JP2747316B2 - Semiconductor device - Google Patents

Description

The present invention relates to a heterostructure having a GaAs layer and an AlGaAs layer,
The present invention relates to a compound semiconductor device having a superlattice structure or a quantum well structure, and more particularly to an improvement in electrical characteristics of a semiconductor device in which an AlGaAs layer is doped with impurities such as Si, Sn, S, and Te.

SUMMARY OF THE INVENTION The present invention provides a heterostructure having a GaAs layer and an AlGaAs layer,
The present invention relates to an improvement of a compound semiconductor device having a superlattice structure or a quantum well structure. In these structures, a deep impurity level caused by doping (adding) Si or the like as an impurity is reduced by doping In. It was made.

2. Description of the Related Art In an electronic device or an optoelectronic device using a compound semiconductor, a heterostructure composed of a GaAs layer and an AlGaAs layer is frequently used as a constituent material. The reason is that the energy bottom seen from the electronic system is higher at the bottom of the AlGaAs conduction band than at the bottom of the GaAs conduction band, and an energy step occurs at the junction between these two materials. As is well known.

In particular, recently, high electron mobility transistors (HEMT),
Such a structure is used in a quantum well laser, a quantum well light emitting diode, or the like. However, when doping n-type impurities such as Si into the AlGaAs region to generate carriers (current carriers) in these materials, deep impurity levels (so-called DX centers) are formed, and the carriers, that is, electrons, have a sufficient density. Is not known to occur (eg, DVLang, RALoagan and M. Jaros “T
rapping Characteristics and a Donor-Complex (DX)
model for the Persistent Photoconductivity Trappin
g Center in Te-Doped Al _x Ga _1-x As "Physical Review
(B) vol.19, No.2, pp1015-1030 1979).

Deep impurity levels do not occur in GaAs, but in AlGaAs mixed crystals.
Occurs when doping impurities such as Si and Te. The density of deep impurity levels is relatively low when the Al component is 20% or less. That is, when the mixed crystal is expressed as Al _x Ga _1-x As, x
If is less than 0.2, there is not much problem. x from 0.2
As it increases to 0.3, the density of deep impurity levels sharply increases. Therefore, although the density of deep impurity levels can be reduced by reducing the Al component ratio x, the conduction band at the hetero interface between GaAs and AlGaAs is reduced because the bottom of the conduction band approaches that of GaAs. The step at the bottom of the is reduced. This step is necessary to confine electrons generated in the AlGaAs layer in the GaAs layer. The confinement of electrons in the GaAs layer is a necessary condition for a device using a two-dimensional electron gas.

Therefore, as a conventional technique, AlGaAs is replaced with a superlattice in which GaAs and AlAs are alternately stacked to a thickness of several tens of angstroms, and an impurity such as Si is doped into the GaAs layer of the superlattice or the GaAs layer and the AlAs layer. (For example, Masatake Ogawa, Hisao Baba, Furu Mizutani "Increasing the electron density of compound semiconductors by superlattice structure and selective impurity doping," Nikkei Electronics January 14, 1985, pp213-240, or K. Kobayashi , M.Morita, N.Kama
ta and T. Suzuki Deep Electron Traps in AlAs-GaAs
Superlattices as Studied by Deep-Level Transient
Spectroscopy, Japan Journal Applied Physics vol.27,
No. 2 pp. 192-195 1988). In this way, a deep impurity level is not created, and thus a high electron density is obtained, and the bottom of the conduction band in the effective sense of the superlattice (actually, the miniband of the superlattice) is relatively reduced. Can be higher.
By appropriately selecting the thickness ratio and period of AlAs and GaAs of this superlattice, Al _x G having any desired Al component ratio x can be obtained.
The same band gap as the mixed crystal of a _1-x As can be obtained.

[Problems to be Solved by the Invention] To manufacture the above-described superlattice, a considerable number of layers of GaAs and AlAs having a thickness of several tens of angstroms must be stacked. Although this is possible with techniques such as molecular beam epitaxy (MBE) or metal-organic vapor phase epitaxy (MOCVD), the manufacturing process is considerably more complicated. Further, the operation of crystal growth is further complicated in order to prevent doping of the interface between the layers of the superlattice with impurities. Also, when the impurity doping density is increased, there is a risk that the superlattice may be mixed and crystallized due to a disordering phenomenon. Even if the temperature of the device rises excessively during the use of the semiconductor crystal during growth or after manufacture, the superlattice portions may be mixed and crystallized due to the disordering phenomenon.

The present inventor discovered the following while making various semiconductor materials and measuring deep impurity levels. Ie
Doping Al _x Ga _{1 -x} As with Si and then doping it with In by several% reduces the density of deep impurity levels.

FIG. 2 shows how the density of deep impurity levels decreases when In 0.3 is doped into Al _0.3 Ga _0.7 As (x = 0.3). The characteristic curve A is a case where Si is doped so that the electron density becomes 1 × 10 ¹⁸ cm ⁻³ at room temperature, and the characteristic curve B
Is a case where Si is doped so as to be 4 × 10 ¹⁷ cm ⁻³ . In any case, it can be seen that doping about 4% of In lowers the density of deep impurity levels by about one digit.

Therefore, an object of the present invention is to reduce a deep impurity level by forming a superlattice as in the related art, with the intention of reducing the deep impurity level by utilizing the above-described knowledge of the present inventor. It is an object of the present invention to provide a compound semiconductor device which solves the conventional problems of the resulting complicated manufacturing process, complicated crystal growth operation, and the possibility of mixed crystal formation of the superlattice.

[Means for Solving the Problems] In order to achieve such an object, in the first embodiment of the present invention, a GaAs layer and Si, Sn, S or Te are doped as impurities. In the semiconductor device constitutes a heterostructure by the Al _x Ga _1-x As layer, Al _x Ga _1-x As set the component ratio x of Al in the range of 0.2 ≦ x ≦ 0.4 in the layer, and the GaAs layer and the Al _x G
Each of the a _1-x As layers is doped with 1 to 10% (at%) of In.

Second embodiment of the present invention, GaAs layer and Si, Sn, in a semiconductor device having a superlattice structure constituted by the Al _x Ga _1-x As layer S or Te is doped as an impurity, Al _x G
The Al component ratio x in the a _1-x As layer is set in the range of 0.2 ≦ x ≦ 0.4, and ₁ to 10% of In is contained in each of the GaAs layer and the Al _x Ga _1-x As layer.
(At%).

A third embodiment of the present invention is directed to a semiconductor device having a quantum well structure including a GaAs layer and an Al _x Ga _1-x As layer doped with Si, Sn, S, or Te as an impurity.
The _x Ga _1-x As composition ratio of Al in the layer x set in the range of 0.2 ≦ x ≦ 0.4, and the In each of the GaAs layer and the Al _x Ga _1-x As layer 10
% (At%) doping.

[Operation] According to the present invention, a heterostructure of an AlGaAs layer and a GaAs layer having a small deep impurity level is formed by uniformly doping In both the GaAs layer and the Al _x Ga _1-x As layer with In. As a result, when the AlGaAs layer is doped with Si or the like as an impurity, a high electron density is obtained, and the temperature dependence of the electron density is eliminated. Therefore, when this material is applied to a HEMT (High Electron Mobility Transistor), the characteristics of the element can be improved. For example, the transfer conductance Gm can be increased and the temperature change of the threshold voltage Vth can be suppressed. According to the present invention, a deep impurity level can be reduced by simply doping In, a complicated structure such as a conventional superlattice structure is not required at all, and the manufacturing cost can be significantly reduced.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1A shows a cross section of a heterostructure in one embodiment of the compound semiconductor device of the present invention.

Here, GaAs is doped on the substrate 1 while doping 5% of In.
Grow the layer. An Al _0.3 Ga _0.7 As layer 3 is grown on the GaAs layer 2 while doping with Si and 5% of In to form a heterostructure having a hetero interface 4. If the Al _0.3 Ga _0.7 As (Si) layer 3 is doped with 5% of In, the density of deep impurity levels can be reduced by one digit or more as described above. However, doping In produces a mixed crystal of AlGaAs and InAs. InAs has a narrow band gap of about 0.36 eV, the bottom of the conduction band of AlGaAs is lowered by about 46 meV. In this state, the step (band offset) from the bottom of the conduction band of GaAs decreases, and the ability to confine electrons in the GaAs layer decreases.

Therefore, in the present invention, the GaAs layer 2 is similarly doped with In to lower the conduction band bottom in advance. In
Assuming that the doping amount of GaN is 5%, the bottom of the conduction band is about 35meV.
As shown in FIG. 1 (B), a step almost equal to that when In is not doped can be formed. Although there is no method for directly and accurately measuring the step difference experimentally, it can be obtained by the following calculation. GaAs and Al
The width of the band gap of _0.3 Ga _0.7 As is 1.42 eV and 1.8 eV, respectively.
247 meV, which is 65% of the difference of 0.38 eV, is the step at the bottom of the conduction band of GaAs and Al _0.3 Ga _0.7 As when In is not doped.
The width of the forbidden band of InAs is about 0.36 eV, the amount of 72meV corresponding to 5% of the difference 1.44eV with that of Al _0.3 Ga _0.7 As is forbidden band of Al _0.3 Ga _0.7 As is decreased due to 5% doped In It is. Is sized to 46meV corresponding to 65% of this is lowered bottom of the conduction band of Al _0.3 Ga _0.7 As doped with In.
It is now widely accepted that 65% of the difference between the band gaps of GaAs and Al _0.3 Ga _0.7 As is the step at the bottom of the conduction band. It is unclear what percentage of the bandgap is the difference between the bottom of the conduction band and InAs and GaAs, or InAs and AlGaAs, but in the case of a heterostructure of InGaAs and GaAs. There is a report that it is about 60%, which is about the same as that of GaAs and AlGaAs (for example, Ando, Toshima, Okamoto, Ito "InGaAs
Fabrication and Analysis of Strained-Quantum Well Resonant Tunneling Diodes "
106 pp13-20 (1986)). The doping amount of In is 5
%, So the calculation of the step at the bottom of the conduction band is GaAs and Al
The calculation can be performed in the same way as the calculation for _0.3 Ga _0.7 As, that is, using the rule that 65% of the forbidden band width becomes a step at the bottom of the conduction band.

Similarly, the forbidden band width of GaAs and InAs is 1.42 eV and 0.36 eV
Is 1.06 eV, an additional 65% of these 5%
meV. This is the size at which the bottom of the conduction band is reduced by doping GaAs with 5% of In.

In the present invention, by doping In both the GaAs layer and the AlGaAs layer with In, Al _0.3 Ga _0.7 As (Si) deep impurity levels are not generated, and the energy step with the GaAs side is kept almost unchanged. be able to. The step is small (46me
(V-35meV = 11meV) To prevent the decrease, GaAs
On the side, it is also possible to produce a heterostructure in which the density of impurity levels is reduced without doping the step at all by doping about 2% extra In.

FIG. 1 (A) shows an example of a simple heterostructure.
In a quantum well structure in which AlGaAs barrier layers are arranged on both sides of the layer 2 or a superlattice structure in which the GaAs layers 2 and the AlGaAs layers 3 are alternately and periodically stacked, In is doped in the same manner as in the heterostructure. As a result, the generation density of deep impurity levels that generate impurities such as Si can be reduced.

The larger the doping amount of In, the more effective in reducing the deep impurity level. However, since the lattice constant with the substrate 1 becomes inconsistent, it is preferable to keep it within about 10%.

[Effects of the Invention] According to the present invention, by uniformly doping In both the GaAs layer and the Al _x Ga _{1 -x} As layer, the heterostructure of the AlGaAs layer and the GaAs layer having a small deep impurity level is obtained. As a result, when the AlGaAs layer is doped with Si or the like as an impurity, a high electron density is obtained, and the temperature dependence of the electron density is eliminated. Therefore, when this material is applied to a HEMT (High Electron Mobility Transistor), the characteristics of the element can be improved. For example, the transfer conductance Gm can be increased and the temperature change of the threshold voltage Vth can be suppressed. According to the present invention, a deep impurity level can be reduced by simply doping In, a complicated structure such as a conventional superlattice structure is not required at all, and the manufacturing cost can be significantly reduced.

[Brief description of the drawings]

FIG. 1A is a configuration diagram showing a configuration example of a semiconductor device having a hetero structure as one embodiment of the present invention, and FIG. 1B is a configuration diagram of the hetero device of the embodiment shown in FIG. 1A. FIG. 2 is an energy level diagram showing the energy relationship at the bottom of the conduction band at the interface. FIG. 2 is a characteristic diagram illustrating how the density of deep impurity levels is reduced when In is doped. 1 ... substrate, 2 ... GaAs layer, 3 ... AlGaAs layer, 4 ... heterointerface.

Claims (3)

(57) [Claims] 1. A semiconductor device having a heterostructure comprising a GaAs layer and an Al _x Ga _1-x As layer doped with Si, Sn, S or Te as an impurity, wherein the Al _x Ga _1-x As layer is Is set in the range of 0.2 ≦ x ≦ 0.4, and ₁ to 10% of In is added to each of the GaAs layer and the Al _x Ga _1-x As layer.
%) A semiconductor device characterized by being doped. 2. A semiconductor device having a superlattice structure comprising a GaAs layer and an Al _x Ga _1-x As layer doped with Si, Sn, S or Te as an impurity, wherein the Al _x Ga _1-x As
The Al component ratio x in the layer is set in the range of 0.2 ≦ x ≦ 0.4,
In addition, in each of the GaAs layer and the Al _x Ga _1-x As layer,
% (At%) doped semiconductor device. 3. A GaAs layer and Si, Sn, in a semiconductor device having an S or a quantum well structure Te is constituted by the Al _x Ga _1-x As layer is doped as an impurity, the Al _x Ga _1-x
The component ratio x of Al in the As layer is set in the range of 0.2 ≦ x ≦ 0.4, and In is added to each of the GaAs layer and the Al _x Ga _1-x As layer by one.
A semiconductor device characterized by being doped with up to 10% (at%).