Light emitting device having flat growth GaN layer

Details Light emitting device having flat growth GaN layer Light emitting device having flat growth GaN layer

1997-04-21

2001-11-20

Tran, Minh Loan (Department: 2811)

Active solid-state devices (e.g., transistors, solid-state diode

Incoherent light emitter structure

With particular dopant concentration or concentration profile

C257S103000

Reexamination Certificate

active

06320207

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to a light emitting device and a method of manufacturing the light emitting device and, more particularly, to a structure of the light emitting device such as a light emitting diode and a semiconductor laser and a manufacturing method thereof.
Known hitherto as a practical material of the light emitting device is a gallium nitride system compound semiconductor of gallium nitride (GaN), indium gallium nitride (InGaN) and gallium aluminum nitride (GaAlN).
The following are explanations of a structure of the light emitting diode, a manufacturing method thereof and problems inherent therein by way of one example of the light emitting device manufactured by use of the above materials with reference to
FIGS. 7A
,
7
B,
8
A and
8
B.
FIG. 7A
is a sectional view illustrating the light emitting diode having a heterojunction, wherein a plurality of grown layers are formed based on an epitaxial growth. Further,
FIG. 7B
shows a profile of N-type impurities in the light emitting diode shown in
FIG. 7A
, wherein the axis of abscissa indicates an impurity concentration of the N-type impurity while the axis of ordinates indicates a distance from the underside of a substrate, corresponding to FIG.
7
A.
The prior art light emitting diode is, as illustrated in
FIG. 7A
, constructed of stacking of grown layers such as a buffer layer
112
(a first GaN layer) composed of amorphous GaN, a spacer layer
113
(a second GaN layer) composed of monocrystalline GaN, a high-concentration N-type layer
114
(a third GaN layer) doped with the N-type impurity at a high concentration, an active layer
115
(an InGaN layer) composed of InGaN, an AlGaN layer
116
doped with a P-type impurity, and a contact layer (a fourth GaN layer) doped with the P-type impurity at a high concentration on the surface of a substrate
111
composed of sapphire and SiC.
The impurity concentration of the N-type impurity is on the order of 1-5×10
18
atoms•cm
−3
in the third GaN layer. In other layers, the impurity concentration of the N-type impurity is on the order of 1×10
15
atoms•cm
−3
defined as a background level. Further, these respective grown layers are formed by changing temperatures and sorts of gasses introduced thereinto, which involves the use of a vapor phase growth method such as a MO-CVD (Metal Organic Chemical Vapor Deposition) method. In the configuration given above, the second GaN layer
113
is formed by introducing hydrogen as a carrier gas, and ammonia (NH
3
) and TMGa (trimethyl gallium) as raw gases into the reaction chamber at 1000° C.-1100° C., and thereafter the third GaN layer
114
is so formed as to be doped with the N-type impurity at a high concentration by further supplying SiH
4
(silane gas) while consecutively introducing the above gases. Incidentally, it is desirable that the second GaN layer has a thickness of 0.01 &mgr;m or larger, and the third GAN layer has a thickness of 0.1 &mgr;m.
By the way, the second GaN layer
113
is not functionally necessary essentially. Namely, if the third GaN layer doped with the N-type impurity at the high concentration is provided on the first GaN layer functionally provided as the buffer layer, the operation required of the light emitting device is to be performed. When a high-concentration monocrystalline GaN layer is provided on the surface of an amorphous GaN layer, however, as shown in, e.g.,
FIGS. 8A and 8B
, a pin hole
211
is produced in the surface of the first GaN layer
112
, or an abnormal growth
212
of the GaN layer with a dopant being a core, might occurs in some cases. Accordingly, in the prior art light emitting diode, the monocrystalline second GaN layer
113
is provided as a spacer layer on the surface of the first GaN layer
112
, and subsequently the fourth GaN layer
114
doped the N-type impurity at a high concentration is formed.
As described above, in the semiconductor device using the prior art gallium nitride system compound semiconductor, when forming a high-concentration N-type layer under the active layer functioning as a light emitting layer, an undoped monocrystalline GaN layer is previously provided as a spacer layer beneath the high-concentration N-type layer in order to enhance the crystallinity thereof. Although the vapor phase growth method such as the MO-CVD method and so on for forming those respective grown layers, there must be formed the originally functionally unnecessary layer exhibiting a low growth velocity, and this results in a decreases in terms of throughput. Further, as the functionally unrequited layer is to be formed, the thickness of the entire light emitting device is to increase. When the layer thickness increases, a distortion quantity of each grown layer enlarges due to a lattice unjointed state, with the result that the functionally necessary grown layers must be deteriorated.
SUMMARY OF THE INVENTION
It is a primary object of the present invention, which was contrived in view of the above problems, to provide a novel light emitting device using a gallium nitride system compound semiconductor and a manufacturing method thereof enough to enhance a quality and a throughput thereof when manufacturing the light emitting device.
To accomplish the above object, according to one aspect of the present invention, a light emitting device comprises a substrate, a first N-type gallium nitride system compound semiconductor layer provided on the substrate so as to increase an impurity concentration from an impurity concentration of a first N-type impurity to an impurity concentration of second N-type impurity, a second N-type gallium nitride system compound semiconductor layer having the impurity concentration of the second N-type impurity and provided on the first N-type gallium nitride system compound semiconductor layer, and a P-type gallium nitride system semiconductor layer provided on the second N-type gallium nitride system compound semiconductor layer. Further, an impurity concentration of an N-type impurity in the first N-type gallium nitride system compound semiconductor layer changes exponent-functionwise or rectilinearly or curvilinearly of saturation or stepwise corresponding to a layer thickness. Moreover, the impurity concentrations of the first and second N-type impurities fall within a range of 1×10
−13
atoms•cm
−3
to 1×10
23
atoms•cm
−3
. Also, a thickness of the first N-type gallium nitride compound semiconductor layer falls within a range of 0.01 to 2.00 &mgr;m.
According to another aspect of the present invention, a method of manufacturing a light emitting device, comprises a step of providing a first gallium nitride system compound semiconductor layer on a substrate in a reaction chamber, and a step of providing a second N-type gallium nitride system compound semiconductor layer doped with an N-type impurity on the surface of the first gallium nitride system compound semiconductor layer with SiH
4
introduced as a doping gas. Based on this manufacturing method, the second N-type gallium nitride system compound semiconductor layer is formed by increasing an impurity concentration thereof from the side of the substrate, which involves changing a flow quantity of SiH
4
to be introduced into the reaction chamber.
According to the present invention, without forming an undoped monocrystalline GaN layer as a spacer layer that has hitherto been formed in the prior art light emitting device, the N-type modulation doped layer and the high-concentration N-type layer can be provided on the surface of the buffer layer, exhibiting a stabilized crystallinity with no abnormal growth only by consecutively changing the flow quantity of the silane gas. Hence, the throughput relative to manufacturing the light emitting device can be enhanced. Further, the thickness of the whole light emitting device can be reduced to some extent, and therefore it is feasible to prevent both the distortion quantity from enlarging due to the lattice mismatching and the g

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