1nP cladding layer 6 side lζ using Au-Zn for Op-type InP substrate I II
An n-side metal electrode 21 using Au-Ge-Ni is formed. After cutting into chips between the folds, they are fused together with the gold it electrode 21 on the heat sink Icn side made of diamond or silicon facing downward.

0) P 1111 electrode 20 on the element, positive, nNi, pole 2
When applying a bias voltage with 1 as negative, V'1m
In the vicinity of 10, the forward bias of the pn junction occurs, so the 1noaAsP active layer optical waveguide 4c, which is a double heterojunction region,
The injected carriers are confined and radiative recombination occurs.

However, since the area other than the vicinity of the V groove lo is a pnpn junction, almost no current flows until the applied voltage is as high as about 10 V and switching occurs.

Therefore, since the injection flow was effectively concentrated in the groove, the oscillation threshold showed a low value of about 15 mA. This structure differs from a conventional buried type semiconductor laser in which a trench is buried, and a p-type InP substrate 1 and a p-type InP current block diffusion layer 3 are used.
is used. Therefore, the reactive current component that flows outside the I n Ga A s P active layer optical waveguide 5c is p
type 1nP substrate 1 → p type InP current block diffusion layer 3 → p
InP type cladding layer 4→InGaAsP active layer 5-+ The current component flowing to the H type InP cladding layer 6 and the current component flowing through the pnpn layer, the former is p type. Since the resistivity of the InP layer is more than one order of magnitude higher than that of the n-type InP layer, when the p-type InP current block diffusion N3 is n-type (when an n-type 1nP substrate is used) (!: it is reduced by about one order of magnitude compared to Also, the latter pn p
The current component flowing through the n-layer is caused by the sum of the current gains of the pnp) and npn) transistors forming the pnpp layer or by switching on the pnpn by increasing the applied voltage J to approach l. In this case, considering the short diffusion length of holes, an increase in the current gain of the npn transistor in which electrons become minority carriers has a large effect.

In the structure of the embodiment shown in FIG. 1, since the p-type InP substrate 1 is used, the npn transistor part has a structure in which the rjIn(]aAsP active layer 5 with a small band gap energy is sandwiched between the npn The efficiency of injecting electrons, which are minority carriers, from the 1-nP cladding layer 6 to the p-type InP cladding layer 4 is low, and therefore the current gain of the npn transistor portion is small.

As a result, the switching voltage of the pnpn layer exhibits a high value of about 1OV as described above, and almost no current flows at an applied voltage of 2 to 3 V or less in normal operation. As described above, since there are few reactive current components flowing outside the In0aAsP active layer optical waveguide 5C, the linearity of the injection current vs. optical output is good, and the optical output on one side is about 30 mW, which is very straight forward. The output increased and a CW optical output of 50 mW or more was obtained. In addition, even if the oscillation threshold current density increases due to high temperature, the increase in reactive current component is small and the temperature characteristics are good.The characteristic temperature To is between 70 and 80, and the maximum CW humidity temperature is 120.
It was possible to improve the temperature to about ℃.

FIG. 2 is a perspective view showing a second embodiment of the invention.

There are four differences from the first embodiment: the 7-shaped groove is n-shaped I
nP'IT: vrf, formed to a depth that reliably penetrates the confinement layer 2, and the p-type InPt flow block growth layer 7 is grown entirely on the substrate on which the figure 7-shaped tiles are formed by epitaxial growth. The three points are that the 1n (1aAsP active layer 5) is formed with a substantially uniform film thickness over the p-type InP current block growth layer 7, and that the 1n (1aAsP active layer 5) is formed directly on the p-type InP current block growth layer 7. The sP active layer optical waveguide step portion 5C is formed above the groove portion 1o and separated from the flat portion as in the first embodiment.The embedded semiconductor laser of the second embodiment is also similar to the first embodiment. It has the same characteristics as the example and is capable of high-output, high-temperature CW operation.Compared to the first example, it depends on the film thickness of the n-type 1 n P current block growth layer 3, and the In(] Since the shape of the aAsP active layer photoconducting active layer optical waveguide width portion 5 changes, greater controllability of the film thickness of the p-type InP current block growth layer 3 is required.
The process of forming the current block diffusion layer 3 by Zn diffusion in the embodiment shown in the figure can be omitted, which has the advantage of shortening the process steps.To summarize the features of the present invention, it is possible to eliminate the process of forming the current blocking diffusion layer 3 by Zn diffusion in the embodiment shown in the figure. To improve the temperature characteristics of p
type InP substrate, n-type InP current confinement layer, p-type I
By using an nP current blocking layer, In0aAsP
It was possible to reduce the reactive current flowing outside the active layer optical waveguide, and therefore the linearity of the injection current-first output was good, resulting in a high optical output, and the temperature characteristics were improved.
The maximum CW humidity temperature of about ℃ was obtained, etc.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a first embodiment of the present invention, and FIG. 2 is a perspective view showing a second embodiment of the present invention. In the figure, 1 is a p-type 1nP substrate; Form InP'fi
Flow confinement layer, 3 is p-type I n PM flow lock diffusion layer, 4 is p-type TnP cladding layer, 4c+
IP type InP cladding layer trench, 5Ci T n
G a A s P active layer optical waveguide section, 6 is n-type T
nP cladding layer, 7 is p-type InP current block growth star 1
011V groove, 20 is a p-side metal electrode, and 21 is an n-side metal electrode.

Claims (1)

[Claims] 1. An n-type InP 'rL flow confinement layer is formed on the p-type InP substrate, a V-shaped groove is formed from above the n-type InP current confinement layer, and a lower part of the V-shaped groove is formed. The n-type InP IIt current confinement layer is interrupted only at the surface of the n-type InP current confinement layer.
A p-type InP current blocking layer is formed with a substantially uniform thickness over the entire surface of the p-type InP current blocking layer, and is formed on the p-type InP current blocking layer inside the V-shaped groove and in a region outside the groove. The InGaAsF active layer As is formed separately from the InGaAsF active layer As.
A multilayer film including at least 2M of an n-type InP crab layer is formed over the entire surface of the P active layer, and a multilayer film including at least 2M of n-type InP crab layers is formed separately in the groove.
Embedded semiconductor laser 0 characterized in that the P active layer is a region that performs radiative recombination.