JPS6262076B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a gallium chloride (GaP) compound semiconductor electrode for a light emitting device.

Generally, compound semiconductor light emitting devices include GaP,
A crystal such as GaAs or GaAs is used. These elements are, for example, as shown in Figure 1.
When a GaP crystal is used, an n-type GaP layer 11 is formed on the n-type GaP crystal substrate 11 by liquid phase epitaxial growth.
A and P-type GaP layers 12 are sequentially formed to form a p-n junction 13 to obtain an element body. A film 14 of a valent metal such as beryllium (Be) or zinc (Zn) is coated as an electrode on the P-type layer of this main body, and a film 14 of a valent metal such as beryllium (Be) or zinc (Zn) is coated as an electrode on the n-type GaP crystal substrate 11 as an electrode such as Au-Si or Au.
-Ge alloy films 15 are formed respectively. After this, heat treatment is performed to diffuse the constituent elements of the electrode into the GaP crystal and establish ohmic contact.

Furthermore, a normal Au layer 14 is formed on each of the above electrode films.
a, 15a, and Au layer 1 on the P-type layer side.
A lead wire 14b is bonded to 4a.

Incidentally, the valent metal used as the electrode of the P-type layer 12, especially Zn, easily evaporates due to its high vapor pressure, but the amount deposited on the GaP crystal plane is small compared to the amount used as an evaporation source, so heat treatment is performed after evaporation. Also GaP
There was a problem that a sufficient amount of Zn was not diffused into the crystal, making it impossible to establish ohmic contact. Furthermore, since Zn has poor adhesion to the GaP crystal, peeling occurs at the interface with the GaP crystal, making subsequent processing steps extremely difficult.

For the reasons explained above, it has been extremely difficult to obtain reliable and stable ohmic contact using Zn or Zn alloy as the electrode of the P-type layer of a GaP light emitting device.

The present invention has been made in view of the above-mentioned points.
A method for forming an electrode for a compound semiconductor light-emitting device, which allows reliable ohmic contact with a P-type layer of a compound semiconductor crystal, has excellent bonding properties, and can be formed to form a strong connection. It provides:

That is, in the present invention, as an electrode for a P-type layer forming a p-n junction, for example, as shown in FIG. 2, a thin gold layer 24 is first formed on a P-type layer 12 of a compound semiconductor crystal, and then this gold Film thickness 2.5μ on thin layer 24
A gold-zinc alloy layer 24a containing 20 to 260 μg/cm ² of zinc per m is deposited, and the layers are heated together in an argon (Ar) or nitrogen (N ₂ ) atmosphere at 460°C to 550°C.
This is a method for forming a compound semiconductor light emitting device which is heat-treated in the temperature range of 0.degree. C. and has stable ohmic contact and excellent bonding properties.

Embodiments of the present invention will be described below with reference to the drawings. In this example, the compound semiconductor light emitting device is
When GaP crystal is used, an n-type GaP layer 11a and a p-type GaP layer 1 are grown on an n-type GaP crystal substrate 11 by liquid phase epitaxy as shown in FIG.
2 are sequentially formed to form a pn junction 13 to obtain an element body. Therefore, on the element body obtained as described above, a thin gold layer 2 is placed on the P-type layer 12 side.
4 is deposited to a thickness of about 600 Å, and on top of this, an Au-Zn alloy layer 2 is deposited.
4a is deposited to a thickness of about 2.5 μm so that Zn is contained in the Au-Zn forming layer at a concentration of about 130 μg/cm ² .
Note that as in the past, Au is placed on the n-type GaP crystal plate 11 side.
-Si alloy layer 15 and Au layer 15a are formed. Thereafter, heat treatment is performed for 5 to 20 minutes in an inert atmosphere such as Ar at about 500 DEG C. to alloy the above-mentioned respective alloy layers and obtain an ohmic contact.

The electrodes 24, 24a on the P-type layer side of the GaP light emitting device thus obtained have good ohmic contact with a contact resistance Rs of 30Ω or less, and the bonding properties of the lead wire 14b are also stable. It was hot. Of course, good ohmic contact was also made with the electrode on the n-type substrate side.

By the way, the thin gold layer 24 used in the above embodiment is effective even if it is very thin.
Even if it is attached to a thickness of about 100 Å, the effect can be fully demonstrated. In other words, when a thin layer of gold adheres to the P-type GaP surface, the gold and GaP immediately react, causing some
Au-Ga alloy is formed. For this reason, vacancies are generated at Ga lattice points in the GaP crystal lattice. After this, Au
- When Zn is layered and further heat treated, Zn and Au diffuse into GaP, but at this time, the presence of vacancies facilitates the diffusion. Furthermore, Zn in the pores
By locating , ohmic properties can be obtained. On the other hand, Zn is very easy to alloy with Au and reacts even at room temperature in a thin film. Therefore GaP
By attaching Au to the surface first, the Zn that comes from the evaporation source forms an alloy as soon as it reaches the Au surface. At this time, some Ga also contributes to alloying.
A ternary alloy of Au-Zn-Ga is produced. Therefore, no peeling occurs.

Moreover, the gold-zinc alloy layer 24a used in the above example
Although the film contained 130 μg/cm ² of Zn, it may contain 20 to 260 μg/cm ² of Zn. That is, as shown by the dashed line in Fig. 3, the Zn concentration in the film is
If the range is 20 to 260μg/cm2, the heat treatment temperature should be set to 460μg/ ^cm2 .
A stable ohmic contact can be obtained by selecting a temperature within the range of ~550°C. Furthermore, as shown by the dashed line in Fig. 3, if the Zn concentration is less than 20 μg/cm ² , it is difficult to obtain ohmic contact even if the heat treatment temperature is changed, and if the Zn concentration is 260 μg/cm ² or more, ohmic contact cannot be obtained. As shown by the dotted line in FIG. 3, even if the heat treatment temperature is lowered, the bonding properties deteriorate. Note that when the thickness of the Au-Zn alloy layer is constant, ohmic contact tends to be obtained when the heat treatment temperature is increased, and conversely, when the heat treatment temperature is increased, bonding properties tend to decrease.

As explained above, the Zn amount treatment temperature was selected so that the film was within the range between the dashed line and the dotted line, which intersect the region that satisfies both ohmic properties and bonding properties as shown in Figure 3 when the film is 2.5 μm thick. do. That is, ohmic properties and bonding properties can be obtained by combining a Zn content in the range of 20 to 260 μg/cm ² and a heat treatment temperature of 460 to 550°C. Particularly good ohmic contact and bonding properties are exhibited within the shaded area surrounded by solid lines in FIG.

Regarding bonding properties, during heat treatment,
A ternary alloy of Au-Zn-Ga progresses in the Au layer, preventing Ga from depositing on the electrode surface during heat treatment, and at the same time, a portion of Zn is also trapped by Ga.

Therefore, when an Au lead wire is bonded, the bonding performance and bonding strength are significantly improved compared to the case where there is no Au layer, and almost the same level of bonding performance and bonding strength as those bonded to a metal Au layer can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the structure for explaining a conventional method of forming an electrode for a GaP light-emitting device, and FIG. 2 is a cross-sectional view of the structure for explaining a method of forming an electrode for a GaP light-emitting device according to an embodiment of the present invention. 3 are curve diagrams illustrating ohmic properties and bonding properties, which are the effects of the present invention. In Fig. 2, 11 is an n-type GaP crystal substrate;
1a is an n-type GaP layer, 12 is a p-type GaP layer, and 13 is a p-type GaP layer.
-n junction, 24 is a gold thin layer, 24a is an Au-Zn alloy layer, 14b is a lead wire, 15 is an Au-Si alloy layer,
15a is an Au layer.

Claims (1)

[Claims] 1 A step of forming a P-type GaP layer on the n-type GaP layer to form a light emitting device body, a step of forming a thin gold layer on the P-type GaP layer, and a step of forming a thin gold layer on the thin gold layer formed by the step. Add 20 to 260 zinc per film thickness of 2.5μm.
The method is characterized by comprising a step of forming a gold-zinc alloy containing μg/cm ² and then performing heat treatment in an argon or nitrogen atmosphere in a temperature range of 460 to 550°C to make ohmic contact and bond lead wires to the formed layer. A method for forming an electrode for a GaP light emitting device.