JP3605907B2 - 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, 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 tends to be large, which causes an increase in operating voltage (FIG. 3, FIG. 3). for 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, but for n-type). 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 in terms of life.
[0004]
[Means for Solving the Problems]
When fabricating an AlGaInN-based LED by MOCVD or MBE, we use a thin-film GaP _x N _1-x (x ≧ 0.9) layer and a thin-film GaP _y N ₁ between an InAlGaN-based layer and an electrode. _-Y (y ≦ 0.1) by inserting a multilayer film in which layers are alternately laminated, more preferably the GaP _x N _1-x (x ≧ 0. 9) The above problem has been solved by inserting a layer and a GaP _x N _1-x (x ≦ 0.1) layer.
[0005]
The GaPN mixed crystal 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. I have. However, it is considered that the growth of a mixed crystal having an intermediate composition is difficult due to the existence of a missibility gap. Therefore, by stacking a superlattice composed of a GaP-rich thin film and a GaN-rich thin film, a band structure similar to that of a GaPN bulk can be realized. Therefore, in order to reduce the contact resistance, a thin band GaP _x N _1-x (x ≧ 0.9) layer and a thin film GaP _y N _{1− of} a wide band gap semiconductor having a very small or zero band gap to reduce contact resistance. By inserting a multilayer film in which _y (y ≦ 0.1) layers are alternately stacked, a potential barrier formed between the electrode and the surface layer can be formed even if the carrier concentration cannot be extremely increased. It is greatly reduced, and it becomes very easy to obtain an ohmic contact (FIG. 5, in the case of n-type).
[0006]
In this case, the number of layers of the multilayer film is not particularly limited as long as it is 2 (one cycle) or more, but is preferably 5 cycles or more. In addition, the amount may be arbitrarily set within a range that does not particularly cause a problem such as resistance.
In this specification, an AlGaInN-based layer includes one in which the composition of Al or In is zero.
[0007]
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.
[0008]
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 (NH ₃ ) 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 a superlattice in which one molecular layer of GaP and three molecular layers of GaN are alternately stacked on the epitaxial film growth substrate for ten periods is grown as a contact resistance reducing layer. 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. The _{GaP 0.2} 5 _{N 0. When the} contact resistance reducing layer ₇₅ is too thick, it increases the absorption of emitted light. However, as in the above embodiment, even a very thin thin film having no influence of light absorption is very effective in reducing the contact resistance. is there. In addition, the contact resistance reducing layer has a very low resistivity, and thus plays a role of spreading the current on the surface.
[0009]
An electrode was formed on the surface 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 3.4 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.
[0010]
In the above embodiment, the light emitting diode is used. However, it is needless to say that a semiconductor laser has the same effect, and that the same characteristics can be improved in other semiconductor devices.
[0011]
【The invention's effect】
According to the present invention, a semiconductor device in which the resistance between an AlGaInN-based semiconductor layer and an electrode is reduced can be obtained. When this semiconductor device is used as a light-emitting device, the operating voltage can be greatly reduced, and the ultraviolet to red AlGaInN-based The characteristics of the light emitting element and the life of the element can be significantly 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 a diagram showing a thin-film GaP _x N _1-x (x ≧ 0.9) layer and a thin-film GaP _y N _1-y (y ≦ 0.1) on the AlGaInN-based semiconductor layer of the present invention. It is explanatory drawing of the energy band at the time of installing an electrode by inserting the multilayer film which laminated | stacked the layer by turns.
FIG. 6 is an explanatory diagram of the manufacturing apparatus used in the first embodiment.

Claims (3)

A multilayer in which a thin-film GaP _x N _1-x (x ≧ 0.9) layer and a thin-film GaP _y N _1-y (y ≦ 0.1) layer are alternately stacked between an AlGaInN-based layer and an electrode. A semiconductor device having a film. The _Ga x P _{1 over} x N (x ≧ 0.9) layer and _{GaP y N 1-y (y} ≦ 0.1) layer of 1 per cycle thick layer of claim 1 wherein more than 10 molecular layers Semiconductor device. 3. The semiconductor device according to claim 1, wherein said AlGaInN-based layer is p-type.

Images