JPH02262388A - Manufacture of semiconductor light-emitting device - Google Patents

Abstract

PURPOSE:To enhance a carrier concentration in a p-type clad layer by a method wherein a mesa stripe is formed at a double heterojunction structure part on an n-type GaAs substrate, then, N-type GaAs current stopping layers are respectively grown under the side parts of the mesa stripe. CONSTITUTION:An n-type In0.5(Ga0.3Al0.5)0.5P clad layer 12, an undoped In0.5Ga0.5P active layer 13, a p-type In0.5(Ga0.3Al0.7)0.5P clad layer 14, a P-type In0.5Ga0.5P contact layer 15 and an n-type GaAs cap layer 16 are continuously grown on an n-type GaAs substrate 11. Then, the layer 16 is removed using an (H2SO4+H2 O2+H2O) etching liquid. subsequently, an SiO2 film 17 is formed. The layer 15 is removed using a (Br2+HBr+H2O) etching liquid using the film 17 as a mask and moreover, the layer 14 is etched with a hot phospheric acid to a desired depth to form a mesa stripe. N-type GaAs blocking layers 18 which each act as a current stopping layer are selectively grown under the side parts of the mesa stripe using the film 17 as a mask. After the film 17 is removed, a P-type GaAs ohmic layer 19 is grown. Thereby, a rib waveguide type semiconductor laser is completed.

Description

[Detailed Description of the Invention] [Object of the Invention] Industrial Field of Application) The present invention relates to a semiconductor light emitting device using an InGaAIP compound semiconductor material, and in particular to manufacturing a semiconductor light emitting device using a double heterojunction epitaxial wafer. Regarding the method.

(Conventional technology) In recent years, chemical vapor deposition method using organic metals (hereinafter referred to as MOC) has been developed.
InGaA is deposited on a GaAs substrate using the VD method (abbreviated as VD method).
It has become possible to form IP, and visible light semiconductor lasers using this technology are attracting attention.

FIG. 5 is a sectional view showing the schematic structure and manufacturing process of a rib waveguide type laser using InGaAIP material. To create this laser, first, as shown in Figure 5 (a),
On an n-GaAs substrate 51, an n-1nGaAIP cladding layer 52.degree. InGaP active layer 53. p-1nGaAIP cladding layer 54. p-InGaP contact layer 55 and p-InGaP contact layer 55 and p-InGaP contact layer 55
-GaAs cap layers 5.6 are sequentially formed by the MOCVD method. Then, as shown in FIG. 5(b), a 5in2 film 57 is formed on the cap layer 56, and using this as a mask, the cap layer 5. Then, the contact layer 55 is etched, and the 92971 layer 54 is further etched to a desired depth to form a mesa stripe.

Next, as shown in FIG. 5(c), an n-GaAs block layer (current blocking layer) 58 is selectively grown on the side of the mesa stripe using the 5in2 film 57 as a mask.
After removing the 02 film 57 and the cap layer 56, as shown in FIG.
A p-GaAs ohmic layer 59 is grown as shown in d).

Here, in the substrate and each layer, the n-type impurities include St, p
Zn is used as the type impurity.

However, semiconductor lasers manufactured by this type of method have the following problems. That is, in a semiconductor laser using an InGaAIP-based material, when Zn is used as a p-type impurity, it is said that the carrier concentration obtained under certain doping conditions is lower than that of a GaAlAs-based material (for example, Journal or Crystal Grow).
th 77 (1986) 374-379). especially,
The higher the Al composition ratio, the more difficult it becomes to grow a crystal with a high carrier concentration, and the carrier concentration tends to be saturated even if the amount of Zn supplied is increased. On the other hand, in terms of element design, a crystal with a high Al composition ratio is desired for the p-cladding layer to provide a sufficient difference in refractive index with the active layer, and high-concentration p-type doping with a high Al composition is required.

An internal current confinement type laser as shown in FIG. 6 is an example of a laser having a gain guide structure that can be created by two crystal growth steps including a double heterojunction similar to the rib waveguide type laser. To create this laser, first see Figure 6(a).
As shown in FIG. 2, in the first crystal growth step, a layer structure similar to that up to the contact layer 55 of the rib waveguide laser is formed, and then an n-GaAs block layer 66 is formed.
grow. Thereafter, as shown in FIG. 6(b), a portion of the block layer 66 is etched to form striped windows. Next, as shown in FIG. 6(C), p-G is deposited on the contact layer 55 and the block layer 66 exposed in the window.
Re-grow the aAs ohmic layer 59.

In the laser manufacturing process shown in FIGS. 5 and 6, the double heterojunction structure (n-cladding layer 52 to contact layer 55) was grown under the same conditions, and the carrier concentration in each layer after growth was examined. While they are equal in the n-cladding layer 52, they are different in the Zn-doped 92971 layer 54, and the carrier concentration in the former epitaxial wafer (the example shown in FIG. 5) is lower. When 5 x 1017 cm-' is obtained with the structure shown in Fig. 6 under doping conditions where the carrier concentration is saturated with respect to the amount of Zn supplied, the structure shown in Fig. This results in only a low carrier concentration.

S I M S (Secondary Ion Hi
When the Zn9 degree of the 92971 layer 54 in the epitaxial crystal was investigated by s Spectrometry analysis, it was shown that the incorporated Znp degree itself was the same.

This suggests that the rate at which Zn incorporated into the crystal becomes a carrier (activation rate) is different between the two, and cannot be improved by increasing the amount of Zn absorbed.

In addition, when forming a structure in which the surface layer contains a layer containing Zn, P, etc., which has a high vapor pressure, or Al, etc., which is easily oxidized, a cap layer (about several hundred to several thousand layers) is required to prevent deterioration of the surface layer. Although a layer covering a surface that does not directly contribute to the laser structure is sometimes provided, this is not effective against the problem of the carrier concentration of the Zn-doped p cladding layer 54 being reduced as described above.

Furthermore, upon study by the present inventors, the above-mentioned figure 5 (a
) of p-GaAs cap layer 56 in FIG. 6(a).
- When the thickness is the same as that of the second layer 66 of the GaAs blower, and after the formation of the double heterojunction structure, FIG. 6(a)
Even when heat treatment is applied at the same temperature and for the same time as during the growth of the block layer, the p-cladding layer 54 in the rib waveguide laser
carrier concentration was not improved.

Note that in this type of semiconductor laser, the carrier concentration of the 92971 layer is one of the important parameters that determines the device characteristics, and if a sufficiently high carrier concentration is not obtained, the oscillation threshold current will increase.

This causes a decrease in temperature characteristics. Further, the same problem is not limited to semiconductor lasers, but also applies to light emitting diodes and the like.

(Problem to be Solved by the Invention) In the production of a semiconductor laser using InGaAIP-based materials as described above, the growth of the double heterojunction (n-cladding layer, active layer, 92971 layer) is the same in one crystal growth process. Despite the conditions, the carrier concentration of the Zn-doped 92971 layer differs depending on the presence or absence of the layer to be grown afterwards or its composition, making it difficult to create a rib waveguide laser from an epitaxial wafer as shown in Figure 5(a). In this case, there was a problem that a sufficiently high carrier concentration could not be obtained.

The present invention has been made in consideration of the above circumstances, and its purpose is to be able to increase the carrier concentration of the 92971 layer in a rib waveguide type, and to suppress the deterioration of temperature characteristics due to the low carrier concentration. However, it is an object of the present invention to provide a method for manufacturing a semiconductor light emitting device that can contribute to improving device characteristics.

[Structure of the Invention (Means for Solving the Problems) The gist of the present invention is that when producing a semiconductor light emitting device using a double heterojunction structure made of InGaA I P,
After the growth of the double heterojunction structure, low GaA is added to the top layer.
The purpose is to increase the carrier concentration of the 92971 layer by forming the s layer.

That is, the present invention provides a method for manufacturing a rib waveguide type semiconductor light emitting device, in which 1 n+-Y (
After growing a double heterojunction structure consisting of Ga+-xAlx)yP and growing an n-type GaAs cap layer on this double heterojunction structure, this cap layer is removed, and then a double heterojunction is formed. A mesa stripe was formed on the structure, and then a 7m n-type GaAs flow blocking layer was grown on the sides of the mesa stripe, and then a p-type GaAs ohmic layer was grown on the double heterojunction structure and the current blocking layer. This is the method I used.

(Function) According to the present invention, after forming the double heterojunction structure, by growing an n-GaAs layer on the top layer, 9297
A heat treatment effect equivalent to that of the laser shown in FIG. 6 is applied to one layer. As a result, the activation rate of Zn incorporated into the 92971 layer is increased, and in the first crystal growth step for forming the double heterojunction structure, the n-Ga
A high carrier concentration equivalent to that of a laser produced by growing up to the As block layer can be obtained.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a sectional view showing the manufacturing process of a semiconductor laser according to an embodiment of the present invention. First, as shown in FIG. 1(a), an n-GaAs substrate (Si doped: 3 x 10I
8c10l811 Top 1: By M OCV D method,
Thickness 0.8 μm n I no, (Gao, i A 10.7) o
, s P cladding layer (Si-doped 5 x 1017c1
1-3) 12, undoped I with a thickness of 0.06 μm
nO, 5G aO, 5P active layer 13. p-1n0°s with a thickness of 0.8 μm (Ga 0.3 A I 0.7
) o, s P cladding layer (Zn doped: 5X
10"cm-3) 14, thickness 0.05.c
z m pI no, 5 Gao, sp contact layer (Zn doped: 7 x 1017 cab-') 15
and a 0.7 μm thick n-GaAs key layer (
Si-doped: 8 x 10110l8') 16 is continuously grown.

Next, as shown in FIG. 1(b), the n-GaAs cap layer 16 is removed using a (H2504+H202+H20) etching solution, and then a 5in2 film 17 is formed. Using this 5in2 film 17 as a mask,
), the contact layer 15 is (Br2+HBr+
H20) The p-cladding layer 14 is removed using an etching solution, and then the p-cladding layer 14 is etched to a desired depth using hot phosphoric acid to form a mesa stripe.

Next, as shown in FIG. 1(d), using the 5in2 film 17 as a mask, an n-GaAs block layer (Si doped: 8
X 1018 cm-3) 1 g was selectively grown to a thickness of 1.5 μm. Next, as shown in FIG. 1(c),
After removing O2l1i17, a p-GaAs ohmic layer (Zn doped, IX
1019cm-3) By growing 19 to a thickness of 3 μm, a rib waveguide semiconductor laser is completed.

Here, the conditions for the first crystal growth step to form the structure shown in FIG. 1(a) are the growth temperature T. -750℃, pressure P
-25Torr, current jlVs -11) /mln
.

The molar ratio (V/III) of group (Ⅰ) and group V elements (V/III) is set to -500, and the n-GaAs layer 18. The growth conditions for the second and third crystal growth steps for forming the p-GaAs ohmic layer 19 are: Ta = 650°C, P-50 Torr,
Vs=IN/win, V/m-250
shall be.

When the carrier concentration of the p-Clarad layer of the wafer prepared by the method of this example was measured by the CV method, it was found to be 5 x
1017c*-' was obtained, which was about twice as improved as the wafer produced by the conventional method (FIG. 5). The semiconductor laser made from this wafer has improved temperature characteristics, such as a reduction in thermal resistance and an increase in the maximum oscillation temperature from 50°C to 70°C, due to the increased carrier concentration in the p-cladding layer 14. It showed stable operation even at high temperatures. Note that if the cap layer 16 formed at the top layer of the double heterojunction structure is made of n-GaAs, the above-mentioned carrier concentration improvement effect can be obtained, but if it is made of p-GaAs, the carrier concentration cannot be improved. There wasn't.

Thus, according to this embodiment, in fabricating a rib waveguide semiconductor laser using a double heterojunction structure made of InGaAIP formed on a GaAs substrate 11, after forming the double heterojunction structure, n-GaAs is added to the uppermost layer. layer 16
By forming the p-1nGaAIP cladding layer 14, the carrier concentration of the p-1nGaAIP cladding layer 14 can be sufficiently increased, making it possible to improve the device characteristics of the semiconductor laser.

Next, another embodiment of the present invention will be described.

InGaAIP-based materials have the largest energy gap among the m-v group semiconductor compounds, excluding nitrides, with an energy gap of 0.5
It is attracting attention as a material for light-emitting devices in the ~0.6 μm band.

In a semiconductor light emitting device made of InGaAIP, the emission wavelength is determined by the bandgap energy of InGaAIP, which is the light emitting region. InGaA
It is known that, depending on the crystal growth method and growth conditions of IP, the atomic arrangement in the crystal differs and the band gap energy differs even though the mole fraction of the elements in the crystal, that is, the composition is the same. (e.g. J,Crysts
l Growth 93 (19H) 40B-411
), It has also been reported that the bandgap of p-type InGaP changes depending on the doping amount (
Jpn, J, Appl, Phys, 27 (198g)
L1549-L1552).

The present inventors have found through a series of experiments that the band gap changes significantly by doping Zn into a quaternary mixture of I nl-x-v GaXA Iy P. As shown in Figure 2, the point at which the bandgap changes occurs is when the hole concentration is around IX10I810l8 in the case of y-0;
, 2, the band gap changes at a lower value around 3×10 17 cl−′. Furthermore, I of y-0,2
In nl-x-y GaxA Iy P, it was discovered that the amount of change in the relative bandgap is more than twice as large in the case of y-0.

Generally, a double heterostructure is used to effectively confine carriers in semiconductor light emitting devices. In that case, in order to increase the band gap of the p-type semiconductor layer, it is necessary to increase the Al composition in InGaAIP.

However, when Zn is used as a p-type dopant, AI
The group composition is 0. - When the resistance exceeds 25, the Zn incorporation rate and the electrical activation rate of Zn in the crystal decrease rapidly, making it difficult to create a low-resistance p-type layer. In fact, a double-heterostructure LED was prototyped using p-type 1nGaAIP with a high Al composition, but the series resistance was very high and the element generated a lot of heat, resulting in poor life characteristics.

As described above, it has been difficult to achieve high luminous efficiency and obtain sufficient luminous intensity in a single heterostructure, homostructure, or double heterostructure semiconductor light emitting device having a luminescent layer made of InGaAIP. This embodiment improves this point and realizes a semiconductor light emitting device with high luminous efficiency.

FIG. 3 is a sectional view showing a schematic configuration of a light emitting diode (LED) in this example. 31 in the figure is p-GaAs
Substrate, 32 p-Xia no, 5 Gao, 3 A 10.2 P semiconductor layer, 33 pI no, s Gao, i A l
O, 2P light emitting layer, 34 is n I nQ, 5 A 1
o, s P semiconductor layer, 35 is n-side ohmic electrode, 36
is the p-side ohmic electrode. The p-type semiconductor layer 32 has a hole concentration of 5 x 10"cll-' and a thickness of 2.5.c.
zm, and the hole concentration of the p-type light emitting layer 33 is I X 1
The n-type semiconductor layer 34 has a donor concentration of I x 1018 cm-3 and a thickness of 3 μm.

FIG. 4 shows the relationship between the current and emission intensity of the LED shown in FIG. 3. As shown by the solid line in Fig. 4, the LED of this example
The luminescence intensity increased in proportion to the current, and we were able to obtain a luminescence intensity sufficient for practical use. The conventional example is shown by a broken line in FIG. 4, and when compared at a current value of 200 mA, the LED according to the present example can obtain a light emission intensity that is five times or more.

The reason why such high luminous efficiency can be achieved is as follows. FIG. 2 shows changes in the hole concentration of InGaA I P and the band gap energy determined from the P L 791 constant at room temperature. As the hole concentration increases, the bandgap energy changes toward higher energy. In other words, the hole concentration in the p-type semiconductor layer is 7X10I
7cts-3, the energy gap is 1.17eV, but the hole concentration in the p-type light emitting layer is I x 10I10l
Since the energy gap at 7' is 2.12 cV,
Although the two layers have the same composition, there is an energy gap difference of 50 eV. This energy gap difference makes it possible to effectively confine carriers within the light-emitting layer, making it possible to achieve high light-emitting efficiency as described above.

Furthermore, as can be seen from FIG. 2, the amount of change in the energy gap is larger in y-0,2 than in y-0. In other words, y
-In has a luminescent layer near o and z and emits green light.
This embodiment has great effects in the GaAIP semiconductor light emitting device. In n-type InGaA I P, the band gap energy did not change depending on the donor concentration. For n-type, the bandgap energy is y-
The band gap energy was 1.88 eV at 0 and 2.12 eV at y-0,2, which was the same as the band gap energy in the low doping region of p-type 1nGaAIP.

In other words, even if the light-emitting layer is n-type, p-type I nGaA
The same effect as described above can be obtained by increasing the doping amount of the IP semiconductor layer and increasing the energy gap. Also, in the above example, we talked about LED, but
As for the active layer and the p-type cladding layer, it is of course applicable to the semiconductor laser shown in FIG. 1 and other semiconductor lasers.

[Effects of the Invention] As detailed above, according to the present invention, when a semiconductor laser is manufactured using a double heterojunction structure made of InGaAIP, an n-GaAs layer is formed as the uppermost layer after the double heterojunction is grown. By forming p
It is possible to manufacture a semiconductor laser that can increase the carrier concentration of the cladding layer, suppress deterioration of temperature characteristics due to low carrier concentration, and contribute to improvement of device characteristics.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the manufacturing process of a semiconductor laser according to an embodiment of the present invention, and FIGS. 2 to 4 are for explaining other embodiments of the present invention, and FIG. Characteristic diagram showing the relationship between concentration and band gap energy,
Figure 3 is a cross-sectional view showing the LED structure, Figure 4 is a characteristic diagram showing the relationship between current and luminous intensity, and Figures 5 and 6 are process cross-sectional views to explain the problems of the conventional technology. . 11--n-G a As substrate 12-n-1
n G a A I P cladding layer 13---1 n
GaP active layer 14-p -InGaAIP cladding layer 1
5...p-1nGaP contact layer 16...n-G
aAs cap layer 17...5in2 film (mask) 18...n-GaAs block layer (current blocking layer) 19
... p-GaAs contact layer applicant agent Patent attorney Takehiko Suzue (a) (b) (C) No. (d) (e) (f) Hall J 戊 (cm-tsu- 3rd FIA current (mA) ) Figure (d) Figure 5 (a) (b) (C)

Claims (2)

[Claims] (1) In_1_-_Y(Ga_1_-_XAl_X)_YP on n-type GaAs substrate
growing a double heterojunction structure, growing an n-type GaAs cap layer on the double heterojunction structure, removing the cap layer, and then forming a mesa on the double heterojunction structure. A step of forming stripes, and n-type GaA on the sides of the mesa stripes.
A method for manufacturing a semiconductor light emitting device, comprising the steps of: growing an s-current blocking layer; and growing a p-type GaAs ohmic layer on the double heterojunction structure and the current blocking layer. (2) The Al composition of the p-type cladding layer of the double heterojunction structure is the same as or higher than that of the active layer, and the p-type impurity of the p-type cladding layer is n-type InGa having the same composition.
2. The method of manufacturing a semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is doped to a range where the energy gap is larger than that of AlP.