JPS63153883A - Quantum well type semiconductor light-emitting element - Google Patents

Abstract

PURPOSE:To inject carriers efficiently without harming the quantum effect by a method wherein the thickness of a harrier layer and well layer is so designed as to be largest at the middle of an active layer in a multiple quantum well (MQW). CONSTITUTION:On an InP substrate 1, an n-InP buffer layer 2, MQW active layer 3, and p-InP clad layer 6 are formed in that order. In the MQW active layer 3 on the n-InP buffer layer 2, an InGaAs well layer 4 is 70Angstrom thick and an InP barrier layer 5 is 40Angstrom thick. The InGaAs well layer 4 is allowed to grow thicker at an increment of 6-8Angstrom toward the middle while the InP barrier layer 5 is allowed to grow thicker at an increment of approximately 10Angstrom toward the middle so that they may be as thick as 100Angstrom and 80Angstrom at the middle, respectively. The MQW active layer 3 itself is approximately 0.15mum thick. An MQW laser to this design is of a surface electrode structure in which the average oscillation threshold current density is near 800A/cm<2>, which is only 50-60% of the 1.2-1.5KA/cm<2> in a conventional DH laser.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a quantum well type semiconductor light emitting device.

(Prior Art) A quantum well type semiconductor laser having a semiconductor multilayer thin film as an active layer has a lower threshold current and a higher characteristic temperature T0. It has excellent characteristics such as small spectrum spread during modulation. As one example, Dutta et al. of AT&T Be11 Laboratory published Applied Physics Letters (Ap61.
s, Lett,, vol, 46゜p1036-10
38.1985), an InGaAsP well layer with an emission wavelength of 1.31 m and an InG well layer with a composition of 1.03 μm.
We have reported a multiple quantum well (MQW) laser in which several layers of aAsP barrier M (all approximately 300 layers thick) are laminated. This laser has excellent characteristics such as low threshold current and high efficiency.Dutta et al. evaluated the temperature dependence of the carrier lifetime at the threshold, and found that the temperature characteristics of the MQW laser compared to a normal DH laser. proved to be superior.

(Problems to be Solved by the Invention) In the case of MQW lasers, in order to make the quantum effect more pronounced and further improve the laser characteristics, it is effective to increase the energy difference between the well layer and the barrier layer. For example, M Q W in the wavelength 1.55-band
When considering a laser, I n O,! ! 30a6.47A
A combination in which the B layer is used as a well layer and the InP layer is used as a barrier layer has the largest energy difference, and a more significant quantum effect can be expected. As for the concrete M structure, the former is 100 people,
By making the latter 80 layers thick and alternately stacking 10 layers each, an MQW laser that oscillates at approximately 1.55 μm can be obtained. FIG. 3(a) shows the cross-sectional structure of such a laser, and FIG. 3(b) shows the energy band diagram of the conduction band in that structure.

However, when attempting to operate as a laser, it is necessary to efficiently inject carriers into the active region.
In such a structure, it is difficult to do this efficiently; for example, electrons injected from the n-type cladding layer reach the active region and become an InPn layer, but with the thickness as described above, the transmission of electron wave packets is difficult. It is conceivable that the ratio of is not sufficiently large, and as a result, the electron wave function is not sufficiently uniformly distributed over the entire MQW active layer 3, but is distributed biased towards the n-type 1nP layer 2 side.
A similar problem occurs with holes, and as a result, the characteristics of the quantum well laser, such as the low threshold characteristics of the laser, may not be fully exploited.

SUMMARY OF THE INVENTION An object of the present invention is to provide a quantum well type semiconductor light emitting device in which a quantum effect appears significantly and characteristics are improved.

(Measures for Solving Problems Vi) The present invention provides a quantum well type semiconductor light emitting device having a semiconductor multilayer thin film as an active layer, wherein the thickness M of the semiconductor thin film constituting the active layer is larger than the active layer. The above-mentioned problems are solved by a quantum well type semiconductor light emitting device characterized in that the active layer is larger in the center than in the vicinity of the sandwiching cladding layers.

(Function) In order to solve the above-mentioned problem, one way is to make the barrier layer 5 thinner, so that the electron wave packet can be distributed more uniformly in the active layer 3. However, the I of the entire active layer 3
As expected, the quantum effect becomes smaller when the nPn width is 9. Therefore, in the central part of the active layer 5, the well 7114 is made to have 100 people and the barrier layer 5 is made to have 80 people, and the barrier layer 5 is made thinner in the vicinity of the cladding layer, and the well layer 4 is also made thinner. By setting the base quantization level to approximately 1.551 m, carriers can be efficiently injected into the active layer 3 without impairing the quantum size effect, and a quantum well semiconductor laser with excellent characteristics can be obtained. Obtainable.

Figure 2 shows the electron distribution and energy band diagram to explain the operation and principle of the present invention. Figure 2 (a) corresponds to the case of the conventional example, where all the well layers have the same thickness and the barrier layers have the same thickness over the entire active layer, and the injected electrons are wave bundled by the thicker barrier layer. is attenuated and shows a skewed distribution. In Figure 2(b), compared to the same figure (a), only the barrier layer has a smaller thickness at the periphery.In this case, the electrons are distributed relatively uniformly, but the fundamental quantum level differs in each well. Figure 2 (c) corresponds to the present invention, in which the electron distribution is changed by changing the well layer width so that the fundamental quantum level is almost the same in all well layers. It is possible to obtain an MQW laser with excellent characteristics, which is relatively uniform and has a narrow emission spectrum width.

(Example) The present invention will be explained in more detail with reference to the drawings showing examples below. An example according to the present invention is shown in FIG. 1. 1st
Figure 1(a) shows the cross-sectional structure, and Figure 1(b) shows the energy band diagram (conduction band only) around the active layer.

In the production of this example, n-I
The nP buffer layer 2 has a thickness of 0.5n, the MQW active layer 3, and the p-InPn type cladding layer 6th order 8f layer.
In the W active layer 3, from the n-InPn double layer, the InGaAs well layer 4 is increased by 70 layers, the InPn rim 9 is increased by 8 layers, and the barrier layer is increased by about 10 layers, and in the central part, each layer is increased by 10 layers.
It was set to 0 and 80 people. The total thickness of the active layer 3 was approximately 0.15 m.

The MQW laser fabricated in this way has a full-surface electrode configuration, and has an average oscillation threshold current density of 800 A/-, which is 50 to 6 A/- compared to 1.2 to 1.5 of a normal DH laser.
We were able to reduce it to 0%. Furthermore, this laser wafer was made into a buried structure using the LPE method, and its characteristics were evaluated. The lasing threshold current at room temperature CW was 15 to 20 nA,
A device with a differential quantum efficiency of about 25% per side was obtained with good reproducibility.

When the temperature characteristics of the laser were evaluated, the characteristic temperature T0
was 90 to 100, which was a significant improvement compared to a normal DH structure laser. The temperature dependence of the carrier lifetime at the threshold value also has a smaller rate of change compared to DHtR, and furthermore, MQW'! It was found that the oscillation spectrum spread during pulse modulation was also reduced by 172 to 1/3 compared to the DHIIII laser, reflecting the step-like density of states function due to the PI structure.

(Effects of the Invention) As described above, in the present invention, in an MQW laser, by increasing the thickness of the barrier layer and the well layer in the center of the active layer, carrier injection can be performed efficiently without impairing the quantum effect. This made it possible to provide a quantum well type semiconductor laser with excellent characteristics.

Although InP and InGaAs semiconductor materials were used in the examples, the material systems used in the present invention are of course not limited to these, and include GaAJ! There is no problem in using other materials such as As to GaAs, and although a semiconductor laser has been described above as a device, the structure of the present invention is also effective for a light emitting diode.

[Brief explanation of the drawing]

FIG. 1(a) is a cross-sectional structural diagram of an embodiment of the present invention, FIG. 1(b) is an energy band diagram around the active layer in the embodiment, and FIG. 2 is an electron diagram for explaining the invention in detail. Distribution, energy band diagram, Fig. 3 (a) is M according to the conventional example.
The cross-sectional structural diagram of the QW laser, FIG. 3(b), is its energy band diagram. In the figure, 1 is a substrate, 2 is an n-InPl layer, 3 is an MQW active layer, 4 is an InGaAs well scrap, 5 is an In°P barrier layer, and 6 is a p-InP ground layer. (a) (b) 1st c! I (a) (b) Figure 2

Claims (1)

[Claims] A quantum well type semiconductor light emitting device having a semiconductor multilayer thin film as an active layer, characterized in that the thickness of the semiconductor thin film constituting the active layer is larger in the center of the active layer than in the vicinity of the cladding layer sandwiching the active layer. A quantum well type semiconductor light emitting device.