JPH10261815A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a semiconductor device into a structure, wherein a P side metallic electrode does not come into contact directly with a through lattice defect, and to prevent a metallic element from being diffused fast by a method wherein a P-type IV compound semiconductor region is formed on a crystal region consisting of a nitride semiconductor material and moreover, the metallic electrode is formed on this IV compound semiconductor region. SOLUTION: A P-type IV compound semiconductor region is formed on a crystal region consisting of a nitride semiconductor material and moreover, a metallic electrode is formed on this IV compound semiconductor region. That is, an N-type GaN layer 30, an undoped GaInN buffer layer 29, an undoped GaInN luminous layer 28, an undoped GaInN buffer layer 27, a P-type AlGaN layer 26 and a P-type GaN layer 25 are grown on a substrate crystal 31. Subsequently, a P-type polysilicon layer 24 is adhered to the layer 25 and a P-type polysilicon layer 23 is grown on the layer 24. The obtained wafer is subjected to dry etching from a P side and is subjected to mesa etching until the N-type nitride layer appears, a metallic electrode 22 is formed on the surface of a P-type mesa and a metallic electrode 21 is formed on the N-type nitride layer exposed by the etching.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a semiconductor device comprising a group III-V compound semiconductor composed of a group III element such as Al, Ga and In and a group V element such as N, P and As. The present invention relates to an electrode suitable for a semiconductor device formed of a semiconductor material containing at least N (nitrogen) as an element, that is, a so-called nitride semiconductor material. The semiconductor device of the present invention is, for example, AlN, Ga
The present invention is implemented as an electronic device or an optical device using an N or InN crystal as a basic constituent material.

[0002]

2. Description of the Related Art As devices using nitride semiconductors, semiconductor lasers, field effect transistors, photodetectors, etc., including visible light emitting diodes, have been developed one after another.
In order for these devices to exhibit the expected performance, ohmic electrodes having low resistance and high reliability must be developed.

[0003] Ohmic electrodes in nitride semiconductors are:
Almost satisfactory results have been obtained for n-type crystals, but not enough for p-type crystals.

A description will be given of an example of deterioration of a light emitting diode made of a nitride crystal. FIG. 1 shows a simplified structure of an active light emitting diode. p-side metal electrode (Ni / Au) 11
Although attached to the p-type nitride crystal layer 12, it is known that the nitride crystal layer has a high density of lattice defects (up to 10 ¹⁰ cm ^-3 ) penetrating it almost vertically. Have been. The degradation of the diode is caused by the fact that the metal element constituting the p-side metal electrode diffuses along the penetrating lattice defect, and the light emitting layer 13
To short-circuit the pn junction.
(Reference: M. Osinsky and DLBarton, DegradationM
echanisms in III-N Blue Light Emitting Diodes, pap
er Th-01, Proceedingsof theInternational Symposium
on Blue Laser and Light Emitting Diodes, Chiba, Ja
pan 1996) Further, since the driving condition of the semiconductor laser is much harsher than that of the light emitting diode, the lifetime at the time of continuous oscillation at room temperature is only 20 to 30 hours. The degradation mechanism of this laser is also considered to be essentially the same as that of the light emitting diode. Therefore, prevention of the deterioration phenomenon caused by the p-side metal electrode is a very important technical issue.

[0005]

As described above, in order to improve the reliability of a semiconductor device using a nitride crystal, the metal element constituting the p-side metal electrode must have a nitride crystal through a penetrating lattice defect. We need to stop the phenomenon of diffusion inside.

[0006]

According to the present invention, in order to solve the above-mentioned problems, a p-type crystal layer is further interposed between a p-side metal electrode and a nitride crystal, whereby a p-side metal electrode is formed. It is intended to have a structure that does not directly contact the penetrating lattice defect and to prevent rapid diffusion of metal elements. In addition, the presence of this intervening layer can delay the time required for the metal element diffused by another mechanism to reach the nitride layer. Further, by making this layer a semiconductor having a narrow bandgap, energy in the valence band can be reduced. Since the continuous amount is reduced and a high hole concentration is obtained, a highly reliable electrode having low contact resistance can be obtained.

Therefore, in the present invention, at least N (nitrogen) is used as a constituent element in a group III-V compound semiconductor composed of a group III element such as Al, Ga and In and a group V element such as N, P and As. In a semiconductor device formed of a semiconductor material containing (a nitride semiconductor described above and below), a p-type group IV semiconductor and a p-type IV- A layer (or a laminated structure) made of at least one group IV semiconductor is formed. The crystal region of the nitride semiconductor includes any single-layer or multiple-layer nitride crystal layer formation modes that differ depending on the specifications of the semiconductor device (for example, whether the device is an electronic device or an optical device). As an example, the crystal region of the nitride semiconductor may be formed on a crystal substrate (material is not particularly limited). In any of the above-described p-type semiconductor layers or the stacked structure thereof, the main constituent element is a group IV element, and thus is hereinafter generally referred to as a group IV semiconductor region.

That is, the semiconductor device of the present invention forms a p-type group IV semiconductor region on a crystal region made of a nitride semiconductor,
Further, the present invention is characterized in that a metal electrode is formed on the group IV semiconductor region, and an ohmic contact with the group IV semiconductor region is established to complete the structure. The basis for forming the group IV semiconductor region between the nitride semiconductor region and the p-type electrode as described above is that the diffusion of impurities in the group IV semiconductor is slower than that of the nitride semiconductor. Therefore, in the semiconductor device according to the present invention, the diffusion of the material (for example, Au, Ti, Ni, W, etc.) constituting the p-type electrode into the nitride semiconductor region (element portion) is suppressed by the group IV semiconductor region. In the nitride semiconductor region, the function of a junction that defines a channel layer in which carrier movement related to switching of an electronic device occurs or a light emitting layer (active layer) in which carrier recombination related to a light emission phenomenon of an optical device occurs is determined by the function of an electrode constituent material. Damage due to inflow can be avoided. For example, the short circuit of the pn junction in the light emitting diode described above is also eliminated by the present invention.

Further, in addition to the above effects, the group IV semiconductor region can be doped with a higher concentration of p-type impurities than the nitride semiconductor, so that a large amount of carriers are generated by the p-type impurities introduced at a high concentration. Also, the effect of reducing the electric resistance between the p-type electrode and the nitride semiconductor region can be realized. As an element constituting the group IV semiconductor region, for example,
Si (silicon) and SiC (silicon carbide) are used.

When the group IV semiconductor region is made of SiC, which is a group IV-IV semiconductor (also called random alloy), carrier movement at the interface due to reduction of band discontinuity at the interface with the nitride semiconductor region, that is, current can be easily reduced. The effect that can be flowed to the can be realized. That is, by adjusting the ratio of Si to C (carbon) in SiC, the bandgap of the group IV semiconductor region can be set to a value close to that of the nitride semiconductor. Therefore, the effect of reducing the electric resistance between the p-type electrode and the nitride semiconductor region can be realized even if the impurity concentration introduced into the group IV semiconductor region is suppressed to some extent. In order to obtain this effect, the group IV semiconductor region has a laminated structure in which a Si layer and a SiC layer are combined, or a SiC layer and a SiC layer are formed on a nitride semiconductor region.
The layers may be formed in this order, and a p-type electrode may be provided on the Si layer.

The mode of the above-mentioned group IV semiconductor region is not particularly limited, but at least a part has a crystal structure (a regular atomic arrangement) so that the p-type impurity introduced into this region is activated. Is desirable. For example, polycrystal or a mixture of polycrystal and amorphous portion may be used. It should be noted that the temperature should be set so as not to desorb constituent elements of the underlying nitride semiconductor region when the group IV semiconductor region is formed. As an example of the standard, the group IV semiconductor region formation temperature may be set to 1000 ° C. or lower.

The p-type impurities (acceptors) introduced into the group IV semiconductor region, ie, contained in the group IV semiconductor region when the semiconductor device is completed, include, for example, B (boron), Al
Group III elements such as (aluminum) and Ga (gallium) are preferably used.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One preferred embodiment of a semiconductor device having a p-type intervening layer (sometimes called a contact layer or a cap layer) characterized by the present invention described above will be described below. A specific description will be given with reference to the embodiment and FIG.

Specific examples of the p-type intervening layer suitable for the semiconductor device made of the above-described nitride semiconductor include p-type polysilicon (poly Si), p-type polycrystalline silicon carbide (poly SiC), and p-type polycrystalline silicon carbide (poly SiC). It is good to use a combination. In the example,
An example in which an intervening crystal layer in which p-type polycrystalline silicon (p-type poly Si) and p-type polycrystalline silicon carbide (p-type poly SiC) are combined will be described. The mode of the intervening crystal layer is not limited.

<Example> Silicon was doped on a sapphire substrate crystal 31 by a standard metal organic chemical vapor deposition method.
4 μm n-type GaN layer 30 and 50 undoped GaInN buffer layer 29
Å, 25Å undoped GaInN light-emitting layer 28, undoped GaInN
Buffer layer 27 of 50 °, p-type Al doped with magnesium
GaN layer 26 is 200mm, also p-type doped with magnesium
The GaN layer 25 is grown by 0.5 μm. Subsequently, a mixed gas of propane, monosilane, and diborane is flowed to form the p-type poly SiC layer 24 by 0.1.
μm, propane gas was stopped at this point, and p-type po
The ly Si layer 23 is grown to 4 μm. The wafer thus obtained is subjected to mesa etching from the p side by dry etching until an n-type nitride layer appears. Ti / W / Al on the surface of p-type mesa
Formed metal electrode 22 and exposed by dry etching n
A Ti / Al metal electrode 21 is formed on the type nitride layer. A lead wire is bonded to each bonding pad to complete a light emitting diode.

The light emitting diode is supplied with a current density of 0.1 kA / cm ^-2
The rate of decrease in the light emission output when driven at was 0.001% / hr.

On the other hand, the output reduction rate of the conventional light emitting diode having no poly SiC or poly Si layer was 0.1% / hr, and the effect of the intervening layer was clearly recognized.

[0018]

As can be seen from the above embodiment, the reliability of the device is greatly improved by inserting a p-type group IV or IV-IV semiconductor layer between the p-side metal electrode and the nitride crystal. Can be improved. This is considered to be mainly because the electrode metal does not directly contact the nitride crystal, so that rapid diffusion of the electrode metal through a penetrating lattice defect in the nitride crystal does not occur. Furthermore, the band gap becomes smaller in the order of SiC and Si, so that the discontinuity of the valence band is reduced. It can be understood that the effect has been added.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a light-emitting diode using a nitride crystal of a current (prior art).

FIG. 2 is a cross-sectional view of a light emitting diode using a nitride crystal according to the present invention.

[Explanation of symbols]

11 ... p-side metal electrode, 12 ... p-type nitride crystal layer, 13 ... light-emitting layer, 14 ... n-type nitride crystal layer, 15 ... n-side metal electrode, 16 ... sapphire substrate crystal, 21 ... n-side metal electrode, 22 ... p-side metal electrode, 23 ... p-type poly Si layer, 24 ... p-type poly SiC layer, 25 ...
p-type GaN layer, 26 ... p-type AlGaN layer, 27 ... GaInN buffer layer, 2
8 ... GaInN light emitting layer, 29 ... GaInN buffer layer, 30 ... n-type GaN
Layer, 31 ... Sapphire substrate crystal.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shoichi Akamatsu 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Inside Central Research Laboratory, Hitachi, Ltd.

Claims (5)

[Claims] 1. A semiconductor device comprising: a crystal region made of a nitride semiconductor; a p-type group IV semiconductor region formed on the crystal region; and a metal electrode formed on the group IV semiconductor region. A semiconductor device characterized by the above-mentioned. 2. The group IV semiconductor region includes a group IV semiconductor layer and
2. The semiconductor device according to claim 1, comprising at least one of a group IV-IV semiconductor layer. 3. The semiconductor device according to claim 2, wherein said group IV semiconductor layer is made of silicon. 4. The semiconductor device according to claim 2, wherein said IV-IV group semiconductor layer is made of silicon carbide. 5. The semiconductor device according to claim 1, wherein the group IV semiconductor region contains at least one element selected from B, Al, and Ga as an impurity.