JPS62130565A - Field effect type semiconductor device - Google Patents

Abstract

PURPOSE:To reduce a decrease in a saturated current by forming an energy barrier layer in a hetero junction of a channel layer for generating secondary electron gas to suppress transition of the gas. CONSTITUTION:A buffer layer 2 made of non-doped GaAs, an non-doped AlxGa1-xAs layer 3 (x=0.3), and a spacer layer 5 made of non-doped AlxGa1-xAs (x=0.3) are sequentially formed on a semi-insulating GaAs substrate 1. A channel layer 6 made of non-doped GaAs is formed through a barrier layer BB on the layer 5. An Si-doped AlxGa1-xAs layer 7 (x=0.3), a cap layer 8 made of Si-doped GaAs and source and drain electrodes 9, 10 are sequentially formed through a barrier layer BA on the layer 6. The layers BB, BA are both formed of non-doped AlxGa1-xAs (x>0.3) or AlAs and so formed thin in the degree as not to tunnel carrier.

Description

[Detailed Description of the Invention] C Overview] This is a high power HEMT structure in which A11 has a large band gap at the hetero interface of the channel layer where two-dimensional electron gas is formed! Energy such as GaAs or AlAs
Improving power gain by forming a barrier.

[Industrial application field]

The present invention relates to a high-output field effect transistor HEMT, and particularly to an element structure in which an energy barrier layer is provided at a heterointerface of a channel layer where two-dimensional electron gas is generated.

[Conventional technology]

Conventionally, high-power HEMT (high electron mobility transistor)
As, double hetero type selective doping As/rL-A
l13; Ga1-zAs heterostructure (x=0.3) is used.

FIG. 4 shows a cross section of the main part of the element. In FIG. 4, 41 is a semi-insulating GaAs substrate, 42 is a buffer layer, and 43 is an undoped A 1.21. G a +-jcA
s Jtiii (x=0.3), 44 is Si-doped Al z G 11 + -z A 5 (x=0
．． 3) layer 45 is a spacer layer of undoped 4, Ga
, -□As, 46 is undoped GaA of the channel layer
,,r,47 is Si-doped AlxGalzAs
The layer (,=0.3), 48 is a CrctAs layer of 5i) as a cap layer, and the source and drain electrodes 49
and 5o are formed.

FIG. 5 shows a cross-sectional composition diagram of the element shown in FIG. 4, in which the horizontal axis represents the distance from the surface, and the vertical axis represents the X value (Lulu molar ratio). In FIG. 5, the shaded area represents the n-type impurity doped layer, and the doped A
Since electrons are supplied from the lGaAs layer to the channel layer 46, the electron density can be increased. At this time, if the channel layer 46 is formed sufficiently thin (about 150A)
The wave functions of electrons from the carrier supply layers on both sides completely overlap to form a single carrier. Therefore, such a structure allows the two-dimensional electron gas to have a large electron density, and is capable of producing high output H.
Enables the provision of EMT.

[Problem that the invention seeks to solve]

However, the conventional high-output HEMT described above has a drawback in that the source/drain saturation current 1tss decreases considerably on the high voltage side.

FIG. 6 shows a characteristic diagram of a conventional high-output HEMT. In FIG. 6, the horizontal axis shows the source/drain voltage VDs (v), and the horizontal axis shows the source.

As shown in the figure, which shows a drain-to-drain current value of 17 s (mA), in a conventional high-output HEMT, the source/drain saturation current 1 dss decreases greatly when VDS is high (indicated by a solid line). This decrease in saturation current on the high voltage side is caused by GaA
This can also be seen in the case of 3M E S F E T (indicated by the dotted line), but it is considerably larger than this and becomes an obstacle in increasing the power gain.

[Means for solving problems]

Therefore, the present inventors conducted various studies, and found that the decrease in saturation current of 1 dss on the high electric field side (2■) or higher in the high power HEMT is due to GaAs MESFET.
This was found to be unique to the HEMT structure, and could not be explained solely by a decrease in mobility due to thermal causes. It was concluded that the reason for this is that the two-dimensional electron gas transitions to AlGaAs in real space due to a high electric field, resulting in an effective decrease in mobility. Therefore, it is possible to first increase the hetero barrier by increasing the X value of Lue Ga1-xAs to more than 0.3, but this is because the effect of gettering impurities appears when the crystal mismatch or Al content increases. This is practically impossible because a clean interface is not formed.

Therefore, in the present invention, a GaAr lamp with a large band gap at the hetero interface of the channel layer where a two-dimensional electron gas is formed is used to prevent electrons from tunneling through an energy barrier (hereinafter referred to as a barrier layer) such as AIAs. The present invention provides a high power HEMT element structure that is formed as thin as possible.

[For production]

In a saturated state where a high voltage is applied between the source and drain, the electrons gain energy from the high electric field and become hot. As a result, the GaAs used in normal HEMT
/Al, ,; Ga+-z:As (x = 0.3
), the channel electrons cross the barrier of the heterojunction
78 protrudes toward the engineering Ga 1-, A, and S layers. In particular, due to gate bias, AIGaAsN on the substrate side
There is a lot of electron leakage. Here, AlGaAs is G
In addition to having a lower mobility than aAs, its mobility is further reduced due to the presence of doped impurities. A like this
11 electrons from the channel layer leak out to eGahs Fi (
Then, the current will decrease accordingly.

However, according to the configuration of the present invention, since the barrier layer is provided, the two-dimensional electron gas AIGαA, ? It is possible to suppress the transition to the high voltage side, prevent the saturation current from decreasing on the high voltage side, and obtain a high output IEMT with a large power gain.

〔Example〕

FIG. 1 shows a cross section of a main part of a high-output HEMT according to the present invention, and FIG. 2 shows its composition (A5 molar ratio). In FIG. 1, 1 is a semi-insulating GaAs substrate, 2 is a buffer layer, and 3 is an undoped A l z G (
11-jCA S VA, 4 is Si-doped A1.21
゜Ga1-, : A, layer, 5 is a spacer layer, 6 is a non-tope Ga As of the channel layer, 7 is a Si dove layer A
e: tGa, + -, xAs layer, 8 is Si cap layer
Doped GaAs h, 9.10 are source and drain electrodes.

Each layer is formed by MBE (Molecular Beam Epitaxial Growth) or M
It is formed by OCVD (organic vapor phase growth method). Each layer epitaxially grown on a substrate will be described in detail below as an example.

2: Single layer, undoped GaAs, thickness 3oo
o, Z3: undoped AI: tGa1-xA' Fi
(x = 0.3), thickness 500A 4:n (impurity Si) type AxxGα1-xA5N(x
-〇, 3), thickness 100 ohms, carrier concentration 1 x 10
18m-3 5 varnish spacer layer, undoped Al xGa 1-x
As layer (X = 0.3) thickness 80A 6: Channel layer undoped GaAs, thickness 150A
Al: n (impurity Si) type Al 3; Ga 1
-3; As-layer (X = 0.3), thickness 300
A, carrier concentration 1×101810l 8: camp layer n (impurity Si) type GaAs s layer, thickness 600A BB, BA: barrier layer, undoped AlxGα1-3Ju
(x>0.3) or AI! A, 9, several tens of amps thick (typically 20 to 30 amps) After forming each layer, source and train electrodes 9.10
formed by conventional processes.

In the above structure, the barrier layers BA and BB need to be formed thin enough to prevent carriers from tunneling, as described above. The barrier layer formed extremely thin is GaAs or AIA! has no crystallographic problems. It is a superlattice and A IA s
This is the same reason why GaAs crystals can be obtained in good condition, and is thought to be due to the effect of releasing strain caused by mismatch in the lateral direction. AlAs with the largest mismatch
/ In the case of GaAs, the thickness of AlAs in the barrier layer is 20
~50 i is optimal.

FIG. 3 shows a characteristic diagram of the embodiment, and as shown in the figure, the drop in saturation current on the high electric field side is much smaller than in the conventional high-output HEMT.

Although the GaAs/AlGaAs-based HEMT has been described above, the present invention is not limited to this and can be modified in many ways.
It can also be applied to AIIrLAS and the like.

〔Effect of the invention〕

As described above, according to the high-output HEMT of the present invention, even under high voltage, the two-dimensional electron gas AIGaAEI9
Since the real space transition to is suppressed, there is a small decrease in the saturation current I≆55, and there is an advantage that a high power gain can be obtained.

[Brief explanation of drawings]

Fig. 1 is a sectional view of the main part of the embodiment of the present invention, Fig. 2 is a cross-sectional composition diagram of the embodiment, Fig. 3 is a characteristic diagram of the embodiment, Fig. 4 is a sectional view of the main part of the conventional example, and Fig. 5 is a sectional view of the main part of the embodiment of the present invention. The figure is a cross-sectional composition diagram of a conventional example, and FIG. 6 is a characteristic diagram of the conventional example. 1 ・= GaAS substrate 2 . . . Buffer single layer 3 ・= AI GaAs H 4 . . . N-type F-type layer 5 . . . Spacer single layer 6 . 7018...Camp layer 9.10...Electrode BA, BB...Barrier layer Patent applicant: Fuji Tsutsu Co., Ltd. Agent Patent attorney: Hisashi Tamamushi Gobu (1 other person) Cross-sectional composition of embodiments of the invention Figure 2 Characteristic diagram of VQ5 (V) Example Figure 6 Cross-sectional view of main parts of conventional example Figure 4

Claims (1)

[Claims] A channel layer made of a first semiconductor and a carrier supply layer made of a second semiconductor having a smaller electron affinity than the first semiconductor on both sides of the channel layer are crystallographically compatible. A field effect semiconductor device comprising: a barrier layer made of a semiconductor having a larger bandgap than the second semiconductor at an interface between the channel layer and the second semiconductor layer on at least the substrate side; Device.