JP2758598B2 - Semiconductor laser - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly reliable and high-output semiconductor laser. [Prior Art] Conventionally used semiconductor lasers are of a current injection type, and have a double hetero structure in which a semiconductor serving as an active layer is sandwiched by a semiconductor having a band gap energy larger than that as a cladding layer. Further, in a usual semiconductor laser, the composition of the active layer and the carrier concentration due to impurity doping are uniform over the entire cavity. However, it is known that it is effective to form the active layer in the vicinity of the end face with a material having a larger band gap than the central active layer in order to prevent the end face serving as the light reflection or emission face from being deteriorated or damaged. One example is a wind stripe laser (IE
Fig. 2 shows the structure of the EE Journal of Quantum Electronics, QE-15, 775 pages (1979). By sandwiching the Al _0.06 Ga _0.94 As active layer 103 between the Al _0.3 Ga _0.7 As clad layers 102 and 104, a double hetero structure is formed. First, all are formed as n ⁺ -type, and then a p-type impurity such as zinc is selectively diffused into the central portion other than the vicinity of the end face, and the region from the surface to the active layer is made p ⁺ -type. Thus, the center of the active layer 103 is p ⁺ , and the vicinity of the end face is n ⁺ type. In the case of the same material, the n ⁺ type has a larger effective energy gap than the p ⁺ type, and thus the energy gap can be increased only near the end face. As a result, absorption of the end face 109 is reduced, and deterioration and damage of the end face 109 can be prevented, and high reliability and high output can be realized. This concept can be applied not only to the AlGaAs system but also to other material systems. [Problems to be Solved by the Invention] In the above-mentioned prior art, the entire area of the active layer is doped with p ⁺ or n ⁺ . For this reason, the crystal quality is reduced, the absorption coefficient due to free carriers is increased, and the laser oscillation threshold value is increased and the efficiency is reduced. In addition, since the light comes out to the surface together with the p region and the n region, in order to attach the p-side electrode 106, it is necessary to contact the p region avoiding the n region.
The electrode structure becomes complicated. Further, since the pn junction must be taken between the active layer and the n-cladding layer, it is difficult to control the diffusion. Further, since the region where the laser gain is applied has a high impurity concentration, there is a problem in reliability. The conventional structure has several disadvantages as described above. Therefore, an object of the present invention is to provide a highly reliable and high performance semiconductor laser that eliminates the above-mentioned disadvantages by utilizing the properties of crystal growth and the properties of materials. [Means for Solving the Problems] The semiconductor laser of the present invention has a multilayer structure including an active layer, and has different bond lengths between group III atoms and group V atoms in a crystal. Ternary or higher II in which the energy gap is smaller than the mixed crystal state
An active layer is made of an IV compound mixed crystal, and the impurity concentration of at least the active layer in the vicinity of an end face which is a light reflection surface or an emission surface is about 5 to 15 × 10 ¹⁷ cm ⁻³ . Further, the semiconductor laser of the present invention has a multilayer structure including an active layer, has different bond lengths between group III atoms and group V atoms in a crystal, and has an energy gap larger than that of a normal mixed crystal state in the same mixed crystal composition. The active layer is a ternary or more III-V compound mixed crystal in a small mixed crystal state, and the impurity concentration of at least the active layer in the vicinity of an end surface serving as a light reflecting surface or an emitting surface is about 5 × 10 ¹⁷ cm ^-3 or more. It is characterized by doing. Examples of III-V compounds having different bond lengths include InGaP, AlGa
There are many such as InP, GaInPAs, GaAsSb, etc., which are applied in any case. [Action] The energy gap of a mixed crystal of a III-V compound has conventionally been considered to be uniquely determined by its composition. But,
For example, as in GaInP and AlGaInP grown by metal organic chemical vapor deposition (MOVPE), depending on the growth temperature, the ratio of group V material to group III material (V / III ratio) in the gas phase, and impurity doping, It has been shown that the energy gap can be different even when the mixed crystal composition is constant (for example, the 34th Spring Meeting of the 1987 Spring 1987 Conference on Applied Physics, the first volume of the proceedings of the lecture, lecture number 28)
p-ZA-4 and 28p-ZA-5 (1987)). In other words, when a certain combination of the growth temperature and the value of the V / III ratio is used, GaInP
The energy gap of AlGaInP or AlGaInP is typically up to 50-80 meV less than what is commonly known for mixed crystals. When an impurity of 5 × 10 ¹⁷ to 10 ¹⁸ cm ⁻³ or more is introduced (either n-type or p-type), the reduced energy gap value is restored to the original mixed crystal. This is related to the immiscible region due to the different bond lengths such as Ga-P and In-P in GaInP or Al-P and In-PGa-P and In-P in AlGaInP. I have. Therefore, the development is not remarkably observed in the case where the bond lengths are almost equal, such as Al-As and Ga-As in AlGaAs. The same development is performed in a material such as GaInAs, AlGaInAs, or GaAsSb which is composed of those having different group III-V bond lengths in the crystal. Ga _0.5 In grown by MOVPE using the function of the present invention.
_A description will be given using _0.5 P as an example. In this case, the growth temperature is 650 ° C,
If the V / III ratio is 400, the value of the energy gap is 1.85 eV. This is obtained, for example, when growing at a growth temperature of 700 ° C. and a V / III ratio of 58. It is smaller by about 50 meV than 1.90 eV, which is known as a value of a normal Ga _0.5 In _0.5 P mixed crystal. This 1.85eV
When impurities are introduced into Ga _0.5 In _0.5 P of (5 to 10) × 10 ¹⁷ cm ⁻³ or more, the energy gap (Eg) recovers the value of 1.90 eV. This is applied to a semiconductor laser using Ga _0.5 In _0.5 P as an active layer. Eg to 1.85 eV in the center of the resonator
Of Ga _0.5 In _0.5 P, and an impurity (5
10) Introduce 10 ¹⁷ cm ^-3 or more, and make Eg 1.90 eV or more.
Since the region where Eg is increased does not contribute to the laser gain, it is desirable that the region be kept to the minimum necessary. Therefore, the impurity introduction region is limited to 60 μm or less from the end face for the purpose of suppressing a rise in the oscillation threshold. Laser oscillation
Since it occurs at a value determined by 1.85 eV, light absorption does not occur near the end face having a large Eg, so that optical damage and end face deterioration can be prevented. Further, it is not necessary to make the region for giving the laser gain a high impurity concentration. For this reason, a highly reliable and high output semiconductor laser can be realized. Further, as will be apparent from the next embodiment, the present structure can be realized more easily than the conventional example. Embodiment Next, an embodiment of the present invention will be described with reference to the drawings, so that the configuration of the present invention will be more specifically shown. FIG. 1 is a side view of an embodiment of the present invention. An AlGaInP-based visible light semiconductor laser oscillating in a band at 600 nm will be described as an example. n
N-type (Al _0.4 G
a _0.6 ) _0.5 In _0.5 P clad layer 2, Ga _0.5 In _0.5 P active layer 3, p-type (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P clad layer 4, P ⁺ type
A GaAs cap layer 9 is sequentially grown. The active layer 3 is grown at a temperature of 650 ° C., a V / III ratio of 400, and no impurity doping. Only in the vicinity of the end face 8 is diffused zinc, which is p-type impurity, so that at least the active layer portion near the end face is 1.5 × 10
^{Have a} concentration of ¹⁸ cm ^-3 . The diffusion front is n- (Al
_0.4 Ga _0.6 ) _0.5 In _{0.5 The} P layer 2 may slightly enter. The total resonator length is 200-300 μm, and the Zn diffusion region 5 near the end face is
It was set to about 20 μm inside from the end face. The end face 8 is formed by cleavage. The n-type electrode 7 is on the substrate 1 side, and the p-type electrode 6 is p ⁺ GaAs
It is formed on the contact layer 9. The semiconductor laser obtained in this way has a threshold value rise of 5% or less as compared with a semiconductor laser having no impurity diffusion region, and the end face deterioration is reduced, so that the reliability is dramatically improved. In addition, the maximum light output was improved several times to prevent optical destruction of the end face.
When this structure is formed, the manufacturing process is easy because the control of the diffusion depth is not strict and the diffusion region is not required to be insulated. Therefore, the manufacturing yield is good and the cost is low. However, if the p-type electrode corresponding to the region where Eg is increased is insulated by a SiO ₂ film or the like, the current component that does not contribute to the laser gain is reduced, so that the efficiency is improved and the threshold value hardly increases. Since high-concentration impurities are not introduced into the region where the laser gain is given, the reliability is high. In the example shown here,
The same effect can be obtained even if the p-type and n-type are reversed. It goes without saying that other material systems can be applied as long as the conditions are satisfied. In the embodiment, the structure in which the active layer is sandwiched by the clad layers has been described. However, the same applies to other laminated structures, for example, a laminated structure in which an optical guide layer is provided adjacent to the active layer and the clad layer is arranged outside the optical guide layer. The effect of is obtained. Also, instead of the Fabry-Perot cavity type laser (Example),
A DFB or DBR type laser having a diffraction grating may be used. The stripe structure can be applied to any type such as a buried type or a planar type. The essential effect of the method of introducing impurities is not changed even by a method other than diffusion, for example, ion implantation. [Effect of the Invention] As described above, by adopting the structure of the present invention, it is possible to prevent deterioration and damage to the end face due to light absorption of the end face, and to realize a semiconductor laser with higher reliability and higher output than the conventional one at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side view of an embodiment of the present invention, and FIG. 2 is a schematic side view of a conventional example. 1... N-GaAs substrate, 2... N- (Al _0.4 Ga _0.5 ) _0.5 In
_0.5 P cladding layer, 3 ... Ga _0.5 I _0.5 P active layer, 4 ...
p- (Al _0.5 Ga _0.6 ) _0.5 In _0.5 P clad layer, 5... Zn diffusion region, 6,106 p-type electrode, 7... n-type electrode, 8,109.
... end face, 9 ... p ⁺ GaAs cap layer, 102, 104 ... n-Al
_0.3 Ga _0.7 As clad layer, 103 ... n ⁺ Al _0.06 Ga _0.94 As active layer.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/00-3/19

Claims (1)

(57) [Claims] A ternary element that has a multilayer structure including an active layer, has different bond lengths between Group III atoms and Group V atoms in the crystal, and has a mixed crystal state with the same mixed crystal composition and a smaller energy gap than a normal mixed crystal state. The above III-V compound mixed crystal is used as an active layer, and the impurity concentration of at least the active layer in the vicinity of an end face that is a light reflection surface or an emission surface is set to about 5 to 15 × 10 ¹⁷ cm ^−3. Semiconductor laser. 2. A ternary element that has a multilayer structure including an active layer, has different bond lengths between Group III atoms and Group V atoms in the crystal, and has a mixed crystal state with the same mixed crystal composition and a smaller energy gap than a normal mixed crystal state. A semiconductor laser characterized in that the above III-V compound mixed crystal is used as an active layer, and the impurity concentration of at least the active layer in the vicinity of an end face serving as a light reflection surface or an emission surface is about 5 × 10 ¹⁷ cm ⁻³ or more. .