JPH0330486A - Multi quantum well light emitting element - Google Patents

Abstract

PURPOSE:To make carriers uniform in distribution so as to obtain a muliple quantum well light emitting element excellent in characteristics by a method wherein donors and acceptors are partly added to the P-clad layer side and the N-buffer layer side of a semiconductor thin film which constitutes an active layer respectively. CONSTITUTION:An N-InP buffer layer 2, a muliple quantum well active layer 3 composed of an InGaAs well layer 4 and an InP barrier layer 5, and a P-InP clad layer 6 are successively laminated on an InP substrate 1, and then a P- electrode 7 and an N-electrode 8 are provided to the P-InP clad layer 6 and the rear side of the substrate 1 to form a light emitting element. Moreover, donors are wholly added to the part of the active layer 3 close to the clad layer 6 and acceptors partly added to the part of the active layer 3 close to the buffer layer 2.

Description

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

[Conventional technology]

Quantum well type semiconductor lasers, which have a semiconductor multilayer thin film as an active layer, reflect the fact that the density of states is step-like, and compared to normal double heterojunction (D H) structure semiconductor lasers,
Low threshold, high characteristic temperature To.

It has excellent characteristics such as narrow spectrum spread during modulation. As one of them, Dutta et al. of AT&T Be11 Laboratory published Applied Physics Letters magazine (^pp1. Phys, Lett,, voi.

46, p1036-1038.1985), an InGaAsP well layer with an emission wavelength of 163 μm composition (hereinafter abbreviated as 1.3 μm composition) and an InGaAsP barrier layer with a 1.03 μm thickness (both approximately 300 μm thick)
reported a multi-quantum well laser with an active layer consisting of several layers stacked alternately. Here, Dutta et al. evaluated the temperature dependence of carrier lifetime at the threshold value and reported that the temperature characteristics of a multiple quantum well laser are superior to that of a normal semiconductor laser. In addition, Takano et al.
9-35. (October 24, 1988), experiments showed that quantum well lasers have a narrower spectral linewidth than ordinary semiconductor lasers, and that the fewer the number of well layers, the narrower the spectral linewidth. It was clearly revealed.

[Problem to be solved by the invention]

In a multiple quantum well laser, it is necessary to uniformly inject carriers into each quantum well, and if the injection is performed non-uniformly, there is a risk that the characteristics of the multiple quantum well laser will not be sufficiently developed. In particular, in multi-quantum well lasers with a large number of quantum well layers, characteristic deterioration due to non-uniform carrier distribution is remarkable.

In a normal multi-quantum well laser in which impurities are not added to the quantum well active layer, during laser oscillation,
As shown in FIGS. 3(a), (b), and (c), holes decrease on the n-type cladding layer side, and electrons decrease on the p-type cladding layer side. That is, the n-type cladding layer (Fig. 3 (
In case a), the electrons injected from the buffer layer 2 are sequentially injected into adjacent quantum wells due to the diffusion effect, the drift effect due to the electric field, and furthermore, when the barrier layer 5 is thin, the tunnel effect. go. Therefore, the electron density is high in quantum wells close to the n-type cladding layer, and the electron density is low in quantum wells close to the p-type cladding layer 6. Furthermore, since holes are injected from the opposite direction to electrons, the hole density is low in quantum wells near the n-type cladding layer, contrary to the distribution of electron density, and in quantum wells near the p-type cladding layer 6, holes are injected from the opposite direction to electrons. This results in a dense distribution. Therefore, a quantum well near the center of the quantum well active layer can have a gain, but a quantum well near the p-type cladding layer and the n-type cladding layer causes no gain but a loss. Furthermore, since the carrier density of each quantum well is fixed at a carrier density that balances the loss and gain generated as described above, even during laser oscillation, as shown in FIG. 3(b), ? (
This results in non-uniform carrier distribution as shown in c). The same applies to light emitting diodes.

The object of the present invention is to provide a multilayer multi-quantum well light emitting device,
The object of the present invention is to provide a multi-quantum well light emitting device with excellent characteristics by making the carrier distribution uniform.

[Means to solve the problem]

The present invention is characterized in that, in a multi-quantum well light emitting device having a semiconductor multilayer film as an active layer, a donor is partially added to the p-cladding side of the semiconductor thin film constituting the active layer, and a 7xbuter is partially added to the n-cladding side of the semiconductor thin film constituting the active layer. A multi-quantum well light emitting device solves the above problems. Alternatively, the above-mentioned problem can be solved by a multi-quantum well light emitting device characterized in that a donor is added to the entire active layer.

[Effect]

In order to solve the above-mentioned problem, it is conceivable to reduce the thickness of the barrier layer in order to uniformly inject carriers, and to uniformly inject carriers into each quantum well by the tunnel effect. However, this makes it impossible to ignore the coupling of electron wave functions between quantum wells, resulting in the formation of many subbands. As a result, the width of the gain curve widens and the gain decreases, making it impossible to bring out the excellent characteristics of the quantum well laser.

The present invention is directed to a multi-quantum well laser in which the carrier density is non-uniformly distributed in each quantum well, by adding impurities to the quantum well active layer in advance to reduce the deterioration in characteristics caused by this.

FIG. 3(a) shows an example of the potential of a normal multiple quantum well laser in which no impurity is added to the quantum well active layer. As shown in the figure, during laser oscillation, it is expected that the carrier density in each quantum well is considerably non-uniform. Here, since electrons and holes are injected from opposite directions, both electrons and holes are injected into the quantum well near the center of the multi-quantum well active layer, which can provide gain. However, near both ends of the quantum well active layer away from the center of the active layer, the hole density is low in areas with high electron density, and the electron density is low in areas with high hole density, which causes an increase in internal loss. Cause.

Therefore, if a reverse carrier distribution is created in advance in the active layer by adding a donor to the side of the quantum well active layer near the p-cladding layer and a donor to the side near the n-cladding layer, current can be injected. It is possible to improve the uniformity of carrier distribution at the time. As a result, an increase in internal loss caused by non-uniform distribution of carriers can be avoided, and a multi-quantum well light emitting device with a small threshold current and excellent characteristics can be provided.

Furthermore, in quantum wells, it has been revealed through logical analysis that the decrease in electron density is about 10 times larger than the decrease in hole density, so adding donors throughout the active layer is necessary. This is also an extremely effective means for increasing loss in the active layer. Regarding the hole density, although carrier non-uniformity may occur, the loss due to this is small.

On the other hand, since a decrease in electron density can be avoided compared to the case of a non-doped active layer, an increase in loss can be prevented, and a multi-quantum well light emitting device with excellent characteristics can be obtained.

〔Example〕

In the following, the present invention will be explained in more detail with reference to the drawings showing examples. An embodiment according to the present invention is shown in FIGS. 1 and 2.

FIG. 1(a) of the first embodiment is a cross-sectional structural diagram, FIG. 1(b) is an energy band diagram of the conduction band, FIG. 1(C) is the distribution of donor impurities, and FIG. 1(d) 1 shows the distribution of acceptor impurities, and FIGS. 1(e) and 1(f) show the electron and hole distributions during laser oscillation. In the fabrication of this example, an n-InP buffer layer 2 is formed on an InP substrate l to a thickness of 0.
．． 5. um, InGaAs well layer 4. The multi-quantum well active layer 3 made of an InP barrier layer 5 has a thickness of 0.245. u
After sequentially laminating p-InP cladding layers 6 with a thickness of 0.5 μm, p-electrodes 7. The configuration is such that an n-electrode 8 is attached. Also,
The multi-quantum well active layer 3 has 15 layers including 70 InGaAs well layers 4 and 100 InP barrier layers 5.
It has a structure in which 14 layers are stacked alternately in sequence.

In this embodiment, a maximum of 8Xl□itam-3n
-Maximum of 8 acceptors near the InP buffer layer 7
X 1017an-'' is added. The state of this impurity addition is shown in FIGS. 1(c) and 1(d).

By adding the impurities as described above, the non-uniformity of the carrier density in the stacking direction during laser oscillation is reduced, and areas with extremely low electron and hole densities no longer exist. When the threshold current density of the Okel electrode was measured during laser oscillation, it was found to be about 800 A/cJ. This is 1.2-1.5 of a normal DEI laser.
This is a value 50% lower than K A/d. Furthermore, this stacked structure was processed into a striped structure, and semiconductor layers were formed on both sides of the striped stacked structure using the LPE method to create a buried structure. Differential quantum efficient per 2
A 5% multiple quantum well laser was obtained.

Further, the characteristic temperature T0 of the laser is 90=100, which is significantly improved compared to a normal DB structure laser.

The temperature dependence of the carrier lifetime at the threshold value also has a smaller rate of change compared to the DH structure, and the oscillation spectrum broadening during pulse modulation also differs from that of the DH structure laser, reflecting the step-like density of states due to the multiple quantum well structure. Compared to 1
/2-1/3.

The energy band diagram of the second embodiment is shown in FIG. 2(a).
The distribution of donors is shown in FIG. 2(b), the distribution of acceptors is shown in FIG. 2(c), and the distribution of electrons and holes during laser oscillation is shown in FIG. 2(d) and (e). The cross-sectional structure of the multiple quantum well laser was the same as that of the first embodiment.

In the second example, donors were added to the entire multi-quantum well active layer 3 in a maximum amount of 8 x 10 cm-'. The state of this impurity addition is shown in FIGS. 2(b) and 2(c).
It is expected that a multi-quantum well laser having almost the same excellent characteristics as the first embodiment can be obtained in this embodiment as well.

〔Effect of the invention〕

As described above, in the present invention, by adding impurities to the multi-quantum well active layer of a multi-quantum well laser, it is possible to provide a multi-quantum well laser with excellent characteristics in which the uniformity of the injection carrier distribution is improved.

In the examples, InP and InGaAs semiconductor materials were used, but the material used for the tip of the present invention is of course not limited to these, and may include GaAs, AlG, etc.
There is no problem in using other materials such as aAs-based materials. Further, although the above description has been made regarding a semiconductor laser, the structure of the present invention is also effective for a light emitting diode.

[Brief explanation of drawings]

FIG. 1 shows a first embodiment of the present invention, in which (a) is a cross-sectional structural diagram, (b) is an energy band diagram around the active layer, and (c) and (d) are impurity A diagram showing the state of addition, (e) and (r) are electrons during laser oscillation,
FIG. 3 is a diagram showing hole distribution. FIG. 2 shows a second embodiment of the present invention, in which (a) is an energy band diagram of the active layer Jffi side, and (b) and (c) are diagrams showing how impurities are added. (d) and (e) are diagrams showing electron and hole distributions during laser oscillation. Figure 3 shows a conventional multiple single-well laser in which no impurities are added to the active layer. Figure 3 (a) is an energy band diagram around the active layer, Figure 3 (b), and Figure 3 (c). shows the electron and hole distribution during laser oscillation. In the figure, 1 is an n-InP substrate, 2 is an n-type nP buffer layer, 3 is a multiple quantum well active layer, 4 is an InGaAs well layer, 5 is an InP barrier layer, 6 is a p-InP cladding layer, 7
8 indicates a p-electrode and 8 indicates an n-electrode.

Claims (2)

[Claims] (1) In a multi-quantum well light emitting device having at least a stacked structure in which an active layer with a multi-quantum well structure made of a semiconductor multilayer thin film is sandwiched between a p-type cladding layer and an n-type cladding layer, the semiconductor constituting the active layer A multi-quantum well light emitting device characterized in that a donor is partially added to the p-cladding side of the thin film, and an acceptor is partially added to the n-cladding side of the thin film. (2) In a multi-quantum well light-emitting device that includes at least a stacked structure in which an active layer with a multi-quantum well structure made of a semiconductor multilayer thin film is sandwiched between a p-type cladding layer and an n-type cladding layer, donors are provided throughout the active layer. A multi-quantum well light-emitting device characterized by doping.