JPH0290691A - Surface emitting type semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a surface emitting type semiconductor laser which is excellent in reproducibility, small in operating current, and high in output power by a method wherein a multilayer compound semiconductor layers are laminated on a compound semiconductor substrate, and a hetero-structure containing an active layer is formed on the side face perpendicular to the base of the multilayer semiconductor layer. CONSTITUTION:The following are laminated only on the side face etched through a gas source MBE method using an organic metal gas as a source which is capable of executing selective growth: an n-type AlAs buffer layer 105; an n-type Al0.3Ga0.7As clad layer 106; a p-type AlGaAs active layer 107; a p-type Al0.3Ga0.7As clad layer 108, and a GaAs cap layer 109. Lastly, an n-electrode 110 and a p-electrode 111 are built on an n-type GaAs cap layer 104 and a p-type GaAs cap layer 109 respectively after an SiO2 film has been removed. In result, carriers injected into a pn junction formed in a lateral direction are recombined in the active layer 107 and propagate as being confined in the active layer, but a part of light leads out to the n-type clad layer 106 and reaches to a multilayer film 103. At this point, the multilayer film 103 acts as a Bragg reflecting mirror, so that laser light is outputted in a planar direction.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a light source used in optical information processing and optical communication systems.

(Prior Art) With the rapid progress of LSI technology, calculation speed and storage capacity are also becoming extremely large. However, the current situation is that the information transfer speed and reading/recording speed are not commensurate with this. One promising means to solve this problem is parallel processing and transfer of information. Although various configurations can be considered, a light emitting device that emits light in a plane direction is ultimately required as the basic device. Among them, surface-emitting lasers (hereinafter abbreviated as SE lasers) are devices that can be expected to have high transfer speeds.
“C1rcula” by Inoshita and Iga
r Buried Hetero-structure
(CBH) GaAlAs/GaAs 5urfac
e Emitting La5ers” (I Triple E Journal of Quantum Electronics IEE
E Journal of QuantumElect
ronics,) V○L, QE-23, No. 6
．． June 1987. PP, 822-888)
There is.

This conventional example will be briefly explained below. FIG. 3 is a sectional view of this conventional example. Its structure is basically p-G
The top and bottom of the aAs active layer 307 are covered with p-Al. ,4Gao,6
As cladding layer 308, n-Alo, 3Gao, ? As
It is epitaxially grown on an n-GaAs substrate 301 sandwiched by cladding layers 302 and etched into a circular mesa shape (diameter 14 pm).
．． It has a structure embedded with 304.305. As a reflecting mirror, an Au/Zn ring electrode 311 is used on the upper part of the epitaxial layer, and a SiO□/T'io2 multilayer film is used on the lower part. Carriers are injected into the active layer 307 from the ring-shaped p-electrode 312 and the bottom n-electrode 311, recombine and emit light, and the Au1Zn ring electrode 311 and SiO2/T
While being repeatedly reflected by the iO□ multilayer film 310, the laser beam is amplified and emitted in the direction 313. A major feature of the SE laser is that it can be integrated two-dimensionally in this way. As a result, the pulse threshold current value is 68mA.
, a value of 5% was obtained as the differential quantum efficiency.

(Problem to be solved by the invention) However, this surface emitting laser has several drawbacks.

First, the optical output is extremely small at several mW.

This is attributable to the fact that the waveguide mechanism of the SE laser is cylindrical, and the active region cannot be enlarged to lower the oscillation threshold current value. That is, since the oscillation gain is theoretically large and the carrier injection direction is the same as the oscillation direction, the length of the active region cannot be made larger than the carrier diffusion length (2 to 3 μm). Second, the manufacturing method is extremely complicated and has poor reproducibility. In the conventional example, extremely high precision control and reproducibility are required for etching and growth in order to obtain devices with desired characteristics.

Thirdly, the operating current value is high. This is SiO□/Tl1o, which has high absorption for laser light as a reflecting mirror.
This is because the reflectance cannot be increased because 2 is used. This is extremely disadvantageous in terms of Joule heat when forming a two-dimensional array.

An object of the present invention is to provide a surface emitting semiconductor laser that has excellent reproducibility, has a small operating current value, and is capable of high output operation.

(Means for Solving the Problems) The present invention is realized by forming a double heterostructure in which multilayer compound semiconductor layers are stacked on a compound semiconductor substrate and includes an active layer on the side surface perpendicular to the bottom surface of the semiconductor layer. This is a surface-emitting semiconductor laser that is characterized by the following characteristics.

Further, the present invention is a surface emitting semiconductor laser characterized in that the angle of the etched side surface with respect to the bottom surface is set arbitrarily.

(Operation) The intention of the present invention is to independently optimize the carrier injection mechanism and waveguide mechanism to have a structure suitable for low threshold and high power operation, and for the resonator to independently optimize a structure suitable for surface coupling and integration. There is a particular thing.

A semiconductor multilayer film with different refractive indexes acts as a distributed reflector. The oscillation wavelength is λ, the effective refractive index of the laser medium is n,
If the thickness of the semiconductor layer is d, the black reflection condition is d=A
/2n. Furthermore, if two types of semiconductors with low absorption are used, a large reflectance can be obtained when multilayered, even if the difference in refractive index is small. In the present invention, a multilayer reflective mirror is created in the first crystal growth, side surfaces are formed by etching, and a laser structure is formed by epitaxially growing a double heterostructure including an active layer on this side surface in the second crystal growth. It is something to do. In the second crystal growth, a structure excellent in low threshold operation and high output operation can be arbitrarily selected.

(Example 1) FIG. 1 is a schematic diagram of an example of the present invention. The most basic configuration is shown for simplicity. First, semi-insulating (SI
After growing a 1.0-layer n-type GaAs buffer layer 102 on a GaAs substrate 101, a multilayer film 103 consisting of an n-type GaAs layer and an n-type AlAs layer is grown to a thickness of 160 nm.
are stacked 50 times as a unit structure, and an n-type GaAs layer 104 is further grown to 0.511 m as a cap layer. A suitable growth method at this time is the molecular beam epitaxial method (MBE method), which has excellent layer thickness controllability. After this, <01〒>
An etching mask is formed along the direction. This etching mask has a two-layer structure of a SiO2 film and a resist. Next, a vertical etched side surface with a depth of 1011 m, in this embodiment a (011) plane, is formed by an etching method that has excellent anisotropy and causes little damage to the crystal, such as reactive ion beam etching. After removing only the resist of the two-layer etching mask, an n-type AlAs buffer layer 105 (thickness: 0.2 pm) is formed only on the etched side surface by gas source MBE using an organometallic gas as a source, which allows selective growth. ), n-type Alo, 3Gao, 7
As cladding layer (thickness 0.3 pm) 106, p-type Al
GaAs active layer (500 layers thick) 107, p-type A1o,
3Gao, 7As cladding layer 108 (thickness 1.0pm)
, a GaAs cap layer 109 is stacked. At this time, 5
It can also grow on the bottom surface of the I-GaAs substrate, but if the etched side surface is sufficiently deep, no problem will occur in terms of characteristics. Finally 81
The embodiment of the present invention is completed by forming an n electrode 110 on the nWGaAs cap layer 104 and a p electrode on the p-type GaAs cap layer 109 after removing the 02 film. As a result, carriers injected into the pn junction formed laterally are recombined in the active layer 107 and propagate while being confined in the active layer, but some light is transmitted to the n cladding layer 107.
Leakage reaches the multilayer film. At this time, since the multilayer film 103 acts as a black reflector, the laser beam is transmitted in the in-plane direction (1
12 directions).

In the case of this example, the threshold current is 30 mA or less, and the optical output is 2
It is 0 mW or more, and the reproducibility is also good.

(Example 2) In Example 1, the etched side surface was 90° to the bottom surface.
Generally speaking, when the angle is e, the effective period of the multilayer film is 1/Ic compared to when the angle is 90°.
becomes osθ1. In other words, it becomes longer. Usually AlGaA
Since the gain width of an s-based semiconductor laser is 50 meV or more, the black wavelength can be controlled by adjusting the etching angle.

(Example 3) In the case of a single-period distributed reflection laser, there can theoretically be two oscillation axis modes. A λ/4 phase shift grating is effective for stable single-axis mode oscillation.

The production of a λ14 phase shift distributed reflection laser, which has been extremely difficult in the past, can be easily achieved according to the present invention. That is, it is sufficient to shift one layer of the multilayer film by λ/2.

(Example 4) FIG. 2 is a sectional view of an example in which a two-dimensional array is formed. By separating the n-electrodes or p-electrodes of adjacent elements, independently driven surface emitting lasers can be easily two-dimensionally integrated. Furthermore, when a two-dimensional array is formed, a variety of wavelengths can be produced by creating a laser whose etched side surface is oblique to the bottom surface as in Example 2, and combining it with a 90° laser, or by combining diagonal lasers with different angles. A surface emitting laser array can be obtained.

Although AlGaAs-based lasers have been described in Examples 1 to 3 above, the present invention is also effective with other materials, such as GaInAsP-based lasers.

(Effects of the Invention) The effects of the present invention are that a surface emitting laser can be manufactured two-dimensionally with good reproducibility. The present invention allows the active region and the reflector to be set independently, so compared to the conventional operating current level, the current level is 2.
This is advantageous in terms of Joule heat when monolithically formed on the same substrate. Further, by selecting the etching angle, surface emitting lasers with different oscillation wavelengths can be obtained, and surface emitting arrays capable of emitting various wavelengths can be formed on the same substrate.

[Brief explanation of the drawing]

FIGS. 1 and 2 are schematic diagrams of an embodiment, and FIG. 3 is a schematic diagram of a conventional example. 101...5I-GaAs substrate, 1
02...n-type GaAs buffer layer, 103-n-type GaAs/AlAs multilayer film, 104-n-type GaAs cap layer, 105, n-type GaAs buffer layer, 106-
n-type AlGaAs cladding layer, 107 ・p-GaAs
active layer, 108...p-AlGaAs cladding layer,
109 ・p-GaAs contact layer, 110 ・n
Electrode, 111 ・P electrode, 112-... Emitted light, 301
・N-type GaAs substrate, 302 ・N-type AlGaAs cladding layer, 303.305 ・p-AlGaAs current blocking layer, 304 ・n-AlGaAs current blocking layer, 306...Sio2 film, 307 ・p-GaAs active layer, 308 -p-AlGaAs cladding layer, 309
・p-AlGaAs cap layer, 310...SiO□
/T'102 multilayer film, 311...n electrode, 312...ring-shaped p electrode, 313...emitted light. Diagram

Claims (1)

[Claims] 1) Multilayer compound semiconductor layers are stacked on a compound semiconductor substrate, and a double heterostructure including an active layer is formed on the side surface of this semiconductor layer perpendicular to the bottom surface. A surface-emitting semiconductor laser. 2) The multilayer compound semiconductor layer is characterized in that two types of semiconductor layers having different refractive indexes are alternately and periodically laminated, and the periodic structure unit thereof is equal to the black wavelength of the oscillation wavelength in the laser. surface-emitting semiconductor laser. 3) The multilayer compound semiconductor layer is characterized in that two types of semiconductors having different refractive indexes are periodically laminated except for one layer, and the front and back of this one layer are shifted by 1/4 of the unit periodic structure. The surface emitting semiconductor laser according to item 1 or 2. 4) The surface emitting semiconductor laser according to claim 1, 2 or 3, wherein an angle of the etched side surface with respect to the bottom surface is set arbitrarily.