JP2752061B2 - Quantum well semiconductor laser - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quantum well semiconductor laser. 2. Related Art and Problems Thereof The oscillation wavelength of a quantum well semiconductor laser is mainly determined by the quantum well width. As shown in FIG. 3 (A), the conventional quantum well semiconductor laser oscillation has the lowest quantum level of electrons.
It is based on the transition between m _e = 1 and the hole quantum level m _h = 1, and the transition wavelength between the lowest levels is the oscillation wavelength. In order to obtain laser oscillation of a shorter wavelength, as shown in FIG. 3 (B), an attempt is made to reduce the width of the quantum well and increase the energy between the lowest quantum levels. However, when the well width is reduced in this way, unevenness caused by unevenness of the thickness of the barrier layer causes in-plane unevenness in the well width and fluctuations in the quantum level. was there. SUMMARY OF THE INVENTION An object of the present invention is to provide a quantum well semiconductor laser capable of obtaining a short wavelength laser oscillation without reducing the quantum well width. SUMMARY OF THE INVENTION The present invention provides a Fabry-Perot quantum well semiconductor laser in which two or more dielectric layers having different refractive indices are alternately laminated over four or more layers. At least on the rear end face of the laser, the dielectric layer has a thickness of 1/4 of the emission wavelength due to the desired transition between higher levels of the quantum well. According to the present invention, the transition wavelength between higher-order quantum levels is selectively reflected by the reflective film, and the short-wavelength light resonates and oscillates with laser. Since the reflection film is substantially transparent with respect to the transition wavelength between the lowest levels, laser oscillation of this long wavelength light does not occur. Thus, according to the present invention, laser oscillation of a short wavelength can be obtained without narrowing (thinning) the quantum well width, and the laser oscillation threshold can be kept relatively low. DESCRIPTION OF THE EMBODIMENTS Referring to FIG. 1, a quantum well semiconductor laser is provided on a substrate 1 with a buffer layer 2, a lower cladding layer 3, an active layer 4 having a quantum well structure, and an upper layer, as is well known. The clad layer 5 and the cap layer 6 are sequentially formed. The active layer 4 may have either a single quantum well structure or a multiple quantum well structure. Electrodes (not shown) are formed on the lower surface of the substrate 1 and the upper surface of the cap layer 6, respectively. Generally, both front and rear end surfaces of the semiconductor laser are reflection surfaces, and constitute a Fabry-Perot resonator. According to the present invention, a reflective film 7 having wavelength selectivity is formed on the rear end face of such a Fabry-Perot quantum well semiconductor laser. The reflective film 7 has a refractive index of each _{n a, n b (n a} ≠ n b) a is the dielectric layer 7a, the 7b, multilayer laminated alternately to 1/4 the thickness of the crystal within the wavelength of each light These dielectric layers can be manufactured by, for example, an electron beam evaporation method. As can be seen from the concept diagram of the quantum well levels level indicated a single quantum well as a model in Figure 2, in general the quantum well structure, between m _e = m _h = 1 the lowest quantum level transition not only, higher order optical transitions of m _e = m _h ≧ 2 is also induced. However, since the laser gain between the lowest levels is most satisfied, oscillation occurs due to the transition between the lowest levels, and high-order oscillation is unlikely to occur. In the present invention, the dielectric layers 7a and 7b of the reflection film 7 are used.
The transition wavelength between desired higher-order levels ( _me = _mh ≧ 2) is adopted as the wavelength in the crystal of the light defining the thickness of the layers 7a and 7b.
b is laminated four or more layers. Therefore, this reflection film 7
Is higher only for the emission wavelength due to the selected higher-level transition, and higher-order, ie, shorter-wavelength laser oscillation can be obtained. The reflection film 7 for the transition wavelength between the lowest levels
Most become transparent body, laser oscillation of m _e = m _h = 1 does not occur. In this way, short-wavelength laser oscillation can be obtained without reducing the width of the quantum well.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG. 2 shows an energy level in a quantum well. FIGS. 3A and 3B are energy level diagrams for explaining the oscillation of a conventional quantum well semiconductor laser. 7 ... reflection film, 7a, 7b ... dielectric layer.

Claims (1)

(57) [Claims] In the Fabry-Perot quantum well semiconductor laser, a reflective film having wavelength selectivity, which is formed by alternately laminating two or more dielectric layers having different refractive indices over four or more layers, is provided on at least a rear end face of the semiconductor laser. A quantum well semiconductor laser, wherein the dielectric layer has a thickness of 1/4 of the emission wavelength due to a desired transition between higher levels of the quantum well.