JPS6332989A - Quantum-well semiconductor laser - Google Patents

Abstract

PURPOSE:To enable laser beams to be oscillated with short wavelength, by making an active layer smaller in width than a specified dimension and then by composing this element with large internal loss. CONSTITUTION:An active layer part 11 is formed of a GaAs active layer, and a transverse-locked layer 12 is formed by diffusion of Si. The width (w) of the active layer 11 is made to be 10 micronmeter or less, and then non-periodical recessed and projected parts are formed in the boundary 11a between the active layer 11 and the transverse-locked layer 12, so that the element with large internal loss can be formed. Total loss of the oscillatory laser in the resonator is expressed in an equation I. State densities g(epsilon) to energy epsilon of a single quantum well are changed stepwise respectively for electrons (a), light holes (b), and heavy holes (c). Because this element is formed with large internal loss alphai, the total loss alphatotal becomes large. Therefore, laser oscillation does not occur between the n=1 levels, but occurs between the n=2 or more levels, so that laser beams can be oscillated with short wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an Amakoido semiconductor laser, and particularly to shortening its oscillation wavelength.

[Conventional technology]

Figures 6(a) and (b) are, for example, magazines [Appl,
Phys.

Lθ11. Volume 39, pages 786-788 (198
FIG. 1 is a front view showing an example of a Dojido semiconductor laser published in 2010), and an explanatory view showing a cross section taken along line A-A of an active layer portion. In the figure, (1) is the upper electrode, (2) is the current blocking layer, and (3) is the first conductivity type, for example, p-type GaAs.
The contact layer (4) is a first conductivity type cladding layer, for example, p fjlALyGaj-yAs cladding layer, (5)
is an active layer, for example, an A4GaAa/GaAθ multi-quantum well active layer, and (6) is a second conductivity type cladding layer, for example, n
Type A! yGal-7A8 cladding layer, (7) is a second conductivity type buffer layer, for example, an n-type GaAs buffer layer, (
8) is an n-type GaAs substrate, (9) is a lower electrode, (+01
is a lateral confinement layer provided on the active layer (5) and cladding layer +41+61 side, for example, AJ! zGa+-zAθ
It is an embedded layer, and z>1. Umekomi Jfj (
Reference numeral 101 is provided to face the active layer (5) and the cladding layer +4 (61 side).The active layer (5) narrowed by the embedded layer (10) forms a stripe portion.

Next, the operation will be explained. Holes injected from the upper electrode fi+ and electrons injected from the lower electrode (9) recombine in the active layer (5) to emit light. The electrons and holes injected here do not flow there because the band gap of the embedded layer (lO) is high, but flow only through the central stripe. It can be included.

Here, when more than a certain number of carriers are injected and the light emission becomes stronger, laser oscillation occurs. The minimum current required to cause laser oscillation is called the threshold current. At this time, the light is guided through the stripe portion in the direction along the embedded layer +lot, travels back and forth within the resonator formed by the opposite ends of the active layer (6), and is extracted from the active layer (5) as a laser beam. . Due to the quantum size effect in the active layer (6), the band gap is larger than that of ordinary GaAs, and the light oscillates in a shorter period of time.

Note that the conventional stripe portion is configured to be orthogonal to the end face of the resonator, that is, the end face of the active layer facing the optical waveguide direction, and its width is constant.

The oscillation wavelength at this time is determined by the size of the band gap, and oscillation occurs at the lowest quantum level (nw) level. In order to shorten this oscillation wavelength, there is a method of reducing the width of the quantum well, but this requires the use of an extremely thin quantum well of, for example, 50A, which is difficult to form. There was also a limit to the shortening of the wavelength using this method.

[Problem that the invention seeks to solve]

Since conventional quantum well semiconductor lasers are configured as described above, there is a problem in that it is difficult to shorten the wavelength of laser light.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain a quantum well semiconductor laser that can shorten the wavelength.

[Means for solving problems]

The quantum well semiconductor laser according to the present invention includes a first conductivity type cladding layer, an active layer and a second conductivity type cladding layer laminated between a pair of electrodes, and a lateral direction layer provided on the side of the active layer and the cladding layer. A semiconductor laser including a confinement layer is characterized in that the active layer has a width of 10 micrometers or less and has a structure with large internal loss.

[Effect]

Since the active layer according to the present invention has a structure with a large internal loss, the overall loss within the resonator becomes large.

Furthermore, since the width of the active layer is narrow, less than 10 micrometers, the internal loss has a severe effect on the laser characteristics, and oscillation does not occur at the lowest quantum level (n = 1), but at the Doji level at higher levels. For example, it oscillates at n-2.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, (11+ is the active layer, for example, the thickness is 100
A GaA3 active layer (12) is a lateral confinement layer formed by diffusing, for example, Sl. This embodiment uses a lateral confinement method by disordering quantum wells by diffusion of impurities, and this formation method is described in the journal
, App: L, Phys, Vol. 58, No. 12, pp. 4515-4520 (1985)). Figure 2 shows the active layer (11) portion I4- in Figure 1.
11 is an explanatory diagram showing a cross section taken along line 11. FIG. As shown in the figure, the width (W) of the active layer (11) is 10 micrometers or less, preferably 6 micrometers or less, in this case 1.3
It is expressed in micrometers. Furthermore, aperiodic unevenness is provided at the boundary (lla) between the active layer (11) and the lateral confinement layer Q21, which increases the internal loss. In addition, in Fig. 1, S shown in Fig. 6 is
The pole (91) is shown without the current blocking layer (2). This non-periodic unevenness can be formed by using a pattern with unevenness when forming the mask pattern. The resonator length is approximately 500 microns. It is in meters.

As in the conventional case, in the active layer (11), the effective refractive index of the lateral confinement layer 112) in which 81 is diffused decreases and the bandgap increases, so that both current and light are absorbed by the lateral confinement layer (12). It is trapped in the sandwiched stripe part.

The stripe portion is connected to the active layer (I1) and the lateral binding WJ (
Aperiodic unevenness is formed on the boundary between the light source 121 and the light source 121, resulting in a large amount of light scattering, that is, a large internal loss.

The total loss within the resonator of the semiconductor laser is expressed as in Equation 1.

Here, αtota′l′ is the total loss, α1: internal loss, refractive index).

Also, the state and state density g for the energy ε of a single quantum well
(ε) is shown in FIG. In the figure, (a) shows electrons, trunk) shows light holes, and (c) shows heavy holes, and the stiffness similarly changes in a stepwise manner. This state with the lowest energy is nm2, nm3, etc. in order from the n-11th order. It is called the level of... In a normal quantum well semiconductor laser, oscillation occurs between n-=1, which is the lowest energy. However, if the overall loss of the resonator expressed by Formula 1 is large and the active layer (Il+ width is narrow), a state will occur in which the gain sufficient to cause laser oscillation cannot be obtained between n-1. Oscillation occurs at a level of nm2 or higher, where the density of states is larger and the wavelength is shorter.Furthermore, as n becomes larger, the density of states becomes larger, so the temperature characteristics of the threshold change of the laser improve.

In the above embodiment, as described above, since the structure has a large internal loss α1, the overall loss αtotaj- becomes large according to equation 1 when compared with a semiconductor laser having the same mirror loss. Therefore, in this embodiment, laser oscillation does not occur between n-1 and laser oscillation occurs at a level of n-2 or higher, thereby making it possible to shorten the wavelength. The aperiodic unevenness in the above embodiment effectively increases internal loss by setting the width of the active layer Cl1l to 6 micrometers or less. For example, with the same structure as this example, active J (
The rooting wavelength of the structure with no unevenness formed on 1 (It) is 8
500A, and the rooting wavelength of the above example was 8000A.

The width of the active layer (11) is set to 10 micrometers or less, preferably 6 micrometers or less, in order to effectively increase the internal loss.If it is larger than this, the internal loss due to light scattering due to the unevenness of the boundary line is reduced. The effect is in the active layer (
11) will be less affected. Especially the active layer (1
1) When the width is 1.5 micrometers or less, the effect of the unevenness of the boundary line becomes extremely apparent.

Further, when the thickness of the active layer (11) is set to 300 Å or less, electrons and holes are not distributed to the upper level, and excavation can occur more effectively at n-2 or more.

In the above embodiment, in order to increase the internal loss, aperiodic unevenness was formed at the boundary between the active layer (11+) and the lateral confinement F1a (+2), but as shown in FIG.
Even if the width of one active layer (11) is changed with respect to the direction in which light is guided, the internal loss can be increased. The width of the active layer (11) is, for example, about 1 micrometer at one end of the resonator and about 4 micrometers at the other end. In this active layer (11), light can be reflected in the central 1 micrometer stripe (inside the two dotted lines in FIG. 4), but it cannot be reflected in other areas, resulting in a large internal loss.

Furthermore, as shown in FIG. 5, even if the boundary line between the active layer (11) and the lateral confinement layer (1) is configured not to be substantially perpendicular to the resonator I41 plane, the above-described implementation is possible. Similarly to the example, the internal loss can be increased.In this case, the active layer (11) also has a stripe width of about 1 micrometer that can reflect light at the center, and the active layer (11)
The width of (ll) is approximately 4 micrometers. Here, the shape of the active layer (11) is not limited to the above embodiment, and may be configured in other shapes to increase internal loss. Further, it is preferable to provide a light trapping layer between the cladding layer and the active layer.

Further, the lateral confinement layer (121) may be anything that can produce a refractive index waveguide structure, such as an embedded heterostructure or a ridge waveguide structure.

Furthermore, the active layer structure is not limited to the AjGaAa single quantum well structure, but may be a multiple quantum well structure. Just [7, @ magazine [IEI, TOURNAL OF' QUANTUM
FLFCTRONIC3゜VOL, QE-16,N
O, 2, i, pp. 170 to 186 (1980)), in general, the use of multiple quantum wells requires a reduction in the well thickness.

Furthermore, if the active layer has a thickness of 0.5 micrometer or less, the internal loss always has a certain degree of size, so the above phenomenon can be expected even if the conventional shape is used.

Note that it is also possible to increase the overall loss and shorten the wavelength by increasing the mirror loss shown in Equation 1.

This can be done by shortening the resonator length (L), for example, in Proceedings of the 33rd Japan Society of Applied Physics (Spring 1986), No. 151.
Reported on page 2P-2. However, according to the method of shortening the wavelength by shortening the resonator length (L), the characteristics of the laser element are determined by the length of the resonator, so lasers with different wavelengths can be placed on the same substrate. It becomes difficult to accumulate.

〔Effect of the invention〕

As explained above, according to the present invention, the first conductivity type cladding layer, the active layer, and the second conductivity type cladding layer are laminated between a pair of electrodes.
In a semiconductor laser comprising a conductive cladding layer, the active layer, and a lateral confinement layer provided on the side of the cladding layer, the width of the active layer is 10 micrometers or less, and the structure has a large internal loss. This feature enables laser excavation between higher-order quantum levels, whereas conventional laser excavation occurs between the lowest energy levels, and the quantum well can shorten the excavation wavelength. This has the effect of providing a semiconductor laser.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the main parts of a quantum well semiconductor laser according to an embodiment of the present invention, and FIG. 2 is a ll-11 shown in FIG.
An explanatory diagram showing a line cross section, Figure 3 is a diagram showing the relationship between the state density and energy of electrons and holes in a quantum well structure, Figure 4
5 and 5 are explanatory views showing other embodiments of the present invention, respectively, and FIGS. 6(a) and 6(b) are explanatory views showing a front view and a cross section taken along the line A of the conventional semiconductor laser. be. if+...upper electrode, (4)...first conductivity type cladding layer, (6)...second conductivity type cladding layer, (9)...
- Lower electrode, (11)...active layer, (121...lateral confinement layer). In the drawings, the same reference numerals indicate the same or equivalent parts.

Claims (10)

[Claims] (1) Quantum well comprising a first conductivity type cladding layer, an active layer and a second conductivity type cladding layer laminated between a pair of electrodes, and a lateral confinement layer provided on the side of the active layer and cladding layer. A quantum well semiconductor laser, characterized in that the active layer has a width of 10 micrometers or less and has a structure with large internal loss. (2) The quantum well semiconductor laser according to claim 1, wherein the width of the active layer is 6 micrometers or less and the structure has a large internal loss. (3) The quantum well semiconductor laser according to claim 1 or 2, which has a light confinement layer between the cladding layer and the active layer. (4) Any one of claims 1 to 3, characterized in that aperiodic irregularities are formed on the boundary between the active layer and the lateral confinement layer to increase internal loss. Quantum well semiconductor laser described in . (5) A quantum well according to any one of claims 1 to 3, characterized in that the width of the active layer is changed with respect to the direction in which light is guided to increase internal loss. semiconductor laser. (6) The boundary line between the active layer and the lateral confinement layer is made not to be substantially perpendicular to the resonator end face, thereby increasing internal loss. Quantum well semiconductor laser according to any one of Item 3. (7) The width of the active layer is 1.5 micrometers or less,
A quantum well semiconductor laser according to any one of claims 1 to 3, characterized in that the internal loss is increased. (8) The quantum well semiconductor laser according to any one of claims 1 to 7, wherein the active layer is a multiple quantum well. (9) The quantum well semiconductor laser according to any one of claims 1 to 7, wherein the active layer is a single quantum well. (10) The quantum well semiconductor laser according to any one of claims 1 to 9, wherein the active layer has a thickness of 300 Å or less.