JPH0697702B2 - Tunnel barrier control type photo detector - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light receiving element whose light receiving wavelength and light receiving sensitivity can be controlled from the outside.

2. Description of the Related Art At present, various light receiving elements are used, and as a semiconductor light receiving element, a pn junction element, a photoconductive type element, a photoelectron emission type element or the like is used. Among these, the photoelectron emission type device has high sensitivity, but has a drawback that a vacuum container is required and cannot be miniaturized. Since the pn junction type element and the photoconductive type element are extremely miniaturized without requiring a vacuum container or the like, they are widely used at present. But those pn
Since the junction type element and the photoconductive type element are two-terminal elements, the gain or response speed cannot be controlled independently by the third contact. Further, the light receiving wavelengths of all of these elements are uniquely determined by the semiconductor material, such as using Si in the visible light region and using compound semiconductors in the near infrared region, and therefore are controlled from the outside. It is not possible.

SUMMARY OF THE INVENTION Therefore, the present invention is to provide a light receiving element capable of controlling the light receiving wavelength and the light receiving sensitivity from the outside.

Means for Solving the Problems The inventor of the present invention has conducted various studies for the above purpose and focused on a tunnel barrier type two-terminal device. Tunnel barrier type 2
In the terminal element, if the tunnel barrier height can be controlled by some means, for example, the charge of photoexcited carriers, it is possible to control the tunnel current, that is, the light receiving sensitivity. The carrier can be accumulated by providing a potential well, and if an electrode capable of controlling the charge accumulation time can be provided, the light receiving sensitivity can be controlled by the electrode.

Further, if a potential barrier and a potential well are formed adjacent to both the conduction band and the valence band, the conduction band valley and the valence electron can be controlled by controlling the external electric field so as to give a gradient to the energy band structure. The energy long gap limit can be changed by changing the energy gap with the valley of the band.

The present invention has been made based on such findings. That is, according to the present invention, provided inside the semiconductor layer,
A multilayer structure region composed of a plurality of impurity layers having a thickness of about a monoatomic layer separated from each other in a direction perpendicular to the layer direction, and an electrode for applying an electric field to the multilayer structure region in parallel to the layers, An electrode for applying an electric field to the multilayer structure region in the thickness direction of the layers, and the impurity layer of the multilayer structure region has an energy band structure, a potential peak forming a potential barrier, and a potential well. Has a pattern of impurity concentration formed adjacent to the valley of potential, and is close to each other to such an extent that electrons or holes can pass through the potential barrier by a tunnel phenomenon. Will be provided.

Action As described above, the multilayer structure region of the light receiving element according to the present invention has the potential barrier and the potential barrier well due to the plurality of impurity layers.

The photo-excited carriers are accumulated in the potential well and act to reduce the height of the potential peak forming the potential barrier. Therefore, if the height of the potential peak changes, the thickness of the potential barrier also changes, and the probability of carriers passing through the potential barrier changes due to the tunnel effect.

Thus, the amount of potential well charge accumulated by photoexcitation reduces the height or thickness of the potential barrier and correspondingly increases the tunneling current.
That is, it is possible to obtain a current according to the amount of received light. This current can be detected as a current between electrodes that applies an electric field to the multilayer structure region in the thickness direction of the layers.

On the other hand, the amount of carriers accumulated in the potential well increases or decreases depending on the amount of photoexcitation, but by applying and adjusting the electric field to the multilayer structure region in parallel with those layers, the potential well is It is possible to extract the accumulated carriers. In other words, the amount of charge stored in the potential well should be adjusted by adjusting the voltage between the electrodes that apply an electric field in the direction parallel to the layers in the multilayer structure region as described above. You can The amount of charge stored in the potential well controls the tunnel current. That is,
Adjust the sensitivity. Therefore, the sensitivity can be adjusted by adjusting the voltage of the electrodes for applying an electric field parallel to the layers in the multilayer structure region.

As is apparent from the above description, the light receiving element according to the present invention is different from the conventional light receiving element in that the tunnel barrier height is controlled by the photoexcited carrier, and the storage time of the carrier is controlled by the externally applied voltage. The sensitivity can be adjusted.

Further, the sensitive long wavelength limit of the above-described light receiving element according to the present invention is determined by the energy gap, like other light receiving elements. In the energy band structure of the light receiving element of the present invention as described above, the energy gap between the valley of the conduction band and the valley of the valence band can be changed by controlling the inclination of the potential barrier by the external electric field. .

Therefore, the energy gap of the light receiving element according to the present invention adjusts the voltage between electrodes for applying an electric field to the multilayer structure region in the thickness direction of the layers without changing the material of the semiconductor layers as in the conventional element. By doing so, the longest sensitive wavelength can be changed.

In the light-receiving element according to the present invention, the semiconductor layer is formed of an intrinsic single semiconductor or a compound semiconductor, and the multilayer structure region is formed by alternately arranging p-type impurity layers and n-type impurity layers. In the embodiment of the present invention, it is preferable that the multi-layer structure region is composed of four impurity layers, and the distance between the impurity layers is in the range of 10Å to 1000Å. The lower limit of 10Å is a value to secure the interval between the impurity layers in order to make a multilayer structure because the thickness of the monoatomic layer is on the order of 2Å, and the upper limit of 1000Å is the peak and valley of the potential. This is the limit at which the advantages of the multilayer structure to be formed can be obtained.

Further, the impurity area density of the impurity layer is preferably in the range of 10 ¹⁰ to 10 ¹³ cm ^-2 . When the surface density is about 10 ¹⁵ cm ^-2 , the layer is completely made of only impurities, so the ratio of impurities is 0.001 to 1%. In particular, in the case of the four-layer structure, the amounts of impurities contained in the two outer impurity layers are equal to each other, and the amounts of impurities contained in the two inner impurity layers are equal to each other and the two outer impurity layers are contained. It is preferable that the amount is approximately twice the amount of impurities contained in. By doing so, potentials other than the peaks and valleys of the potential can be flattened when no electric field is applied.

Embodiments Embodiments of the light receiving element according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic sectional view showing a basic shape of a light receiving element according to the present invention. The photodetector shown is an n ⁺ Si single crystal substrate 10.
The i-type Si semiconductor layer 12 is formed on the substrate 10. The semiconductor layers 12 are separated from each other by n ⁺
Region 14 and p ⁺ region 16 are provided. The n ⁺ region 14 reaches the n ⁺ Si single crystal substrate 10 and is electrically connected as shown, but the p ⁺ region 16 does not reach the n ⁺ Si single crystal substrate 10. A multilayer impurity layer 20 is formed inside the semiconductor layer 12 between such regions 14 and 16, and the n ⁺ region is formed between the regions 14 and 16 to a depth that does not reach the multilayer impurity layer 20. 22 is further provided. And those n ⁺ regions 14 and p ⁺ regions 16
Contacts 24, 26, 28 are provided in the n ⁺ region 22. Thus, as will be described later, with respect to the multilayer impurity layer 20, the substrate 10 and the region 22 act as electrodes for applying an electric field in the thickness direction of the layer, and the regions 14 and 16 generate an electric field in the direction parallel to the layer. Acts as an electrode for applying a.

The multilayer impurity layer 20 has a structure having four impurity layers each having a thickness of a monoatomic layer, which are separated from each other in a direction perpendicular to the layers. The layer relationship is shown in Fig. 2a.

In FIG. 2a, the vertical line on the left side shows the surface of the semiconductor layer 12, that is, the upper surface of the n ⁺ region 22, and the horizontal axis shows the distance from the substrate surface. The vertical axis represents the impurity concentration, the p-type impurity is above the horizontal axis, and the n-type impurity is below the horizontal axis.

That is, an n ⁺ region 22 exists over a certain depth from the surface, and an n-type impurity layer 30 doped with Sb having a thickness corresponding to a monoatomic layer is provided at a position apart from the n ⁺ region 22. _At the depth of ₁ , the thickness of monolayer
A p-type impurity layer 32 doped with Ga is provided, and an n-type impurity layer 34 doped with Sb having a thickness corresponding to a monoatomic layer is further provided at a depth of the distance L ₂ . And
A p-type impurity layer 36, which is doped with Ga and has a thickness corresponding to a monoatomic layer, is provided at a portion at a distance L ₃ from the layer 34. Further, the n ⁺ type substrate 10 is located deeper than that.

In the above structure, L ₁ , L ₂ and L ₃ are about 10Å to 1000Å, and the surface concentration of impurities in each impurity layer is 10 ₁₀
It is about 10 ¹³ cm ^-2 . However, the impurity concentration of the impurity layers 32 and 34 is sufficiently higher than that of the impurity layers 30 and 36,
For example, double or more.

Such a multi-layered impurity structure is, for example, an i-type on a Si substrate 10.
When Si is grown by MBE, the step of stopping the growth of Si, applying the impurity material at the above density, and then growing Si again is repeated at the position in the thickness direction at which the impurity layer is to be formed, Can be realized.

The energy band structure in the equilibrium state of the above four impurity layers is shown in FIG. 2b. In FIG. 2b, the lines E _C and E _V show the conduction band and the valence band, respectively, and the line E _F shows the Fermi level. As can be seen from FIG. 2b, the four impurity layers form triangular potential peaks, that is, potential barriers 38 and 40,
Also, potential wells 42 and 44 are formed. Then, electrons are confined in the potential well, and the heights of the potential barriers 38 and 40 are changed by the charges accumulated in the potential wells 42 and 44.

FIG. 3a shows a band structure in which a certain voltage is applied to the contacts 24 and 28 of FIG. 1, that is, a certain voltage is applied between the electrode 22 and the electrode 10. At that time, the doping interval and the doping amount in FIG. 2a are adjusted in advance so that electrons and holes do not tunnel through the potential barriers 46 and 48, respectively. The dotted arrow indicates the state where no tunnel is performed.

FIG. 3b shows a state in which carriers are accumulated in the potential wells 58 and 60 by light irradiation in the voltage applied state of FIG. 3a. The height of the potential barriers 54, 56 is reduced by the accumulated carriers, and the electrons and holes accelerated by a certain voltage described above are tunneled through the barriers as indicated by solid arrows. Since the potential wells 58 and 60 are extremely narrow, the transmitted electrons and holes pass ballistically without falling into the potential wells 58, and become a signal current and flow into the electrodes.

Therefore, by controlling the gradient of the band structure shown in FIG. 3a by the electric field that acts at right angles to the impurity layer, that is, the voltage between the electrodes 10 and 22, by controlling the tunnel current to flow during light irradiation, Electrons excited by light irradiation
The current due to the holes can be detected as the current between the contacts 24 and 28. Since this current changes according to the amount of received light, a photoelectric signal can be obtained by extracting the AC component of the current between the contacts 24 and 28.

Moreover, controlling the voltage across contacts 24 and 28, ie between electrodes 10 and 22, to control the slope of the band structure shown in FIG. 3a also changes the energy difference at the bottom of potential wells 50 and 52. Since this energy difference is the lowest excitation energy, it is possible to change the lower limit of the wavelength of the light to which the light receiving element is sensitive.

The accumulated carriers are maintained by the amount of doping shown in FIG. 2a so as not to degenerate, so that the electric field generated by the voltage applied between the contacts 24 and 26 of FIG. At the time of extraction in the direction perpendicular to the paper surface, the time required for this, that is, the time required to return to the state of FIG. Therefore, by controlling the voltage between contacts 24 and 26, the amount of charge that remains in the potential well can be adjusted, and thus the height of potential barriers 46, 48 can be varied. Changing the height of the potential barrier is
By changing the thickness of the potential barrier, the magnitude of the tunnel current can be controlled. Therefore, by controlling the voltage between the contacts 24 and 26, the photosensitivity of the device can be adjusted.

As can be seen from the above, the sensitivity can be adjusted by the voltage between the electrodes 14 and 16, and the light receiving wavelength can be controlled independently by controlling the voltage by the voltage between the electrodes 10 and 22.

On the other hand, accompanying this, the gain of the signal current for a single optical pulse is also controlled at the same time.

Note that the photosensitive long wavelength limit of the device is determined by the energy difference between the bottoms of the potential wells 50 and 52 shown in FIG. 3a, as described above. The energy difference can be changed by controlling the doping amount and the doping interval shown in FIG. 2a without changing the base material. This effect is a great effect considering that the constituent base material of the conventional light receiving element has to be changed. Therefore, in the light receiving element of the present invention, the contacts 24 and 28
It is possible to control the photosensitive long-wavelength limit by not only controlling the voltage between and, but also adjusting the doping amount and the doping interval in FIG. 2a in advance.

In particular, the adjustment of the doping amount and the doping interval does not affect the photosensitivity while the voltage between the contacts 24 and 28 influences the photosensitivity. Therefore, it is preferable to preliminarily adjust the relative relationship with the bias voltage applied between the electrodes 10 and 22.

Although the above embodiment is an example of a light receiving element using Si, the present invention can be applied to a light receiving element using a simple semiconductor material other than Si or a compound semiconductor material such as GaAs.

EFFECTS OF THE INVENTION As described above, the light receiving element according to the present invention can be designed according to an arbitrary wavelength of light, and the response speed and the signal gain can be controlled by the external electrodes, so that the light receiving element can be matched with the optical signal system. The light receiving element can be realized.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a basic structure of a light receiving device according to the present invention, FIGS. 2a and 2b are views showing a doping structure and a band structure of the light receiving device shown in FIG. 1, 3a and 3b. FIG. 3b is a diagram showing a band structure of the light receiving element during operation. [Main reference numbers] 10 …… n ⁺ semiconductor substrate 12 …… semiconductor layer 14, 22 …… n ⁺ region 16 …… p ⁺ region 20 …… multilayer impurity layer

Claims (3)

[Claims] 1. A multi-layer structure region provided inside a semiconductor layer, comprising a plurality of impurity layers separated from each other in a direction perpendicular to the layer direction and having a thickness of about a monoatomic layer, and the layers for the multi-layer structure region. And an electrode for applying an electric field in the thickness direction of the multilayer structure region to the multilayer structure region, and the impurity layer in the multilayer structure region has an energy band structure. Has an impurity concentration pattern in which a potential peak forming a potential barrier and a potential valley forming a potential well are adjacent to each other, and to the extent that electrons or holes can pass through the potential barrier by a tunnel phenomenon. A light receiving element characterized by being close to each other. 2. The multilayer structure region is composed of an intrinsic semiconductor layer in which p-type impurity layers and n-type impurity layers are alternately arranged. Light receiving element. 3. The multilayer structure region is composed of four impurity layers, and the distance between the impurity layers is in the range of 10 to 1000Å. The light-receiving element described in the item.