JPH06163606A - Acoustic charge transfer element - Google Patents

Abstract

PURPOSE:To eliminate the need for strictly controlling dope quantity and film thickness of a charge supply layer and to make charge capacity larger. CONSTITUTION:An AlxGa1-xAs epitaxial layer (the third epitaxial layer) on a non-dope GaAs epitaxial layer 3, to be the second epitaxial layer, is to be non-dope, so that it does not work as a charge supply layer, and instead, an n-type impurities area 10 provided so as to reach the second, third and fourth epitaxial layers 3, 14, and 5, respectively, under an input diode 7, is made to work as a charge supply layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustic charge transfer device used as a high speed analog signal processing device for transferring signal charges in a CW traveling wave type potential well accompanying the propagation of a surface acoustic wave (SAW).

[0002]

2. Description of the Related Art This type of acoustic charge transfer device (Acoustic C
harge Transport Device) as a pair of Al _x G _a1-x
A _s the epitaxial layer made of GaAs epitaxial layer sandwiched by DH (Double Heterojunction) heterozygous acoustic charge transfer potential well structure as the transfer channel (HACT) devices have been proposed in the following literature (Appl. Phys.Lett., Vol.52, NO.1, pp.18-20,198
8.).

FIG. 5 shows the structure of a conventional heterojunction type acoustic charge transfer device proposed in the above document.
Non-doped Al _x G on the semi-insulating GaAs substrate 1
_a1-x A _s epitaxial layer (first epitaxial layer)
2, non-doped GaAs epitaxial layer (second epitaxial layer) 3, n-type Al _x G _a1-x A _s epitaxial layer (3 consisting of the epitaxial layer 2 of the same material
4), and a non-doped GaAs epitaxial layer (fourth epitaxial layer) 5 made of the same material as the epitaxial layer 3 are sequentially provided.
Of these, the GaAs epitaxial layer 3 sandwiched between the pair of GaAs epitaxial layers 2 and 4 operates as a potential well as a channel layer to trap a signal charge packet. Further, generally, the GaAs substrate 1 is provided with a buffer layer for reducing dislocations and defects in the epitaxial layer, but the illustration thereof is omitted here.

Further, on the non-doped GaAs epitaxial layer 5, a Schottky diode having a SAW transducer 6 forming a CW traveling wave type potential well for transferring signal charges, an ohmic electrode 7A and a gate electrode 7B is formed. An input diode 7, a detection electrode 8 for nondestructively detecting and outputting a signal along the direction of transfer charge transfer, and a charge extraction electrode 9 for extracting transfer charge from the channel layer are provided. The SAW CW potential excited from the SAW transducer 6 corresponds to a clock signal of a normal charge transfer device (CCD). The RF signal input to the input diode 7 and the DC bias control the amount of charges injected into the GaAs epitaxial layer 3 as the channel layer. The signal detected by the detection electrode 8 becomes an output signal after signal processing.

[0005] Here, n-type Al _x G _a1-x A _s epitaxial layer 4 operates as a charge supply layer for injecting the lower portion of the GaAs layer (channel layer) 3 to the charge, is generally n-type impurity to 2 It is uniformly doped at about 10 ¹⁷ cm ^-3 .
This doping amount does not short-circuit the potential well of the SAW and supplies electrons necessary for filling the surface level of the surface of the upper GaAs layer 5 so that excess electrons do not remain in the channel layer 3. A relatively low value is set. If the doping amount is too large, the barrier height of the SAW potential well is lowered and signals cannot be transferred, and excess electrons remain in the channel layer 3 and are indistinguishable from signal charges. . On the other hand, when the doping amount is small, the depletion end is excessively extended and it becomes impossible to efficiently inject charges into the channel layer 3.

Further, n which operates as this charge supply layer
The film thickness of the type Al _x G _a1-x A _s epitaxial layer 4, the end of the neutral region under the ohmic electrodes, i.e. it is desirable to place the channel layer 3 in the depletion edge, thereby enabling efficient charge injection Becomes Thus, in order to efficiently operate the heterojunction acoustic charge transfer device, it is necessary to strictly control the doping amount and the thickness of n-type Al _x G _a1-x A _s epitaxial layer 4 is a charge supply layer is there.

On the other hand, in the heterojunction type acoustic charge transfer device, the transfer charge is confined in the GaAs layer 3 which is the channel layer. However, the current thickness of the channel layer 3 is not increased more than necessary and the charge is not increased. In order to increase the capacity,
And in order to minimize the quantum effect, for example ~ 60nm
Is set to. Also, Al mixed crystal ratio of the upper portion of the n-type Al _x G _a1-x A _s epitaxial layer 4 of the channel layer 3 is limit to 0.3 for the ohmic electrode formation, which by the height of the barrier - It becomes 0.25 eV. The charge capacity of the channel layer 3 is an important factor that determines the magnitude of the output signal and the dynamic range of the signal processing device. In this respect, further expansion of the charge capacity is desired.

[0008]

The conventional heterojunction type acoustic charge transfer device has the following problems in terms of charge injection into the channel layer and charge capacity of the channel layer. 1. Since the doping amount and the film thickness of the charge supply layer for injecting charges must be strictly controlled, the margin of device design becomes small and the yield at the time of device manufacturing cannot be improved. 2. Since the charge capacity of the channel layer does not increase, it becomes impossible to expand the size of the output signal and the dynamic range of the signal processing device, and further it becomes impossible to improve the performance of the signal processing device, reduce the loss, and increase the gain.

The present invention has been made in consideration of the above problems, and eliminates the need for strictly controlling the doping amount and the film thickness of the charge supply layer and increases the charge capacity. It is intended to provide a charge transfer device.

[0010]

In order to achieve the above object, the present invention provides a semi-insulating substrate, a non-doped first epitaxial layer provided on the substrate, and a first epitaxial layer on the substrate. A non-doped second epitaxial layer provided on the second epitaxial layer, a non-doped third epitaxial layer formed on the second epitaxial layer and made of the same material as the first epitaxial layer, and the third epitaxial layer on the third epitaxial layer. A non-doped fourth epitaxial layer made of the same material as that of the second epitaxial layer, a circuit element provided on the fourth epitaxial layer and including at least an input diode, and the first diode below the input diode. And a first conductivity type impurity region provided so as to reach each of the second, third and fourth epitaxial layers. It is an butterfly.

Still another aspect of the present invention is to provide a semi-insulating substrate, a non-doped first epitaxial layer provided on the substrate, and a non-doped second epitaxial layer provided on the first epitaxial layer. An epitaxial layer and the second
Non-doped third and fourth epitaxial layers having different thicknesses, which are made of different materials and have a predetermined value or less, and the same material as the first epitaxial layer provided on the fourth epitaxial layer. A first conductive type fifth epitaxial layer, a non-doped sixth epitaxial layer formed on the fifth epitaxial layer and made of the same material as the second epitaxial layer, and the sixth epitaxial layer And a circuit element which is provided above and includes at least an input diode.

Still another aspect of the present invention is that a semi-insulating substrate, a non-doped first epitaxial layer provided on the substrate, and a non-doped second epitaxial layer provided on the first epitaxial layer. An epitaxial layer, non-doped third and fourth epitaxial layers formed on the second epitaxial layer and made of different materials and having a thickness of a predetermined value or less, and the second epitaxial layer formed on the fourth epitaxial layer. A non-doped fifth epitaxial layer made of the same material as the second epitaxial layer, a circuit element provided on the fifth epitaxial layer and including at least an input diode and a charge extraction electrode, and the input diode and the charge extraction electrode. A first conductive layer provided at a lower portion so as to reach the second, third, fourth and fifth epitaxial layers, respectively. It is characterized in that it has an impurity region.

[0013]

According to the structure of the present invention as set forth in claim 1, the non-doped third epitaxial layer formed on the second epitaxial layer and made of the same material as the first epitaxial layer is the channel layer below this. The first conductivity type impurity region provided so as to reach the second, third and fourth epitaxial layers below the input diode instead of operating as a charge supply layer for a certain second epitaxial layer supplies a charge. Act as a layer. Thereby, it becomes unnecessary to strictly control the doped layer and the film thickness of the charge supply layer.

According to the structure of the present invention as defined in claim 2, the non-doped second layer provided on the first epitaxial layer.
And the non-doped third epitaxial layer, which is provided on the second epitaxial layer and has a thickness of not more than a predetermined value, operate as a channel layer. As a result, the charge capacity can be increased.

According to the third aspect of the present invention, the charge supply layer and the channel layer are formed by combining the configuration of the first aspect of the invention with the configuration of the second aspect of the invention. Thereby, it becomes unnecessary to strictly control the doping amount and the film thickness of the charge supply layer, and the charge capacity can be increased.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a first embodiment of the acoustic charge transfer device of the present invention. The semi-insulating GaAs substrate 1, 2 Al _x G _a1-x A _s epitaxial layer of non-doped (first epitaxial layer) 3 is GaAs epitaxial layer of non-doped (second epitaxial layer), 5 the epitaxial Undoped GaA made of the same material as layer 3
s epitaxial layer (fourth epitaxial layer), 6 is a SAW transducer, 7 is an input diode, 8 is a detection electrode, 9 is a charge extraction electrode, and the above parts are the same as in the conventional example of FIG.

[0017] 14 the second epitaxial layer 3 provided on the first epitaxial layer 2 and the undoped Al _x G _a1-x A _s epitaxial layer of the same material (third epitaxial layer), 10 The input diode 7
Is an n-type impurity region provided so as to reach the second, third, and fourth epitaxial layers 3, 14, and 5 below. In this embodiment, since the third epitaxial layer 14 is non-doped, it does not operate as a charge supply layer for the second epitaxial layer 3 which is the lower channel layer. Therefore, the channel layer 3 is in a depleted state with no excess electrons remaining. Instead, the n-type impurity region 10 operates as a charge supply layer for the channel layer 3.

A large amount of electrons to be supplied to the channel layer 3 exist in the n-type impurity region 10, and the charge injection process into the channel layer 3 is controlled by an electric signal applied to the input diode 7 as in the conventional case. To be done. The n-type impurity region 10 is easily formed by an ion implantation method capable of controlling impurity doping with higher accuracy than the diffusion method,
The impurity concentration and depth of the n-type impurity region 10 can be accurately controlled by adjusting the doping amount and acceleration energy during ion implantation. The n-type impurity region 10 may be formed not only below the input diode 7 but also below the charge extraction electrode 9. The fourth epitaxial layer 5 may not be non-doped, but may be doped with an n-type impurity at a low concentration in order to fill the surface level with electrons to some extent.

[0019] Thus, according to the first embodiment. Thus to operate the charge supply layer by a conventional manner such n-type Al _x G _a1-x A _s epitaxial layer is not n-type impurity regions 10, It becomes unnecessary to strictly control the doping amount and the film thickness of the charge supply layer. As a result, the charge injection process is facilitated, so that efficient charge injection is facilitated, the device design margin can be increased, and the yield in device manufacture can be improved. In addition, n as a charge supply layer
Since the type impurity region 10 exists only under the input diode 7 as shown in FIG. 1, extra electrons do not remain in the channel layer 3. In addition, the presence of the n-type impurity region 10 can improve the contact of the ohmic electrode. Further, the n-type impurity region 10 is formed by using the ion implantation method, so that the impurity concentration and the depth can be accurately controlled.

FIG. 2 is a sectional view and an energy level distribution diagram showing a second embodiment of the present invention. In this embodiment, 1
1 is non-doped GaA which becomes the second epitaxial layer
undoped I _ny provided on the s epitaxial layer 3
G _a1-y A _s epitaxial layer (third epitaxial layer), 12 is the third provided on the epitaxial layer 11 a first epitaxial layer 2 and a non-doped made of the same material Al _x G _a1-x A _s It is an epitaxial layer (fourth epitaxial layer). The third and fourth epitaxial layers 11 and 12 are both extremely thin with a thickness of about 20 nm,
The third epitaxial layer 11 operates as a channel layer together with the lower second epitaxial layer 3.

The third epitaxial layer 11, I _ny G
_Since the lattice constant of _a1-y A _s is different from that of GaAs and Al _x G _a1-x A _s , a large number of dislocations are generated in the layer when it is formed thick. Dislocations do not occur due to the thick formation. As is clear from the energy level distribution chart shown on the right side of FIG.
Of an epitaxial layer I _ny G _a1-y A _s epitaxial layer 11 as the fourth epitaxial layer Al _x G _a1-x
Energy difference at the hetero interface between the A _s epitaxial layer 12 is larger than the energy difference between the heterojunction surface between the conventional Al _x G _a1-x A _s epitaxial layer and the GaAs epitaxial layer. FIG. 3 shows an energy level distribution diagram of the conduction band in the charge transfer channel.

The charge confinement in the heterojunction acoustic charge transfer device is realized three-dimensionally. In the charge transfer direction, that is, in the SAW traveling direction, the charge is confined by the barrier of the potential well of the SAW. S
The height of the potential barrier of the AW is as high as about 1V. The charge confinement in a direction perpendicular to the SAW traveling direction and parallel to the substrate is generally performed by semi-insulating by proton injection, or Esaetch, and the charge confinement in this direction is almost completely performed. Therefore, in charge confinement in the heterojunction acoustic charge transfer device,
It can be said that the depth direction of the substrate is the most insufficient, and the charge capacity of the transfer channel is determined by the charge confinement in the depth direction of the substrate.

The degree of charge confinement in the depth direction of the substrate depends on the energy difference at the heterojunction interface.
The introduction of the _{InyG a1-y} A _s epitaxial layer as shown in this embodiment increases the energy difference, so that charge confinement becomes more complete. In particular the distribution of the signal charge in the transfer channel for uniformly distributed on the surface, the introduction of I _ny G _a1-y A _s epitaxial layer to expand charge capacity of reliably channel layer.

[0024] Thus the second according to the embodiment, the channel layer below a predetermined value which is provided on the a GaAs epitaxial layer 3 of undoped thickness non-doped I _ny
Since it is operated by the G _a1-y A _s epitaxial layer 11, the charge capacity can be increased.
As a result, the size of the output signal and the dynamic range of the signal processing device can be expanded, and further, the performance of the signal processing device can be improved, the loss can be reduced, and the gain can be increased. That is, as a channel layer, undoped _InyG
a1-y A _s an epitaxial layer 11 of non-doped GaAs
By using it together with the epitaxial layer 3, it becomes possible to completely confine charges.

FIG. 4 is a sectional view showing a third embodiment of the present invention, showing a structure in which the first embodiment and the second embodiment are combined. A non-doped Al _x G _a1-x A _s epitaxial layer 2 of undoped GaAs epitaxial layer provided on the (second epitaxial layer) 2 to be the first epitaxial layer, provided on the epitaxial layer 2 of the second channel layer is formed by the non-doped I _ny G _a1-y a _s epitaxial layer 11 that is. Second, third, fourth and fifth epitaxial layers 3, 1
The n-type impurity regions 10 provided so as to reach 1, 12, 15 exist not only below the input diode 7 but also below the charge extraction electrode 9.

According to the third embodiment as described above, by combining the configurations of the first and second embodiments, the effects obtained in the respective embodiments can be directly obtained. That is, it is not necessary to strictly control the doping amount and the film thickness of the charge supply layer, and the charge capacity can be increased, so that various effects can be obtained.

[0027]

As described above, according to the present invention, since the device structure is improved, it becomes unnecessary to control the doping amount and the film thickness of the charge supply layer, and the charge capacity is increased. It is possible to provide an acoustic charge transfer device capable of

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of an acoustic charge transfer device of the present invention.

FIG. 2 is a sectional view and an energy level distribution diagram showing a second embodiment of the present invention.

FIG. 3 is an energy level distribution diagram of a conduction band in a charge transfer channel for explaining the operation principle of the second embodiment.

FIG. 4 is a sectional view showing a third embodiment of the present invention.

FIG. 5 is a cross-sectional view showing a conventional example.

[Explanation of symbols]

2 non-doped Al _x G _a1-x A _s epitaxial layer 3 doped GaAs epitaxial layer 5 doped GaAs epitaxial layer 6 SAW transducer 7 input diode 8 detection electrodes 9 charge extraction electrode 10 n-type impurity region 11 doped I _ny G _a1-y A _s epitaxial layer 12 non-doped Al _x G _a1-x A _s epitaxial layer 14 non-doped Al _x G _a1-x A _s epitaxial layer

Claims (3)

[Claims] 1. A semi-insulating substrate, a non-doped first epitaxial layer provided on the substrate, and the first
A non-doped second epitaxial layer provided on the epitaxial layer, a non-doped third epitaxial layer provided on the second epitaxial layer and made of the same material as the first epitaxial layer, and the third epitaxial layer. A non-doped fourth epitaxial layer made of the same material as that of the second epitaxial layer, the circuit element including at least an input diode provided on the fourth epitaxial layer, and the input diode of An acoustic charge transfer device, comprising: a first conductivity type impurity region provided so as to reach the second, third, and fourth epitaxial layers below. 2. A semi-insulating substrate, a non-doped first epitaxial layer provided on the substrate, and the first
A non-doped second epitaxial layer provided on the epitaxial layer, and non-doped third and fourth epitaxial layers provided on the second epitaxial layer and made of different materials and having a thickness of a predetermined value or less. A fifth epitaxial layer of the first conductivity type formed on the fourth epitaxial layer and made of the same material as the first epitaxial layer, and a second epitaxial layer formed on the fifth epitaxial layer And a circuit element including at least an input diode provided on the sixth epitaxial layer and a non-doped sixth epitaxial layer made of the same material as described above. 3. A semi-insulating substrate, a non-doped first epitaxial layer provided on the substrate, and the first
A non-doped second epitaxial layer provided on the epitaxial layer, and non-doped third and fourth epitaxial layers provided on the second epitaxial layer and made of different materials and having a thickness of a predetermined value or less. A non-doped fifth epitaxial layer formed on the fourth epitaxial layer and made of the same material as the second epitaxial layer, and at least an input diode and a charge extraction electrode provided on the fifth epitaxial layer. And a first conductive type impurity region provided below the input diode and the charge extraction electrode so as to reach the second, third, fourth and fifth epitaxial layers, respectively. Characteristic acoustic charge transfer device.