JPH02228088A - Quantum well laser - Google Patents

Abstract

PURPOSE:To improve injection efficiency of carriers into a quantum level by using a semiconductor layer having the same energy as at least one of quantum levels of a quantum well structure except the lowest one, and utilizing tunnel effect. CONSTITUTION:A quantum well active layer is constructed from a first quantum well structure 50, a second semiconductor layer 90 having on both sides of the first well structure 50 the same energy level as a quantum level 52 on the high energy side of the first quantum well structure, and a barrier layer 61 separating the first quantum well structure 50 and the second semiconductor layer 90. The first quantum well structure 50 has quantum levels 51, 52 whose energy gaps are 0.8eV, 0.92eV respectively. A structure, having the same energy level as at least one quantum level except the lowest one, is caused to be adjacent to the quantum well with the spacing therebetween being such that tunnel effect can occur there, so that the state density of this high energy side levels is increased. Thus, carrier injection efficiency for the lowest quantum level 51 can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a quantum well laser used as a light source for optical communication, optical calculation, or optical measurement equipment.

(Conventional technology) In recent years, with the rapid progress of thin film crystal growth technologies such as metal organic vapor phase epitaxy (MOCVD) technology and molecular beam epitaxy (MBE) technology, it has become possible to achieve steep compositions with the precision of a single atomic layer thickness. High-quality semiconductor heterojunction interfaces with variations have now been manufactured.

The potential well structure and superlattice structure formed by these heterojunctions exhibit unique optical and electrical properties compared to bulk semiconductors, and research into device applications is intensifying.

A quantum well structure semiconductor laser with a quantum well layer as an active layer utilizes electronic transitions between quantum levels with a high density of states caused by such a quantum size effect, and is more efficient than a conventional double heterojunction semiconductor laser. It has been reported that it has many characteristics such as ■low oscillation threshold current ■temperature stability ■high luminous efficiency ■increased relaxation oscillation frequency■reduced spectral line width and chirping. These excellent properties are due to quantum mechanical effects caused by localizing electrons and holes within a two-dimensional plane.

(Problem to be Solved by the Invention) However, in a laser structure having such a thin active layer, the optical confinement coefficient decreases significantly as the quantum well layer thickness decreases, and therefore the threshold current density increases. Methods to solve these drawbacks of quantum well lasers include multiple quantum well (Mult IQuanta + l/elf) lasers in which quantum wells are multiplexed to increase the optical confinement coefficient, and optical-carrier separation confinement structures (separate quantum wells).
e Conf'1nsIIent Heterostr
(cuture) laser. However, in order to further reduce the threshold and increase luminous efficiency, it is necessary to increase the injection efficiency of carriers into the quantum level. As described above, conventional quantum well lasers have had the problem of improving the injection efficiency of carriers into quantum levels and lowering the threshold value compared to conventional ones.

(Means for Solving the Problems) Means provided by the present invention to solve the above-mentioned problems are as follows:
A quantum well laser in which an active layer made of a semiconductor multilayer thin film is laminated on a semiconductor substrate, the quantum well active layer having a quantum well structure having a plurality of quantum levels, and a quantum well structure other than the lowest quantum level of the quantum well structure. a first semiconductor layer having the same energy level as at least one of the semiconductor layers; and a second semiconductor layer that separates the quantum well structure having the plurality of quantum levels and the first semiconductor layer from each other. , the second semiconductor layer is so thin that a tunnel effect appears.

(Function) In the present invention, in a quantum well structure semiconductor laser having a quantum well layer as an active layer, a semiconductor layer having the same energy as at least one of the quantum levels other than the lowest quantum level of the quantum well structure is used to create a tunneling effect. is used to improve the injection efficiency of carriers into the quantum level. This principle will be explained in detail below.

In general, the injection efficiency of carriers into the quantum level is considered to depend on the energy difference between the barrier layer and the quantum level and the kinetic energy of the carriers. Consider, for example, a quantum well structure having two quantum levels as shown in the energy band diagram of the conduction band in FIG. 3(a). Although the details of the injection mechanism and relaxation mechanism of carriers into the quantum level are not clear at present, carrier injection into the lowest quantum level 51 is possible in addition to the case where carriers are directly injected into this quantum level. This may be due to the relaxation of carriers injected into the quantum level 52 on the high energy side, and if the efficiency of carrier injection into the quantum level 52 can be increased, the injection of carriers into the lowest quantum level 51 will increase.

As shown in Fig. m3 (b), by placing a structure having the same energy level as at least one of the quantum wells other than the lowest quantum level adjacent to the quantum well at an interval sufficient to cause a tunnel effect, this high-energy level is The density of states at the lowest quantum level increases, and the same effect as effectively increasing the efficiency of injection into the quantum level 52 can be obtained, and therefore the efficiency of carrier injection into the lowest quantum level 51 can be increased. In this case, although the quantum levels of holes in the valence band do not necessarily match, the above-mentioned effect can be obtained only by matching the quantum levels of the conduction band. Further, as shown in the energy diagram of the valence band in FIG. 3(C), a similar effect can be obtained by using a structure in which the hole quantum levels 82 and 83 are made to match and utilize the hole tunneling effect.

(First Example) A first example of the quantum well laser according to the present invention will be described in detail with reference to FIG. Metal organic chemical vapor deposition (MOCVD) was used as the growth method for the quantum well structure.

As shown in the energy band diagram of the conduction band in FIG. quantum well structure 70, and a barrier layer 60 separating the first and second quantum well structures from each other. The first quantum well structure 50 has a thickness of 1.1 μm and a composition of 1 nG.
aAsP barrier 57 (thickness 120), two layers of InG
It consists of an aAs well 55 (thickness 80A) with an energy gap of 0.8eV (λ-1, 55, [Zm
), has quantum levels 51 and 52 of 0.92 eV (λ-1, 35ttm). The second quantum well structure 70 has the same composition as the first quantum well structure 50 and consists of five layers of a well 75 (thickness: 2 OA) and a barrier 77 (thickness: 10 layers), and the quantum level 72 is the same as that of the first quantum well structure 50. It has the same energy level as the quantum level 52 on the high energy side of the quantum well structure. The thickness of the barrier layer 60 separating the first and second quantum well structures from each other is IOA.

Using the quantum well active layer described above, a double channel buried structure (DC-
PBH) to form a distributed feedback (DFB) semiconductor laser. As a characteristic of a device cleaved with a cavity length of 300 μm, the oscillation threshold is 1/2 to 1/3 (5
m A degree), external differential quantum efficiency is 1.5 to 2 times (0,
An improvement of about 3W/A/facet) can be obtained. Furthermore, further improvements in properties can be expected by optimizing the barrier layer thickness and the number of wells.

The above embodiments are based on dual channel embedding (DC-PBH).
) structure has been described as an example, but it is also effective for other buried structures, ridge waveguide structures, etc.

(Second Embodiment) A second embodiment of the quantum well laser according to the present invention will be described with reference to FIG.

As shown in the energy diagram of FIG. 2, there is a first quantum well structure 50 having the same composition and thickness as in the first embodiment, and on both sides there is a quantum well structure 50 on the high energy side of the first quantum well structure. A second semiconductor layer (400 A thick) 90 having the same energy level as the level 52, and a barrier layer (10 A thick) 61 separating the first quantum well structure 50 and the second semiconductor layer 90. It is composed of.

It is expected that such a quantum well laser will also have excellent characteristics similar to those of the first embodiment.

Furthermore, although the above two embodiments have been explained using an InP-based quantum well structure as an example, the present invention is also effective in a general semiconductor quantum well structure such as a GaAs-based quantum well structure.

(Effects of the Invention) As described above, according to the present invention, it is possible to increase the injection efficiency of carriers into quantum levels, and to realize a quantum well laser with a low threshold and high luminous efficiency.

A barrier layer separating the conductor layer 80, 70 a second quantum well structure, 75, 77 a well and barrier layer of the second quantum well structure, 81, 82, and 83 quantum levels of the valence band; 90 is a second semiconductor layer.

[Brief explanation of the drawing]

FIG. 1(a) is an energy band diagram of a conduction band in a first embodiment of the present invention, and FIG. 1(b) is a perspective view of the first embodiment. FIG. 2 is an energy band diagram of a conduction band in a second embodiment of the present invention. FIG. 3 is a detailed explanatory diagram of the present invention.

Claims (2)

[Claims] (1) In a quantum well laser in which an active layer made of a semiconductor multilayer thin film is laminated on a semiconductor substrate, the quantum well active layer has a quantum well structure having a plurality of quantum levels, and the quantum well structure has a lowest quantum level. a first semiconductor layer having the same energy level as at least one of 1. A quantum well laser, wherein the second semiconductor layer is thin enough to cause a tunnel effect. (2) The quantum well laser according to claim 1, wherein the first semiconductor layer has a quantum well structure.