KR20040057865A - Avalnche photodetector and phototransistor ahving internal RF-gain - Google Patents

Abstract

PURPOSE: An avalanche light detecting device having inner RF(Radio Frequency)-gain and a photo transistor are provided to increase sensitivity, and obtain a high speed characteristic and a large bandwidth characteristic by using an avalanche gain structure layer. CONSTITUTION: An avalanche light detecting device is provided with a substrate(10), a conductive type collector layer(12) on the substrate, an emitter layer(30), and a light absorption layer(26) between the emitter and collector layer. The avalanche light detecting device further includes an avalanche gain structure layer between the light absorption layer and the collector layer for generating and controlling RF-gain of high frequency band. The avalanche gain structure includes an electric charge layer(20), an electrode(22) on the electric charge layer, and an amplification layer(18).

Description

Avalanche photodetector and phototransistor ahving internal RF-gain

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to avalanche photodetectors and phototransistors having an internal RF-gain in a high frequency band, and more particularly, to a high frequency band by intervalley transfer of secondary charges between a light absorbing layer and a collector layer. An avalanche photodetector and phototransistor comprising an avalanche gain structure layer capable of generating and controlling an RF-gain

In recent years, research has been actively conducted on optical reception (detection) devices which are essential for ultra-high-capacity optical communication systems and image processing systems, and high speed and high sensitivity of these devices have emerged as major problems.

In recent years, with the development of semiconductor growth technologies such as molecular beam epitaxy and metal organic chemical vapor deposition, development of semiconductor optoelectronic devices using heterojunction structures has been activated.

Bulk band, thin film, based on materials such as GaSb / InAs, InAs / ZnTe, GaAs / Al (Ga) As, InGaAs / InAlAs / InP due to the energy band-up of the semiconductor heterojunction structure. In quantum wells, quantum lines, and quantum dot structures, the phenomenon of absorbing or emitting light in the infrared region by electrons or interband transitions, or electron transitions between quantum-confined states. Research, research on infrared absorption and generation function, tunability (voltage-controlled), etc., high speed of receiving device, high saturation current of receiving device, ultra-high speed research using hot electron phenomenon This is of great importance, which has technical significance in applications such as ultra-fast optical receivers, ultra-high speed swiching devices, and logic devices.

However, conventional avalanche photodetectors have the advantage of having higher sensitivity than PIN photodetectors, but require very high voltage to obtain avalanche gain, and have the disadvantage of being slow in the high current-gain region. In addition, the output current is low, there is a problem that an electrical preamplifier circuit (preamplifier) is required.

Accordingly, an object of the present invention is to provide an avalanche photodetector having a novel structure.

In addition, another object of the present invention is to achieve a high gain by applying a relatively low voltage to increase the sensitivity and obtain high speed characteristics in the high current-gain region, and has a large bandwidth (-3dB bandwith, f _3dB ) characteristics It is to provide a photodetecting device having.

1 is a cross-sectional view of a structure of an internal RF-gain avalanche photodetector in a high frequency band according to an embodiment of the present invention.

2 is a diagram illustrating internal avalanche detection of an internal RF-gain resonator according to an embodiment of the present invention.

3 is a cross-sectional view of a structure of a waveguide-fed photo transistor according to an embodiment of the present invention.

4A to 4H illustrate examples of possible light absorbing layers of an avalanche photodetector according to an embodiment of the present invention.

FIG. 5A is an energy band diagram of an emitter layer, a collector layer, and a charge layer in a state where no voltage is applied (thermal equilibrium) in an avalanche photodetector, and FIG. 5B is an emitter layer, collector layer, and charge layer when an external voltage is applied. Energy band diagram.

6A and 6B are energy band diagrams showing an energy state according to voltage application in an example of a structure of an avalanche photodetector using an inter-interband transition of electrons.

7 to 14 illustrate a high frequency in the high current-gain region due to intervalley transport of secondary electrons when a voltage higher than the avalanche breakdown voltage is applied in the amplification layer of the avalanche photodetector according to an embodiment of the present invention. Characteristic measurement curves of the photodetector showing the internal Rf gain characteristics of the band.

As a means for solving the above problems, one side of the present invention is a Avalanche photodetector comprising a substrate, a conductive collector layer, an emitter layer and a light absorption layer between the emitter layer and the collector layer formed on the substrate; An avalanche photodetector comprising: an avalanche gain structure layer capable of generating and controlling RF-gain in a high frequency band by intervalley transport of secondary charges between a light absorbing layer and a collector layer.

The avalanche gain structure layer may include a charge layer, a charge layer electrode, and an amplification layer formed in turn.

In addition, the amplification layer may be composed of a bulk single material layer or a superlattice structure.

It may further comprise a spacer layer (s) for controlling the diffusion of impurities between the collector layer and the amplification layer and / or between the charge layer and the light absorbing layer.

Meanwhile, a spacer layer is further included between the charge layer and the light absorption layer, and the spacer layer is an i-InGaAlAs gradual spacer layer (in this case, InGa _{0.47 (1-x)} Al _0.47x As, and x is changed from 1 to 0). This is preferred.

In addition, the light absorbing layer and the emitter layer may further include a spacer layer for controlling the diffusion of impurities.

The light absorbing layer may be a bulk single material layer, a self-assembled quantum dot structure, a quantum well structure, an array of quantum dots, or an array of quantum lines. Specifically, the light absorption layer may be formed of at least one layer of i-InGaAs of less than 1000 Hz, one or more laminations of GaAs and InAs quantum dots, one or more laminations of -InAlAs layers, InGaAs quantum well layers, and insulating layers.

On the other hand, the avalanche photodetector is amplified by the voltage applied between the charge layer and the collector while passing through the charge layer and the amplification layer, and secondly the internal RF- of the high frequency region by the intervalley transport of the electrons. The gain can be configured to be generated.

A lower mirror layer of the λ / 4 stack may be further provided between the collector layer and the substrate, and an upper mirror layer may be further provided on the emitter layer. Preferably, the lower mirror layer has a structure in which an I n AlAs / InAlGaAs layer is formed of one or more pairs of λ / 4 (quarter-wave) stacks, and the base mirror layer may be a dielectric multilayer consisting of an MgO / Si layer.

Another aspect of the present invention provides a phototransistor fabricated in an optical waveguide type including the structure of the avalanche photodetecting device described above, and an optical waveguide layer and a guiding layer between the collector layer and the substrate.

The optical waveguide layer may be formed of an InGaAlAs layer, and the guiding layer may be formed of an InAlAs layer.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, embodiments of the present invention may be modified in various forms, and the scope of the present invention is limited by the embodiments described below. It should not be construed as Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

1 is a cross-sectional view of an internal RF-gain avalanche photodetector structure in the high frequency band. A cross-sectional view of a high power three-terminal photodetector device structure with internal RF-gain characteristics in the high frequency band under high current gain.

The avalanche photodetector includes a conductive collector layer 12 formed on the substrate 10, a collector electrode 14 formed on a portion thereof, an amplification layer 18, a charge layer 20, a light absorption layer 26, And an emitter layer 30, an emitter electrode 32, and a charge layer electrode 22. Meanwhile, the first spacer layer 16 is disposed between the collector layer 12 and the amplification layer 18, between the charge layer 20 and the light absorption layer 26, and between the light absorption layer 26 and the emitter layer 30, respectively. The second spacer layer 24 and the third spacer layer 28 may be added. The spacer layers 16, 24, and 28 perform functions such as diffusion control of impurity.

The avalanche gain structure layer of electrons comprises a charge layer 20, a charge layer electrode 22, and an amplification layer 18, and is added between the light absorption layer 26 and the collector layer 12.

For example, a structure that may be applied to the light absorption layer 26 may be described as a bulk-type single material layer, a self-assembled quantum dot structure, a thin film, a quantum well structure, and an array of quantum dots. Or an array of quantum wires.

The multiplication layer 18 may be made of a bulk single material layer or a superlattice structure.

As an example of a material applicable to the present embodiment, the emitter electrode 32 may be formed of Ti / Pt / Au, and the emitter layer 30 may be formed of P + -InAlAs, and the third spacer layer 28 of 1000 Å or less may be formed. i-InAlAs, light absorbing layer 26 is an i-InGaAs single material of about 1 μm or less, i-InGaAlAs graded spacer layer 24 of 1000 μs or less (in this case InGa _{0.47 (1-x)} Al _0.47x As, x changes from 1 to 0), an avalanche gain structure layer (p-InAlAs charge layer 20 of 1000 Å or less, Ti / Pt / Au charge layer electrode 22, i-InAlAs amplification layer of 2000 Å or less) (18))) and an n-InAlAs space layer 16 of 1000 ns or less, an n-InAlAs collector layer 12 of 3000 ns or more, an Au / Ge / Ni collector electrode 14, and an SI-InP substrate 10. Can be done.

Hereinafter, another application example of the above-described avalanche photodetector will be described. FIG. 2 is a diagram illustrating an internal RF-gain resonant avalanche photodetector in a high frequency band according to an embodiment of the present invention, and FIG. 3 is a waveguide-fed phototransistor. It is sectional drawing of a (photo transistor) structure.

The resonance sphere avalanche detector of FIG. 2 includes a conductive collector 112 formed on the substrate 110, a collector electrode 114 formed on a portion thereof, an amplifying layer 118, a charge layer 120, and a light absorbing layer ( 126, including an emitter electrode 132 and a charge layer electrode 122, between the collector layer 112 and the amplification layer 118, between the charge layer 120 and the light absorption layer 126, and light The configuration in which the first spacer layer 116, the second spacer layer 124, and the third spacer layer 128 are added between the absorber layer 126 and the emitter layer 130 is almost similar to that of FIG. 1. Therefore, for the convenience of description, the description will be made based on the structure and difference of FIG. 1.

The resonance structure is a λ / 4 (quarter-wave) stack made of InAlAs / InAlGaAs or the like between the collector layer 112 and the substrate 110 (for example, 30 pairs of InAlAs layers (about 1121 Hz) / InGaAlAs layers (about 1110 Hz). Lower mirror layer 36, and an upper mirror layer 134 formed of a dielectric multilayer of about 1,100 Å / about 2000 Å on the emitter layer 130 The introduction of such a resonant cavity structure enables the high speed of the photoelectric device.

As an example of the material applicable to the resonant avalanche detector, the emitter layer 130 is P + -InAlAs, the third spacer layer 128 is i-InAlAs, and the light absorption layer 126 is i-InGaAs of 1000 Å or less. Single material, i-InGaAlAs graded spacer layer 124 (in this case, InGa _{0.47 (1-x)} Al _0.47x As, x varies from 1 to 0), avalanche gain structure layer (less than _1000µs ) a p-InAlAs charge layer 120, a charge layer electrode 122, an i-InAlAs amplification layer 118 of 2000 Hz or less), an n-InAlAs space layer 116, and an n-InAlAs collector layer 112 I can't.

Hereinafter, a photo transistor which is another application example of the above-described avalanche photodetector will be described. The waveguide-fed phototransistor of FIG. 3 includes a conductive collector layer 212 formed on a substrate 210, a collector electrode 214 formed on a portion thereof, an amplification layer 218, and a charge layer ( And a light absorbing layer 226, an emitter electrode 232, and a charge layer electrode 222, between the collector layer 212 and the amplification layer 218, and the charge layer 220 and the light absorbing layer ( The first spacer layer 216, the second spacer layer 224, and the third spacer layer 228 are added between 226 and between the light absorption layer 226 and the emitter layer 230, respectively. Almost similar. Therefore, for the convenience of description, the description will be made based on the structure and difference of FIG. 1. The point including the optical waveguide layer 234 and the guiding layer 236 between the collector layer 212 and the substrate 210 is distinguished from the avalanche photodetector of FIG. 1.

As an example of a material applicable to the present optical waveguide phototransistor, the optical waveguide layer 234 may be composed of an InGaAlAs layer of, for example, 1,600 mW, and the guiding layer 236 may be composed of an InAlAs layer of, for example, 5,000 mW. Meanwhile, the emitter layer 230 may be formed of P + -InAlAs, the third spacer layer 228 may be composed of i-InAlAs, and the light absorbing layer 226 may be formed of a single i-InGaAs material of 1000 Å or less. (graded layer: 124) (in this case, InGa _{0.47 (1-x)} Al _0.47x As, x varies from 1 to 0), avalanche gain structure layer (p-InAlAs charge layer 220 of 1000 Å or less), The charge layer electrode 222, the i-InAlAs amplification layer 218 of 2000 mV or less, the n-InAlAs space layer 116, and the n-InAlAs collector layer 212 may be configured.

Hereinafter, the structures applicable to the light absorption layer will be described with reference to FIGS. 4A to 4H.

4A shows a plan view and a cross-sectional view of an emitter of light absorbing layers in a bulk single layer of material, or a thin film. As described above, it may be composed of a single material of i-InGaAs of 1000 mW or less.

4B is a plan view and a cross-sectional view of a single layer or stacked structure of a self-assembled quantum dot array. Reference numeral 401 may be a GaAs layer of 500 mW or less, and 402 may be an InAs quantum dot.

4C illustrates a plan view and a cross-sectional view of a quantum dot array layer structure formed through a horizontal confinement in a double barrier quantum well type epi structure. Reference numeral 501 denotes an i-InAlAs layer, 502 denotes an InGaAs quantum well layer of 100 kΩ or less, and 503 denotes an insulating layer. Also, if the quantum dot array is composed of quantum dots of different sizes, the absorption wavelength band can be widened.

4D is a plan view and a cross-sectional view of a vertical quantum dot array structure layer using a double barrier quantum well structure as an emitter light absorbing layer structure. Reference numeral 501 denotes an i-InAlAs layer, 502 denotes an InGaAs quantum well layer of 100 kΩ or less, and 503 denotes an insulating layer.

4E is a plan view and a cross-sectional view of a vertical quantum line array combination structure layer using a triple barrier quantum well structure as the light absorption layer structure of the emitter, and FIG. 4F is a quantum dot array composed of different quantum dots to change the absorption wavelength band. If it is. Reference numeral 601 may be composed of an i-AlAs layer, a GaAs quantum well layer of 100 kΩ or less, and 603 may be an insulating layer.

4G is a plan view and a cross-sectional view of a horizontal quantum line array combination structure layer using a triple barrier quantum well structure, and FIG. 4H is a case in which the absorption wavelength band is changed by configuring the size of the quantum dot array with different quantum dots.

Hereinafter, the operation principle of the avalanche photodetector according to the preferred embodiment of the present invention will be described with reference to FIGS. 5A and 5B.

FIG. 5A is an energy band diagram of an emitter layer, a collector layer, and charge layers in a state where no voltage is applied (thermal equilibrium state), and FIG. 5B is an example of an operating state of the device when an external voltage is applied. V ₁ is the voltage applied between the emitter and the charge layer, and V ₂ is the voltage applied between the charge layer and the collector. V ₁ and V ₂ have opposite polarities. On the other hand, in the case of the amplification structure using electrons, V ₁ is negatively biased and V ₂ is positively biased. Where V _B2 is the built-in potential in the charge and collector layers, and the strength of the electric field in the avalanche gain structure layer is easily controlled by the voltage V ₂ applied across the gain structure layer. do.

In the light absorbing layer, the electrons are absorbed by infrared rays and the band-to-band transition occurs to the conduction band. The transitioned electrons are amplified by the external applied voltage V ₂ and the built-in potential V _BI inside the device, leading to the collector. The externally applied voltage V ₂ can be easily adjusted so that electrons are amplified as they pass through the charge and amplification layers, while at the same time an internal RF-gain in the high frequency region is created by intervalley transport of electrons. This results in a large -3dB bandwidth (-3dB bandwith, f _3dB ) in the high current region.

In the avalanche photodetector of the present invention, the internal RF-gain effect is easily generated by the intervalley transport of secondary electrons in the avalanche gain structure layer (amplification layer) by adjusting the voltages applied to the respective electrodes. Can be controlled.

Therefore, through this, high speed characteristics are simultaneously achieved in the high current-gain region, and a high gain is achieved by applying a relatively low voltage, thereby increasing the sensitivity, and providing high functionality / new functionality by internal RF-gain, It is possible to implement a photodetector that can increase the stability by reducing the breakdown voltage of the device.

In other words, it is possible to achieve high gain, high sensitivity, high speed and stability due to the avalanche multiplication process in the avalanche gain structure layer including the thin amplification layer and the intervalley transport effect of charges.

It is applicable to the areas needed for high speed long distance communication, single photon counting, and low light absorption. Many advantages of using low voltage, high gain of the device and lower breakdown voltage can be achieved. On the other hand, it can be applied to high-speed photodetector, high-speed infrared signal detection and amplifier, optical receiver (receiver), it is possible to apply to a high-functional high-speed infrared logic device and the like.

Therefore, the incident infrared light causes interband or interband transition of electrons in the light absorbing layer. When an external voltage is applied, electrons (or holes) generated by absorption of an optical signal may be amplified through the charge layer, the amplification layer, and the like, thereby obtaining amplified electric signals.

On the other hand, by applying relative voltages to the emitter electrode and the collector electrode, the avalanche amplification occurs while the photocharges pass through the thin amplification layer, and travel by intervalley transfer of the secondary electrons. Voltages may be applied to produce an RF-gain according to a ring spacer traveling mode of charge mode.

In addition, by applying a relatively low voltage to the thin amplification layer, the bandwidth is increased in the high gain region to obtain a high speed characteristics. The control of the avalanche gain structure layer, that is, the impurity doping level, thickness, and electric field strength imposed on the charge layer, amplification layer, electrode contact layer, etc. , Device gain, speed, and so on. Thin multiplication layers improve the device's speed and noise characteristics.

In addition, emitter light absorbing layer structure with infrared detection function, vertical quantum dot, or array structure of quantum lines, or self-made using epitaxial bulk monolayer, thin film, ultra fine quantum well structure according to wavelength and application An assembled quantum dot combination structure layer or the like is applicable.

6A and 6B are energy band diagrams showing energy states according to voltage application in an example of a structure of an avalanche photodetector using an inter subband transition of electrons.

In this case, the quantum well structure, the quantum dot structure, the quantum well structure, or the quantum wire structure is used as the emitter light absorbing layer structure. In the quantum light absorbing layer, electrons transition to a sharp excited level due to infrared absorption. Happens. This is controlled by the size of the quantum dot, the quantum well or the width of the quantum line.

FIG. 6A is an energy band diagram of the constituent layers of the above device under no voltage (thermal equilibrium) and FIG. 6B is an energy band diagram of the operating state of the device when an external voltage is applied. In this case, electrons in the quantum light absorbing layer transition to a steep excitation level by infrared absorption. At this time, electrons transitioned to the excitation level are amplified in the blocking barrier, the charge layer, and the amplification layer by the external applied voltage and the built-in potential inside the device, and the intervalley transition occurs to reach the collector layer.

The infrared absorption wavelength is determined by the bound energy levels of the quantum dots, quantum wells, or quantum lines of electrons. In addition, the introduction of the mirror structure forms a resonance structure, improves the quantum efficiency, improves the performance of the device, and achieves high speed, thereby enabling an ultra-fast infrared signal detector.

Experimental Example

Hereinafter, a sample of the avalanche photodetector device according to the present invention was manufactured and its properties were investigated. The avalanche photodetector for investigating the characteristics was manufactured in the structure of FIG. 1, and the materials and thicknesses of the layers are described in detail as follows. The photodetectors include a 53Å P + -InGaAs, 3700Å P + -InAlAs emitter layer, a 700Å i-InAlAs spacer layer, a 550Å i-InGaAs light absorbing layer, a 500Å i-InGaAlAs incremental spacer layer, an avalanche gain structure layer (500Å p-InAlAs, 1500Å) i-InAlAs and 1,000Ån-InAlAs) and 4,000Ån-InAlAs collector layer, Ti / pt / Au p-electrode and Au / Ge / Ni n-electrode.

7 to 13 show internal Rf gain characteristics of the high frequency band in the high current-gain region by intervalley transport of secondary and excess electrons when a voltage higher than the avalanche breakdown voltage is applied in the thin amplification layer. Characteristic measurement curves of the photodetecting device.

7 and 8 show negative differential resistance (NDR) characteristics due to intervalley transport of secondary electrons after the avalanche breakdown voltage as an example of a current-positive voltage characteristic measurement curve.

9, 10 and 11 are curves measuring frequency response characteristics, and FIG. 12 is a normalized response curve of FIG. 11. Through the frequency response characteristic measurement curves, as the voltage higher than the avalanche breakdown voltage is imposed, the response characteristic of the high frequency band is improved, showing a frequency response characteristic of an increasingly large 3dB bandwidth.

13 and 14 are bandwidth-gain characteristic curves showing high frequency response characteristics in the high current-gain region.

As mentioned above, although this invention was demonstrated in detail through the specific Example, this invention is not limited to this, It is clear that the deformation | transformation and improvement are possible by the person of ordinary skill in the art within the technical idea of this invention. .

Therefore, when the avalanche gain structure layer having the internal RF gain in the high frequency band according to the device of the present invention is applied, high sensitivity, low voltage performance, and high structure can be achieved simultaneously in the high current gain region. High frequency response characteristics and stability in the gain current region can be achieved.

In addition, the use of low voltage has many advantages, and the high gain achieves many advantages, such as compensation for low light absorption, high output and high speed, and achievement of stability that lowers the breakdown voltage of the device. Is given. This is the opposite effect of the disadvantages of conventional avalanche photodetectors with low bandwidth in the high current-gain region.

In addition, the degree of freedom of selection of the light absorption layer structure enables selection and processing of infrared signals in various regions. It can also be used to request very high sensitivity, such as for long distance communication, single photon counting, and so on.

In addition, the achievement of high current-gain in the high frequency range can be substituted for the preamplifier function, which is applied to high speed photodetectors, high speed infrared signal detectors and amplifiers, and the high speed switching and logic devices due to increased degrees of freedom. It can be applied to digital logic, new function / multifunction high speed infrared logic device, etc., which contributes to the development of photo-receiver.

Claims (15)

Board; A conductive collector layer formed on the substrate; Emitter layer; An avalanche photodetector comprising: and a light absorption layer between the emitter layer and the collector layer. And an avalanche gain structure layer capable of generating and controlling a high-frequency band RF gain by intervalley transport of secondary charges between the light absorbing layer and the collector layer. The method of claim 1, And the avalanche gain structure layer comprises a charge layer, a charge layer electrode, and an amplification layer, which are sequentially formed. The avalanche photodetector device of claim 2, wherein the amplification layer comprises a bulk single material layer or a superlattice structure. The method of claim 1, And an spacer layer (s) for controlling diffusion of impurities between the collector layer and the amplification layer and / or between the charge layer and the light absorbing layer. The method of claim 4, wherein A spacer layer is further included between the charge layer and the light absorption layer, and the spacer layer is an i-InGaAlAs gradual spacer layer (in this case, InGa _{0.47 (1-x)} Al _0.47x As, where x is changed from 1 to 0). Avalanche photodetector, characterized in that. The method of claim 1, And an spacer layer for controlling diffusion of impurities between the light absorption layer and the emitter layer. The method of claim 1, And the light absorbing layer is a bulk single material layer, a self-assembled quantum dot structure, a quantum well structure, an array of quantum dots, or an array of quantum lines. The method of claim 7, wherein The light absorbing layer is an avalanche photodetector, characterized in that composed of a single material i-InGaAs of less than 1000Å. The method of claim 7, wherein The light absorbing layer is an avalanche photodetector, characterized in that the GaAs layer and InAs quantum dot one or more laminated. The method of claim 7, wherein The light absorbing layer is an avalanche photodetector, characterized in that consisting of at least one stack of the i-InAlAs layer, InGaAs quantum well layer and the insulating layer. The method of claim 2, By the voltage applied between the charge layer and the collector, electrons are amplified while passing through the charge layer and the amplification layer, and at the same time, the internal RF-gain of the high frequency region is generated by the intervalley transport of electrons. An avalanche photodetector, characterized in that. The method of claim 1, And a lower mirror layer of a λ / 4 stack between the collector layer and the substrate, and an upper mirror layer on the emitter layer. The method of claim 12, The lower mirror layer is a structure in which an I nAlAs / InAlGaAs layer is formed of one or more pairs of λ / 4 (quarter-wave) stacks, and the upper mirror layer is a dielectric multilayer comprising an MgO / Si layer. Photodetector. A structure of an avalanche photodetector device according to any one of claims 1 to 13; And And a light waveguide layer and a guiding layer between the collector layer and the substrate. The method of claim 14, The optical waveguide layer is formed of an InGaAlAs layer, and the guiding layer is formed of an InAlAs layer.