JPS6356977A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To realize low threshold voltage, by providing a quantum well structure with a first semiconductor layer whose thickness is smaller than the de Broglie wavelength of electron or positive hole, and a second semiconductor layer between which the first layer is put, its forbidden bandwidth being larger than that of the first layer, its thickness being larger than the de Broglie wavelength. CONSTITUTION:The MQW put between HR-AlxGa1-xAs(x=0.7) layers of 1mum thick clad layer is formed by laminating alternately four GaAs layers as a well layer and three AlxGa1-xAs(x=0.7) layers as a barrier layer. The 0.5mum thick GaAs layer being the highest layer is a contact layer for ohmic contact. For the MQW layer, the barrier height is made so high as x=0.7 by transversal injection. The thickness of the barrier layer is made thick so as to be larger than 300Angstrom being the de Broglie wavelength of GaAs by transversal implantation. In accordance with the increase of the x-value of an active layer, the difference of refractive index between the active layer and the clad layer is set sufficiently large, in order to confine the light effectively. Therefor, x=0.7 is applied also to the HR-AlxGa1-x of the clad layer. Thereby, a quantum well laser having a low threshold value and a short wavelength can be obtained.

Description

[Detailed Description of the Invention] [Summary] In a lateral injection laser having a quantum well structure as an active layer, the thickness of the second semi-quaternary layer (barrier layer) constituting the quantum well is made to be at least the de Broglie wavelength. Make it sufficiently large to have a sufficient number of carriers (electrons and holes) in the first semiconductor layer (well N).
By horizontally injecting carriers into the well layer, non-uniformity in carrier injection between the well layers is prevented, and the threshold value of the laser can be lowered.

[Industrial application field]

The present invention relates to a quantum well structure of a lateral injection laser having a quantum well structure as an active layer.

Semiconductor lasers have come to be widely used as power sources for optical communications, and technological developments are being actively conducted to improve their performance.

The present applicant previously filed a patent application in 1983 for a lateral injection laser with a quantum well structure as an active layer, which improved the lateral confinement effect of light, reduced the threshold current, and was integrated. 2
Although disclosed in the specification of No. 7059, the present invention proposes a quantum well structure for further lowering the threshold value and shortening the wavelength of this laser.

[Conventional technology]

Regarding conventional lasers with a quantum well structure as the active layer, in which current flows perpendicular to the quantum well layer,
Low threshold oscillations have been reported.

The reason why a quantum well laser oscillates at a low threshold is because the length of the well layer is set below the de Broglie wavelength, and the electrons or holes in the well layer are converted into two-dimensional electron gas due to the quantum size effect. This is due to the high density of states of the lowest quantum level in the propagation plane and valence band.

Therefore, the relationship between the current density injected into the well layer and the optical gain is such that a large gain can be obtained with a small current compared to a normal double hetero (DH) structure laser, but a single quantum well (SQW) laser , the optical gain is 5
When it exceeds 00 cm-', it shows a tendency to saturate (see Fig. 3).

1) Dutta et al., J., 8pp.
1. Phys, 53 (1982)? 221゜Therefore, we developed a multi-quantum well system in which a large number of quantum wells are arranged close to each other in the vertical direction to improve light confinement and to suppress the optical gain imposed on each quantum well to a small level to oscillate at a low threshold. (MQW) laser was developed.

However, in conventional MQW lasers, carriers (electrons and holes) are injected perpendicularly to the semiconductor layer that makes up the MQW, so the barrier height is large enough to obtain sufficient quantum effects. , and when a thick barrier layer is used, carriers tunnel through each barrier layer and are injected into each well layer, resulting in non-uniformity in the number of injected carriers (see FIG. 4). Therefore, it was not possible to increase the number of quantum wells to be arranged.

^lXGa,, As (barrier layer)/GaAs (well layer) MQW requires a minimum barrier height of x-0.2, and the optimum number of barrier layers is 4 to 6 at most.

If a barrier layer with a lower barrier height is used to improve the non-uniformity of the injected carriers, the wave function localized in each quantum well will spread, making it impossible to obtain a sufficient quantum size effect ( (See Figure 5).

On the other hand, the lateral injection j1Ω proposed by the present inventors
Next, the laser will be explained.

FIG. 6 is a cross-sectional view illustrating the structure of a lateral injection laser having a quantum well structure as an active layer.

In the figure, 1 is a 5r-GaAs substrate, 2.4 is a cladding layer with a thickness of 1 μm, and is a high resistance (HR) -A1xGa+-xA4 (x = 0.45
), 3 is an active layer with a multiple quantum well (M leaf) structure, and 3A is an active layer (emitting region) of a lateral injection laser, with a width of 0.5 to 1.
5μm 5 is a p-type region (p-type electrode region) formed by diffusion of p-type impurity (Zn), 5A is a disordered region by p-type diffusion, 6 is an n-type region formed by diffusion of n-type impurity (St) (n-type electrode region), 6A is a disordered region due to n-type diffusion.

The disordered regions 5A and 6A are made of GaAs and AlGaAs.
In this region, the active layer forms a double heterostructure in the lateral direction, which improves the lateral confinement of light.

Next, an outline of the manufacturing process of this laser will be explained.

First, a 11R'-AIGaAs cladding layer 2 with a M[lW structure An active layer 3 and an HR-AIGaAs cladding layer 4 are sequentially grown.

Next, Zn is diffused at 600° C. to form n-type region 5, and Si is diffused at 850° C. to form n-type region 6.

For forming these regions, ion implantation may be used instead of the above-mentioned vapor phase diffusion.

Through the above steps, a lateral injection MQW laser is formed on the substrate.

Figure 7 shows a conventional MQW structure (GaAs/AlGaAs
A1. Mixed crystal ratio of Ga, As
FIG.

In the figure, one leaf is formed by alternately stacking 5 GaAs layers with a thickness of 80 layers and 4 layers of AlxGa+-Js (x=0.3)at with a thickness of 120 layers.

In the lateral injection MQW laser described above, carriers are directly injected from the electrode into each well layer in the lateral direction (parallel to the well layer), so the number of injected carriers in each well layer is uniform, and therefore the number of MQH layers is can be increased.

[Problem that the invention seeks to solve]

However, even in a lateral injection MQW laser, if the conventional MOW structure is used as the active layer, the barrier layer is thicker than the well layer, but it is still less than the de Broglie wavelength, so the bases of the wave functions of each well overlap. However, the drawback was that a complete quantum size effect could not be obtained.

[Means for solving problems]

The solution to the above problem is to have an active layer with a quantum well structure, a cladding layer of insulating or semi-insulating semiconductor layers sandwiching the active layer, and a conductive impurity that is inserted into the active layer at intervals through the cladding layer. The quantum well structure in the p-type and n-type regions is disordered, and the active layer has a muntin well lateral structure having a double heterostructure in the lateral direction. In the directional injection laser, the quantum well structure includes at least a first semiconductor layer having a thickness smaller than the de Broglie wavelength of electrons or holes, and a semiconductor layer sandwiching the first semiconductor layer and having a forbidden band width of the first semiconductor layer. This is achieved by including a second semiconductor layer that is larger than the semiconductor layer and has a thickness equal to or greater than the de Broglie wavelength.

The quantum well structure may be either a 5 (IW) or an MQW structure.

[Effect]

The present invention can reduce the thickness of the laser element, facilitate integration,
In a lateral injection quantum well laser with a low threshold and small parasitic capacitance, carriers can be uniformly injected into each well layer from the lateral direction, so there are no restrictions on the thickness and height of the barrier layer. Therefore, by making the thickness of the barrier layer of the quantum well structure at least equal to the de Broglie wavelength, and by making the barrier height sufficiently large and localizing the injected carriers at a sufficient density within each well, it is possible to achieve even lower This is the result of thresholding.

〔Example〕

Figure 1 shows the horizontal direction of the present invention! 14 is a distribution diagram of the mixed crystal ratio X of Ga, -, As in the thickness direction.

In the figure, HR-AIXG with a 1 μm thick cladding layer
The 4Q insulator sandwiched between the layers is a well layer with a thickness of 60 μm, and a barrier layer of 300 μm thick AlxGa+−xAs (x =
0.7) Formed by laminating three layers alternately.

The uppermost GaAs layer with a thickness of 0.5 and 1 m is a contact layer for establishing ohmic contact.

When carriers are injected vertically into the MQW layer, the barrier height is as low as x=0.3, but in the present invention, it can be made as high as x=0.7 by lateral injection.

In addition, the thickness of the barrier layer is determined by lateral injection in the present invention.
, the de Broglie wavelength of GaAs can be 300 Å or thicker.

In addition, as the X value of the active layer increases, II! ? -to 1. Ga1
−． The 45th layer is also made larger than the conventional example at X-0.7.

Figure 2 shows the horizontal direction of the present invention! FIG. 2 is a distribution diagram of the mixed crystal ratio X of As in the thickness direction, illustrating another example of the QW laser.

In the figure, a 1 μm thick cladding layer) IR-A1.
The MQW sandwiched between Ga+- and As(x=0.7)N is used as a well layer with a thickness of 60 people AIXGap-Js(x
= 0.2) layers, and six AlAs layers with a thickness of 300 layers are alternately laminated to form a barrier layer.

The oscillation wavelength is 8,300 to 8,500 when the well layer is made of GaAs (example in Figure 1), but in this case it is approximately 6,500.
A short wavelength laser for visible light can be obtained.

When a laser is used for measurement, its accuracy is determined by the wavelength, so short wavelength lasers are often used for measurement. However, gas lasers are the mainstream of current short-wavelength lasers, and the equipment is large, so the emergence of half-four-body lasers has been expected.

In general, it is difficult to lower the threshold voltage of a semiconductor laser for visible light, but by using a shrimp layer with a composition containing AI in the well layer as well, the present invention eliminates non-uniformity of injected carriers and achieves a short wavelength with a low threshold value. Semiconductor lasers are now available.

In the embodiment, a GaAs/AlGaAs-based laser has been described, but exactly the same effect can be obtained with lasers with other compositions that can be disordered (GaP/GaAsP, InGaAs/GaAs superlattice, etc.).

〔Effect of the invention〕

As described above in detail, according to the present invention, a lateral injection quantum well laser with a low threshold value and a short wavelength can be obtained.

[Brief explanation of drawings]

FIG. 1 illustrates an embodiment of the lateral MQW laser according to the present invention. A distribution diagram of the mixed crystal ratio χ of AtXca, -, As in the thickness direction. FIG. 2 is a diagram explaining another embodiment of the lateral MQW laser of the present invention. A distribution diagram of the mixed crystal ratio X of Ga, -, As in the thickness direction. Figure 3 is a diagram of the relationship between optical gain and current density. Figure 4 is a diagram of the relationship between optical gain and current density. Figure 5 shows the spread of the wave function when each barrier layer is lowered. Figure 6 shows the carrier distribution in each well layer when vertical injection is performed in layer 11. Figure 6 shows the spread of the wave function when each barrier layer is lowered. Figure 6 shows the quantum well structure as the active layer. A cross-sectional view explaining the structure of a lateral injection laser, FIG. 7 shows a conventional MQW structure (GaAs/AlGaAs
FIG. 3 is a distribution diagram of the mixed crystal ratio x of AlxGa+-xAs in the thickness direction, illustrating the periodic structure of FIG. In the figure, 1 is a 5I-GaAs substrate, 2.4 is a cladding layer and HR-AIGaAs layer, and 3 is an MQ
Active layer of W structure, 3A is active layer (light emitting region) of lateral injection laser, 5 is p
5^ is a disordered region due to p-type diffusion, 6 is an n-type region (n-type electrode region), and 6A is a disordered region due to n-type diffusion. Settf) ふ臘い行e1对园2 园亭3＠ 4圀亭5因Oh! line? 761th house owner, Ki\L-length゛0 Front 1F Exit 4? 1 6th area/'7QW/: χ intervention map 7

Claims (1)

[Claims] An active layer having a quantum well structure, a cladding layer of insulating or semi-insulating semiconductor layers sandwiching the active layer, and conductive impurities being applied to the active layer at intervals through the cladding layer. the active layer has a double heterostructure in the lateral direction, and the quantum well structure in the p-type and n-type regions is disordered; at least a first semiconductor layer with a thickness smaller than the de Broglie wavelength of electrons or holes, and a semiconductor layer sandwiching the first semiconductor layer with a forbidden band width larger than that of the first semiconductor layer and with a thickness smaller than the de Broglie wavelength of electrons or holes; A semiconductor laser comprising a second semiconductor layer having a thickness equal to or greater than the Broglie wavelength.