JP2740170B2 - Semiconductor laser resonator manufacturing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical integrated circuit, and more particularly to a method for manufacturing a resonator of a semiconductor laser for optical information processing. [Prior Art] In an optical integrated circuit, in particular, a semiconductor laser for optical information processing, a technique for monolithically forming a resonator of the semiconductor laser is required to improve mass productivity and integration.
Dry etching technology can be used in combination with other vacuum process technologies to achieve a high vacuum integrated process.
It is considered that it will become the mainstream of the processing means of the compound semiconductor device in the future that requires miniaturization and high reliability. An example of a semiconductor laser cavity formed by dry etching is described in Uchida et al., “AlGaAs BCM Laser with Etched Mirror by RIBE” Fig. 2 is a schematic diagram for explaining this conventional example, where n-type Ga is used.
An embedded multilayer AlGa called a BCM structure on an As substrate 101
An As layer is epitaxially grown. For simplicity, only the first n-type cladding layer 102, the active layer 103 and the second p-type cladding layer 104 are shown in the figure. Ti / Pt on the surface of this crystal
An electrode 105 made of / Au is formed by an E-gun evaporator, and an electrode pattern is formed by ordinary photolithography and reactive ion etching (FIG. 2a). After this AZ13
Reactive ion beam etching (hereinafter abbreviated as RIBE) is performed using the multilayer resist 106 of 50J / Ti / AZ1350J as a mask. ECR power 200W, chlorine gas pressure 1.2 × 10
Under the condition of ^-3 Torr, extraction voltage of 400 V, and etching time of 45 minutes, an etching groove having a depth of about 10 μm and a width of 50 μm is formed.
The side surface becomes the etched mirror 109 (FIG. 2B). After the etching is completed, the multilayer resist 106 is removed to the atmosphere by oxygen plasma, and the etching mask is removed with oxygen plasma.
By forming 07, the etched mirror laser is completed (FIG. 2c). The etched mirror laser thus formed has a reflectance of 28% which is close to that of a normal cleaved laser in the initial characteristics. [Problems to be Solved by the Invention] However, the etched mirror laser by the conventional dry etching was exposed to the atmosphere without any processing despite being etched in a high vacuum. Was contaminated by atmospheric carbon, oxygen, etc., and even after passivation, its interface was not clean and its effect was extremely small. For this reason, there is a drawback that the operating life is less than half of that of a laser by a normal cleavage, and this has hindered the practical use of an etched mirror laser. [Object of the Invention] An object of the present invention is to solve the above-mentioned problems and to provide an etched mirror laser with higher reliability. [Means for Solving the Problems] The semiconductor laser resonator manufacturing method of the present invention forms an etched mirror by etching a semiconductor laser crystal having a double heterostructure including an active layer in a high vacuum, After highly cleaning the etched mirror surface with hydrogen radicals while maintaining a high vacuum, a compound semiconductor crystal having a larger bandgap than the active layer is epitaxially grown on the mirror surface using a molecular beam epitaxial growth method. And [Function] Since the end face after etching in a high vacuum is activated, exposure to the air as it is will form an unstable compound layer on the surface, and an extremely large number of non-emission interface states will be formed at the interface. Form a position. Therefore, in order to remove this, it is sufficient to keep the etched surface highly clean after etching, and epitaxially grow a semiconductor layer having a larger forbidden band width and a higher resistance than the active layer on the etched surface. As a result, not only the end face of the etched mirror becomes a clean interface, but also light absorption on the light emitting surface is eliminated, so that growth of crystal defects can be prevented, and long life and high output operation can be expected. Embodiment FIG. 1 shows an embodiment of the present invention. First, a multi-layer AlGaAs laser crystal laminated on an n-type GaAs substrate 101 (the first n-type
A resist 106 is provided on the AlGaAs cladding layer 102, the undoped Al _0.15 Ga _0.85 As (oscillation wavelength 0.78 μm) active layer 103, and only the second p-type AlGaAs cladding layer 104 (FIG. 1a). Next, an etched mirror 109 is formed by RIBE using the resist 106 as an etching mask (FIG. 1B). The etching conditions are an ECR power of 200 W, a chlorine gas pressure of 1.2 × 10 ⁻³ Torr, an extraction voltage of 400 V, and an etching time of 45 minutes. Subsequently, the resist mask is removed with oxygen RIBE while maintaining a high vacuum. Appropriate conditions at this time are ECR power of 100 W, oxygen gas of 1 × 10 ⁻³ Torr, extraction voltage of 100 V, and etching time of 10 minutes so as not to damage the etched surface. Further, oxygen and chlorine adsorbed on the etched surface are removed by hydrogen radicals excited by ECR at 50 W. This process is preferably performed in a cleaner chamber vacuum-coupled to the etch chamber. Further, while maintaining a vacuum, a high-resistance compound semiconductor layer having a larger forbidden band width than the active layer, such as an undoped Al _0.5 Ga _0.5 As window layer 108, is etched by molecular beam epitaxy (hereinafter abbreviated as MBE). Epitaxial growth is performed on the mirror end surface with a thickness of 120 nm (half the oscillation wavelength) (FIG. 1c). In the MBE method, a semiconductor layer with a desired thickness can be easily epitaxially grown on the end face of an etched mirror by tilting a sample with strong molecular beam directivity and excellent layer thickness controllability with respect to the molecular beam. It is. By setting the growth temperature to about 750 ° C., the damaged layer of the crystal that has been etched is annealed and recovered. After this,
Further, while maintaining the vacuum, the etched mirror is passivated with Si ₃ N ₄ or Si ₂ O ₃ or the like. Thereafter, the window film and the passivation film on the laser are removed, and finally, the positive electrode 105 and the negative electrode 107 are formed. Thus, the semiconductor laser of this embodiment is completed. [Effects of the Invention] According to the present invention, a highly clean etching interface can be obtained and the end face has no light absorption. Can be prevented, and a high output operation can be performed.

[Brief description of the drawings] FIG. 1 is a schematic diagram showing an embodiment of the present invention, FIG. 2 is a schematic diagram illustrating a conventional example. 101 ... n-type GaAs substrate 102 n-type AlGaAs cladding layer 103 ... Active layer 104 ... p-type AlGaAs cladding layer 105 ... Positive electrode 106 Resist 107 …… Negative electrode 108 …… AlGaAs window film 109 …… etched mirror

Claims (1)

(57) [Claims] Etching a semiconductor laser crystal having a double hetero structure including an active layer in a high vacuum to form an etched mirror, and after highly cleaning the etched mirror surface with hydrogen radicals while maintaining a high vacuum, A method for manufacturing a resonator of a semiconductor laser, comprising epitaxially growing a compound semiconductor crystal having a larger forbidden band width than an active layer on a mirror surface using a molecular beam epitaxial growth method.