Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Compound semiconductor
Reexamination Certificate
2000-07-31
2001-09-04
Picardat, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Compound semiconductor
C438S039000, C438S042000
Reexamination Certificate
active
06284559
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gallium nitride group compound semiconductor light-emitting device, which is capable of emitting light from the blue region to the ultraviolet region of the spectrum, such as a light-emitting diode and a semiconductor laser; and a method for producing the same.
2. Description of the Related Art
FIG. 19
is a cross-sectional view showing the structure of the gallium nitride group compound semiconductor laser disclosed in Japanese Laid-Open Publication No. 8-97507. The gallium nitride group compound semiconductor laser is fabricated by a metal organic chemical vapor deposition method (an MOCVD method). Hereinafter, the structure of the gallium nitride group compound semiconductor laser and a method for fabricating the same will be described.
First of all, a sapphire substrate
101
is inserted into an MOCVD apparatus. Then, an N-type GaN buffer layer
102
, an N-type AlGaN lower cladding layer
103
, an InGaN active layer
104
, a P-type AlGaN upper cladding layer
105
and an N-type AlGaN internal current constricting layer
107
are sequentially grown on the sapphire substrate
101
in this order.
Next, the sapphire substrate
101
having the above-described layers provided thereon, namely a wafer, is taken out from the MOCVD apparatus. Then, the N-type AlGaN internal current constricting layer
107
is etched by photolithography to form a stripe-shaped opening. As a result, a current constricting layer with an opening is formed.
Thereafter, the above-described wafer is again inserted into the MOCVD apparatus. Then, a regrowth step is performed, and a P-type AlGaN upper cladding layer
108
and a P-type GaN contact layer
109
are sequentially formed in this order on the N-type AlGaN internal current constricting layer
107
.
Finally, a P-side electrode
110
and an N-side electrode
111
are formed. In the above-described manner, the gallium nitride group compound semiconductor laser having the structure shown in
FIG. 19
is completed.
According to this type of gallium nitride group compound semiconductor laser, in the case where the internal current constricting layer
107
is etched using wet etching or dry etching to form a stripe-shaped opening until a surface of the P-type AlGaN upper cladding layer
105
is exposed and then the P-type AlGaN upper cladding layer
108
is regrown in the MOCVD apparatus so as to cover the exposed surface of the P-type AlGaN upper cladding layer
105
and surfaces of the N-type AlGaN internal current constricting layer
107
, the substrate temperature needs to be raised to about 1050° C. (A substrate temperature means a temperature of a substrate having layers provided thereon.)
As a result, during a rise in the substrate temperature, an increase in surface roughness at the exposed surface of the P-type AlGaN upper cladding layer
105
; a change in the width of the striped-shaped opening; and a deformation of the stripe-shaped opening formed in the N-type AlGaN internal current constricting layer
107
are generated. Consequently, electrical characteristics of the gallium nitride group compound semiconductor laser are deteriorated due to high resistance at the regrowth interface, and optical characteristics are deteriorated due to the change in the width of the stripe-shaped opening and the deformation of the stripe-shaped opening. Thus, the above-described gallium nitride group compound semiconductor laser has problems of reduced device characteristics.
The above-described problems will be described in detail with reference to FIG.
20
. Since the step of regrowing the regrowth P-type AlGaN upper cladding layer
108
on the exposed surface of the AlGaN upper cladding layer
105
(the surface is exposed by etching) is performed at a high temperature of about 1050° C., as shown in
FIG. 20
, a P-type impurity escapes by evaporation in the gas phase from the exposed surface of the P-type AlGaN upper cladding layer
105
. As a result, a defect is caused on the exposed surface of the P-type AlGaN upper cladding layer
105
and surface roughness is increased at the exposed surface of the upper cladding layer
105
. Accompanying this phenomenon, the stripe-shaped opening in the current constricting layer
107
is deformed. Moreover, Si (an N-type impurity) evaporates in the gas phase from the current constricting layer
107
. As a result, surface roughness is increased at the surface of the current constricting layer
107
. Consequently, crystallinity of the regrowth P-type AlGaN upper cladding layer
108
, which is grown on the current constricting layer
107
, is deteriorated. Thus, the surface condition of the regrowth P-type AlGaN upper cladding layer
108
is deteriorated.
When impurities escape from the interface between layers, resistance becomes high at the interface, thereby deteriorating the electrical characteristics. More specifically, forward voltage, operating voltage, and threshold voltage are increased. As a result, a light emitting pattern cannot be stabilized.
According to the above-described gallium nitride group compound semiconductor laser, the optical characteristics are deteriorated due to a change in the width of the stripe-shaped opening and deformation of the stripe-shaped opening. As a result, crystallinity of the regrowth P-type AlGaN upper cladding layer
108
is deteriorated, thereby causing the deteriorated surface condition of the regrowth upper cladding layer
108
. Thus, reliability of the semiconductor laser is reduced.
According to the above-described conventional gallium nitride group compound semiconductor laser, the regrowth P-type AlGaN upper cladding layer
108
is grown directly on the exposed surface of the P-type AlGaN upper cladding layer
105
and the surfaces of the current constricting layer
107
at a high temperature. Therefore, due to damage caused by heat, the electrical and optical characteristics of the semiconductor laser are deteriorated, thereby reducing its reliability.
At present, however, no suitable wet etching solution for etching a gallium nitride group compound semiconductor is known. Therefore, in the step of removing the growth layer of the gallium nitride group compound semiconductor, it is difficult to leave the layer so as to have a required thickness, and good reproducibility, and to expose the surface of the desired growth layer by using a wet etching solution.
Also, when an internal current constricting layer is etched by photolithography in an ambient atmosphere to form a stripe-shaped opening and thus forming a current constricting layer with an opening, an impurity such as C or O attaches to the exposed surface of the upper cladding layer
105
. As a result, when the regrowth upper cladding layer
108
is grown on the exposed surface of the upper cladding layer
105
, interface level is generated at the regrowth interface. Consequently, series resistance at the interface and forward voltage increase. Thus, electrical characteristics are further deteriorated.
A gallium nitride group compound light-emitting diode having a current blocking layer instead of the current constricting layer has the same problems as those described above.
SUMMARY OF THE INVENTION
According to one aspect of this invention, a gallium nitride group compound semiconductor light-emitting device comprises a substrate and a layered structure provided on the substrate. The layered structure includes: an active layer; an upper cladding layer and a lower cladding layer which is located closer to the substrate than the upper cladding layer, the active layer interposed between the cladding layers; an internal current constricting layer having an opening for constricting a current within a selected region of the active layer, the internal current constricting layer being provided on the upper cladding layer; a surface protecting layer for covering the internal current constricting layer and an exposed surface of the upper cladding layer in the opening of the internal current constricting layer; and a regrowth layer provi
Morrison & Foerster / LLP
Picardat Kevin M.
Sharp Kabushiki Kaisha
LandOfFree
Gallium nitride group compound semiconductor light-emitting... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Gallium nitride group compound semiconductor light-emitting..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gallium nitride group compound semiconductor light-emitting... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2485033