JPS63172A - Semiconductor device - Google Patents

Abstract

PURPOSE:To increase the surface density of a two-dimensional electron gas by alternately laminating non-doped channel layers and electron supply layers, which are made thinner than the channel layers and to which an impurity is atomic-plane doped, and forming the integral two-dimensional electron gases among both hetero-junction interfaces of the channel layers. CONSTITUTION:Non-doped channel layers 3b consisting of sutstances such as GaAs and electron supply layers 3a, to which a donor impurity is atomic-plane doped and which is composed of substances such as AlGaAs, are laminated alternately onto a semi-insulating substrate 1, and two-dimensional electron gases shaped near upper and lower hetero-junction interfaces are unified. The electron supply layer 3a is made thinner than the channel layer 3b for the layer 3a, and a donor impurity is atomic-plane doped at the central position of the layer 3a in high surface concentration. Accordingly, two-dimensional electron gases shaped in each channel layer 3b (and the outside of the electron supply layer 3a on the outermost side) are brought extremely close, high electronic surface density is obtained, using the whole two-dimensional electron gases as one channel, and controllability by a gate is also improved.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a semiconductor device using a two-dimensional electron gas as a channel, and includes a non-doped channel layer and an electron supply layer thinner than the channel layer and atomically plane-doped with donor impurities. A structure in which the two-dimensional electron gas is formed by alternately stacking layers to form an integrated two-dimensional electron gas between both heterojunction interfaces of the channel layer increases the areal density of the two-dimensional electron gas and improves the characteristics of the semiconductor device. .

[Industrial application field]

The present invention relates to improvements in semiconductor devices, particularly in semiconductor devices such as high electron mobility field effect transistors (HEMTs) that use high mobility carriers as channels through spatial separation doping and interface quantization.

For example, in HEMT, carrier mobility is increased by spatially separating the region where two-dimensional electrons move and the region where impurities are doped, and there are strong expectations as a high-speed device. There is a demand for improved characteristics such as an increase in channel current and transfer conductance g.

[Conventional technology]

FIG. 4 shows a schematic side sectional view of a conventional example of a HEMT as an example of a semiconductor device that achieves high mobility through spatial separation doping and interfacial quantization of carriers.

That is, in this conventional example, semi-insulating gallium arsenide (G
aAs) On the substrate 11, a molecular beam epitaxial growth method (
MB2 method) etc., a non-doped i-type GaAs layer 12, which has a smaller electron affinity than this, for example at a concentration of 2×10
An n-type aluminum gallium arsenide (Al x Gal -

From this n-type AlGaAs electron supply layer 13 to i-type GaAs
2 near the heterojunction interface due to the electrons transferred to layer 12.
A two-dimensional electron gas 12e is formed, and the two-dimensional electron gas 12e has an areal density Ns in a Schottky depletion layer formed by the gate electrode 16.
The transistor operation is performed by controlling the two-dimensional electron gas 12e, but there is almost no decrease in mobility due to impurity scattering,
The highest mobility is obtained at low temperatures, such as 77°C or lower, where lattice scattering is reduced.

In this structure, when the energy level difference in the conduction band between the n-type AlGaAs electron supply layer 13 and the i-type GaAs channel layer 12 is small, the areal density of the two-dimensional electron gas 12e is N
s becomes smaller. Therefore, the level difference in the conduction band is 0°24eν
above, that is, n-type A1gGat-xAs electron supply layer 1
It is desirable that the AI composition ratio X of 3 is about 0.3 or more, but on the other hand, when this^1 composition ratio X is larger than about 0.25, the donor level of doped Si etc. becomes deep rapidly. Even if the doping concentration n is increased, a high carrier concentration cannot be obtained, and in addition, the crystallinity deteriorates. areal density Ns#9.0X10"am-", electron mobility island-3X
10'C11"/V, about !11.

Various structural improvements have already been proposed aimed at increasing the areal density Ns of the two-dimensional electron gas beyond this limit. One example is a structure in which n-type AlGaAs electron supply layers are provided above and below an i-type GaAs channel layer with a thickness of about Loam or less, but in this structure, a decrease in electron mobility μ7 is unavoidable, and the electron surface density Ns is There is not much increase either.

As another example, an i-type GaAs channel layer-n-type AlG
There is a structure in which a plurality of aAs electron supply layers are stacked in the same direction, but in this structure, the channel layers are widely separated by the electron supply layer, and nonlinearity appears in the gate voltage-drain current characteristic.

In each of the above-mentioned structures, the n-type electron supply layer is doped with impurities in a normal manner, whereas there is a structure in which the electron surface density Ns is increased by an atomic lane doping method. That is, for example, non-doped A1. , ,G6. ,
, between the As layer and the GaAs channel layer, there is a 14-plane concentration N, 4 nm from the telojunction interface, = 4 X10''
elm-'' Si atomic plane doping, the areal density of the two-dimensional electron gas is Ns; 1.1X10''C
About 11-'' was obtained.

[Problem or point that the invention attempts to solve]

As mentioned above, the two-dimensional electron gas areal density Ns of conventional HEMT
Although efforts are being made to obtain a high areal density that exceeds this constraint, there is a strong desire to further increase the concentration Ns in order to further improve characteristics such as transfer conductance ga and channel current. ing.

[Means for solving problems]

The problem is that the non-doped first semiconductor layer and the first
A second semiconductor layer, which is thinner and has a lower electron affinity than the first semiconductor layer and is doped with donor impurities in an atomic plane, is alternately laminated to form a two-dimensional electron layer integrated between both heterojunction interfaces of the first semiconductor layer. This problem is solved by a semiconductor device according to the present invention in which defects are formed.

[For production]

According to the present invention, as illustrated in the energy diagram of FIG.
Channel layers 3b made of non-doped GaAs, for example, and electron supply layers N3a made of AlGaAs, for example, doped with donor impurities in an atomic plane are alternately stacked.

However, the thickness of the channel layer 3b is set to, for example, about 10 nm or less to integrate the two-dimensional electron gas formed near the upper and lower heterojunction interfaces. Note that in order to prevent electron subbands from being excessively dispersed, it is desirable to set the thickness to about 5 nm or more, for example.

The electron supply layer 3a is thinner than the channel layer 3b, for example, by about 4 am, and is usually atomic plane doped (PD) with a donor impurity such as Si at a high surface concentration N at the center thereof.

With this configuration, the two-dimensional electron gas formed in each channel 1J3b (and outside the outermost electron supply N3a) is very close to each other, and a high electron surface density N can be obtained by using the entire channel as one channel. The controllability is also good.

〔Example〕

The present invention will be specifically explained below using examples.

FIG. 2 is a schematic side sectional view of an embodiment of the present invention, and FIG. 3 is a schematic diagram of its channel region.

The semiconductor substrate of this example is epitaxially grown by sequentially laminating the following semiconductor layers on a semi-insulating GaAs substrate 1. First, 2 is a non-doped GaAs layer having a thickness of, for example, about 0.5 to 11 rm.

3a is an electron supply layer, which is A1.3a having a thickness of, for example, about 4 am. .

3Gao, , surface concentration Nus#4 XI in the center of AsN
Si atomic plane doping (S
i-PD).

Reference numeral 3b denotes a channel layer, which is a non-doped GaAs layer with a thickness of, for example, about 7 am.
A and two channel layers 3b are alternately stacked.

Further, 4 is a non-doped GaAs layer with a thickness of, for example, about nm, and 5 is an n-type GaAs cap layer with Si at a concentration of n.
It is doped uniformly to about B=2×lQI8cm−3.

In this semiconductor substrate, two-dimensional electron gas is generated near the heterojunction interface between the two GaAs channel layers 3b and the electron supply layer 3a of each of the GaAs layers 2.4, and the overall areal density is Ns#2.0×1012 cm− 2 is obtained.

In this embodiment, in which a source/drain electrode 5 is disposed on the n-type GaAs cap layer 5 of this semiconductor substrate, and a gate electrode 7 is disposed on the GaAs layer 4, a transfer conductance g-th 00 m5/ms is obtained, for example. In the conventional structure shown in Fig. 4, areal density of two-dimensional electron gas N5 = 9.0X
In a comparison sample using a 10" row 2 semiconductor substrate and having the same gate electrode structure and dimensions, the transfer conductance was g
va #235m5/mm, which is a significant improvement.

The above explanation is based on GaAs/AlGaAs HEMT.
However, the present invention is not limited thereto, and similar effects can be obtained by the present invention even for semiconductor devices that are made of different semiconductor materials or have different structures.

〔Effect of the invention〕

As explained above (according to the present invention, the two-dimensional electron gas areal density Ns
, an increase in transfer conductance g1, and other improvements have been achieved, resulting in a significant effect on the advancement of this semiconductor device, which has great expectations as a high-speed device.

[Brief explanation of the drawing]

Fig. 1 is an energy diagram of an example of a semiconductor device according to the present invention, Fig. 2 is a schematic side sectional view of the embodiment, Fig. 3 is a schematic diagram of the channel region of the embodiment, and Fig. 4 is a schematic side view of the conventional example. FIG. In the figure, 1 is a semi-insulating GaAs substrate, 2 is an undoped GaAs layer, and 3a is an AlG layer with atomic plane doping of Si.
3b is a non-doped GaAs channel layer; 4 is a non-doped GaAs layer; 5 is an n-type GaAs cap layer; 6 is a source and drain electrode; 7 is a gate electrode. -! 'J's energy - fast-talking j Published on the diagram implementation column's glue 1j Dark side phantom 2 Mouth pig] 7rJ's ji to play the play 劊 arrogant 3 g (Lwoli Buri no filial piety To the noodles / 1.
mouth

Claims (1)

[Claims] A non-doped first semiconductor layer and a second semiconductor layer which is thinner and has a lower electron affinity than the first semiconductor layer and which is atomically plane-doped with donor impurities are laminated alternately, A semiconductor device characterized in that an integrated two-dimensional electron gas is formed between both heterojunction interfaces of one semiconductor layer.