JPS61210677A - Compound semiconductor device - Google Patents

Abstract

PURPOSE:To obtain high electron mobility even when a high electric field is applied, by alternately laminating two kinds of compound semiconductor thin film layers having large lattice irregularities, thereby suppressing electron scattering. CONSTITUTION:On a semi-insulating InP substrate 10, InAs and AlAs are laminated by about 80 layers, respectively. Each layer comprises several atomic layers. Such a crystal structure is provided in AlxIn1-xAs compound- semiconductor-crystal multiple thin film layer 11. The layer 11 is formed as a channel layer in an FET. The total thickness of the multiple thin film layer 11 is 0.1mum. Said multiple thin film layer 11 is formed by using an MBE growing method on the semi-insulating InP substrate 10. On the surface of the multiple thin film layer 11, an AuGeNi ohmic junction electrode 12 is evaporated, and source and drain electrodes are formed. An Al Schottky junction electrode 13 is evaporated, and a gate electrode is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to compound semiconductor devices. More specifically, the present invention realizes an energy band structure different from that of existing so-called mixed crystal compound semiconductors by alternately stacking two types of compound semiconductor thin film layers with different lattice constants.
The present invention relates to a compound semiconductor device with increased electron mobility in a state where a high electric field is applied.

BACKGROUND OF THE INVENTION Epitaxial growth methods are generally used as a manufacturing method for compound semiconductor devices, particularly electronic devices, because of the ease of growing thin, uniform layers and controlling the composition ratio of component elements. Among them, a technique that has recently attracted particular attention is the molecular beam epitaxial growth method (hereinafter referred to as rMBE for simplicity).
``growth method'') is known. For example, W, T,
Nikkei Electronics No. 308 by Tsang.
163 (1983), devices utilizing the MBEF & length method and thin film periodic structures are described in detail.

By following this MBE growth method, the crystal growth rate can be controlled at the monatomic level (J, P, van de
rZiel et al., J. Appl. Phys., 48 (19
77) P4O10) Furthermore, if reflection electron diffraction is used in combination, it is possible to precisely control the composition of a single atomic plane (J. H. Neave et al., Appl. Phys.
By using the MBE method such as that described in S., A3L1 (1983), and Ko, it becomes possible to manufacture a high electron mobility transistor (hereinafter abbreviated as HEMT) as shown in FIG.

Note that microwave elements using conventional compound semiconductors are described in, for example, Japanese Patent Laid-Open No. 59-4085 and Japanese Patent Laid-Open No. 58-147169.

The HEMT structure shown in FIG. 3 has a semi-insulating GaAs substrate 1, on which is formed a GaAs layer 2 which functions as a buffer layer, and further on which is a channel layer. An undoped GaAs layer 3 is formed. Then, on the GaAs layer 3, n GagA
An electron supply layer 4 having a high impurity concentration such as S to I+-M is formed, and a layer 5 made of a semiconductor containing a high concentration of p-type impurity and having a large electron affinity is provided in the center thereof, and , a gate electrode 6 is formed on the layer 5 . Furthermore, the surface region 7 of the electron supply layer 4 sandwiching the layer 5
are alloyed, and source and drain electrodes 8 are formed thereon.

In such a semiconductor device, when an appropriate bias voltage is applied to the gate electrode 6, a two-dimensional electron gas 9 is formed on the channel layer 3 side at the interface between the electron supply layer 4 and the channel layer 3. As a result, a large amount of electrons flows through the channel layer 3, which has a few impurity ions, at a thickness of several tens of layers near the interface. Therefore, impurity ion scattering, which is one of the major factors that limit electron mobility, is reduced, and high mobility can be achieved.

Problems to be Solved by the Invention However, in such a compound semiconductor device, the dependence of electron mobility in a two-dimensional electron gas on the applied electric field strength is extremely large, and although high mobility can be achieved in the case of a low electric field, , in the case of a high electric field, its mobility decreases significantly. Such a phenomenon is, for example, M, Inou
J, J, A, P, 22357 (1983). An example of this is shown in the case of a GaAs layer n-GaXA1+-XAs structure such as the above-mentioned microwave device, as shown by the dotted line in FIG.

Electron scattering mechanisms within semiconductors under such high electric field conditions include intervalley scattering, impact ionization, and phonon (lattice vibration).
Examples include scattering. Therefore, semiconductor crystals generally used as channel layers in ultra-high frequency transistors are required to have the following improved characteristics.

■ To make intervalley scattering less likely to occur, k
The energy difference △E between the valleys in space is large.

■ The energy gap E9 must be large to make impact ionization less likely to occur.

■ The effective mass m1 must be small in order to reduce the loss of kinetic energy of carrier electrons due to phonon scattering.

Parameters such as energy difference between valleys △E1 energy gap E, etc. are described in 1. An example of the energy band structure of a GaAs crystal is shown in FIG. Further, the effective mass m* has a relationship with the energy band structure as m* +I, 2 dk2.

However, in conventional compound semiconductor devices, the compound semiconductor of each layer having a substantial thickness is required to have a uniform composition structure.
was decided by itself. Therefore, there is a barrier to eliminating the above-mentioned scattering, and high electron mobility cannot be achieved in a state where a high electric field is applied.

Therefore, the present invention suppresses the influence of electron scattering described above, and
The present invention aims to provide a compound semiconductor device that has high electron mobility even when a high electric field is applied.

Means for Solving the Problems Therefore, the present inventor conducted various studies on the problem of electron scattering for the above purpose.

As can be seen from the above explanation, the compound semiconductor crystal used as the channel layer in ultra-high frequency transistors reduces intervalley scattering and impact ionization scattering when a high electric field is applied by changing its energy band structure. Alternatively, by reducing the effective mass of electrons, the mobility under high electric field application can be increased.

On the other hand, LCAO regarding the energy band structure of semiconductors
According to theory, the off-diagonal matrix elements of the Hamiltonian, V L L , are important when calculating the energy band structure.
0 is represented by . However, 11 Bi is the azimuthal quantum number of the outermost p-orbital of the adjacent atoms constituting the crystal, m is the magnetic quantum number, d is the internuclear distance of adjacent atoms, mo is the electron mass, η5.・0 is a coefficient depending on the crystal structure, R=h
/2π(hniblank constant).

Also, the diagonal matrix element εsc1εa1 of the Hamiltonian
εPc% ε, a, etc. are relatively related to the product value of an isolated atom. However, εSc is related to the product value of the cation atomic S orbitals of the polar compound semiconductor, and similarly, εa is related to the product value of the anion atomic S orbitals, and ε,′ is related to the product value of the cation atomic P orbitals. , ε, ″ are respectively related to the product value of the anion atomic P orbital.

This established theory (for example, Gai, Harrison.

Blectronic 5structure and
the Properties of Solids;
(1980), by changing the crystal structure or atomic arrangement, that is, by changing the internuclear distance d of adjacent atoms in a compound semiconductor crystal and the type of adjacent atoms, the matrix element V11'mz of the Hamiltonian can be changed.
εS''% ε, , C1εpa1 ε, C can be changed. This means that the energy band structure of the compound semiconductor can be changed by changing the crystal structure or atomic arrangement.

On the other hand, as mentioned above, recent compound semiconductor crystal growth techniques include molecular beam eviaxial growth (MBE), metal organic vapor phase epitaxy ('MO'CVD, and MOVPE).
The control of the growth layer thickness has been improved to the level of a single atomic layer, and it has actually been possible to alternately stack layers of GaAs and ions at the monatomic level. (A, C, Gossard, T'h'1nSolid
Films 57. 3 (1979)).

However, when GaAs and AlAs are alternately laminated, the lattice mismatch is extremely small, about 0.3%, and therefore the strain in the crystal lattice caused by alternately laminating these two types of layers i is small. This means that conventional Ga, A
l This means that compared to the I-XAS mixed crystal, only the atomic arrangement has changed slightly, and the crystal structure has hardly changed,
Therefore, the energy band structure does not show any major changes.

However, when the lattice mismatch between the two types of layers is increased to about 1.5%, a large change in the energy gap E9 has been observed (G, C9[]5bourn et al., J.
Appl, Phys, Yu (1977) 3018)
. That is, when the lattice misalignment is relatively large like this, not only the atomic arrangement but also the crystal structure changes, and a relatively large change in the energy band structure is observed.

However, in the case of this report, each layer thickness is 1
00 to 200 people, and compared to the distorted part of the crystal lattice near the interface between the two types of layers, the part where the crystal lattice is not distorted and has the conventional crystal structure is extremely large. ing.

Therefore, most of the energy band structure is dominated by the energy band structure resulting from the conventional crystal structure of each layer, and the contribution from distorted portions of the crystal lattice is small. The fact that the distortion of the crystal lattice is limited to the vicinity of the interface of each layer in this way suggests that the JoM
, Brown et al., A. P. L. 43 (1983
) 863. Furthermore, the direct result that the crystal structure changes due to distortion based on such lattice misalignment is J, 8, P, 45. No, 9, (1
974) 3789.

From the above, by alternately stacking two types of compound semiconductor thin film layers with large lattice mismatches, the crystal structure or atomic arrangement can be changed over the entire growth layer.

A similar report in terms of a semiconductor device in which compound semiconductor thin film layers are alternately laminated is, for example, published in Japanese Patent Laid-Open No. 59-7.
No. 6468 or T, Yao, J, J, A,
P.

(1983') L680, but they do not improve the energy band structure at all.

The present invention was made as a result of research based on such knowledge. That is, according to the present invention, the channel layer is constituted by alternately stacking two types of compound semiconductor thin film layers having different lattice constants, and the crystal structure or atomic arrangement of the compound semiconductor forming the channel layer is changed. Provided is a compound semiconductor device characterized in that the energy band structure of the compound semiconductor is changed and electron mobility is increased in a high electric field application state within a channel layer.

In the compound semiconductor device described above, the compound semiconductors in each thin film layer forming the channel layer have different lattice constants and are extremely thin, so the energy band structure changes over a substantial portion of each layer, resulting in high It reduces intervalley scattering or scattering due to impact ionization in the electron transport process in the channel layer when an electric field is applied, or reduces the effective mass of electrons.

Therefore, the electron mobility in the channel layer is maintained high when a high electric field is applied.

Example The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a cross-sectional view illustrating an embodiment of a compound semiconductor device according to the present invention. Note that FIG. 1 shows an example in which the present invention is implemented as a field effect transistor (hereinafter abbreviated as FET).

The FET shown in FIG. 1 has a semi-insulating InP substrate 10,
IXI has a crystal structure in which approximately 80 layers of InAs and AlAs are alternately stacked each with several atomic layers each.
n1-X8S compound semiconductor crystal multilayer thin film layer 11 is FET
It is formed as a channel layer. The total thickness of the multilayer thin film layer 11 is 0.1 μm. Incidentally, such a multilayer thin film layer 11 is formed by depositing M on a semi-insulating InP substrate 10.
It was formed using the BE growth method.

Furthermore, AuGeNi ohmic junction electrodes 12 were deposited on the surface of the multilayer thin film layer 11 to form source and drain electrodes. Further, an AI Schottky junction electrode 13 was deposited to form a gate electrode.

Au atoms are diffused into the compound semiconductor crystal multilayer thin film layer 11 by vapor deposition and alloying treatment when forming the uGeNi ohmic electrode 12 . As a result, the periodicity of the laminated structure in the compound semiconductor crystal multilayer thin film layer 11 is disturbed, and the crystal structure in this region 14 is changed to the conventional one.
It becomes the same as the n+-Js mixed crystal.

As a result, the energy band structure in this region was also the same as that of the conventional AlxIn+-Js mixed crystal, and no problem occurred in forming an ohmic junction. A similar phenomenon in which the periodicity of the laminated structure of a compound semiconductor multilayer thin film layer is destroyed by such diffusion has already been observed in N,
■olonyak et al., A, P, L, 39 (19
81) Published in 102, etc.

It was also confirmed that the source electrode 12, drain electrode 12, gate electrode 13, etc. shown in FIG. 1 had a function as an FET by using the conventional technique used in manufacturing a conventional FET structure.

Furthermore, the compound semiconductor crystal multilayer thin film layer 1 in FIG.
It was also confirmed by measurements such as X-ray diffraction and optical absorption that the crystal structure and energy band structure of 1. . As a result, as shown in FIG. 2, the electron mobility in the high electric field region was improved by about three times compared to the conventional ^]jn+-,,As mixed crystal having the same composition.

In addition, when the thickness of each thin film layer of the compound semiconductor crystal multilayer thin film layer 11 was changed from 1 atomic plane to 100 atomic planes using the same structure as the above example, there was a difference compared to the conventional example. However, similar results were obtained. However, the thin film layers having the same composition preferably have the same thickness throughout the multilayer thin film layer.

In the above embodiment, InAs (lattice constant: 6.058), AlAs (5.0
, 662 people) were used. However, the multilayer thin film layer is not limited to the combinations of the above embodiments, and other combinations are also possible, and if the difference in lattice constant is 0.3% or more, more preferably 1.5% or more, Although there are differences in degree, similar effects can be obtained. For example, as a compound semiconductor with a large lattice constant, in addition to TnAs, Ga5b (6,095
In addition, as compound semiconductors with small lattice constants, there are GaAs (5,654 people), In5b (5,479 people), etc.
51 people), In P (5,869 people), etc. A ternary compound semiconductor multilayer thin film channel layer can also be formed by appropriately combining them.

Effects of the Invention According to the semiconductor device of the present invention, by changing the crystal structure or atomic arrangement of the compound semiconductor used in the channel layer of a conventional FET, the energy band structure is changed, and the semiconductor crystal becomes more stable under high electric field application. This makes it possible to reduce various types of scattering within the space and also to reduce the effective mass. Therefore, electron mobility under high electric field application is faster than in conventional compound semiconductor mixed crystals.

[Brief explanation of the drawing]

FIG. 1 shows an F in which a compound semiconductor device according to the present invention is implemented.
A schematic cross-sectional view of ET; FIG. 2 is a graph showing the measurement results of the dependence of electron mobility on applied electric field strength in the compound semiconductor device of the present invention; FIG. 3 is a schematic cross-sectional view of a conventional high electron mobility transistor. , FIG. 4 is a graph showing measurement results of the dependence of electron mobility on applied electric field strength in a conventional high electron mobility transistor, and FIG. 5 is a diagram for explaining the energy band structure of a compound semiconductor. [Main reference numbers] 1. Semi-insulating GaAs substrate, 2. GaAs buffer layer, 3. Ga channel layer, 4. Electron supply layer, 6. Gate electrode, 7. Alloying region , 8... Source electrode, drain electrode, 9... Two-dimensional electron gas, 10... InP substrate 11... Multilayer thin film layer, 12... Source electrode, drain electrode, 13... Gate electrode, 14... Mixed crystal area

Claims (3)

[Claims] (1) The channel layer is constructed by alternately stacking two types of compound semiconductor thin film layers with different lattice constants, and the crystal structure or atomic arrangement of the compound semiconductor forming the channel layer changes to change the energy band of the compound semiconductor. 1. A compound semiconductor device characterized in that the structure is changed so that electron mobility increases in a high electric field application state within a channel layer. (2) The thickness of each layer of the compound semiconductor multilayer thin film layer is 1 to 1.
2. The compound semiconductor device according to claim 1, wherein the area is within a range of 100 atomic planes. (3) The compound semiconductor device according to claim 1, wherein the difference in lattice constant is 0.3% or more.