JP3605906B2 - Semiconductor device having contact resistance reduction layer - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a semiconductor device, and more particularly, to a light emitting element using a gallium nitride-based material, such as a blue to green light emitting diode and a blue to green laser diode, and more particularly to a semiconductor device having significantly reduced contact resistance.
[0002]
[Prior art]
Recent progress in increasing the brightness of blue and green light-emitting diodes (LEDs) is remarkable, and ZnSSe-based and AlGaInN-based materials are used as materials. At present, it is possible to grow a high-quality gallium nitride (GaN) -based compound semiconductor film on a substrate such as sapphire or SiC and to perform a high-concentration p-type doping on a GaN-based semiconductor, so that a high-intensity blue light emitting diode can be manufactured. It has been realized, and a double hetero structure as shown in FIG. 2 is used.
[0003]
[Problems to be solved by the invention]
However, as shown in FIG. 2, since GaN (Eg = 3.39 eV) having a wide band gap is used for the surface contact layer, a potential barrier between the electrode and the electrode is apt to be increased. which leads (in the case of FIG. 3, n-type, E _C is the bottom energy of the conduction band, E _F is the Fermi level, E _V is the bottom of the valence band energy, qφ _B potential barrier). In order to reduce the contact resistance of such a wide band gap semiconductor, first, there is a method of inserting a heavy-doped layer immediately below an electrode, that is, forming a structure of metal-n + -n and metal-p + -p (FIG. 4, where n-type). This leaves a potential barrier, but the thickness of the depletion layer becomes very thin, and carriers can freely pass through the tunnel effect, so that no resistance is exhibited. the hole concentration in n-type GaN is possible doped to a concentration as high as ^{10 19} units, while in the p-type GaN doping can get only up to ^{10 17} units level at present. For this reason, it is difficult to realize a sufficiently low contact resistance especially with a layer made of p-type AlGaInN. This increase in operating voltage leads to heat generation of the element, which is a major problem because it shortens the life.
[0004]
[Means for Solving the Problems]
In manufacturing an AlGaInN-based LED by MOCVD or MBE, we insert a thin-film GaP _x N _1-x (0.1 ≦ x ≦ 0.9) layer between an AlGaInN-based layer and an electrode. As a result, the above problem has been solved.
The reason is that GaPN has a special band structure in which the band gap decreases even if the P composition is increased from GaN or the N composition is increased from GaP, and the band gap becomes zero at the intermediate composition. Because it has. Therefore, in order to reduce the contact resistance, a thin GaP _x N _1-x (0.1 ≦ x ≦ 0.9) layer having a very small or zero band gap is inserted in order to reduce the contact resistance. It is considered that even if the carrier concentration cannot be made very high, the potential barrier formed between the electrode and the surface layer is greatly reduced, and it becomes very easy to obtain an ohmic contact (FIG. 5, FIG. n-type).
[0005]
The thickness, composition, etc. of the thin film GaP _x N _1-x (0.1 ≦ x ≦ 0.9) layer between the AlGaInN-based layer and the electrode, which are the main points of the present invention, are as follows. The thickness of the AlGaInN-based layer differs depending on the carrier concentration and the composition (band gap) of the AlGaInN-based layer, and is not particularly limited. However, the preferred thickness is usually a thickness necessary to satisfy the effect of reducing the contact resistance. It is usually 1 μm or less, and is often used in a thickness of about 5 to 100 nm.
[0006]
The more preferable mixed crystal ratio x is 0.1 or more and 0.9 or less, and more preferably 0.2 or more and 0.8 or less.
In this specification, an AlGaInN-based layer includes one in which the composition of Al or In is zero.
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the examples unless it exceeds the gist.
(Example)
As shown in FIG. 6, the apparatus used for the growth of the present invention is provided with a substrate transfer chamber at the center, one substrate exchange chamber and three reduced pressure MOCVD apparatuses. The growth chamber 1 is a normal MOCVD apparatus and is used for growing an AlGaInN-based compound semiconductor. The growth chamber 2 is also a normal MOCVD apparatus, but is used for growing a group III-V compound semiconductor other than AlGaInN. The growth chamber 3 can radically decompose the raw material by microwave excitation, and is used for nitriding the substrate surface and growing an AlGaInN-based compound. A procedure for growing an epitaxial wafer having a structure as shown in FIG. 1 will be described.
[0007]
First, a sapphire substrate is introduced into the growth chamber 3 and heated and heated. At 500 ° C., before the growth, using nitrogen gas (N ₂ ) as a raw material, radical nitrogen is supplied to the substrate surface by microwave excitation to replace oxygen (O) atoms on the surface with N atoms, that is, nitridation is performed. . On this surface, a GaN buffer layer of 20 nm is grown. Thereafter, the substrate is cooled, and the substrate is moved to the growth chamber 1 via the transfer chamber. The substrate was heated at a growth temperature of 1000 ° C., and an n-type GaN buffer layer of 4 μm, an n-type Al _0.2 Ga _0.8 N cladding layer of 1 μm, and Zn-doped In _0.1 Ga _0.9 N were formed on the epitaxial film growth substrate. An active layer of 0.1 μm, a p-type Al _0.2 Ga _0.8 N cladding layer of 1 μm, and a p-type GaN contact layer of 1 μm are sequentially grown. At this time, hydrogen was used as a carrier gas, and trimethylgallium (TMG), trimethylaluminum (TMA), and trimethylindium (TMI) were used as group III source gases. Ammonia (NH3) is generally used as the group V raw material, but an organic metal such as dimethylhydrazine or ethyl azide, which has high decomposition efficiency at low temperatures, may be used to reduce the growth temperature. Si or Ge was used for the n-type dopant, and Mg or Zn was used for the p-type dopant. If necessary, after the growth, a heat treatment is performed subsequently in the growth chamber to activate the carriers. Thereafter, the substrate is cooled, and the substrate is moved to the growth chamber 2 via the transfer chamber. The substrate is heated to 700 ° C., and GaP _0.2 N _0.8 having a thickness of 20 nm is grown as a contact resistance reducing layer on the epitaxial film growth substrate. At this time, hydrogen was used as a carrier gas, TMG was used as a group III raw material gas, and NH ₃ and phosphine (PH ₃ ) were used as a group V raw material. If the thickness of the GaP _0.2 N _0.8 contact resistance reducing layer is too large, the absorption of emitted light is increased. However, as in the above embodiment, the contact resistance can be reduced even with a very thin thin film having no influence of light absorption. Is very effective in reducing the In addition, the contact resistance reducing layer has a very low resistivity, and thus plays a role of spreading the current on the surface.
[0008]
Electrodes were formed on the front side of the epitaxial wafer grown in this manner, and processed into chips. When this chip was assembled as a light emitting diode and emitted light, a very good value of an emission wavelength of 420 nm and an emission output of 800 μW was obtained at a forward current of 20 mA. At this time, the operating voltage was 3.3 V, and the operating voltage was 4.0 V in the conventional light emitting diode having an electrode formed on the p-GaN surface manufactured for comparison. This reduction in the operating voltage means that the heat generated by the element itself is reduced, and the life of the element can be greatly improved.
[0009]
Although the above embodiment is directed to a light emitting diode, it goes without saying that a semiconductor laser has the same effect, and the resistance of all other semiconductor elements in which electrodes are directly provided on an AlGaInN-based semiconductor layer is reduced. Loss can be reduced and the effect is exhibited.
[0010]
【The invention's effect】
When a thin GaP _x N _{1 -x} (0.1 ≦ x ≦ 0.9) layer is inserted between the AlGaInN-based layer and the electrode to reduce the resistance and use this as a light emitting device In this method, the operating voltage can be greatly reduced, and the characteristics and life of the ultraviolet to red AlGaInN-based light emitting device can be greatly improved.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram illustrating an example of a semiconductor device of the present invention.
FIG. 2 is an explanatory diagram illustrating an example of a conventional semiconductor device.
FIG. 3 is an explanatory diagram of an energy band when an electrode is directly provided on a conventional AlGaInN-based semiconductor layer.
FIG. 4 is an explanatory diagram of an energy band when a heavy dope layer is provided on a conventional AlGaInN-based semiconductor layer and an electrode is provided thereon.
FIG. 5 is an explanation of an energy band when an electrode is provided by inserting a GaP _x N _1-x (0.1 ≦ x ≦ 0.9) layer on the AlGaInN-based semiconductor layer of the present invention. FIG.
FIG. 6 is an explanatory diagram of the manufacturing apparatus used in the first embodiment.

Claims (2)

A semiconductor device having a thin-film GaP _x N _1-x (0.1 ≦ x ≦ 0.9) layer between an AlGaInN-based layer and an electrode. 2. The semiconductor device according to claim 1, wherein said AlGaInN-based layer is p-type.

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