JPH0812928B2 - Semiconductor modulation doped structure - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to semiconductor modulation doped structures.

[Conventional technology]

Modulation doping, in which impurities are doped only in specific layers of a multi-layered structure in which semiconductors are multi-layered, is used for electronic devices such as high electron mobility transistors (HEMT) for ultra-high speed operation, and multiple quantum well (MQW) semiconductors. This was conceived in order to realize ultra-low threshold and ultra-high-speed modulation in the laser, but the diffusion of impurities through the heterojunction interface was a problem during the high temperature process during device fabrication.

In the modulation doping of the conventional example, Si or the like was used as the n-type dopant in HEMT. On the other hand, Zn which is generally used as a p-type dopant in the modulation doping in the active layer of the MQW semiconductor laser.
Has a very large diffusion constant and easily diffuses at a high temperature of 600 ° C. or higher, making it difficult to fabricate a modulation doping structure. Cd and Be are p-type dopants with relatively small diffusion constants, and AlGaAs-based materials grown by molecular beam epitaxy (MBE) have been prototyped by Uomi, Hitachi, Ltd. (Uomi, Applied Physics, Applied Physics, Vol.57, No.5, p.708 (1988)), but due to their strong toxicity, these remain a problem in safety.

[Problems to be Solved by the Invention]

In the above-mentioned conventional techniques, there is no method for safely producing a particularly favorable p-type modulation doping structure (that is, the impurity concentration sharply changes at the heterojunction interface).

An object of the present invention is to eliminate such drawbacks of the prior art and provide a semiconductor modulation doped structure intended for application to various semiconductor devices including optical devices such as MQW semiconductor lasers. .

[Means for solving the problem]

In the semiconductor modulation-doped structure according to the present invention, at least one non-doped spacer layer having a composition different from that of the impurity-doped layer is formed between the impurity-doped layer and a semiconductor layer adjacent to the impurity-doped layer. It is characterized by.

[Action]

In the present invention, by utilizing the phenomenon that the diffusion of impurities is hindered at the hetero interfaces of semiconductor materials having different diffusion constants, a spacer layer made of such materials having different diffusion constants is used to form a modulation doping structure. This is to prevent the impurity atoms of the modulation doping layer (impurity-doped layer) from diffusing to the adjacent non-doped layer through the hetero interface. However, in this case, the total thickness of the spacer layer is so thin that electrons and holes can pass through the spacer layer by the tunnel effect (thickness of about 100 A or less of de Broglie wavelength in the semiconductor of electrons and holes). It is necessary to do.
By doing so, electrons and holes can easily pass through the spacer layer to supply carriers to the non-doped layer, but the impurity atoms of the impurity-doped layer are prevented from diffusing into the non-doped layer by the spacer layer. A good modulation doping structure can be manufactured.

In FIG. 2, at the hetero interface of the semiconductor composed of the InGaAsP layer 21 and the InGaAs layer 22, two kinds of materials having different diffusion constants (in that case, InP and InP This is a comparison of Zn impurity diffusion states under the same diffusion conditions for a spacer layer in which one thin film of InGaAs) is inserted one by one (FIG. 2 (b)). As can be seen from this figure, 0.1 μm from the bonding interface
At a depth of 10 ¹⁸ cm ^{-3 for} a single heterojunction
The Zn concentration is 10 ¹⁷ cm ^-3, which is one digit smaller when the spacer layer composed of the InP layer 23 and the InGaAs layer 22a is sandwiched.
The concentration is. InGaAs has a smaller diffusion rate than InP, and the concentration of Zn diffused in the InGaAs layer 22a becomes significantly smaller when it enters the next InP layer 23. It can be seen that the diffusion of impurity atoms can be significantly controlled by sandwiching materials having different diffusion constants between the hetero interfaces. However, when InGaAs is sandwiched as a spacer layer, the quantum level in this InGaAs layer 22a must be higher than that of the InGaAs layer 22, and therefore it must be sufficiently thinner than the InGaAs layer 22.

〔Example〕

Next, an embodiment of the present invention will be described with reference to FIG.

Here, the present invention was applied to an InGaAsP / InP-based 1.55 μm MQW semiconductor laser, an MQW semiconductor laser having an active layer with a modulation doping structure was prototyped, and its characteristics were evaluated. FIG. 1 is a schematic view of a part of the band structure of the active layer of a modulation-doped MQW semiconductor laser as an example. The MQW active layer was formed by the low pressure MOVPE method, the well layer 11 was non-doped InGaAs (thickness 75Å), and the barrier layer 13 was
1.15μm composition InGaAsP (thickness 150Å), Zn in the barrier layer
Was doped to a concentration of about 10 ¹⁹ cm ^-3 . In the normal modulation doping method, Zn in the barrier layer easily diffuses into the well layer during growth, resulting in a state close to uniform doping, but here the In layer between the well layer 11 and the barrier layer 13 is
P12 (thickness 10Å) and InGaAs16 (thickness 10Å) 2 each
Introducing a spacer layer consisting of a multilayer film consisting of layers
Is prevented from diffusing into the well layer. The total thickness of this multilayer film is 40Å, holes 15 can easily pass through this multilayer film by the tunnel effect, and carriers can be supplied to the well layers.

The modulation-doped MQW semiconductor laser fabricated as described above showed good oscillation characteristics at room temperature, and the threshold current density J _th was 50 A / cm ² . Further improvement in characteristics can be expected by improving the manufacturing process.

Although the spacer layer has two layers of InP and InGaAs here, one layer of InGaAsP having an intermediate composition between the barrier layer and the well layer may be used.

〔The invention's effect〕

The present invention is not limited to the InGaAsP / InP system shown in the embodiment
III-V group compound semiconductors such as aAs / AlGaAs and II-VI
It can also be applied to the modulation-doped structure of group compound semiconductors, and is expected to have a wide range of applications including optical devices. When the modulation-doped structure of the present invention is applied to the gate portion of HEMT, the switching speed is improved due to the steep impurity profile, and the calculation speed is improved by applying these devices to the logic operation circuit of the supercomputer. Further, the MQW semiconductor laser having an active layer having a modulation-doped structure according to the application of the present invention becomes a laser having an extremely low threshold value, and a μA laser can be realized in the future. Further, in the modulation-doped MQW laser, there is a possibility of ultrahigh-speed modulation exceeding 20 GHz, so that the structure of the present invention is also useful in the field of long-distance, large-capacity optical communication.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a part of an active layer band structure of a modulation-doped MQW semiconductor laser as an embodiment of the present invention, and FIG. It is the figure which compared with the structure which sandwiched the spacer layer. 11 …… InGaAs well layer, 12 …… InP, 13 …… 1.15 μm composition p ⁺ −InGaAs barrier layer, 15 …… hole, 16 …… InGaAs,
21 …… InGaAsP layer, 22 …… InGaAs layer, 23 …… InP layer.

Claims (1)

[Claims] 1. A semiconductor modulation-doped structure in which only a specific layer of a multi-layer laminated structure is doped with impurities, wherein the impurity-doped layer is provided between an impurity-doped layer doped with impurities and a semiconductor layer adjacent to the impurity-doped layer. The composition is different,
A semiconductor modulation-doped structure characterized in that at least one non-doped spacer layer having a thickness that allows carriers to pass by the tunnel effect is formed.