JPS6244716B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor light emitting device capable of achieving high luminous efficiency and a method for manufacturing the same.
In particular, the present invention relates to a light emitting semiconductor device in which two parts of the light emitting semiconductor device are provided with measures to improve luminous efficiency, and a method for manufacturing the same.

Gallium arsenide infrared light-emitting diodes (hereinafter referred to as Si-doped GaAsLEDs) doped with silicon, which is an amphoteric impurity, emit light in the p-type region.
Since the emission center is at a deep acceptor level, the peak emission wavelength λ _p is 9300 to 9500 Å. Therefore, there is little reabsorption of light inside the crystal, resulting in higher luminous efficiency than other light emitting diodes, and is widely used in fields such as opto-isolators and optical sensors.

Such Si-doped GaAs LEDs are manufactured by making full use of the well-known liquid phase epitaxial method, but as mentioned above, since the dopant is Si, which is an amphoteric impurity to GaAs, it cannot be used in the liquid phase epitaxial process. Only one solution bath is required, and epitaxial layers of different conductivity types can be successively grown to form a pn junction. In other words, Si, which is an amphoteric impurity, has a higher concentration of gallium than arsenic A at high temperatures.
Since Ga is easily substituted, the resulting epitaxial layer becomes n-type, while at low temperatures, the resulting epitaxial layer becomes p-type because it enters many As positions. It is known that the temperature T _op at which the conductivity type of the epitaxial layer is reversed from n-type to p-type is strongly dependent on epitaxial growth conditions such as Si concentration and cooling rate.

By the way, in the p-type epitaxial layer formed by this method, there are not only Si substituted with As, ie, acceptors, but also Si substituted with Ga, ie, donors. Therefore, a portion of the Si acceptor substituted with As is electrically compensated with the Si donor substituted with Ga. When the numbers N _D and N _A of donors and acceptors both increase and the concentration becomes high enough to exceed 5 × 10 ¹⁸ cm ^-3 , these levels are connected to the bottoms of the conduction band and the filling band, as shown in Figure 1. As shown in , deformed parts 1 and 2 called band tailing occur in the energy band. Further, a compensation phenomenon opposite to the above occurs also in the n-type epitaxial layer, and band tailing similarly occurs.

In addition, in a normal Si-doped GaAs LED, the above-mentioned donor number N _D and acceptor number N _A are 1×10 ¹⁹ cm ^-3
As a result, band tailing occurs in both the n-type epitaxial layer and the p-type epitaxial layer, and since the Si acceptor level is as deep as approximately 0.2 eV, a filled band occurs as shown in Figure 1. Tailing 2 of the energy band becomes stronger.

Si-doped GaAsLED is different from other light emitting diodes
As already mentioned, it has a higher luminous efficiency than LEDs, but in order to obtain such a high luminous efficiency and further increase the luminous efficiency, it is necessary to increase the acceptor level, which is the center of luminescence. For this purpose, it is essential to increase the Si concentration. However, when the Si concentration is increased, the degree of band tailing becomes stronger in both the n-type epitaxial layer and the p-type epitaxial layer, the absorption coefficient for the emission wavelength increases, and the reabsorption of light becomes impossible to ignore. For this reason,
On the contrary, a disadvantage arises in that the luminous efficiency decreases.

The present applicant has proposed a light-emitting semiconductor device and a method for manufacturing the same that can eliminate the above-mentioned disadvantages and obtain high luminous efficiency. A light-emitting semiconductor device and its light-emitting semiconductor device which reduces reabsorption of light in the n-type epitaxial layer and improves luminous efficiency by forming an n-type epitaxial layer containing elements and having no electrical compensation. Manufacturing method and p of a light emitting semiconductor device having such a structure
The part of the p-type epitaxial layer located near the p-n junction is doped with group elements at a higher concentration than other parts, and the degree of band tailing is stronger than that of other parts, and the peak emission wavelength is This is a light-emitting semiconductor in which the absorption effect is further reduced by moving the light to a longer wavelength side than the former, and the electrons and holes are confined within this layer to increase the luminous recombination efficiency, thereby improving the luminous efficiency. We have already proposed a device and its manufacturing method.

The present invention provides a light-emitting semiconductor device and a method for manufacturing the same, which has an extremely high luminous efficiency that greatly exceeds the high luminous efficiency obtained by these light-emitting semiconductor devices. The present invention is characterized by a structure that effectively combines the structures of the above two types of light emitting semiconductor devices, and a manufacturing method for realizing this structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below along with embodiments with reference to the drawings.

FIG. 2 shows a Si-doped structure according to an embodiment of the present invention.
This is a diagram showing the energy band structure of GaAsLED, showing an n-type LED with no band tailing.
It has a structure in which an n-type GaAs epitaxial layer 4 doped with a group element such as tellurium Te is formed on a GaAs substrate 3, and a p-type GaAs epitaxial layer 5 doped with Si is further formed thereon. The p-type GaAs epitaxial layer portion 7 near the junction 6 is doped with Si at a high concentration, thereby making the layer stronger in band tailing than other portions. Although band tailing also occurs in the remaining portion of the p-type GaAs epitaxial layer 5, the degree of band tailing is weaker than that in the p-type GaAs epitaxial layer portion 7.

When a forward current is applied to the Si-doped GaAs LED having such a structure, the p-type GaAs epitaxial layer 5
The electrons e injected into the conduction band are accumulated in the tailing 8 of the p-type GaAs epitaxial layer portion 7.
Further, the holes h enter the tailing 9 of the filled zone and recombine with the electrons e accumulated in the tailing 8. The emission wavelength of light generated by this recombination corresponds to the energy E _p between tailings.

By the way, in the Si-doped GaAs LED of the present invention having the energy band structure shown in the figure, the band tailing of the p-type epitaxial layer 5 other than the p-type GaAs epitaxial layer portion 7 is small, and the energy E between the conduction band and the filling rate is small. _p becomes larger than E _p . On the other hand, in the n epitaxial layer 4, the impurity level formed by Te is shallow and the concentration is about 7 to 9 x 10 ¹⁷ cm ^-3 , so band tailing does not occur, and the interband energy E _N is lower than E _P growing. For this reason, the emitted light is effectively extracted to the outside without being absorbed inside the crystal, and a decrease in luminous efficiency is effectively prevented. In addition, p-type
When the Si concentration in the GaAs epitaxial layer portion 7 is further increased to strengthen the degree of band tailing, the energy E _p between the tails becomes smaller and the peak emission wavelength shifts to the longer wavelength side, so the absorption effect becomes even smaller. Become. Further, according to the structure of the present invention, since electrons and holes are confined in the p-type GaAs epitaxial layer portion 7, the probability of radiative recombination is increased, and a high luminous efficiency is achieved.

Here, when comparing the structure of the light emitting semiconductor device of the present invention and the latter of the light emitting semiconductor devices already proposed by the present applicant, it is found that in the present invention, there is no band tailing in the n-type GaAs epitaxial layer 4; As a result, the energy band E _N of the n-type GaAs epitaxial layer increases, the reabsorption of light in this region further decreases, and as mentioned above, the confinement of electrons and holes also becomes stronger, so the luminous efficiency decreases. It will further increase. Also, compared to the former light emitting semiconductor device,
In the structure of the present invention, the degree of band tailing in the light emitting region is made stronger than the degree of band tailing in other p regions, so that reabsorption of light in the p-type GaAs epitaxial layer 5 is reduced, and the above-mentioned Since a confinement effect is also added, the luminous efficiency is further increased.
When comparing the luminous efficiency of two types of light emitting semiconductor devices already proposed by the present applicant and the light emitting semiconductor device of the present invention, it was found that the light emitting semiconductor device of the present invention is superior to the two types of light emitting semiconductor devices already proposed. , an additional 50% improvement was confirmed.

Figure 3 shows the Si doping of the present invention explained above.
It is a diagram showing the configuration of a liquid phase epitaxial growth apparatus for forming a GaAs epitaxial layer on a GaAs substrate, which is essential for GaAs LEDs, in which reference numeral 10 denotes a substrate support, and 11 is housed in the substrate support part of the substrate support. a Te doped n-type GaAs substrate 12, a melt storage device having melt tanks 13 and 14 and capable of sliding on the substrate support 10, and 15,
16 is a melt.

For example, the epitaxial layer is formed by moving the melt storage device 12 in the direction of arrow X and bringing the melts 15 and 16 into contact with the GaAs substrate 11.

Using such a liquid phase epitaxial growth apparatus, Si-doped films having the energy band structure shown in FIG.
A method for forming a GaAs LED will be specifically described below with reference to examples.

Te to the substrate support part of the substrate support 10 is 6×10 ¹⁷
An n-type GaAs substrate doped at a concentration of cm ^-3 is placed, and a melt 15 is made of metallic gallium Ga, Te and non-doped GaAs polycrystal.
Metallic gallium Ga, Si and non-doped
A melt 16 is formed of GaAs polycrystal. Note that the concentrations of Te and Si charged into the melt are 0.001 to 0.01 and 1 to 2 mol percent relative to Ga, respectively. After sufficiently heating these at a predetermined temperature, for example, 900 to 950°C, so that the melt composition becomes uniform, the melt storage device 12 is slid in the direction of arrow X and stored in the melt tank 13. The molten liquid 15 is brought into contact with the n-type GaAs substrate 11. Next, after maintaining the temperature of the melt 15 at the above temperature for the time necessary to make the contact state uniform, slow cooling is performed by setting the cooling rate C _N to 1 to 2° C./min. Form a GaAs epitaxial layer.

Note that Si doped in the melt 16 is an amphoteric impurity, and the conductivity type of the epitaxial layer to be formed is reversed from n-type to p-type at a predetermined temperature. This temperature is usually called the inversion temperature Tnp. By the way, if the above-mentioned reversal temperature Tnp is, for example, 895°C, then when the temperature of the furnace becomes 895°C or lower and the growth of the p-type GaAs epitaxial layer clearly starts, the melt storage device is further moved in the direction of the arrow X. The melt 16 stored in the melt tank 14 is brought into contact with the substrate 11. Then, set the cooling rate C _p1 to 1°C/min or more to
Start growing the GaAs epitaxial layer.

The amount of Si incorporated into the GaAs epitaxial layer tends to increase as the cooling rate increases.
If C _p1 is set large as described above, the p-type GaAs epitaxial layer formed from this point on will be
Si concentration increases. Therefore, this p-type GaAs
As the number of donors N _D and the number of acceptors N _A of the epitaxial layer increase, the degree of band tailing becomes stronger. p-type GaAs formed under these conditions
The epitaxial layer corresponds to the p-type GaAs epitaxial layer portion 7 in FIG. In this way p
When the growth of the GaAs epitaxial layer progresses and the temperature of the melt 16 reaches a predetermined temperature, for example 850°C, the cooling rate C _p2 is set to 1°C/min or less, which is smaller than the above cooling rate C _p1 . , still p-type
Grow a GaAs epitaxial layer. Under this cooling rate, the p-type GaAs epitaxial layer
The amount of Si incorporated becomes smaller, the number of donors N _D and the number of acceptors N _A of the p-type GaAs epitaxial layer are lower than those under the above conditions, and the p-type GaAs epitaxial layer has a weak degree of band tailing, i.e. , a p-type GaAs epitaxial layer is formed except for the p-type GaAs epitaxial layer portion 7 of FIG. Then, when the temperature of the furnace has decreased to 800 to 700 DEG C., the contact between the n-type GaAs substrate 11 and the melt 16 is cut off, thereby completing the epitaxial growth process.

Under the above growth conditions, n-type GaAs with an n-type carrier concentration of 1.0×10 ¹⁸ cm ^-3 and a thickness of approximately 50 μm was grown.
The average of the epitaxial layer and p-type carrier concentration is
p-type GaAs with a thickness of 0.4 to 0.7×10 ¹⁸ cm ^-3 and a thickness of about 90 μm
The average donor of the p-type epitaxial layer of the Si-doped GaAs LED of the present invention, which forms an epitaxial layer and corresponds to the p-type GaAs epitaxial layer 7 extending from the p-n junction interface to a thickness of 1 to 20 μm. Concentration N _D and average acceptor concentration N _A
is N _D 6 in the p-type GaAs epitaxial layer portion 7.
×10 ¹⁸ cm ^-3 , N _A 6.7×10 ¹⁸ cm ^-3 , and the residual p
N _D 1.0×10 ¹⁸ in GaAs epitaxial layer part
cm ^-3 , N _A is 1.7×10 ¹⁸ cm ^-3 , and the tailing of the p-type GaAs epitaxial layer portion 7 is extremely strong.
The luminous efficiency of the Si-doped GaAs LED of the present invention is higher than that of the conventional Si-doped GaAs LED formed using Si as an amphoteric impurity.
This is a dramatic improvement of approximately 2.3 times compared to Si-doped GaAs LEDs.

FIG. 4 is a block diagram of a liquid phase epitaxial growth apparatus according to another embodiment of the present invention. 17 is a Te-doped GaAs substrate, 18 is a melt tank 19, 20, 21
, a melt storage device that can slide on the substrate support 22, and 23, 24, and 25 are melts.

The compositions of the GaAs substrate 17 and the melt 23 are as described above.
This is the same as the GaAs substrate 11 and the melt 15.
The melt 24 is formed of metallic Ga, non-doped GaAs polycrystal, and Si, and the concentration of Si is 0.2 to 1 mole percent relative to Ga. On the other hand, the melt 25 is also formed of metal Ga, Si, and non-doped GaAs polycrystal, but the concentration of Si is selected to be 2 to 3 mol percent, which is higher than that of the melt 24.

Growth is carried out using these melts as follows. The melt 23 is brought into contact with the GaAs substrate 17 to form an n-type GaAs epitaxial layer in the same manner as in the n-type epitaxial growth described above. Next, when the temperature of the molten liquid 25 reaches 890°C, which is below the reversal temperature Tnp, the molten liquid 25 is brought into contact with the GaAs substrate 17, and the cooling rate is set to 0.3 to 1°C/min.
GaAs epitaxial growth begins. When the furnace temperature reaches 850°C, the molten liquid 25 is removed from the GaAs substrate 17, and then the molten liquid 24 is brought into contact with the p-type GaAs substrate at the same cooling rate as above.
Grow the epitaxial layer.

Then, when the temperature of the furnace has decreased to 800 to 700° C., the contact between the GaAs substrate 17 and the melt 24 is cut off, thereby completing the epitaxial growth process. As already explained, the Si concentration in the melt 25 is higher than that in the melt 24, so
Si in the p-type GaAs epitaxial layer formed by
The concentration is higher than the Si concentration in the p-type GaAs epitaxial layer formed from the melt 24. That is,
The p-type GaAs epitaxial layer portion 7 shown in FIG. 2 is formed by an epitaxial growth process using the melt 25. The LED thus obtained has the same performance as the first embodiment described above.

As is clear from the above description, according to the present invention, a light emitting semiconductor device with much higher luminous efficiency than conventional devices can be realized.

In the above embodiments, GaAs is used as the - group compound semiconductor, but the invention is not limited to this example. Other - group compound semiconductors may also be used, and Te may be used as the group element.
A similar effect can be obtained by using selenium Se or sulfur S instead.

[Brief explanation of the drawing]

Fig. 1 is a band model diagram of an electrically compensated epitaxial layer, and Fig. 2 is a band model diagram of an electrically compensated epitaxial layer.
Diagram showing the energy band structure of GaAsLED, Part 3
4 and 4 are diagrams showing the structure of a liquid phase epitaxial growth apparatus used to manufacture a Si-doped GaAs LED having the energy band structure shown in FIG. 2. 1, 2, 8, 9... deformed part of energy band,
3, 11, 17... n-type GaAs substrate, 4... n-type
GaAs epitaxial layer, 5, 7... p-type GaAs epitaxial layer, 6... pn junction interface, 10, 2
2... Substrate support body, 12, 18... Melt liquid storage device, 13, 14, 19, 20, 21... Melt liquid tank, 15, 16, 23, 25, 24... Melt liquid.

Claims (1)

[Claims] 1. A p-type epitaxial layer containing at least Si and an n-type epitaxial layer containing at least Si are laminated on a - group compound semiconductor substrate, and a p-n junction is formed between both epitaxial layers. At the same time, the Si is doped at a high concentration near the p-n junction in the p-type epitaxial layer, and the degree of deformation of the energy band due to the connection between the impurity level due to the Si and the bottom of the conduction band and the fill band is
A light emitting semiconductor device, wherein the p-type epitaxial layer portion is stronger than other p-type epitaxial layer portions. 2. An n-type - group compound semiconductor substrate is arranged at the bottom of a two-tank type melt storage device that stores a first melt doped with Si and a second melt solution doped with Si, and The first melt and the second melt are brought into contact with the group compound semiconductor substrate in this order, and the first melt forms an n-type epitaxial layer and the second melt forms a p-type epitaxial layer. layer on the - group compound semiconductor substrate, increasing the cooling rate of the melt when forming the p-type epitaxial layer near the p-n junction, and increasing the Si concentration in the p-type epitaxial layer. A method for manufacturing a light emitting semiconductor device, characterized in that: 3 A first melt doped with Si, a second melt doped with Si, and a third melt doped with Si and whose doping amount is selected to be lower than that of the second melt. A - group compound semiconductor substrate is placed at the bottom of a melt storage device that stores the melt.
The first melt, the second melt on the same substrate,
The third melt is brought into contact with the n-type epitaxial layer in this order, and the n-type epitaxial layer is formed with the first melt, and the n-type epitaxial layer is
A p-type epitaxial layer having a predetermined group element concentration is formed using the third melt, and a p-type epitaxial layer having a lower Si concentration than the p-type epitaxial layer is formed using the third melt. A method for manufacturing a semiconductor device.