GaN substrate including wide low - defect region for use in semiconductor element

Abstract

A GaN substrate formed with a substrate, a first GaN layer, a first preventing film, a second GaN layer, and a second preventing film. The first GaN layer is formed on the substrate, and includes a plurality of stripe portions which form at least one first groove between adjacent ones of the plurality of stripe portions. The second GaN layer is formed over the substrate and the first GaN layer. The first preventing film is arranged on upper surfaces of the plurality of stripe portions, and prevents crystal growth of a GaN layer in a vertical up direction from the upper surfaces of the plurality of stripe portions. The second preventing film is arranged on at least one bottom surface of the at least one first groove, and prevents crystal growth of a GaN layer in a vertical up direction from the at least one bottom surface.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to a GaN substrate which is used in a semiconductor element, and in which the defect density is low. The present invention also relates to a process for producing a GaN substrate which is used in a semiconductor element, and in which the defect density is low. The present invention further relates to a semiconductor element including a semiconductor laser device which uses a GaN substrate in which the defect density is low.[0003] 2. Description of the Related Art[0004] S. Nakamura et al. ("Violet InGaN / GaN / AlGaN-Based Laser Diodes Operable at 50.degree. C. with a Fundamental Transverse Mode," Japanese Journal of Applied Physics, vol. 38 (1999) L226-L229) disclose a short-wavelength semiconductor laser device which emits laser light in the 410 nm band.[0005] This semiconductor laser device is formed as follows. First, a GaN substrate is formed by growing a first GaN layer on a sapphire substrate, selectively growing...

AI Technical Summary

Problems solved by technology

However, the defect density in the semiconductor laser device is still high, and therefore the semiconductor laser device is not reliable in the high output power range.

However, the semiconductor laser device produced by the process is reliable only when the semiconductor laser device operates with the output power of 5 mW or less.

However, in this process, the entire base layer on which the above GaN compound semiconductor layer is grown is formed on a substrate, and the lattice-mismatch between the base layer and the substrate is great.

Therefore, the GaN compound semiconductor layer is affected by the substrate, the crystal orientations of the GaN compound semiconductor layer grown in lateral directions vary, and it is difficult to planarize the surface of the GaN compound semiconductor layer.

Further, even when the above process is repeated, differences arise in the orientations of the crystal faces, and it is therefore impossible to reduce the defect density to a practical level.

However, in this process, the crystal axis is likely to incline due to the mismatch between the sapphire substrate and portions of the GaN layer which are laterally grown over the sapphire substrate, or stress generated in the vicinity of the boundary between the sapphire substrate and the portions of the GaN layer.

Further, as mentioned in Japanese Unexamined Patent Publication No. 11 (1999)-312825, a cavity is formed between the sapphire substrate and the laterally grown portions of the GaN layer, and the formation of the cavity is uncontrollable.

However, since the laterally grown portions of the second GaN layer coalesce in central portions of a plurality of regions which are located above the remaining SiO.sub.2 film of the SiO.sub.2 mask, defects tend to gather in the central portions of the plurality of regions above the remaining Sio.sub.2 film.

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