JPH0744307B2 - Semiconductor laser manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor laser having an AlGaAs double heterojunction structure which requires two MBE growth steps.

(B) Prior Art A method of manufacturing a semiconductor laser having a structure that requires two MBE growth steps will be described below, and the problem will be pointed out.

First, after stacking the first growth layer on the surface of the substrate in the first MBE growth step, the substrate is taken out from the MBE apparatus and a stripe groove reaching the first upper cladding layer is formed in the etching step. With this etching process,
Since impurities such as oxides are directly attached to the etched portion, the impurities are evaporated by a predetermined method. Then, the second growth layer is laminated in the second MBE growth step.

Thus, in the step of evaporating the impurities, the first
When the Al composition of the upper cladding layer is 0.4 or more, the impurities are less likely to be evaporated. As a result, the laminated state of the second growth layer deteriorates, causing a problem that current does not flow through this portion. On the other hand, if the Al composition of the first upper cladding layer is 0.4 or less, the laminated state of the second growth layer will be good, but the problem of light confinement efficiency will be reduced.

(C) Purpose The present invention has an object to provide a method for manufacturing a semiconductor laser which can manufacture the shape of a semiconductor laser having the above-described characteristics with good reproducibility and can be easily manufactured, and which can improve the manufacturing yield.

(D) Configuration One method of manufacturing a semiconductor laser according to the present invention is one conductivity type.
On the surface of the substrate made of GaAs, AlGa of the same conductivity type as the substrate is
As lower clad layer, active layer made of Al _X Ga _1-X As, first upper clad layer made of AlGaAs having a conductivity type opposite to that of the substrate, and band gap equal to or higher than that of the active layer due to quantum effect A first growth layer having a film thickness of 1 and a protection layer made of GaAs of the opposite conductivity type to the substrate and a current limiting layer made of AlGaAs of the same conductivity type as the substrate. By a growth step and selective etching of only the current limiting layer with a solution having an etching rate of AlGaAs >> GaAs, a taper is formed so that the surface of the protective layer is exposed and the width becomes narrower toward the substrate side. An etching step for forming a stripe groove having a surface,
Impurities deposited by the etching process are applied by heating the substrate under conditions such that the protective layer made of GaAs does not evaporate while the arsenic molecular beam is applied to the first growth layer in which the stripe grooves are formed. And a thermal cleaning step of evaporating the first thermal growth layer, a second upper clad layer made of AlGaAs having a conductivity type opposite to that of the substrate on the thermal grown first growth layer, and a cap layer for improving ohmic contact. And a second growth step of stacking a second growth layer to be formed.

(E) Embodiment FIG. 1 is a perspective view showing an embodiment of the semiconductor laser according to the present invention. In the figure, 1 is a semiconductor laser, and 1a and 1b are Fabry-Perot reflecting surfaces. 10 is a substrate made of N-type GaAs, 21 is N-type Al _X Ga _1-X As (Al composition _X
= 0.55) and 22 is Al _X Ga _1-X As
An active layer composed of (Al composition _X = 0.12) and 23 are P-type Al _X Ga
_First upper cladding layer made of _1-X As (Al composition _X = 0.55), 24 a protective layer made of P-type GaAs, 25 N-type Al _X Ga _1-X As
(Al composition _X = 0.55) current limiting layer, 41 is P-type Al _Y G
a _1-Y As (Al composition _Y = 0.55) second upper clad layer, 42 a P ⁺ type GaAs cap layer, 50 a P type electrode,
Reference numeral 51 indicates N electrodes, respectively. The protective layer 24
Is set to a film thickness having a band cap equal to or greater than that of the active layer 22 due to the quantum effect.

Specifically, the lower clad layer 21, the active layer 22, the first upper clad layer 23, the protective layer 24, and the current limiting layer 25 constitute a first growth layer.
Twenty are made up. A protective layer 24 is formed on the first growth layer 20.
A stripe groove 30 is formed along the laser resonator wavelength of the semiconductor laser 1 with a depth at which the surface of the semiconductor laser is exposed and having a tapered surface 31 that becomes narrower toward the substrate 10 side. The second upper clad layer 41 and the cap layer 42 form a second growth layer 40. The second growth layer 40 is laminated on the first growth layer 20 so as to have a recessed shape corresponding to the shape of the stripe groove 30.

Then, the stripe groove 30 of the semiconductor laser 1 as described above is used.
The band structure in the center of is as shown in FIG. In FIG. 2, A is the conduction band, B is the forbidden band, and C is the valence band. According to FIG. 2, the band gap of the protective layer 24 is wider than that of the active layer 22 due to the quantum effect. I understand.

FIG. 3 is a reference diagram for explaining the method for manufacturing a semiconductor laser according to the present invention, and the description will be given below with reference to the same figure.

(A) The substrate 10 mounted in an MBE device (not shown) is heated by a predetermined method. The raw materials and impurities stored in the evaporation sources are evaporated in the form of molecular beams. The raw material and the like are monitored by a mass spectrometer (not shown), and the temperature of the evaporation source and the shutter are controlled by a computer (not shown) to stack the first growth layer 20 (first growth step). The thickness of the protective layer 24 is set to about 30 to 40Å.

(B) After taking out the substrate 10 on which the first growth layer 20 is laminated from the MBE device to the outside, the back surface of the substrate 10 is lapped. Next, the current limiting layer 25 other than the portion where the stripe groove is to be formed is covered with a photoresist 60. This photoresist 60
The substrate 10 using the mask as a mask is immersed in a solution having an etching rate of AlGaAs >> GaAs (for example, HCl or the like) to selectively etch the current limiting layer 25, so that the surface of the protective layer 24 is exposed and the substrate is exposed. A stripe groove 30 having a tapered surface that narrows toward the side is formed in the first growth layer 20 (etching step).

(C) The substrate 10 from which the photoresist 60 has been removed is organically washed, and the substrate 10 is mounted again in the MBE apparatus. here,
By heating the substrate 10 while applying an arsenic molecular beam to the substrate 10, impurities such as oxides attached in the etching process are evaporated (thermal cleaning process).

Substrate temperature and Ga in this thermal cleaning process
Table 1 shows the relationship with the evaporation rate of As. In addition, the evaporation rate at each substrate temperature is shown in the unit of (μm / h) in the middle row of Table 1, and the evaporation rate is (Å / s) in the lower row of Table 1.
ec) represents the value converted into units.

The heating temperature and time of the thermal cleaning process are
It is set based on Table 1 on condition that the protective layer 24 having a film thickness of about 30 to 40Å does not evaporate.

In the steps (d) and (c), the temperature of the substrate 10 is set to about 600 ° C., and the second growth layer 40 is laminated on the first growth layer 20 in the same manner as in the step (a) (second). Growth process).

Thereafter, a P-type electrode and an N-type electrode are formed respectively in the same manner as in a usual method for manufacturing a semiconductor laser.

In the above examples, Al _X Ga _1-X As and Al _Y Ga _1-Y
Although the Al composition of each layer made of As is described, it goes without saying that the composition can be changed appropriately. However, in the case of the Al composition as in the above embodiment, light can be efficiently emitted in the active layer 22 due to the light confinement effect of the lower clad layer 21 and the first upper clad layer 23. Further, it is possible to reverse all conductivity types in the above embodiment.

(F) Effect As described in detail above, according to the present invention, only the protective layer is selectively left in the etching step to give the first upper clad layer a passivation effect, so that impurities are not formed on the surface of the first upper clad layer. Since the impurities are evaporated by a relatively simple thermal cleaning without directly attaching them,
The laminated state of the second growth layer can be improved regardless of the Al composition of the first upper cladding layer. That is, according to the present invention, the shape of the semiconductor laser having the above-described characteristics can be manufactured with good reproducibility and easily. As a result, the manufacturing yield can be improved.

[Brief description of drawings]

1 is a perspective view showing an embodiment of a semiconductor laser according to the present invention, FIG. 2 is an explanatory view showing a band structure of the semiconductor laser 1 shown in FIG. 1, and FIG. 3 is a view showing a semiconductor laser according to the present invention. It is a reference drawing for explaining one example of a manufacturing method. 10 ... Substrate, 20 ... First growth layer, 21 ... Lower clad layer, 22 ... Active layer, 23 ... First upper clad layer, 24 ...
Protective layer, 25 ... Current limiting layer, 30 ... Stripe groove, 31 ...
… Tapered surface, 40 …… Second growth layer, 41 …… Second upper cladding layer, 42 …… Cap layer.

Claims (1)

[Claims] 1. An AlGaAs lower clad layer of the same conductivity type as that of the substrate, and Al on the surface of a substrate of one conductivity type GaAs.
_X Ga _1-X As active layer and Al of opposite conductivity type to the substrate
A first upper clad layer made of GaAs; a protective layer made of GaAs having a film thickness equal to or larger than that of the active layer due to a quantum effect and having a conductivity type opposite to that of the substrate; A first growth step of stacking a first growth layer composed of a current limiting layer of the same conductivity type AlGaAs, and selectively etching only the current limiting layer with a solution having an etching rate of AlGaAs >> GaAs An etching step of forming a stripe groove having a tapered surface with a depth exposing the surface of the protective layer and narrowing toward the substrate side; and arsenic on the first growth layer in which the stripe groove is formed. By heating the substrate while applying a molecular beam under conditions such that the protective layer made of GaAs does not evaporate at the heating temperature and time, the impurities attached by the etching process are vaporized. And a second upper clad layer made of AlGaAs having a conductivity type opposite to that of the substrate, and a cap layer for improving ohmic contact. And a second growth step of stacking a second growth layer.