JPH04137771A - Semiconductor device - Google Patents

Abstract

PURPOSE:To increase a life, yield and light emitting efficiency of the device while reducing the cost by using an SiC semiconductor into which group IVb element except for carbon and silicon is added. CONSTITUTION:After the mirrorlike polishing is done to the surface of an n-type SiC crystal substrate 11, the surface of the substrate 11 is etched to be cleaned. Then, an n-type SiC layer 12 and p-type SiC layer 13 are developed in sequence by the LPE method in which silicon and carbon are used as solvents. At this time, a group IVb element such as germanium is added about 1% as a charge to the silicon. Into the n-type layer, Si3N4 is added as a conductivity type determining impurity and metal Al which leads light emission is mixed. Into the p-type layer, metal Al is mixed for determining a conductivity type. After the growth of these layers, an n-type electrode 16 is formed on the substrate side and a p-type electrode 15 is formed by evaporation on the surface of the p-type SiC layer 12. Then, the electrodes 16 and 15 are patterned. After that, the device is subjected to heat treatment for obtaining an ohmic characteristic. Finally, the device is separated into chips. Consequently, a stable light- emitting characteristic is obtained and a life is remarkably extended.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a semiconductor device, and in particular to a silicon carbide (SiC) semiconductor device.
) and semiconductor devices such as light-emitting elements and high-temperature MOSFETs.

(Prior Art) SiC is not only being researched as an environment-resistant element material because it is extremely stable, but also has a forbidden band width of 2.
Since it has a wide variety of crystal structures ranging from 39 to 3.33 eV and can be used to form pn junctions, it is attracting attention as a material for blue and violet light-emitting diodes.

SiC has α (hexagonal) type and β (cubic) type.
The α-type 6H (hexagonal) type crystal is the one that has the type crystal structure or can grow large crystals with good reproducibility, and is the most widely used crystal.

As shown in FIG. 5(a) or FIG. 5(b), the structure of a light-emitting diode using this α-type 6H-type crystal is, for example, a 1μ-thick film on an n-type 5H5fC substrate 1. n
A mold layer 2 and a p-type layer 3 with a thickness of 1 μm are sequentially laminated, and AI! is applied to the front and back surfaces of these layers, respectively. There is one in which an ohmic p-type electrode 4 made of -3i alloy and an ohmic n-type electrode 5 made of Ni are formed.

The difference between the light emitting diode shown in FIG. 5(a) and the light emitting diode shown in FIG. 5(b) is that in the structure of FIG. On the other hand, in the structure shown in FIG. 5(b), the side cross section of the pn junction is constituted by a clean surface 8 created by etching. 7
is the cut plane.

This n-type layer 2 contains nitrogen as a conductivity type determining impurity and also contains A as a luminescent center, and its carrier concentration is 1×
10I70IIl-3 to 5×10I70I11-3, and the p-type layer 3 has A, j! as a conductivity type determining impurity. The carrier concentration is I x 1018 cm-3 or more, and both are formed by liquid phase epitaxial growth or vapor phase epitaxial growth.

The biggest problem with light emitting diodes having this structure is their lifespan.

That is, it is difficult to create a perfect SiC single crystal structure, and it includes many stacking irregularities.

If there is such lamination irregularity, there is a problem that when a blue light emitting diode is formed, the crystal structure changes when electricity is applied, and as a result, the emission wavelength or emission intensity changes.

Further, when diodes are formed on a wafer and then cut into chips and separated, lattice defects are generated on the cut surfaces, which may cause the crystal structure to change during energization.

For this reason, a cleavage surface 7 or an etched surface 8 is used for the current-carrying portion, and a structure is adopted in which the surface is separated from the cut surface 6. Both methods lead to a decrease in yield, and This caused an increase in costs.

In addition, this hexagonal SiC crystal has a forbidden band width of 2°86e.
It has V and is being researched as a material for blue light emitting devices.

However, conventional SiC including this hexagonal system
were all indirect transitions. Therefore, in a light emitting device using such indirect transition type SiC, it is necessary to involve lattice vibration in the light emission process, and the quantum efficiency is very low (the light emission intensity with respect to the current flowing through the device is very weak).
There was a drawback.

(Problems to be Solved by the Invention) As described above, conventional blue light emitting diodes using SiC have problems such as a decrease in life, a decrease in yield, and an increase in cost due to lamination irregularities.

Further, since SiC is an indirect transition type, there are problems in that the quantum efficiency is low and the emission intensity is extremely low.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a SiC light emitting diode with a long life, high yield, and low cost.

Another object of the present invention is to provide a SiC light emitting diode with high luminous efficiency.

[Structure of the invention]

(Means for Solving the Problems) Accordingly, in the first aspect of the present invention, a SiC semiconductor to which a group IVb element other than carbon or silicon is added is used.

In the second aspect of the present invention, a SiC semiconductor containing at least 1X10+9 germanium per square centimeter is used.

(Function) In the first configuration, the group IVb element, which is electrically and optically neutral to the SiC semiconductor, is added, so that it does not affect the carrier concentration.

Since the atomic radius is larger than that of the constituent atoms Si and C, crystal defects can be prevented from growing and a pn junction with good consistency can be formed.

Further, in the second configuration, SiC, which is an indirect transition type, can be changed to a direct transition type by adding germanium (Ge).

In other words, when no impurities are added to SiC, the top of the valence band is at the center point (L point) in momentum space, whereas the bottom of the conduction band is in the <1120> direction (M
point), and is of the so-called indirect transition type. On the other hand, in Ge, the top of the valence band is at the L point, which is the same as SiC, but the bottom of the conduction band is in the <111> direction from the L point (L point).
It is an indirect transition type semiconductor. As a result of repeated experiments, we found that 1×1019 pieces of these two SiC and Ge
It was found that when m-3 or more were mixed, the transition to a direct transition type occurred.

1 x 1019 Ge on SiC effl-'
By mixing the above, a transition is made to a direct transition type, and luminous efficiency is greatly improved.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Example 1 FIGS. 1(a) to 1(e) are diagrams showing the manufacturing process of a light emitting diode according to an example of the present invention.

First, as shown in FIG. 1(a), an n-type SiC crystal (0-face (00
Surface 01) Using a substrate 11, the surface is mirror polished with diamond powder and then etched with chlorine gas to clean the surface.

Then, as shown in FIG. 1(b), liquid phase epitaxial growth (L P
E) n-type SiC layer] 2 and p-type SiC layer 13 by method
grow sequentially. At this time, about 1% of germanium is added to the silicon. In the n layer, Si3N4 is added as a dopant of nitrogen as a conductivity type determining impurity, and AJ! Metallic Al, which is the raw material for this, is mixed. On the other hand, when growing the p-layer, the conductivity type is determined, so the metal Aj! Mix in.

After growing in this way, as shown in FIG. 1(C), an n-type electrode 14 made of Ni is formed on the substrate side,
A p-type electrode 15 made of AJ-Si alloy is deposited on the surface of the p-type SiC layer 12, and after patterning,
Heat treatment is performed at ℃ to obtain ohmic properties.

Finally, as shown in FIG. 1(d), it is separated into chips using a diamond blade.

FIG. 1(e) is an enlarged view of one of them.

The results of measuring the temporal change in peak wavelength during energization of the light emitting diode thus formed are shown by white circles in FIG. The black circles indicate the results of measuring temporal changes in the pic wavelength when the conventional light emitting diode shown in FIG. 5 is energized.

As is clear from these comparisons, in the conventional light emitting diode, the emission wavelength changes with time, and blue emission becomes green emission. In contrast, the light emitting diode of the present invention exhibits stable light emitting characteristics with little change in emission wavelength and has a significantly extended lifespan as a light emitting diode.

In addition, in the above embodiment, n, Pb, etc. can be used in addition to Ge as the rVb group semiconductor to be added.

In particular, by adding Sn, the life span could be made the longest.

Furthermore, the method for growing the n-layer and p-layer is not limited to the LPE method, and other methods such as vapor phase epitaxy (VPE) can also be applied. In addition, by using the VPE method, LP
Sn and Pb, which are difficult to add using the E method, can also be added at high concentrations, making it possible to extend the service life.

Furthermore, by doing so, it is possible to improve the consistency of the interface, so that mesa etching and cleavage are not necessary, and production costs can be reduced.

Embodiment 2 FIG. 3 is a diagram showing a light emitting diode according to a second embodiment of the present invention.

This light emitting diode uses a 5i substrate containing I x 10 "c++1-' nitrogen, which also serves as a carrier injection layer.
Using C21, n-type S was sequentially laminated on this surface.
An iC layer 22 and a p-type SiC layer 23 are grown in sequence.

At this time, as the n-type SiC layer 22, nitrogen as a conductivity type determining impurity is added to I x 10 in a mixed crystal semiconductor of SiC and Ge containing 1 x 10210200 I of germanium.
Contains “c++-” and further includes AJ! 1×10160II
-3 added is used. On the other hand, p-type SiC layer 23
is for determining the conductivity type, AJ! 1×1017cII+-
'Added ingredients are used.

Furthermore, an n-type electrode 24 made of Ni is formed on the substrate 21 side, and AJ! on the surface of the p-type SiC layer 23. A p-type electrode 25 made of -Si alloy is formed.

The light emitting device thus formed was able to obtain a light emission intensity of 100 mcd with respect to a forward current of 20 mA.

On the other hand, the n-type Si0 layer 22 which is the light emitting layer is made of conventional Ge-free SiC, that is, 1 x 10180 [3 nitrogen and I x 1016 cm-' of Ai? A light emitting device using SiC doped with only 20111AO could only obtain a luminescence intensity of 20 wcd with respect to the forward current of 20111AO. These comparisons also show that the luminous efficiency is significantly improved by adding Ge to the luminescent layer as in the present invention.

Next, in order to investigate the relationship between Ge content and luminous efficiency, the luminous intensity was measured while changing the Ge content. The results are shown in FIG. From this figure, it can be seen that the emission intensity tends to increase as the Ge content increases, but in Example 2
It has been found that the highest emission intensity can be obtained using a mixed crystal semiconductor of SiC and Ge containing germanium I x 1020 Cm-' shown in .

Note that the present invention can be implemented with various modifications without departing from the spirit thereof.

For example, as a method for adding Ge to SiC, in the LPE method, Ge powder may be added to St in a graphite melt, and in the CVD method, a gas containing carbon and a material containing silicon may be added. Ge
A method such as supplying a gas containing a substance simultaneously or sequentially may be used.

〔effect〕

As described above, according to the present invention, since the IVb group element is added to the SiC semiconductor, it is possible to provide a SiC light emitting diode with a long life, high yield, and low cost.

Further, according to the present invention, since a SiC semiconductor containing 1×1Q19 or more of germanium per square centimeter is used, direct transition type light emission can be obtained, and a light emitting element with high luminous efficiency can be obtained. be able to.

[Brief explanation of the drawing]

FIG. 1(a) to FIG. 1(e) are diagrams showing the manufacturing process of the light emitting diode of the first embodiment of the present invention, and FIG. 2 shows the emission wavelength of the light emitting diode of the embodiment of the present invention and the conventional example. FIG. 3 is a diagram showing the light emitting device of the second embodiment of the present invention, FIG. 4 is a diagram showing the relationship between Ge content and luminous efficiency, and FIG. 5(a) and FIG. 5(b) is a diagram showing a conventional example of a light emitting diode. 1... N-type 6H3i C substrate, 2... N-type layer, 3
...p-type layer, 4...p-type electrode, 5...n-type electrode,
6... Cut plane, 7... Cleavage plane, 8... Etched plane, 11... SiC crystal (0 plane (0001) plane) substrate, 12-n-type SiC layer, 13-p-type SiC layer , 14-
n-type electrode, 15...p-type electrode, 21...n-type SiC
Substrate, 22...n-type SiC layer, 23.n-type SiC layer, 24-.n-type electrode, 25...p-type electrode. (G) (b) (d) Fig. 1 Current conduction time (h) Fig. 2 SiC middle f) Ge@abundance (cm-3) 4th rf! J

Claims (2)

[Claims] (1) As a SiC semiconductor, materials other than carbon or silicon
1. A semiconductor device characterized by using a group IVb element added to such an extent that the forbidden band width does not change. (2) Germanium 1x per square centimeter
A semiconductor device comprising: a light emitting layer made of a SiC semiconductor containing 10^1^9 or more; and a carrier injection layer in contact with the light emitting layer.