Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With heterojunction
Reexamination Certificate
2001-03-19
2003-11-04
Crane, Sara (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With heterojunction
C257S096000, C257S103000
Reexamination Certificate
active
06642546
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device and a method of forming the same, and more particularly to a life-time improved gallium nitride based semiconductor laser diode with a gallium nitride based active layer and a method of forming the same.
A nitride semiconductor layer of a luminescent device has many through dislocations. For this reason, a design concept for a layered-structure of the nitride based semiconductor device is largely different from the other semiconductor devices. Normally, it is preferable that the active layer of the semiconductor laser diode is uniform in compositional profile and in energy band gap profile. If the active layer of the semiconductor laser diode is not uniform in compositional profile and in energy band gap profile, then the photo-luminescent efficiency is dropped, resulting in an undesired multiple wavelength laser emission. In the nitride semiconductor laser diode, however, the active layer has many defects. Carriers are likely to be captured by the defects and non-luminescence recombination is likely to appear at the defects. In order to avoid this problem, it is effective to form in-plane fluctuations of the potential of the active layer, so that the carriers are localized in the potential valleys provided by the potential fluctuations. If the carriers are localized in the potential valleys, then it unlikely appears that the carriers are captured by the defects and non-luminescence recombination appears at the defects. Differently from the other semiconductor devices, a non-uniform compositional profile of the active layer is preferable for the nitride semiconductor laser diode.
In general, the active layer of the gallium nitride based semiconductor device is made of InAlGaN which is hard to be grown in amorphous state, wherein a phase separation between InN and GaN or AlN is likely to appear. For this reason, the InAlGaN active layer is non-uniform in indium composition. This phase separation is naturally formed, and the in-plane potential fluctuation is formed in the active layer, thereby suppressing the non-luminescent recombination of carriers, resulting in an improvement in the photo-luminescent efficiency and in the reduction of the threshold voltage.
The above described technical matters are disclosed in Japanese laid-open patent publication No. 10-12969. This Japanese laid-open patent publication also describes as follows. InGaN is hard to be grown in amorphous state and a high tendency of phase separation of InN and GaN is shown. The in-plane non-uniformity in the indium composition of the quantum well layer causes that the quantum well layer is non-uniform in band gap profile, wherein a high indium composition region has a low potential energy and a low indium composition region has a high potential energy. Electrons and holes are localized in the high indium composition region having a low potential energy, whereby localized excitons are formed. The localized excitons drops the threshold value of the laser diode and increases the output.
The following similar technical matters are also disclosed in Applied Physics Letters, vol. 71, p. 2346, 1997. The INGaN is hard to be grown in amorphous state due to phase separation. The InN composition is fluctuated in the InGaN quantum well layer. Quantum disks or quantum dots restrict motion of excitons, whereby non-luminescent recombination is suppressed. A large fluctuation in the indium composition is effective to suppress the non-luminescent recombination and improve the luminescent efficiency.
The following similar technical matters are also disclosed in Applied Physics Letters, vol. 70, p. 983, 1997. The indium compositional fluctuation of the InGaN quantum well structure is observed on the basis of a cross sectioned transmission electron microscope photograph. Localization of exceptions suppresses the non-luminescent path, whereby a high quantum efficiency of the InGaN based laser diode can be obtained.
In case of the semiconductor laser diode having the InGaN quantum well layer, the phase separation of InN and GaN is likely to be caused in the InGaN layer. This phase separation causes the indium composition fluctuation which improve the luminescent efficiency, the threshold value and the laser output.
The indium compositional fluctuation in the active layer causes the fluctuation or non-uniformity in the energy band gap profile in the active layer, whereby a multiple wavelength laser emission is caused and a variation in photo-luminescent wavelength distribution due to injection current is caused.
In Japanese laid-open patent publication No. 11-340580, it is discussed that in order to avoid the above problem, it is effective to realize the uniformity in composition of the active layer, which is measured by a photo-luminescence peak wavelength distribution. The compositional uniformity is suppressed within ±0.03 to obtain a photo-luminescence peak wavelength distribution of not more than 150 meV, thereby suppressing the multiple wavelength laser emission.
In recent years, the requirement for improving the life-time of the nitride based semiconductor laser diode has been on the increase. If the nitride based semiconductor laser diode is applied to a light source for the next generation optical storage device such as digital video disk, then at least 5000 hours or longer life-time is necessary, wherein the life-time is measured by an APC examination at 70° C. and 30 mW.
In Physica Status Solidi (a) vol. 176, p. 15, 1999, it is disclosed that reduction in dislocation density of substrate is effective for improving life-time of the laser diode. The laser diode uses a substrate with a reduced dislocation density and AlGaN/GaN modulation-doped cladding layer. If the APC examination is carried out at room temperature and 2 mW, then the life-time of not less than 10000 hours can be obtained. If, however, the APC examination is carried out at 60° C. and 30 mW, then the obtained life-time is only 400 hours. This conventional laser diode does not satisfy the above requirement.
A recently developed method “facet-initiated epitaxial lateral growth” is disclosed in Applied Sysics, vol. 68-7, 1999, pp. 774-779. This method is effective to obtain a GaN substrate with a largely reduced dislocation density.
FIG. 1
is a cross sectional elevation view illustrative of a conventional gallium nitride based semiconductor laser diode over an n-GaN substrate with a low surface dislocation density which is prepared by the facet-initiated epitaxial lateral growth. An n-type cladding layer
102
is provided on a top surface of the n-GaN substrate
101
, wherein the n-type cladding layer
102
comprises an Si-doped n-type Al
0.1
Ga
0.9
N layer having a silicon impurity concentration of 4×10
17
cm
−3
and a thickness of 1.2 micrometers. An n-type optical confinement layer
103
is provided on a top surface of the n-type cladding layer
102
, wherein the n-type optical confinement layer
103
comprises an Si-doped n-type GaN layer having a silicon impurity concentration of 4×10
17
cm
−3
and a thickness of 0.1 micrometer. A multiple quantum well layer
104
is provided on a top surface of the n-type optical confinement layer
103
, wherein the multiple quantum well layer
104
comprises two In
0.2
Ga
0.8
N well layers having a thickness of 4 nanometers and Si-doped In
0.05
Ga
0.95
N potential barrier layers having a silicon impurity concentration of 5×10
18
cm
−3
and a thickness of 6 micrometers. A cap layer
105
is provided on a top surface of the multiple quantum well layer
104
, wherein the cap layer
105
comprises an Mg-doped p-type Al
0.2
Ga
0.8
N layer. A p-type optical confinement layer
106
is provided on a top surface of the cap layer
105
, wherein the p-type optical confinement layer
106
comprises an Mg-doped p-type GaN layer having a magnesium impurity concentration of 2×10
17 cm
−3
and a thickness oil 0.1 micrometer. A p-type cladding layer
107
is provided on a top surface of the p-type
Kuramoto Masaru
Yamaguchi Atsushi
LandOfFree
Nitride based semiconductor device and method of forming the... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Nitride based semiconductor device and method of forming the..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nitride based semiconductor device and method of forming the... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3129224