In recent years, higher power laser beams have been demanded of semiconductor laser apparatuses used as light sources in optical disk drives to write, erase, and read information on optical disks. This is because high power laser beams can improve writing speeds on optical disks. For this reason, in a semiconductor laser chip, an optical gain region has been expanded by increasing a length (laser cavity length) in an outgoing direction and a radiating area has been also expanded, so that a high optical output has been stably obtained. However, as the laser cavity length of the semiconductor laser chip increases, a stress caused by assembling or the structure is applied in a direction that pulls the semiconductor laser chip.
FIG. 11 shows a semiconductor laser apparatus of the prior art. A semiconductor laser chip 1 is joined to a heat sink 3 via a submount 2. The heat sink 3 is used for preventing emission efficiency from decreasing due to a temperature increase on the semiconductor laser chip 1 during a laser operation and preventing breakage and the like of the semiconductor laser chip 1. Reference numerals 11, 12, and 12a in FIG. 11 respectively denote an electrode, an end face, and an emission region on a surface of the semiconductor laser chip 1.
When the semiconductor laser apparatus configured thus is exposed to a high temperature during joining and then is cooled to room temperature, a stress is generated by a difference in thermal expansion coefficient between the submount 2 and the heat sink 3 and a tensile stress is generated on the surface of the semiconductor laser chip 1. When the surface of the semiconductor laser chip 1 has recessed portions including marks 13, stresses are concentrated on the steps of the recessed portions, so that cracks may occur on the semiconductor laser chip 1, starting from portions where stresses are concentrated. This tendency is currently noticeable because long and thin semiconductor laser chips 1 have been used in response to increased laser cavity lengths.
As a method for reducing the stress of a semiconductor laser chip, for example, Japanese Patent Laid-Open No. 2006-108262 discloses a substantially square die bonding surface formed on a semiconductor laser chip which is equal in length in the resonator direction and the width direction. However, this method increases the area of the semiconductor laser chip and the manufacturing cost.
Further, Japanese Patent Laid-Open No. 2008-91768 discloses a limited junction region. However, this method interferes with heat radiation and thus reduces thermal reliability particularly in a high-power semiconductor laser chip.