JP2003100777A - High electron mobility transistor and epitaxial growth compound semiconductor crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high electron mobility transistor having stable characteristics by manufacturing based on a condition which can provide relations between a doping amount to a stable electron supply layer and two-di mensional electron gas concentration, and to provide an epitaxial growth com pound semiconductor crystal. SOLUTION: This high electron mobility transistor comprises a heterojunction consisting of a first compound semiconductor having a large band gap, doped with an n-type dopant, and a second compound semiconductor having a smaller band gap than that of the first compound semiconductor, and the first compound semiconductor works as an electron supply layer, and the second compound semiconductor works as a channel while enclosing electrons two dimensionally within the second compound semiconductor. The oxygen concentration in the first compound semiconductor is set to be 5×10<16> cm<-3> or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high electron mobility transistor (hereinafter, referred to as HE).
(Abbreviated as MT) and HEMT as a basic element, and an epitaxially grown compound semiconductor crystal suitable for manufacturing a semiconductor integrated circuit.

[0002]

2. Description of the Related Art Conventionally, HEMT-structured epitaxial crystals have generally been produced by metal organic vapor phase epitaxy (Metal Organic Chromatography).
emical Vapor Deposition; hereinafter referred to as MOCVD method) and Molecular Beam Epitaxy;
Hereinafter, referred to as MBE method).

HEMT is a two-dimensional electron gas (2 di
mensional electron gas; sometimes referred to as 2DEG hereinafter. ) Is a compound semiconductor device having a heterostructure. The HEMT has three electrodes of a source, a drain and a gate provided on a compound semiconductor in which thin films are laminated, and by applying a voltage to the gate electrode, the two-dimensional electron gas concentration under the gate electrode is changed to control the source-drain current. Have the function to

For example, on a semi-insulating GaAs substrate, a HE having a heterojunction of a non-doped InGaAs channel layer and an electron supply layer made of a semiconductor having a smaller electron affinity than InGaAs and heavily doped with n-type impurities
The MT structure is known. The feature of this HEMT structure is that it uses 2DEG having a high electron mobility formed in a high-purity InGaAs channel layer as a carrier, and thus is excellent in high speed and noise characteristics. The material of the electron supply layer is AlGaAs, InGaP or InG
Often, aAlP or the like is used.

[0005]

[PROBLEMS TO BE SOLVED BY THE INVENTION]
It is generally inferred that in an MT structure epitaxial crystal, the lower the impurity content in the crystal, the better.
At present, it has not been clarified as to what degree of impurities should be reduced to improve the characteristics of HEMT. For example, in the MOCVD method and the MBE method, the impurity concentration in the crystal changes depending on the growth condition of the epitaxial crystal and the state of the apparatus, and thus the optimum control has not been achieved.

[0006] Usually, when an HEMT structure is manufactured by growing an epitaxial crystal, the electron supply layer is doped with an n-type dopant. The concentration of the two-dimensional electron gas formed in the channel is controlled by HEMT by this doping amount. However, not all of the dopants doped in the electron supply layer form a two-dimensional electron gas, and some may not be activated. And
It is thought that this activation rate changes depending on the growth conditions and the impurity concentration, but it is not clear which impurities most affect this activation rate change and to what level it needs to be reduced. It was

The present invention has been made in view of the above problems, and is based on the conditions found to obtain a stable relationship between the doping amount in the electron supply layer and the two-dimensional electron gas concentration. Another object of the present invention is to provide a high electron mobility transistor and an epitaxially grown compound semiconductor crystal whose characteristics are stabilized.

[0008]

In order to achieve the above object, a high electron mobility transistor according to the present invention comprises a first compound semiconductor having a large band gap doped with an n-type dopant, and the first compound semiconductor. A heterojunction with a second compound semiconductor having a bandgap smaller than that of the compound semiconductor, the first compound semiconductor serving as an electron supply layer, and electrons being two-dimensionally confined in the second compound semiconductor,
In the high electron mobility transistor having a structure in which the second compound semiconductor is a channel layer, the oxygen concentration in the first compound semiconductor is 5 × 10 ¹⁶ cm ⁻³ or less.

That is, the inventors of the present invention have conducted intensive research to clarify which impurity should be reduced to what concentration by paying attention to impurities in the electron supply layer, and as a result, the epitaxial wafer used for HEMT By keeping the concentration of oxygen, which is one of the impurities in the electron supply layer of, below a certain concentration,
HE that stabilizes the activation rate of the dopant to the electron supply layer of HEMT and has a stable two-dimensional electron gas concentration with good reproducibility
It was found that MT can be manufactured. Based on this, the oxygen concentration in the first compound semiconductor is set to 5 × 1.
The present invention has been completed by deriving the optimum condition of 0 ¹⁶ cm ⁻³ or less. As a result, the concentration of the two-dimensional electron gas can be stabilized and the HEMT characteristics can be stabilized. The first compound semiconductor may be an AlGaAs layer or an InAlAs layer.

Further, the epitaxially grown compound semiconductor crystal according to the present invention comprises a first compound semiconductor doped with an n-type dopant and having a large band gap, and the first compound semiconductor.
In the epitaxially grown compound semiconductor crystal grown by stacking so as to have a heterojunction with a second compound semiconductor having a band gap smaller than that of the first compound semiconductor, the oxygen concentration in the first compound semiconductor is 5 × 10 ¹⁶ cm ^−3.
It is as follows.

As a result, an epitaxially grown compound semiconductor crystal capable of stabilizing the concentration of the two-dimensional electron gas when the HEMT is formed can be obtained, and the HEMT having the stabilized characteristics by using the epitaxially grown compound semiconductor crystal is obtained. Can be manufactured. The first compound semiconductor may be an AlGaAs layer or an InAlAs layer.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. In this embodiment, an example in which an AlGaAs layer is used as an electron supply layer and an InGaAs layer is used as a channel layer is applied to an epitaxial crystal having a pseudo-lattice matching high electron mobility transistor (Pseudomorphic HEMT; hereinafter referred to as p-HEMT) structure. Indicates.
Here, the p-HEMT is a field effect transistor having an active layer of two-dimensional electrons with high mobility accumulated in a heterojunction that is pseudo-lattice matched.

FIG. 1 is a structural diagram showing the structure of an epitaxial layer of the p-HEMT structure according to this embodiment. As shown in FIG. 1, the p-HEMT structure according to this embodiment has a semi-insulating Ga.
AlGaAs / GaAs superlattice (15n
m / 5 nm × 40 periods), undoped Al _0.25 Ga _0.75
As (100 nm), Si-doped Al _0.25 Ga _0.75 As
(5 nm Si doping amount; N = 2.5 × 10 ¹⁸ ), undoped Al _0.25 Ga _0.75 As (3 nm), undoped I
_{n 0.20 Ga 0.80 As (15nm)} , an undoped Al _{0. 25}
Ga _0.75 As (3 nm), Si-doped Al _0.25 Ga _0.75
As (15 nm Si doping amount; N = 2.5 × 1)
0 ¹⁸ ), undoped Al _0.25 Ga _0.75 As (15n
m), Si-doped GaAs (50 nm Si-doped amount;
N = 2.0 × 10 ¹⁸ ) is sequentially epitaxially grown.

In FIG. 1, the electron supply layer is composed of the third and seventh Si-doped Al _0.25 Ga _0.75 As layers from the top, and has a total thickness of 20 nm (= 15 nm + 5 nm). Therefore, the Si doping amount is 2.5 × 10
Since a ^18, for example, 2-dimensional electron gas concentration in the case the activation rate is ^{100%, 2.5 × 10 18 (cm -3} ) ×
20 (nm) = 5.0 × 10 ¹² (cm ⁻² ).

In this embodiment, the buffer layer is made of Al.
P-HE using GaAs / GaAs superlattice with different oxygen concentration in AlGaAs layer as electron supply layer under some growth conditions
An MT structure epitaxial wafer was grown. The epitaxial layers were grown so that the film thickness and the doping concentration were constant. In addition, the plurality of growth conditions are those in which the substrate temperature, the dose, etc. are changed.

Next, regarding the impurity concentration in the grown epitaxial layer, SIMS (Secondary Ion Mass Spect
roscopy; secondary ion mass spectrometry). The two-dimensional electron gas concentration was evaluated by Hall measurement.

Here, FIG. 2 shows the p-HEMT according to the present embodiment.
3 is a graph showing the relationship between the oxygen concentration in the AlGaAs layer and the two-dimensional electron gas concentration in the epitaxial wafer having the structure. According to the graph of FIG. 2, it can be seen that the two-dimensional electron gas concentration decreases as the oxygen concentration increases, and the two-dimensional electron gas concentration increases as the oxygen concentration decreases. The oxygen concentration is about 5 × 10 ¹⁶ cm ^-3
It can be seen that the concentration of the two-dimensional electron gas is substantially constant around the above range.

As a result, the oxygen concentration in the electron supply layer is
It has been found that a stable two-dimensional electron gas concentration can be obtained under the same growth conditions (constant doping concentration) if the two-dimensional electron gas concentration is controlled to be saturated.
In the present embodiment, the AlGaAs / InGaAs-based p-HEMT structure is shown, but the lattice-matched AlGaAs / GaAs-based or InAlAs on the InP substrate is used.
It is considered that the same condition holds for / InGaAs and the like.

The electron supply layers (third and seventh Si-doped Al from the top in FIG. 1) thus grown are
_0.25 Ga _0.75 As layer) in the oxygen concentration of 5 × 10 ¹⁶ cm
By using an epitaxial layer having a p-HEMT structure of ^-3 or less, the concentration of the two-dimensional electron gas in the channel layer (the fifth undoped In _0.20 Ga _0.80 As from the top in FIG. 1) can be stabilized, and the characteristics Stabilized HEMT
Can be obtained.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments and can be modified without departing from the scope of the invention.

[0021]

According to the present invention, a heterojunction of a first compound semiconductor having a large bandgap doped with an n-type dopant and a second compound semiconductor having a bandgap smaller than that of the first compound semiconductor is formed. , The first
In the high electron mobility transistor having a structure in which the compound semiconductor as an electron supply layer, electrons are two-dimensionally confined in the second compound semiconductor, and the second compound semiconductor is used as a channel, the first compound By setting the oxygen concentration in the semiconductor to 5 × 10 ¹⁶ cm ⁻³ or less, the concentration of the two-dimensional electron gas can be stabilized and the HEMT characteristics can be stabilized.

[Brief description of drawings]

FIG. 1 is a structural diagram showing a structure of an epitaxial layer of a p-HEMT structure according to this embodiment.

FIG. 2 is a graph showing the relationship between the oxygen concentration in the AlGaAs layer and the two-dimensional electron gas concentration in the epitaxial wafer having the p-HEMT structure according to this embodiment.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yu Ota             3-17-35, Shinsōnan, Toda City, Saitama Prefecture Stock             Company Nikko Materials Toda Factory F-term (reference) 5F102 FA00 GB01 GC01 GD01 GJ05                       GJ06 GK05 GK06 GK08 GL04                       GM06 GQ01 GQ02 HC01

Claims (6)

[Claims] 1. A heterojunction between a first compound semiconductor having a large bandgap doped with an n-type dopant and a second compound semiconductor having a bandgap smaller than that of the first compound semiconductor. A high electron mobility transistor having a structure in which the first compound semiconductor is an electron supply layer, electrons are two-dimensionally confined in the second compound semiconductor, and the second compound semiconductor is a channel layer. Oxygen concentration in the compound semiconductor of 5 × 10 ¹⁶ cm
A high electron mobility transistor characterized by being ^-3 or less. 2. The high electron mobility transistor according to claim 1, wherein the first compound semiconductor is an AlGaAs layer. 3. The high electron mobility transistor according to claim 1, wherein the first compound semiconductor is an InAlAs layer. 4. A layered growth so as to have a heterojunction between a first compound semiconductor having a large bandgap doped with an n-type dopant and a second compound semiconductor having a bandgap smaller than that of the first compound semiconductor. In the epitaxially grown compound semiconductor crystal, the oxygen concentration in the first compound semiconductor was 5 × 10 ¹⁶ cm 2.
^-3 or less, the epitaxial growth compound semiconductor crystal characterized by the above-mentioned. 5. The epitaxially grown compound semiconductor crystal according to claim 4, wherein the first compound semiconductor is an AlGaAs layer. 6. The epitaxially grown compound semiconductor crystal according to claim 4, wherein the first compound semiconductor is an InAlAs layer.