JP2680804B2 - Semiconductor laser - Google Patents

Description

The present invention relates to a high performance and highly reliable embedded semiconductor laser. Conventional semiconductor lasers that operate at high current densities have had large drive currents of 100 mA to 200 mA, so it is necessary to efficiently dissipate the heat generated by the device to the heat sink. Therefore, the heat sink is the up-side where the active region is located. In general, a so-called up-sidu down method of fusion-bonding and assembling elements has been used.
However, in this method, the active region is separated from the fusion part with the heat sink by only about several μm, and the fusion strain due to the difference in the thermal expansion coefficient between the fusion metal and the semiconductor and the penetration of the fusion metal into the semiconductor. There are many factors that deteriorate the reliability and yield of the device, such as deterioration of the crystallinity of the active region due to the above and short circuit due to adhesion of a part of the fusion metal to the side surface of the device. Therefore, a so-called up-side up method of assembling the up side upward is desirable. Recently, as a structure of a semiconductor laser, an embedded heterostructure semiconductor laser having a shape of burying an active layer optical waveguide having a width of about 2 μm has been developed, and the driving current is greatly reduced because it has a low threshold value. In the embedded semiconductor laser described in Japanese Patent Application No. 56-166666, which uses an InP substrate and an InGaAsP-based material, the oscillation threshold current is 2 mA.
The optical output characteristics have a differential quantum efficiency of about 70% and a maximum cw operating temperature of about 120 ° C. Since the drive current for obtaining an optical output of 10 mW on one side at room temperature is about 50 mA, the oscillation threshold is 10
Compared to the conventional structure of about 0mA, the power consumption has been reduced to less than half and the amount of heat generated has decreased. Therefore, even if this device is assembled by the up-side-up method, which was not able to obtain sufficient device characteristics due to poor heat dissipation efficiency, the maximum cw operating temperature is 10
A good result of about 0 ° C was obtained. However, when an element assembled by the up-side-up method is used, the p-side and the n-side of the element are inverted, so that the electrode polarity of the package in which the element is attached changes. Therefore, it was necessary to change the polarity of the drive circuit to match the polarity of the drive circuit, or to use a heat sink as an insulator to float the laser electrode from the heat sink. An object of the present invention is to provide an embedded semiconductor laser which has sufficiently good device characteristics even when assembled by an up-side-up method and which can utilize the electrode polarity of a conventional package as it is. According to the present invention, at least the active layer is penetrated to the surface of the multilayer semiconductor substrate in which at least three layers of the first conductivity type clad layer, the active layer and the second conductivity type clad layer are laminated on the semi-insulating semiconductor substrate. On the multilayer film semiconductor mesa substrate in which two grooves having depths parallel to each other are formed, only the current blocking layer of the second conductivity type and the upper part of the mesa region narrowed between the two grooves are formed. Except for the first conductivity type current confinement layer and at least three layers of the second conductivity type burying layer, which is further laminated so as to cover the entire surface, are formed, and the first electrode is filled with the second conductivity type. Is formed on the upper layer of the layer or on the second conductive type electrode forming layer laminated on the second conductive type buried layer, and on the upper surface of the first conductive type clad layer exposed by etching the second electrode. Formed and the active layer in the mesa region A semiconductor laser which is a laser resonator body which performs the recombination is obtained. Next, the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of an embedded type semiconductor laser showing a first embodiment of the present invention. First, when showing the manufacturing process,
(001) -faced Fe-doped semi-insulating InP substrate 1 (resistivity ρ = 8
× 10 ⁷ Ω ・ cm) and n-type InP clad layer 2 (Sn-doped, 1
X 10 ¹⁸ cm ^-3 ) with a film thickness of about 10 μm, InGaAsP active layer 3 (undoped, film thickness 0.2 μm), and p-type InP clad layer 4 (Zn-doped, 7 × 10 ¹⁷ cm ^-3 , film thickness) 1 μm) is laminated using a normal LPE method to produce a multilayer film wafer. Next, two grooves 30 and 31 parallel to the <110> direction are formed by an ordinary photolithography technique using an etching solution of Br-methanol. In this case, the width of the groove is 5 μm, and the upper width of the mesa stripe 10 narrowed to two grooves is about 2 μm. In the buried LPE growth, the p-type InP current blocking layer 5 (Zn-doped, 2 × 10 ¹⁸ cm ^-3 , the thickness of the flat portion 0.5 μ was first used).
m), n-type InP current confinement layer 6 (Te-doped, 3 × 10 ¹⁸ cm
^-3 , a flat portion having a thickness of 0.5 μm) is stacked on the mesa stripe 10 by adjusting the supersaturation degree of the growth solution so as not to grow. Next, p-type InP buried layer (Zn-doped, 1 × 10 ¹⁸ cm ^-3 ).
The flat portion is grown to a thickness of about 2 μm and is laminated so as to cover the whole. Finally, a p-type InGaAsP cap layer (composition of 1.2 μm in emission growth, Zn-doped, 5 × 10 ¹⁸ cm ⁻³ , flat portion film thickness 0.5 μm) is laminated to complete the fabrication of a buried structure wafer. Next, in order to provide an n-side electrode, the n-type InP clad layer 2 was etched in parallel with the <110> direction from the surface using an etching solution of Br-methanol with the SiO ₂ film as a mask to form the electrode mounting flat portion 40. Form. At this time, the terrace side surface portion 41 formed by etching has a shape that bites inward from the surface because the vicinity of the <111> plane is selectively exposed. The p-side electrode 20 and the n-side electrode 21 are formed in the same vapor deposition process. That is, in FIG. 1, when a vapor deposition source is provided above and vapor deposition is performed, the electrode material is not vapor deposited in the vicinity of the terrace side surface portion 41 because it becomes a shadow for vapor deposition atoms flying almost linearly from the vapor deposition source, so that the p-side electrode 20 and the n-side are not deposited. The electrode 21 is formed separately. The electrode consists of three layers of Ti / Pt / Au. Ti is p-type InGaAsP
Although it is a material that forms a Schottky junction with the cap layer 8 and the n-type InP clad layer 2, since both layers have a high carrier concentration, a good ohmic characteristic of about 4Ω was exhibited due to the tunnel effect. Next, in order to facilitate the cleavage, the substrate side is polished, the entire thickness is set to about 100 μm, and then the fusing metal 22 made of Cr / Au is deposited. The above is the basic manufacturing process of the device. Using a package having a conventional structure, a fusion metal 22 is fused to a heat sink such as diamond or silicon with the substrate 1 side down. Substrate 1 is 10 ⁷ Ω
It has a high resistivity of about −cm and has a heat sink and p
There is almost no conduction with the side electrode 20 and the n-side electrode 21. Therefore, the p-side electrode 20 and the n-side electrode 21 can be connected to the conventional polar electrode portion of the package by the p-side electrode lead wire 50 and the n-side electrode lead wire 51 using an Al wire or the like. Next, element characteristics are shown. When a bias voltage is applied with the p-side electrode lead wire 50 being positive and the n-side electrode lead wire 51 being negative, the mesa stripe 10 portion is a forward bias of the pn junction, and the holes are from the p-side electrode 20 to the p-type InGaAsP cap layer. 8, p type InP
Buried layer 7, p-type InP clad layer Mesa 4m through InGaAsP
Electrons injected into the active layer optical waveguide 3m and electrons are n-side electrode
InGaAs, which is a double heterojunction region, is also injected from 21 to the n-type InP cladding layer 2 into the InGaAsP active layer optical waveguide 3m.
Emission recombination of holes and electrons occurs efficiently in the P active layer optical waveguide 3m portion. Outside the region of the mesa stripe 10, since the structure of the multilayer film is a pnpn junction, no current flows at a voltage of about 2V normally applied to the device. Therefore, the current is efficiently confined in the region of the mesa stripe 10. As a result, the oscillation threshold current was small and showed a value of about 15 to 20 mA. Injection current-optical output characteristic differential quantum efficiency is 60
~ 70%, also empirically The parameter To, which indicates the temperature dependence of the oscillation threshold current, which is considered to change at 70 to 80 K, and the maximum cw temperature was about 100 ° C. Due to the difference in heat dissipation efficiency between the element assembled by the up-side-up method and the conventional up-side-down method, a difference in injection current-optical output characteristics can be seen from about 70 ° C. However, even an element assembled by the up-side-up method can obtain an optical output of 10 mW or more at 70 ° C, and the fusion part to the heat sink is In
GaAsP active layer The optical layer is about 100 μm from the optical waveguide 3 m, which is several tens of times farther than the 2 μm to 3 μm of the up-side-down method, so that the fusion strain or the fusion layer penetrates into the semiconductor crystal to activate the active layer. Since there is no adverse effect such as deterioration of the crystallinity of the device, there is almost no increase in the drive current even in the reliability evaluation test under the normal operating condition of 70 ° C-5mW constant light output operation. -It was found that the device has a high reliability of the same level as or higher than that of the element assembled by the side-down method. FIG. 2 is a perspective view of a buried type semiconductor laser showing a second embodiment of the present invention. The difference from the first embodiment is p
The current blocking layer 5 is laminated in a substantially uniform thickness of about 1 μm over the entire surface of the substrate in the first step of the buried LPE growth. By doing so, only one layer of the n-type InP current confinement layer 6 is formed into the mesa stripe 1.
Since it suffices that the growth is interrupted at the upper part of 0, in the first embodiment shown in FIG. 1, two layers of the p-type InP current blocking layer 5 and the n-type InP current confinement layer 6 are formed into the mesa stripe 1.
The reproducibility of growth was improved and the device yield was improved as compared with the case where the growth was interrupted at the upper part of 0. Finally, enumerating the features of the present invention, since it is an up-side-up assembly method, the active layer and the fusion layer are far away from the adverse effects such as fusion strain or penetration of fusion metal into the semiconductor. Due to the laser structure, even in the up-side-up assembly method, a light output of 10 mW or more can be obtained at a high temperature of 70 ° C, and at normal operating temperatures, characteristics almost comparable to the up-side down method can be obtained. , P-side electrode by using semi-insulating substrate, n
Since it has a planar structure in which both side electrodes can be taken out from the up side, the electrode polarity of the conventional package can be used as it is, and it has versatility in matching with the drive circuit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an embedded semiconductor laser showing a first embodiment of the present invention, and FIG. 2 is a perspective view of an embedded semiconductor laser showing a second embodiment of the present invention. Is. In the figure, 1 ... semi-insulating InP substrate, 2 ... n-type InP cladding layer, 3 ... InGaAsP active layer, 4 ... p-type InP cladding layer, 5 ... p-type InP current blocking layer, 6 ... ... n-type InP current confinement layer, 7 ... p-type InP buried layer, 8 ... p-type InG
aAsP cap layer, 10 ... Mesa stripe, 3m ... InGaAs
P active layer optical waveguide, 4m ... P-type InP clad layer mesa part, 30
And 31 ... two parallel grooves, 40 ... n-side electrode formation part,
20 …… p side electrode, 21 …… n side electrode, 22 …… fusion metal, 41
...... Terrace side surface, 50 …… P side electrode lead wire, 51 …… n
It is a side electrode lead wire.

Claims (1)

(57) [Claims] At least three layers of a first conductivity type clad layer, an active layer, and a second conductivity type clad layer are laminated on a semi-insulating semiconductor substrate, and at least a depth of penetrating the active layer is formed on the surface of a multilayer semiconductor substrate. On a multilayer semiconductor mesa substrate in which two parallel grooves are formed, except for a current block layer of the second conductivity type and an upper portion of a mesa region narrowed between the two grooves. At least three layers of a first conductivity type current confinement layer to be stacked and a second conductivity type buried layer further covering the entire surface are formed, and the first electrode is composed of the second conductivity type buried layer. An active layer in the mesa region, which is formed on an upper portion of the first conductivity type cladding layer and is exposed by etching a second electrode, is a laser resonator body that performs radiative recombination. A semiconductor laser characterized by: 2. 2. The semiconductor according to claim 1, wherein the first electrode is formed on an upper part of a second-conductivity-type electrode forming layer laminated on the second-conductivity-type buried layer. laser.