GAN group crystal base member having low dislocation...

Details GAN group crystal base member having low dislocation... GAN group crystal base member having low dislocation...

1998-03-24

2001-05-01

Pham, Long (Department: 2823)

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

Heterojunction device

With lattice constant mismatch

C257S194000, C117S101000

Reexamination Certificate

active

06225650

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a GaN (gallium nitride) group crystal base member, use thereof (e.g., semiconductor light emitting element), and manufacturing methods thereof.
BACKGROUND OF THE INVENTION
A conventional method for crystal growth of a GaN semiconductor material to give a thick film generally comprises forming a buffer layer of ZnO and the like on a sapphire substrate and growing a GaN semiconductor material by an HVPE method. An improved technique thereof involves the use of a substrate such as one made from spinel, LGO, LAO, ZnO, SiC and the like or a substrate showing easy cleavage performance, instead of the sapphire substrate.
However, the crystal growth of a GaN semiconductor material to give a thick film results in tremendous amounts of stress applied on the interface between GaN and sapphire substrate due to different lattice constants and coefficients of thermal expansion, which in turn leads to a problem in that GaN is broken and a bulky substrate cannot be obtained. In addition, this method produces only a substrate having an extremely great dislocation density (e.g., 1×10
9
cm
−2
-1×10
10
cm
−2
). By dislocation is meant here a defect that occurs when a semiconductor layer is grown on a substrate under a lattice mismatch. The dislocation thus created advances upward along with the growth of the crystal layer and passes through an active layer to form a continuous defective portion called a dislocation line (continuous dislocation). Inasmuch as this dislocation is a crystal defect, it acts as a non-radiative recombination center or as a path of a current to ultimately induce current leakage when such GaN semiconductor material is used for a light emitting element, which in turn degrades light emitting performance and shortens the service life.
It is therefore an object of the present invention to provide a GaN group crystal base member having a low dislocation density.
Another object of the present invention is to provide use of the aforementioned GaN group crystal base member.
Yet another object of the present invention is to provide a method for producing the aforementioned GaN group crystal base member and a method for producing a light emitting element which is one use thereof.
SUMMARY OF THE INVENTION
The GaN group crystal base member of the present invention comprises a base substrate, a mask layer partially covering the surface of said base substrate, and a GaN group crystal layer which is grown thereon to cover the above-mentioned mask layer and which is partially in direct contact with the non-masked region of the base substrate. Said base substrate allows growth of a GaN group crystal in the C axis orientation as the thickness direction, and the mask layer is made from a material substantially free from GaN group crystal growth.
The base substrate partially covered with a mask layer is hereinafter simply called a “substrate for growth” to mean a substrate used to grow a GaN group crystal The GaN group crystal layer grows from the non-masked region of the substrate for growth as the staring point until it covers the mask layer, whereby a GaN group crystal base member comprising the base substrate, mask layer and GaN group crystal layer is provided.
The method for manufacturing the GaN group crystal base member of the present invention comprises partially covering the surface of the base substrate with a mask layer made from a material substantially free from crystal growth, and then growing a GaN group crystal layer from the non-masked region on the base substrate surface as the starting point to a thickness sufficient to cover said mask layer.


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K. Hiramatsu et al., Growth Mechanism of GaN grown on sapphire with AIN buffer alyer by MOVPE, Journal of Crystal Growth, Vo. 115(1991) pp. 628-633.

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