JPH09293854A - Heavily doped semiconductor and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enlarge an application range for a semiconductor by providing a semiconductor, and its manufacturing method, which is doped more than a doping concentration limit which has been thought to be principal for a semiconductor, for increased design freedom for the semiconductor. SOLUTION: Relating to a semiconductor containing an n-type semiconductor layer 1 to which donor impurities are added, a joint to a semiconductor layer 2 is provided wherein its energy value from a vacuum level to a Fermi level is larger than the energy value from a vacuum level to a conductive band bottom end in the N-type semiconductor 1. A donor impurity concentration (Nd ) within a range of a depletion layer thickness caused in the n-type semiconductor layer 1 adjoining the joint interface is more than 2.7×10<3> exp -5.5(EC-EFS)}×NC (where EC is an energy value (unit: eV) from a valence band top end to a conductive band bottom end of the n-type semiconductor 1, EFS is an energy value (unit: eV) from a valence band top end to an electric charge neutral level of the n-type semiconductor 1, NC is an effective state density (unit: cm<-3> ) of conductive band of the n-type semiconductor 1).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor doped with impurities, particularly a semiconductor doped with high concentration of impurities, and a method for manufacturing the same.

[0002]

2. Description of the Related Art High-concentration doping of impurities in semiconductor devices is an important technique. For example, in GaAs and AlGaAs used for manufacturing high speed devices, Si is used as an n-type impurity having a small diffusion coefficient and excellent thermal stability, and doping is performed up to ³ to 5 × 10 ¹⁸ / cm ^3. Such a high-concentration doping layer is used for an electrode extraction layer (GaAs) in a field effect transistor or a bipolar transistor and an electron supply layer (AlGaAs) in a heterojunction field effect transistor using a modulation doping structure. Has contributed to performance improvement. However, with recent miniaturization and higher performance of devices, reduction of element resistance is becoming more important than ever. Therefore, reduction of channel resistance in the heterojunction field effect transistor and reduction of electrode contact resistance in various transistors are demanded, and further high-concentration doping is being demanded at present.

There is a metallurgical solid solution limit value for impurity doping. When the solid solution limit of impurities in the base semiconductor material is exceeded, precipitation of an impurity phase or extreme deterioration of crystallinity occurs. The solid solubility limits of various impurities have been relatively well investigated for typical semiconductors.

On the other hand, it is known that electron concentration saturation actually occurs at an impurity concentration lower than the metallurgical solid solution limit. For example, S in GaAs
In the case of i-impurity, 5 × 10 ¹⁹ / cm ³ or more of solid solution
It is generally known that a limit value of about 5 × 10 ¹⁸ / cm ³ is an actually active donor. Below the limit value, the Si concentration and the electron concentration match, but above the limit value, the Si concentration is higher.
It is known that the electron concentration saturates or decreases despite the increase in concentration.

Such concentration saturation has been investigated in various semiconductors, and Tokumitsu et al. Investigated the highest electron concentration in various semiconductors reported in the past and found that the value was the charge neutral level and conduction band or valence electron in each semiconductor. It was found to have a close correlation with the energy position of the band (Japanes Journal of App.
lied physics. Vol. 29, no. 5,
L698-L701, (1990)).

From the results, it was found that the electron (or hole) concentration saturation in the semiconductor is closely related to the Fermi level in the semiconductor system. That is, n
In the case of a type semiconductor, the Fermi level rises due to doping, but in reality, there is an upper limit value at the position of the Fermi level, and even if doping is carried out beyond this level, a compensation effect will occur due to the generation of intrinsic defects, etc. , It saturates at a constant value.

This model actually explains well that the conventionally known semiconductor has a small saturation concentration value in a semiconductor with a large forbidden band and that a compensation phenomenon (self-compensation effect) due to an intrinsic defect is likely to occur. There is. Experimentally, GaAs,
In AlGaAs, it has been confirmed that Ga vacancies (acceptors) of high concentration are generated as the doping concentration is increased.

Further, it was confirmed that even if Si was added to GaAs at a saturation concentration or more, by simultaneously adding an acceptor to lower the Fermi level, no vacancy is generated and Si enters the donor site. Therefore, it supports the importance of the Fermi level position for activation as a donor.

Here, the empirical formula reported by Tokumitsu et al. Is described below. In the case of n-type semiconductor: n / N _C = 2.7 × 10 ³ exp (−5.5 (E _C −E _FS )) (1) In the case of p-type semiconductor: p / N _V = 4. 0 × 10 ³ exp (−6.1 (E _FS −E _V )) ・ ・ ・ (2)

Here, n is the effective donor concentration (unit: cm
^-3 ), p is the acceptor concentration (unit: cm ^-3 ), N _C is the effective density of states in the conduction band (unit: cm ^-3 ), and N _V is the effective density of states in the valence band (unit: cm ^-3 ). , E _C is the energy value from the top of the valence band to the bottom of the conduction band (unit: eV),
E _FS represents an energy value (unit: eV) from the upper end of the valence band to the charge neutral level. Further, E _V indicates the energy value at the upper end of the valence band, but since the same energy value is used as the reference value, E _V = 0 (eV). The value of E _FS -E _V is,
J. Physical Rev by Tersoff
new Letters Vol. 56, no. 25,
p 1775-2758 (1996), Table 1 (p
2756) can be used. The value of E _FS is, for example, 0.5 eV for GaAs and 1.
It can be seen that it is 05 eV. Further, regarding other substances not described in the above literature, for example, W. A. Harr
ison and J. Journal by Tersoff
of VacuumScience and Tech
biology4 (4), p1068-1073 (1)
The mixed orbital energy value (εh−εv) in Table 1 (p1070) described in 986) can be used.
For mixed crystal semiconductors, the value of each constituent semiconductor and its component ratio can be calculated using the Vegard's law.

The empirical formulas (1) and (2) in the above literature have been widely considered to give the theoretical concentration limit values in known semiconductors.

On the other hand, several attempts have been made in order to realize even higher concentration doping, for example, self-compensation in GaAs is triggered by the generation of Ga vacancies, and Ga vacancies are taken into consideration. Si doping up to 2 × 10 ¹⁹ / cm ³ has been realized by performing low-temperature crystal growth that does not give activation energy necessary for generating holes. Also, high-concentration doping is realized by planar doping different from normal doping (for review, RC Newman, Semi).
onducer Science and Tech
noology, 9, p1749-1762 (1994)
reference).

On the other hand, however, it has been shown that in these highly doped crystals, impurities are easily diffused and deteriorated by heat treatment. All of these methods are not thermally stable because they are manufactured under strongly non-equilibrium conditions, and there has been a demand for thermally stable semiconductors that are highly doped above the conventional limit. . For example, GaAs, AlGa
If As is used, a highly-doped semiconductor which can be produced at a temperature of preferably 550 ° C. or higher, more preferably 600 ° C. or higher, and a method for producing the same have been demanded.

[0014]

SUMMARY OF THE INVENTION The object of the present invention is to overcome the doping concentration limit which is considered to be the principle in semiconductors, and to dope more than the doping concentration defined by the formulas (1) and (2). It is intended to provide a semiconductor and a manufacturing method thereof, and to expand the scope of semiconductor application by increasing the degree of freedom in designing the semiconductor.

[0015]

In view of the above problems, the inventors of the present invention have conducted extensive studies on doping in semiconductors, and as a result, when a semiconductor is used alone, the electron concentration is constant as described above. It was found that, when the target semiconductor is saturated at the limit, but the target semiconductor is brought into contact with a semiconductor having a different property, the appearance is different near the contact part and the electron concentration limit changes.

As a result of a more detailed study, in the case of a semiconductor including an n-type semiconductor, when a second semiconductor having a larger electron affinity than the n-type semiconductor is joined to the n-type semiconductor, the vicinity of the junction is It has been found that it is possible to increase the effective electron concentration of the n-type semiconductor beyond the conventionally known saturation value.

That is, according to the present invention, [1] in a semiconductor having an n-type semiconductor layer 1 doped with a donor impurity, the value of energy from the vacuum level to the Fermi level is
Has a junction connected to the semiconductor layer 2 having a value larger than the value of energy from the vacuum level to the lower end of the conduction band in the n-type semiconductor 1, and in the n-type semiconductor layer 1 in contact with the junction interface. The donor impurity concentration (N _d ) within the range of the depletion layer thickness generated is 2.7 × 10 ³ exp {−5.5 (E _C −E _FS )} × N
_C (where E _C is the energy value from the top of the valence band of the n-type semiconductor 1 to the bottom of the conduction band (unit: eV), E _FS is the charge neutral level from the top of the valence band of the n-type semiconductor 1) Up to the energy value (unit: eV), N _C represents the effective density of states (unit: cm ⁻³ ) of the conduction band of the n-type semiconductor 1).

The present invention also provides [2] a method of manufacturing a semiconductor having an n-type semiconductor layer 1 doped with a donor impurity, wherein the n-type semiconductor layer 1 doped with a donor impurity is changed from a vacuum level to a Fermi level. Whose energy value is larger than the energy value from the vacuum level to the lower end of the conduction band in the n-type semiconductor 1 is bonded to the n-type semiconductor layer 1 in contact with the bonding interface. The donor impurity concentration (N _d ) was 2.7 × 10 ³ exp {−5.5 (E _C −E _FS )} × N within the range of the thickness of the depletion layer to be generated.
_C (however, E _C , E _FS , and N _C have the same definitions as in [1].) The present invention relates to the method for producing a semiconductor according to [1], in which a donor impurity is doped.

Furthermore, according to the present invention, [3] in a semiconductor having an n-type semiconductor layer 1 to which a donor impurity is added, the energy value from the vacuum level to the bottom of the conduction band is the vacuum level in the n-type semiconductor 1. To the bottom of the conduction band, the heterojunction connected to the semiconductor layer 2'having a value larger than the value of the energy, and the n
The donor impurity concentration (N _d ) within the range of the depletion layer thickness generated in the type semiconductor layer 1 is 2.7 × 10 ³ exp {−5.5 (E _C −E _FS )} × N
_C (where E _C is the energy value from the top of the valence band of the n-type semiconductor 1 to the bottom of the conduction band (unit: eV), E _FS is the charge neutral level from the top of the valence band of the n-type semiconductor 1) Up to the energy value (unit: eV), N _C represents the effective density of states (unit: cm ⁻³ ) of the conduction band of the n-type semiconductor 1).

The present invention also relates to [4] a method of manufacturing a semiconductor having an n-type semiconductor layer 1 doped with a donor impurity, wherein the n-type semiconductor layer 1 doped with a donor impurity has a vacuum level to a conduction band lower end. The semiconductor layer 2 ′ having a higher energy value than the energy value from the vacuum level to the lower end of the conduction band in the n-type semiconductor 1 is hetero-junctioned, and the n-type semiconductor layer 1 in contact with the junction interface Within the range of the depletion layer thickness generated in the inside, the donor impurity concentration (N _d ) is 2.7 × 10 ³ exp {−5.5 (E _C −E _FS )} × N
_C (however, E _C , E _FS , and N _C have the same definitions as in [3].) The present invention relates to the method for producing a semiconductor according to [3], in which a donor impurity is doped.

Furthermore, the present invention provides [5] a semiconductor having a p-type semiconductor layer 3 to which an acceptor impurity is added,
The junction has a junction connected to the semiconductor layer 4 in which the energy value from the vacuum level to the Fermi level is smaller than the energy value from the vacuum level in the p-type semiconductor 3 to the lower end of the conduction band. And the p that contacts the joint interface
Type acceptor impurity concentration in the range of the depletion layer thickness occurring in the semiconductor 3 (N _a) ^{is, 4. 0 × 10 3 exp {} -6. 1 (E FS -E V)} × N
_V (where E _FS is the energy value from the upper end of the valence band of the p-type semiconductor 3 to the charge neutral level (unit: eV), E _V is the energy value of the upper end of the valence band (unit: eV), N _V is the effective state density (unit: cm) of the valence band of the p-type semiconductor 3.
^-3 ). ) The present invention relates to the semiconductor.

The present invention also provides [6] a method of manufacturing a semiconductor having a p-type semiconductor layer 3 containing an acceptor impurity, wherein the p-type semiconductor layer 3 containing an acceptor impurity is changed from a vacuum level to a Fermi level. Of which the energy value is smaller than the energy value from the vacuum level in the p-type semiconductor 3 to the lower end of the conduction band is generated in the p-type semiconductor 3 in contact with the junction interface. in the range of the depletion layer thickness, acceptor impurity concentration (N _a) ^{is, 4. 0 × 10 3 exp {} -6. 1 (E FS -E V)} × N
_V (however, E _FS , E _V , and N _V are the same as defined in [5].) The present invention relates to the method for manufacturing a semiconductor as described in [5], in which acceptor impurities are doped.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Conventionally, in the case of an n-type semiconductor, it was considered that the upper limit value of the concentration of donor impurities that can be active is determined by the value expressed by the formula (1) depending on the substance.
However, when the substances having different upper limit values of the donor concentration are brought into contact with each other, the inventors of the present invention, due to the action of the semiconductor having the higher upper limit value of the donor impurity concentration, within the range where electron transfer near the junction occurs (in the depletion layer). It has been found that it is possible to increase the upper limit of the donor impurity concentration of a semiconductor having a low upper limit of concentration.

In other words, the present inventors
When semiconductors with different Fermi levels are brought into contact with each other, the Fermi level is locally reduced in the semiconductor layer depleted by the movement of electrons, and self-compensation phenomena such as defect generation due to the Fermi level saturation mechanism do not occur and donor impurities Have been found to be effectively activated.

That is, the method of manufacturing a semiconductor according to the present invention is as shown in FIG.
In the method for manufacturing a semiconductor having the n-type semiconductor layer 1 to which the donor impurity is added, as shown in FIG.
The semiconductor layer 2 having the energy value from the vacuum level to the Fermi level larger than the energy value from the vacuum level to the lower end of the conduction band in the n-type semiconductor 1 is bonded to the type semiconductor layer 1. The donor impurity is doped within the range of the depletion layer thickness generated in the n-type semiconductor layer 1 in contact with the junction interface. By the manufacturing method, the donor impurity concentration (N _d ) is 2.7 × within the range of the depletion layer thickness generated in the n-type semiconductor layer 1 in contact with the junction interface.
10 ³ exp {−5.5 (E _C −E _FS )} × N _C (The meaning of each symbol is as described above.) Or more.

Here, the thickness of the depletion layer in the n-type semiconductor layer is obtained by dividing the total amount of electrons transferred from the n-type semiconductor layer 1 to the semiconductor layer 2 by the impurity concentration of the n-type semiconductor layer 1. Defined by value. Theoretically, in the electron density distribution obtained by solving Poisson's equation and wave equation in a self-consistent manner in consideration of the conduction band structure in the semiconductor layers 1 and 2, the layer thickness and the impurity distribution, In the semiconductor layer 1 near the junction interface with 2, the electron density per unit volume is preferably 10 ¹² / cm ³ or less, more preferably 10 ¹⁵ / cm ³ or less, and particularly preferably 10 ¹⁷ / cm ³ or less. It corresponds to the thickness of such a part.

In the method for producing a semiconductor of the present invention, preferably, in the above method, the value of energy from the vacuum level to the lower end of the conduction band is replaced with the value of energy from the vacuum level to the Fermi level. And the method. By the manufacturing method, the donor impurity concentration (N _d ) is within the range of the depletion layer thickness generated in the n-type semiconductor layer 1 in contact with the junction interface.
2.7 × 10 ³ exp {−5.5 (E _C −E _FS )}
× N _C (the meaning of each symbol is as described above). The temperature of the atmosphere when doping impurities is preferably 550 ° C or higher.

The semiconductor of the present invention having the n-type semiconductor layer 1 may be a compound semiconductor or an elemental semiconductor. Compound semiconductors include Group 3-5 compound semiconductors,
Examples of the group 2-5 compound semiconductor include a group 4 semiconductor or a mixed crystal semiconductor thereof. Four
Specific examples of group semiconductors include diamond, Si, and G.
e. Further, as the semiconductor layer 1 in the present invention, Al _x Ga _(1-x) As (0 ≦ x ≦ 1), In _y A
l _z Ga _(1-yz) As (0 ≦ y ≦ 1, 0 ≦ z ≦ 1) or the like can be used. Further, as the semiconductor layer 2 or the semiconductor layer _2'in the present invention, In _y Ga _{(1 -y)} As is used.
(0 ≦ y ≦ 1) or the like can be used.

When a certain n-type semiconductor is doped with a donor impurity, another n-type semiconductor having a proper energy band structure is brought into contact with the n-type semiconductor to perform doping at a concentration which has been impossible in the conventional n-type semiconductor. It has become possible. It has also become possible to provide a semiconductor substrate including at least two semiconductor layers including a semiconductor layer having such a high-concentration doping layer.

The concentration of donor impurities in the n-type semiconductor layer at this time is 2.7 × 10 ³ exp {-5.5.
(E _C −E _FS )} × N _C or more, but in order to bring out the merit of increasing the concentration, the concentration is 3.9 × 10 ^3.
It is more preferable that it is not less than exp {-5.5 (E _C −E _FS )} × N _C. The concentration is more preferably 5.0 × 1
_{^{0 3 exp {-5.5 (E C}} -E FS)} is a × N _C or more, particularly preferably 6.0 × 10 ³ exp {-5.5
(E _C −E _FS )} × N _C or more.

The upper limit of the electron density in the semiconductor layer 1 is based on the maximum impurity concentration defined by the equation (1) in the semiconductor layer 2 to be joined. In addition to this, it goes without saying that the metallurgical solid solution limit of the donor impurity in the n-type semiconductor gives the upper limit.

Further, the thickness of the n-type semiconductor layer capable of being doped at a concentration higher than the concentration limit expressed by the equation (1) is within the range of the thickness of the depletion layer formed at the portion in contact with the interface, In the region of the n-type semiconductor layer separated by more than the thickness of the depletion layer, the effective donor concentration is saturated with the same upper limit value as in the case of a single substance, and even if a dopant is added more than the saturation value, the intrinsic defect serving as a compensation center increases. . Since such an intrinsic defect deteriorates the quality of the semiconductor, it is preferable that the concentration of the added impurity is set to be equal to or lower than the value given by the equation (1) in the region other than the depletion layer.

The essential point of the present invention is to reduce the Fermi level of the n-type semiconductor layer locally within the range of the interface depletion layer by contacting the semiconductor layer having a lower Fermi level during high-concentration n-type doping, It is to suppress the generation of compensation defects and realize high-concentration doping which is impossible with the semiconductor single layer.

Therefore, the semiconductor layer in contact with the n-type semiconductor for obtaining the desired high concentration doping may be a semiconductor layer having a Fermi level lower than that of the high concentration doping layer. In addition to the heterojunction, a semiconductor layer having a low electron concentration, a semiconductor layer having a large amount of impurities or defects having a deep electron trap level in the forbidden band or a surface semiconductor layer having a surface level, a p-type semiconductor layer, or the like is used. be able to.

Although the n-type semiconductor layer has been described above, the same applies to the p-type semiconductor as in the case of the n-type semiconductor, by contacting with a system having a higher Fermi level, which is the opposite of the n-type semiconductor. In the range of the depletion layer generated in the vicinity of the surface, high-concentration doping that is equal to or higher than the doping upper limit value given by equation (2) is possible. That is, the present invention provides a method for manufacturing a semiconductor having a p-type semiconductor layer 3 containing an acceptor impurity as shown in FIG.
In the p-type semiconductor layer 3 added with the acceptor impurity, the energy value from the vacuum level to the Fermi level is smaller than the energy value from the vacuum level to the top of the valence band in the p-type semiconductor 3. It is characterized in that a certain semiconductor layer 4 is joined and an acceptor impurity is doped within the range of the thickness of the depletion layer generated in the p-type semiconductor 3 in contact with the junction interface.

Here, the thickness of the depletion layer in the p-type semiconductor layer is obtained by dividing the total amount of holes transferred from the p-type semiconductor layer 3 to the semiconductor layer 4 by the impurity concentration of the p-type semiconductor layer 3. It is defined by the value. Theoretically, in the hole density distribution obtained by solving Poisson's equation and wave equation in a self-consistent manner, considering the valence band structure in the semiconductor layers 3 and 4, the layer thickness and the impurity distribution, In the semiconductor layer 3 near the junction interface with the semiconductor layer 4, the hole density per unit volume is preferably 10 ¹² / cm ³ or less, more preferably 10 ¹⁵ / cm ³ or less, and particularly preferably 10 ¹⁷ / cm ³ It corresponds to the thickness of the following parts.

Further, in the method for producing a semiconductor of the present invention, preferably, in the above method, instead of the value of energy from the vacuum level to the Fermi level, the energy from the vacuum level to the top of the valence band is changed. It is the method of using the value. By the manufacturing method, the acceptor impurity concentration (N _a ) within the range of the depletion layer thickness generated in the p-type semiconductor 3 in contact with the junction interface was 4.0 × 10 ³ exp {−6.1 (E _FS
−E _V )} × N _V (however, the meaning of each symbol is as described above). Also,
The temperature of the atmosphere when doping impurities is preferably 550 ° C. or higher.

As the semiconductor of the present invention having the p-type semiconductor layer 3, those exemplified as the semiconductor having the n-type semiconductor layer 1 can be mentioned. Similarly, as the semiconductor layer 3 in the present invention, Al _x Ga _(1-x) As
(0 ≦ x ≦ 1), In _y Al _z Ga _(1-yz) As (0 ≦
y ≦ 1, 0 ≦ z ≦ 1) or the like can be used, and as the semiconductor layer 4 in the present invention, In _y Ga _(1-y) As can be used.
(0 ≦ y ≦ 1) or the like can be used.

As for the dopant, it is possible to use not only a single dopant but also a plurality of dopants having different solid solution limits or incorporation sites at the same time.

[0040]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited thereto. Comparative Example 1 Using a semi-insulating GaAs single crystal as a substrate, an n-type AlGaAs crystal was first produced by the following method by metal organic thermal decomposition method (MOCVD method). A GaAs single crystal having a clean surface and a substrate having a plane inclined by 0.4 ° from the (100) plane in the <0-11> direction was placed in an epitaxial growth furnace under a hydrogen gas and arsine mixed gas atmosphere. Heat cleaned. Then, the concentration of arsine in the atmosphere was adjusted to 0.83 mol% at 650 ° C., and 2.95 × 10 ⁻³ mol of trimethylgallium was added to the atmosphere.
%, A GaAs layer having a thickness of 50 nm is epitaxially grown, and trimethylaluminum is added to 7.38%.
× 10 ⁻⁴ mol% was added, and Al _0.2 having a thickness of 300 nm was added.
A Ga _0.8 As layer was epitaxially grown. Subsequently, disilane was added at 5.80 × 10 ⁻⁷ mol% to 4.09 × 10 ^−5.
n-type Al with a thickness of 500 nm added in the range of mol%
_{After the 0.2} Ga _0.8 As layer was epitaxially grown, it was cooled and the semiconductor crystal was taken out from the growth furnace. At this time, the flow rate of hydrogen gas used as a carrier gas was 45
It was an SLM, and the epitaxial growth rate of the Al _0.2 Ga _0.8 As layer was about 20 nm / min. here,
1 SLM (1 Standard Litter pe)
r Minute) is a gas flow rate such that the gas flow rate in the standard state (0 ° C., 1 atmospheric pressure) is 1 liter / min.

The crystal thus taken out was cut into a rectangle of about 5 mm square by cleavage, and indium dots were attached to its four corners.
After annealing at 350 ° C. for 5 minutes in a hydrogen atmosphere to form an ohmic electrode, hole measurement was performed by the Van Der Pauw method to determine the electron concentration. In the measurement at this time, in order to avoid the influence of a deep defect level caused by a donor impurity itself, which is a so-called DX center peculiar to AlGaAs, white light is applied to the sample immersed in liquid nitrogen and cooled for about 1 minute. After irradiation, hole measurement was performed. A sample prepared separately from the above was subjected to secondary ion mass spectrometry (SIMS) to quantitatively analyze Si atoms in the n-type Al _0.2 Ga _0.8 As layer.

The obtained electron concentration, Si concentration and silicon
The relationship with the doping amount is shown in FIG. The horizontal axis is
The electron concentration is 2 × 10¹⁸/
cm ^ThreeDoping amount is 2 × 10¹⁸/ Cm^ThreeAs
The flow rate of disilane was standardized. That is, [Siri
Condoping amount] = 2 × 10¹⁸/ Cm^Three× Disilane flow
Amount / (n = 2 × 10¹⁸/ Cm^ThreeFlow rate of disilane)
It is.

In a region where the disilane doping amount is relatively small and the electron concentration is 3 × 10 ¹⁸ / cm ³ or less, the doping amount and the electron concentration are proportional. However, when the doping amount is further increased, the Si concentration by SIMS continues to be doped. Although it increases in proportion to the amount, the electron concentration saturates to about 3
It was found that the increase did not exceed 10 ¹⁸ / cm ³ .
Also, when this was observed by photoluminescence at 77 K, the band edge emission intensity decreased in the sample with saturated electron concentration, and the broad emission intensity in the 1.32 eV band, which is considered to be derived from the composite defect of Si donor and Ga vacancy. Was found to be increasing.

In the Al _0.2 Ga _0.8 As layer, the maximum electron concentration expected from the equation (1) is 3.5 ×.
At 10 ¹⁸ / cm ³ , it was almost in agreement with the saturation value obtained in the experiment.

Example 1 A heterojunction crystal made of a 3-5 group compound semiconductor having the structure shown in FIG. 4 was prepared. Regarding the crystal growth procedure and conditions, trimethylindium was added as a raw material during epitaxial growth of the In _0.2 Ga _0.8 As layer, and I
except that the growth temperature of n _0.2 Ga _{0. 8} As layers and 600 ° C. is the same as in the n-type Al _0.2 Ga _0.8 As in Comparative Example 1. The silicon doping amount in the n-type Al _0.2 Ga _0.8 As layer in FIG. 4 is 3 to 6 under the same conditions as in Comparative Example 1.
It was changed within a range of × 10 ¹⁸ / cm ³ .

The obtained crystal has the above-mentioned n-type Al _0.2 Ga.
_The hole measurement was performed in the same manner as for the _0.8 As layer to determine the sheet electron density. Further, a sample for measuring the capacitance-voltage characteristic was prepared as follows. A part of the epitaxial crystal sample was taken out by splitting it by about 1/4, and aluminum metal was vacuum-deposited by about 200 nm on the entire surface. Next, aluminum metal is separated into a circular portion having a diameter of 800 μm and another portion having a distance of 50 μm from the circular portion by photolithography, and a pseudo Schottky diode having the circular portion as a Schottky electrode and the other portion as a counter electrode. Was produced. Using this diode, the electron concentration profile was obtained by the capacitance voltage method in which a negative voltage was applied to the Schottky electrode side, and the voltage value when the electron concentration decreased to 1 × 10 ¹⁵ / cm ³ was determined as the threshold voltage (Vt). Sought as.

Next, theoretical electrical characteristics of the epitaxial crystal manufactured as described above were obtained as follows. That is, based on the manufactured structure, Shroedi
The electron distribution of the same structure was obtained by solving Nger's wave equation and Poisson's equation in a self-consistent manner. The GaAs surface level at this time is 0.
It was assumed to be 9 eV.

As a result of calculation, almost all the electrons are InGaA.
Since it was found to exist in the s quantum well, the sheet electron concentration Ns was obtained by integrating the electron concentration. Next, the surface level is increased by 0.01 eV, the sheet electron concentration is calculated each time, and the increase from the surface level of 0.9 eV is ΔV, and the correlation between ΔV and Ns is calculated, and Ns is 1
The ΔV value when it was lowered to 0 ¹⁰ / cm ² was defined as the theoretical threshold voltage (Vt). The sheet electron concentrations Ns and Vt at ΔV = 0 were obtained when the active donor concentration of the n-AlGaAs doping layer was changed in the range of 2 to 6 × 10 ¹⁸ / cm ³ . The results obtained are shown by the solid line in FIG.

The sheet electron density Ns value obtained by the Hall measurement and the Vt value obtained by the capacitance voltage method are shown in FIG. 5 (black circles). The crystal growth conditions and the disilane doping amount of the n-Al _0.2 Ga _0.8 As crystal layer are the same as those used in the thick film evaluation in Comparative Example 1, and n-AlGaA
s Doping layer concentration is 3 × 10 ¹⁸ / c as the result of thick film
If saturated around m ³ , the experimentally obtained Ns value and Vt value should be constant values shown by the dotted line values in the figure, but the experimental value is actually proportional to the doping amount and the calculated value. It turned out that it almost agrees with. From this,
In the thin film n-AlGaAs doping layer in contact with the InGaAs interface, it was revealed that the doping was significantly higher than the saturation concentration conventionally observed in the thick film.

Example 2 A heterostructure crystal made of a 3-5 group compound semiconductor having a structure shown in FIG. 6 was produced. The crystal growth procedure and conditions are the same as in Example 1, except that n-type Al _0.2 in FIG.
The amount of silicon doping in Ga _0.8 As is 3 × 10.
^It was changed in the range of ¹⁸ / cm ^{3 to} 2.4 × 10 ¹⁹ / cm ³ . The obtained crystal was subjected to hole measurement in the same manner as in Example 1 to determine the sheet electron density (Ns). In addition, the threshold voltage (V
t) was determined. Next, based on the manufactured structure, Example 1
And Shroedinger's wave equation and P
The theoretical values of the sheet electron concentration (Ns) and the threshold voltage (Vt) were obtained by solving the Oisson's equation in a self-consistent manner.

The sheet electron density Ns value obtained by the Hall measurement and the Vt value obtained by the capacitance voltage method are shown in FIG. 7 (black circles). The Ns value and Vt value obtained by calculation are shown by solid lines. silicon doping conditions in the n-type Al _{0 .2} Ga _0.8 As is the same as that used in the thick film evaluation in Comparative Example, thick film of the silicon doping concentration in the n-type Al _0.2 Ga _0.8 As is the comparative example As shown in the result of 1., if saturated around 3 × 10 ¹⁸ / cm ³ , the experimentally obtained Ns value and Vt value should be constant values shown by the dotted line in the figure, but the experimental value is actually Was found to increase with the increase of the doping amount, almost in agreement with the calculated value. From this, it was clarified that in the thin film n-AlGaAs doping layer close to the InGaAs interface, doping significantly exceeding the saturation concentration conventionally observed in the thick film was realized.

Example 3 A heterostructure composed of a 3-5 group compound semiconductor having the structure shown in FIG.
Structural crystals were prepared. Crystal growth procedure and conditions
Is the same as in Examples 1 and 2, but the crystal layer structure is G
aAs and In_0.2Ga_0.8It is composed of As. substrate
The silicon doping concentration of the side GaAs layer is 3 × 10¹⁸
/ Cm^ThreeAt a constant value of 12 nm In _0.2Ga_0.8As
Layer is undoped (Sample B) or silicon doping amount
To 3 × 10¹⁹/ Cm^Three(Sample C) or 6 × 10¹⁹/ C
m^Three(Sample D), 10 nm n grown on top
Type GaAs layer is undoped (Sample B) or silicon
Doping concentration 3 × 10¹⁹/ Cm^Three(Sample C) or
6 × 10¹⁹/ Cm^Three(Sample D).

Next, a metal electrode was attached to the produced crystal and the contact resistance was measured. That is, the distance between the electrodes on the sample crystal surface is 5, 10, 15, 20, 25, 30 μ.
A rectangular metal electrode group of 150 μm × 100 μm of m was formed by photolithography and vacuum deposition method, and TLM (Tr
The contact resistance value was determined by the ansmission Line Method) method. In addition, the semi-insulating substrate portion is removed by mesa etching except for the electrode group and the portion where the electrode interval is defined to be 5 to 30 μm. Metal electrodes are Al (400 nm), Ti (50 nm) / A
u (300 nm), and AuGe (600 nm) / N
There are three types of i (200 nm) / Au (300 nm).

As a reference sample (Sample A), 5 × 1
N doped with silicon to a thickness of 0 ¹⁸ / cm ³ and having a thickness of 500 nm
-A GaAs crystal was prepared, a metal electrode was formed in the same manner, and the contact resistance was measured. In addition, the measurement is performed immediately after forming the electrode and once in a hydrogen atmosphere at 380
The heat treatment was performed at 90 ° C. for 90 seconds. Contact resistance measurement value (unit is × 10)
^-5 cm ² ) is shown in Table 1.

[0055]

[Table 1]

As the ohmic electrode for n-GaAs, a heat-treated AuGe / Ni / Au electrode is often used. It is generally known that in GaAs, when silicon is doped, the concentration is saturated in the vicinity of 5 to 6 × 10 ¹⁹ / cm ³ . In the sample (A) having a silicon concentration close to this saturation value, when various metal electrodes are attached as shown in Table 1, the semiconductor electrode interface has a high resistance and cannot be energized, or the contact resistance is high. However, the contact resistance at the AuGe / Ni / Au electrode is 3.8 × 10 ⁻⁵ Ωcm ^{2, which} is a good value after the heat treatment.

From the results shown in Table 1, a heterojunction with InGaAs and a high concentration (> 1 × 10 ¹⁹ / c) were obtained.
In the samples (B, C, D) having a m ³ ) GaAs layer structure, when Ti / Au and AuGe / Ni / Au were used, heat treatment was performed without performing heat treatment.
It was found that a contact resistance equivalent to that of the reference sample A using Ni / Au was obtained.

Since GaAs has a high-density surface state, an interface Schottky barrier is generally generated at the interface between the metal and the GaAs by the depletion layer generated on the semiconductor side regardless of the kind of metal used as the electrode. Are known. Therefore, in order to form an ohmic electrode, it has been practiced to dope the interface depletion layer at a high concentration to make the interface depletion layer thin, and to make a current flow easily by a tunnel effect to effectively form an ohmic electrode. Usually about 2 × in GaAs
It is said that ohmic conversion can be achieved by doping at a concentration of 10 ¹⁹ / cm ³ or more, but heat-treated Au Ge / N
In the i / Au system, it is considered that such high-concentration doping is performed near the interface due to the diffusion of Ge that occurs in the heat treatment step and becomes an ohmic electrode.

In samples B, C and D, AuGe / Ni heat-treated even in the metal electrode without any heat treatment.
Since a contact resistance equivalent to that of the reference sample using the / Au electrode is realized,
It is considered that the structure shown in FIG. 8 realizes high silicon doping that enables ohmic conversion.

[0060]

According to the present invention, it is possible to dope high-concentration impurities higher than the conventionally known concentration, and improve the performance of a heterojunction device having a high-concentration doped layer, or use it for an ohmic contact layer, It becomes possible to widely use semiconductors for various devices, which have been conventionally hindered by high-concentration doping, such as use in devices utilizing tunnel junctions, and its industrial significance is extremely large.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structure of a semiconductor of the present invention.

FIG. 2 is a sectional view showing a structure of a semiconductor of the present invention.

3 is an electron concentration and Si obtained in Comparative Example 1. FIG.
The figure which shows the relationship between atomic concentration and silicon doping amount.

FIG. 4 is a cross-sectional view of the heterojunction crystal used in Example 1.

5 is a diagram showing the relationship between the sheet carrier concentration and the silicon doping amount in the heterojunction crystal having the structure of FIG. 4 (where the solid line indicates the calculated value and the dotted line indicates the thick film nA).
The expected values of Vt and Ns under the assumption of electron concentration saturation similar to those in the 1GaAs crystal are shown, and the black circles show experimental values. ).

6 is a cross-sectional view of the heterojunction crystal used in Example 2. FIG.

7 is a diagram showing the relationship between the sheet carrier concentration (Ns) / threshold voltage (Vt) and the silicon doping amount in the heterojunction crystal having the structure of FIG. 6 (where the solid line indicates the calculated value and the dotted line indicates the (Shown are calculated values of Vt and Ns under the assumption of electron concentration saturation similar to that in the thick film n-AlGaAs crystal, and black circles show experimental values.)

FIG. 8 is a cross-sectional view of a heterojunction crystal used in Example 3.

[Explanation of symbols]

1 ... n-type semiconductor layer 2 ... semiconductor in which the energy value from the vacuum level to the Fermi level is larger than the energy value from the vacuum level to the bottom of the conduction band in the n-type semiconductor 1. Layer 2 '... Semiconductor layer 3 ... p in which the energy value from the vacuum level to the lower end of the conduction band is larger than the energy value from the vacuum level in the n-type semiconductor 1 to the lower end of the conduction band -Type semiconductor layer 4 ... A semiconductor layer in which the energy value from the vacuum level to the Fermi level is smaller than the energy value from the vacuum level in the p-type semiconductor 3 to the lower end of the conduction band 5. Substrate 6 ... undoped GaAs layer (thickness 300n
m) 7 ... Semiconductor layer 2 or semiconductor layer 2'in the present invention
Undoped Al _0.2 Ga _0.8 As layer (thickness: 500 nm) 8 ... corresponding to the semiconductor layer 1 of the present invention, a doped Al _0.2 Ga _0.8 As layer (thickness: 6 nm, silicon doping amount: 3 × 10 ¹⁸ / cm ³ ) 9: undoped Al _0.2 Ga _0.8 As layer (thickness: 2 nm) 10: undoped, which corresponds to the semiconductor layer 2 or semiconductor layer 2 ′ of the present invention In _0.2 Ga _0.8 A
s layer (thickness 15 nm) 11 ... Doped Al _0.2 Ga _0.8 As layer (thickness 6 nm, silicon doping amount is 3 to 5 × 10 ¹⁸ / cm ³ ) corresponding to the semiconductor layer 1 in the present invention 12. ..Undoped Al _0.2 Ga _0.8 As layer (thickness 28 nm) 13 ... Undoped GaAs layer (thickness 5 nm) 14 ... Substrate 15 ... Undoped GaAs layer (thickness 300n
m) 16 ... Semiconductor layer 2 or semiconductor layer 2 in the present invention
'Corresponding to undoped Al _0.2 Ga _0.8 As
Layer (thickness 500 nm) 17 ... Doped Al _0.2 Ga _0.8 As layer (thickness 5 nm, silicon doping amount is 3 × 10 ¹⁸ / cm ³ ) 18 ... Doped corresponding to the semiconductor layer 1 in the present invention Undoped Al _0.2 Ga _0.8 As layer (thickness 2 nm) 19 ... Undoped In _0.2 Ga _0.8 A corresponding to the semiconductor layer 2 or the semiconductor layer 2 ′ in the present invention.
s layer (thickness 15 nm) 20 ... undoped Al _0.2 Ga _0.8 As layer (thickness 2 nm) 21 ... doped Al _0.2 Ga _0.8 As layer (thickness corresponding to the semiconductor layer 1 in the present invention 5 nm, silicon doping amount is 3 × 10 ¹⁸ / cm ^{3 to} 2.4 × 10 ¹⁹ / c
m ³ ) 22 ... Undoped Al _0.2 Ga _0.8 As layer (thickness 15 nm) 23 ... Undoped GaAs layer (thickness 5 nm) 24 ... Substrate 25 ... Doped GaAs layer (Thickness: 300 nm, silicon doping amount: 5 × 10 ¹⁸ / cm ³ ) 26 ... In _0.2 Ga _0.8 As layer (thickness: 15 n, corresponding to the semiconductor layer 2 or the semiconductor layer 2 ′ in the present invention)
m, undoped or silicon doping amount 3 × 10 ¹⁹
/ Cm ^{3 to} 6 × 10 ¹⁹ / cm ³ ) 27 ... Doped GaAs layer (thickness 10 nm, silicon doping amount is 3 × 10 ¹⁹ / cm ^{3 to} 6 × 10 ¹⁹ ) corresponding to the semiconductor layer 1 in the present invention. / Cm ³ )

Claims (15)

[Claims] 1. In a semiconductor having an n-type semiconductor layer 1 doped with a donor impurity, the energy value from the vacuum level to the Fermi level is the energy from the vacuum level to the bottom of the conduction band in the n-type semiconductor 1. Has a junction connected to the semiconductor layer 2 having a value larger than the value of n, and the donor impurity concentration (N is within the range of the depletion layer thickness generated in the n-type semiconductor layer 1 in contact with the junction interface). _d ) is 2.7 × 10 ³ exp {−5.5 (E _C −E _FS )} × N
_C (where E _C is the energy value from the top of the valence band of the n-type semiconductor 1 to the bottom of the conduction band (unit: eV), E _FS is the charge neutral level from the top of the valence band of the n-type semiconductor 1) Up to the energy value (unit: eV), N _C represents the effective density of states (unit: cm ⁻³ ) of the conduction band of the n-type semiconductor 1) or more. 2. A method for manufacturing a semiconductor having an n-type semiconductor layer 1 doped with a donor impurity, wherein the n-type semiconductor layer 1 doped with a donor impurity has an energy value from a vacuum level to a Fermi level of The semiconductor layer 2 having a value larger than the value of energy from the vacuum level to the lower end of the conduction band in the n-type semiconductor 1 is bonded to the n-type semiconductor 1 and the n-type semiconductor 1 is in contact with the bonding interface.
Within the range of the depletion layer thickness generated in the type semiconductor layer 1, the donor impurity concentration (N _d ) is 2.7 × 10 ³ exp {−5.5 (E _C −E _FS )} × N
_C (however, E _C , E _FS and N _C are the same as defined in claim 1.) The method for producing a semiconductor according to claim 1, wherein the donor impurity is doped as described above. 3. In a semiconductor having an n-type semiconductor layer 1 to which a donor impurity is added, the energy value from the vacuum level to the bottom of the conduction band is the energy from the vacuum level to the bottom of the conduction band in the n-type semiconductor 1. Has a heterojunction connected to the semiconductor layer 2 ′ having a value larger than the value of, and the donor impurity concentration within the range of the depletion layer thickness generated in the n-type semiconductor layer 1 in contact with the junction interface. (N _d )
Is 2.7 × 10 ³ exp {−5.5 (E _C −E _FS )} × N
_C (where E _C is the energy value from the top of the valence band of the n-type semiconductor 1 to the bottom of the conduction band (unit: eV), E _FS is the charge neutral level from the top of the valence band of the n-type semiconductor 1) Up to the energy value (unit: eV), N _C represents the effective density of states (unit: cm ⁻³ ) of the conduction band of the n-type semiconductor 1) or more. 4. A method of manufacturing a semiconductor having an n-type semiconductor layer 1 doped with a donor impurity, wherein the n-type semiconductor layer 1 doped with a donor impurity has a value of energy from a vacuum level to a conduction band lower end. A semiconductor layer 2 ′ having a value larger than the value of energy from the vacuum level to the bottom of the conduction band in the n-type semiconductor 1 is heterojunctioned, and the thickness of the depletion layer generated in the n-type semiconductor layer 1 in contact with the junction interface. Within the range of
The donor impurity concentration (N _d ) is 2.7 × 10 ³ exp {−5.5 (E _C −E _FS )} × N
_C (however, E _C , E _FS , and N _C are the same as defined in claim 3). The method for producing a semiconductor according to claim 3, wherein the donor impurity is doped as described above. 5. In a semiconductor having a p-type semiconductor layer 3 added with an acceptor impurity, the energy value from the vacuum level to the Fermi level is the energy from the vacuum level in the p-type semiconductor 3 to the bottom of the conduction band. Has a junction connected to the semiconductor layer 4 having a value smaller than the value of n, and the acceptor impurity concentration (N) within the range of the depletion layer thickness generated in the p-type semiconductor 3 in contact with the junction interface.
_a) ^{is, 4. 0 × 10 3 exp {} -6. 1 (E FS -E V)} × N
_V (where E _FS is the energy value from the upper end of the valence band of the p-type semiconductor 3 to the charge neutral level (unit: eV), E _V is the energy value of the upper end of the valence band (unit: eV), N _V is the effective state density (unit: cm) of the valence band of the p-type semiconductor 3.
^-3 ). ) A semiconductor characterized by the above. 6. A method of manufacturing a semiconductor having a p-type semiconductor layer 3 doped with an acceptor impurity, wherein the p-type semiconductor layer 3 doped with an acceptor impurity has an energy value from a vacuum level to a Fermi level of Within the range of the thickness of the depletion layer generated in the p-type semiconductor 3 which is in contact with the junction interface, the semiconductor layer 4 having a value smaller than the energy value from the vacuum level in the p-type semiconductor 3 to the lower end of the conduction band is joined. In addition, the acceptor impurity concentration (N _a ) is 4.0 × 10 ³ exp {−6.1 (E _FS −E _V )} × N
_V (however, E _FS , E _V and N _V are the same as defined in claim 5.) The method for producing a semiconductor according to claim 5, wherein the acceptor impurities are doped as described above. 7. The method for producing a semiconductor according to claim 2, wherein the temperature of the atmosphere when doping the impurities is 550 ° C. or higher. 8. The semiconductor according to claim 1, 3 or 5, wherein the semiconductor is a 3-5 group compound semiconductor. 9. The method for producing a semiconductor according to claim 2, 4 or 6, wherein the semiconductor is a Group 3-5 compound semiconductor. 10. The semiconductor layer 1 comprises Al _x Ga.sub. _(1-x) As (0
≦ x ≦ 1), and the semiconductor layer 2 is made of In _y Ga _(1-y) As.
The semiconductor according to claim 1, wherein (0 ≦ y ≦ 1). 11. The semiconductor layer 1 comprises Al _x Ga.sub. _(1-x) As (0
≦ x ≦ 1), and the semiconductor layer 2 ′ is made of In _y Ga _(1-y) A.
The semiconductor according to claim 3, wherein s (0 ≦ y ≦ 1). 12. The semiconductor layer 3 comprises Al _x Ga.sub. _(1-x) As (0
≦ x ≦ 1), and the semiconductor layer 4 is made of In _y Ga _(1-y) As.
The semiconductor according to claim 5, wherein (0 ≦ y ≦ 1). 13. The semiconductor layer 1 comprises Al _x Ga.sub. _(1-x) As (0
≦ x ≦ 1), and the semiconductor layer 2 is made of In _y Ga _(1-y) As.
3. The method of manufacturing a semiconductor according to claim 2, wherein (0 ≦ y ≦ 1). 14. The semiconductor layer 1 comprises Al _x Ga.sub. _(1-x) As (0
≦ x ≦ 1), and the semiconductor layer 2 ′ is made of In _y Ga _(1-y) A.
5. The method for manufacturing a semiconductor according to claim 4, wherein s (0 ≦ y ≦ 1). 15. The semiconductor layer 3 comprises Al _x Ga.sub. _(1-x) As (0
≦ x ≦ 1), and the semiconductor layer 4 is made of In _y Ga _(1-y) As.
7. The semiconductor manufacturing method according to claim 6, wherein (0 ≦ y ≦ 1).