CN113644150A - High-gain photoelectric detector - Google Patents
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Abstract
The invention discloses a high-gain photoelectric detector, which comprises an emitter, a base, an absorption layer, a collector and a periodic quantum structure layer, wherein the emitter, the base, the absorption layer and the collector are sequentially arranged from bottom to top; the periodic quantum structure layer comprises a plurality of periodic repeating structures, and each period contains a semiconductor heterojunction. The periodic quantum structure can prevent base holes from diffusing to an emitter, improve the electron injection ratio of an emitter junction and the amplification factor of a transistor, and restrict holes with larger effective mass in a multilayer quantum structure to reduce recombination loss, so that the service life of the holes in a device exceeds the transport time of electrons, and superimposed photoconductive gain is generated in a phototransistor.
Description
Technical Field
The invention relates to the technical field of semiconductor photodetectors, in particular to a high-gain photodetector.
Background
Photodetectors have very wide applications in optical communication, imaging, environmental monitoring, driving assistance, and various experimental tests. For a photoelectric detector, the responsivity is an important index, the high-responsivity semiconductor photoelectric detector with internal gain can realize high-sensitivity detection of weak optical signals at normal temperature and low bias voltage, and an additional signal amplifier can be omitted, so that a photoelectric detection system is more simplified and portable, and the cost is low. An n-p-n type phototransistor is a commonly used semiconductor photodetector with internal gain, whose principle of photoelectric gain is: under the suspended state of the base region, holes generated by light absorption in the collector junction drift to the base electrode under the action of an internal field and an external electric field to be accumulated, so that the potential barrier of the emitter junction is reduced, electron injection of the emitter is caused, and light induced current with internal gain is generated.
On the basis, another commonly used improved structure is a heterojunction phototransistor, and an emitter junction is designed into a heterojunction by adopting an emitter material with a wider forbidden band, so that the effects of blocking hole diffusion and improving the electron injection ratio and the transistor magnification are achieved.
However, the current phototransistor and heterojunction phototransistor have disadvantages, such as the very limited number of photo-generated holes for weak light signals, even single photon incidence conditions, and the difficulty in significantly affecting the barrier height of the emitter junction, thereby limiting the detection of very weak light by the phototransistor. Other common internal gain mechanisms of detectors have respective limitations, such as: avalanche photodetectors require a very low material defect density to avoid premature breakdown and require a high operating voltage; the dark current of the photoconductive detector is high, and an uncontrollable gain process generally involving a trap state can seriously deteriorate the response speed of the detector, so that although the device can obtain high responsivity, the response speed is generally in the order of milliseconds or even seconds, and the application range is severely limited.
Disclosure of Invention
The present invention is directed to overcoming at least one of the above-mentioned disadvantages of the prior art, and providing a high-gain photo detector with low dark current, higher responsivity, very weak photo detection capability, and high-speed response.
The technical scheme adopted by the invention is as follows:
a high-gain photoelectric detector comprises an emitter, a base, an absorption layer and a collector which are sequentially arranged from bottom to top, and further comprises a periodic quantum structure layer, wherein the periodic quantum structure layer is arranged between the emitter and the collector, or is arranged in the base, or is arranged in the emitter;
the periodic quantum structure layer comprises a plurality of periods of repeated structures, and each period contains a semiconductor heterostructure, so that multiple valence band bands and corresponding hole potential wells and barriers are formed. Wherein, the semiconductor junction formed by two adjacent heterogeneous materials is a heterojunction.
In the technical scheme, the emitter, the base, the absorption layer and the collector form a main device structure of the phototransistor, and the periodic quantum structure layer is added on the main device structure to improve the electron injection ratio and the device amplification factor and provide the superposed photoconductive gain to obtain higher responsivity. Meanwhile, because the superposed photoconductive gain is from a periodic quantum structure rather than a trap state, the hole life can be regulated and controlled by controlling the structural parameters, so that the response speed of the device is ensured while high gain is realized. Specifically, the periodic quantum structure layer forms a series of valence band hole barriers to block the diffusion of holes from the base to the emitter by using the periodic quantum structure, and the structure has no conduction band electron barrier or electron barrier thickness to allow electrons with smaller effective mass to directly tunnel through, so that the diffusion of electrons from the emitter to the base can not be influenced, and the electron injection ratio of the emitter of the phototransistor and the amplification factor of the phototransistor can be improved. In addition, since the periodic quantum structure comprises multiple valence band steps, the diffusion barrier effect on holes is better than that of a heterojunction phototransistor structure with single valence band step, namely, higher electron injection ratio and amplification factor can be provided than that of the heterojunction phototransistor.
Furthermore, the periodic quantum structure can restrain a part of photogenerated holes in a hole potential well of the device structure while blocking the base hole from diffusing to the emitter, the service life of the holes in the potential well is influenced by escape mechanisms such as thermal emission and tunneling, and the probability of the holes escaping from the quantum well depends on the depth of the hole potential well and the thickness of a hole barrier. The depth (valence band step difference) of the hole potential well can be regulated and controlled by selecting different heterogeneous semiconductor materials, and the thickness of the hole potential well can be directly controlled by the material thickness of each layer in the periodic structure. Therefore, the hole life can be regulated and controlled by changing the structural parameters, so that the hole life exceeds the electron transit time, the superposed photoconductive gain is obtained, and the responsivity of the detector is further improved.
And because the service life of the cavity in the periodic quantum structure can be regulated and controlled by the structural parameters, the reduction of the response speed caused by overlong service life of the cavity can be avoided, and high-speed response is obtained while high photoelectric gain is realized.
The photoconductive gain mechanism of the invention is as follows: through the periodic quantum structure, a series of hole potential wells are formed, a hole constraint effect is obtained, the service life of a hole is longer than the time required by electron transit, and therefore after photogenerated electrons transit to an electrode and are collected, the hole is still constrained in the quantum structure, so that the cathode continuously emits electrons to maintain electroneutrality, after the circulation is repeated for many times, the photoelectron current collected by the phototransistor is far higher than the photoelectron current directly collected for the first time, and a photocurrent gain effect is formed, wherein the gain multiple is the ratio of the service life of the hole to the transit time of the electron.
Further, the periodic quantum structure layer may be interposed between the emitter and the collector, or may be embedded inside the base or inside the emitter.
Further, the hole lifetime can be controlled by the depth (valence band step size, depending on the material used) of the hole potential well and the thickness of each layer in the periodic structure, so that the response speed of the detector can be regulated, and high-speed response can be realized while high gain is obtained.
Further, a hole potential well layer and a hole barrier layer formed by a heterostructure valence band offset exist in the periodic quantum structure layer. Further, the depth of the hole potential well is higher than 3 kT; where k is the boltzmann constant and T is the operating temperature. When the depth of the potential well is less than 3kT, holes can easily escape out of the potential well layer through thermal emission, and the hole binding effect of the periodic quantum structure is ineffective.
The hole potential well formed in the quantum structure is obtained through the valence band step of the heterostructure, so that the confinement effect on the holes is strong, but no potential well exists for electrons, or the electrons can escape from the electron potential well through tunneling by controlling the thickness, even if the effective mass of the electrons is smaller than that of the holes, tunneling is easier to occur, and the confinement effect on the electrons is very weak.
In another embodiment, the electron potential well layer and the electron barrier layer exist in the periodic quantum structure layer at the same time, and the probability of the electrons escaping from the electron potential well layer is higher than that of the holes in the hole potential well layer, namely the binding effect of the electron potential well to the electrons is weaker, so that the time required for the electrons to transit is still less than the lifetime of the holes. Therefore, the effect of high gain can also be obtained.
Specifically, if an electron potential well and an electron potential barrier exist in the periodic quantum structure layer, the thickness of the electron potential barrier layer in the periodic quantum structure layer should not exceed the de broglie wavelength of electrons in the electron potential well layer; when the thickness of the periodic quantum structure is shorter than the wavelength of electrons, electrons can tunnel through, the blocking effect is weak, and thus the constraint effect of the whole periodic quantum structure layer on holes is stronger than the constraint effect on the electrons, so that the time required by electron transit is shorter than the service life of the holes.
Further, the periodicity of the periodic quantum structure layer is more than or equal to 3. The binding effect of the holes is weakened when the number of cycles is too small, the photoconductive gain is not obvious, and the electron injection ratio and the transistor amplification factor are reduced.
In one embodiment, the periodic quantum structure layer is a quantum well layer.
In another embodiment, the periodic quantum structure layer is a superlattice layer.
The quantum well layer or superlattice layer forms a series of valence band steps that function as hole potential wells such that holes are bound in the potential wells, thereby extending the hole lifetime t1 beyond the electron transit time t2 to create the effect of photoconductive gain. Specifically, the photoconductive gain is t1/t2 in magnitude.
Further, the periodic quantum structure of the present disclosure may also be other structures that can form a hole-confinement effect, such as a structure with only a hole potential well and no electron potential well.
Further, the periodic quantum structure is one of an AlGaN/GaN superlattice structure, an AlGaN/GaN multiple quantum well structure, an AlGaAs/GaAs superlattice structure and an AlGaAs/GaAs multiple quantum well structure.
In one embodiment, the device further comprises an upper contact electrode and a lower contact electrode.
In one embodiment, ohmic contacts are formed between the upper contact electrode and the collector, and between the lower contact electrode and the emitter, or the height of the contact barrier is lower than 0.5eV, so as to avoid reducing the photocurrent of the device.
Further, the lower contact electrode and the upper contact electrode are Ti/Al/Ni/Au or Au/AuGeNi alloy.
In one embodiment, the emitter and collector are of n-type conductivity semiconductor material with electron concentration higher than 5 × 1016cm-3。
Further, the emitter is n-type AlGaN or n-type AlGaAs or n-type GaN. The collector is n-type GaN or n-type GaAs where too low an electron concentration of the emitter results in a reduction in photocurrent.
In one embodiment, the substrate is a p-type conductive semiconductor material with a hole concentration greater than 1 × 1016cm-3。
Wherein too low hole concentration in the base region also causes early base region punch-through and dark current rise.
Further, the base is a p-type GaN layer.
In one embodiment, the absorption layer is an intrinsic or an unintentional doped semiconductor material with a hole or electron concentration below 5 × 1017cm-3。
The carrier concentration of the absorption layer is too high, so that the width of a depletion layer is reduced, the collection efficiency of photon-generated carriers is reduced, and the responsivity of the detector is degraded.
Further, the absorption layer is unintentionally doped GaN or unintentionally doped GaAs.
Compared with the prior art, the invention has the beneficial effects that:
according to the technical scheme, the periodic quantum structure layer is added on the device structure, so that holes are bound in the transportation/moving process of photo-generated electron holes, more electrons are injected into the electrodes, current gain is formed, and the effect of high gain is achieved.
The technical scheme realizes the photoelectric high-gain effect on the basis of no trap state introduction, no degradation of device response speed and controllable speed.
The invention realizes blocking the diffusion of holes from the base electrode to the emitter electrode and does not influence the diffusion of electrons from the emitter electrode to the base electrode by adding the periodic quantum structure layer, thereby improving the electron injection ratio of the photoelectric transistor and the amplification factor of the transistor.
The invention introduces the superposed photoconductive gain with controllable speed on the basis of the phototransistor, which can not only make up the deficiency of weak light response of the phototransistor, but also further improve the overall gain; the method has the beneficial effect of realizing high-speed and extremely high-responsivity photoelectric detection under low bias voltage without demanding the crystal quality of the material.
The invention forms a series of hole potential wells and barriers by introducing a periodic quantum structure to regulate the transportation of photo-generated electrons and holes, thereby superposing photoconductive gain on a photo-induction mechanism of a phototransistor. The periodic quantum structure can prevent base holes from diffusing to an emitter, improve the electron injection ratio of an emitter junction and the amplification factor of a transistor, and restrict holes with larger effective mass in a multilayer quantum structure to reduce recombination loss, so that the service life of the holes in a device exceeds the transport time of electrons, and superimposed photoconductive gain is generated in a phototransistor. In addition, in the device structure provided by the invention, the service life of a cavity can be controlled through material selection and thickness proportion of the periodic structure, so that the response speed of the detector is regulated, and high-speed response is realized while high photoelectric gain is obtained.
Drawings
Fig. 1 is a schematic structural diagram of embodiment 1 of the present invention.
Fig. 2 is a diagram showing the band simulation result of the periodic quantum structure (AlGaN/GaN superlattice) in example 1 of the present invention, and the process of escaping potential wells through Thermal Emission (TE) and tunneling (T) of conduction band electrons and valence band holes.
Fig. 3 is a schematic structural diagram of embodiment 4 of the present invention.
Fig. 4 is a schematic structural diagram of embodiment 6 of the present invention.
Fig. 5 shows the test result of the dark current characteristics of the photodetector in embodiment 1 of the present invention.
Fig. 6 shows the response speed test result of the photodetector in embodiment 1 of the present invention.
Detailed Description
The drawings are only for purposes of illustration and are not to be construed as limiting the invention. For a better understanding of the following embodiments, certain features of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
Example 1
As shown in fig. 1, a GaN-based high-gain photodetector structure mainly includes an emitter layer 201, a periodic quantum structure layer 202, a base layer 203, an absorber layer 207, and a collector layer 204, which are sequentially arranged from bottom to top.
In this embodiment, the lower contact electrodes 205 are disposed on two sides of the upper surface of the emitter layer 201, and the upper contact electrodes 206 are disposed on two sides of the upper surface of the absorber layer 205.
Wherein the emitter layer 201 is made of n-type AlGaN, has an Al component of 20%, and has an electron concentration of 2 × 1018cm-3The thickness is 300nm, and the preparation method is not limited. Specifically, a substrate layer and/or a buffer layer are/is further arranged below the emitter layer.
The periodic quantum structure layer 202 is an AlGaN/GaN superlattice structure, in which the Al component is 20%, the periodicity is 20, the AlGaN layer thickness is 2nm, and the GaN layer thickness is 4nm in each period.
The base layer 203 is a p-type GaN layer with a hole concentration of 1 × 1018cm-3And the thickness is 100nm, and the preparation method and the doping method are not limited.
Both the lower contact electrode 205 and the upper contact electrode 206 were Ti/Al/Ni/Au with a thickness of 15/80/20/60 nm.
The absorber layer 207 is unintentionally doped with GaN and has a thickness of 150 nm.
Fig. 2 shows the band simulation results of the AlGaN/GaN superlattice layer in this embodiment and the process of escaping the electron/hole wells through Thermal Emission (TE) and tunneling (T).
Due to the influence of the Quantum Confined Stark Effect (QCSE), electrons and holes will be spatially separated, the amount of wave function overlap is reduced, resulting in a low recombination rate of electrons and holes, and thus radiative recombination lifetime and non-radiative recombination lifetime will be large. The carrier lifetime τ is now determined mainly by the escape mechanism, i.e.:
the tunneling lifetime of the carrier can be written as the carrier rate according to the WKB approximation theory in quantum mechanics
And tunneling probability (T (E)n) In relation to (c):
and thermal emission lifetime (tau)TE) Mainly depending on the effective barrier height:
in the formula LwThe thickness of the quantum well is represented by,
representing the greater value of the potential energy of the electron and hole barriers, EnFor the subband level height of the AlGaN quantum well, it can be written as:
the energy band shape obtained by simulation is substituted into the above three formulas for calculation, and the escape lives of electrons and holes are respectively 1.4 multiplied by 10-11s and 8.3X 10-8And s. Through calculation results, the escape lifetime of electrons in the quantum structure of the embodiment is far shorter than that of holes, namely, the electrons more easily escape from the quantum well. Further, the equivalent mobility and the drift velocity of electrons in the periodic structure can be calculated through the process, so that the transit time of the electrons can be calculated. The electron transit time calculation in this configuration is about 4.9 × 10-9s, the resulting superimposed photoconductive gain is approximately 17 times.
Since the hole life calculation result in the structure is about 80ns, the device can achieve high-speed response of ns level while obtaining higher gain.
Example 2
The present embodiment is different from embodiment 1 in that: the material of the emitter layer is n-type GaN, the periodic quantum structure layer is a multi-quantum well of AlGaN (6nm)/GaN (3nm), and the period number is 10.
Example 3
The present embodiment is different from embodiment 1 in that: in the AlGaN/GaN superlattice layer of the periodic quantum structure layer, the Al component of AlGaN is 15%, the thickness of AlGaN is 3nm in each period, and the thickness of GaN is 4 nm.
Example 4
As shown in fig. 3, a GaN-based high-gain photodetector structure mainly includes an emitter layer 301, a base layer 3031, a periodic quantum structure layer 302, a base layer 3032, an absorption layer 307 and a collector layer 304, which are sequentially arranged from bottom to top. Lower contact electrodes 305 are provided on both sides of the upper surface of the emitter layer 301, and upper contact electrodes 306 are provided on both sides of the upper surface of the absorber layer 305.
The present embodiment is different from embodiment 1 in that: in this embodiment, the base layer is divided into a base layer 3031 and a base layer 3032, and the periodic quantum structure layer 302 is located in the base layer, i.e. between the base layer 3031 and the base layer 3032, as shown in fig. 3.
Example 5
The present embodiment is different from embodiment 1 in that: the periodic quantum structure layer is composed of 15 layers of AlGaN/GaN repeated overlapping, wherein the thickness of GaN in each period is 4nm, and AlGaN includes 3 thicknesses: when viewed from top to bottom, in the first 5 periods of the periodic quantum structure layer, the thickness of each layer of AlGaN is 1.5nm, in the middle five periods, the thickness of each layer of AlGaN is 2.5nm, and in the lowest five periods, the thickness of each layer of AlGaN is 4 nm. In the periodic quantum structure arranged in the way, the hole barrier layer is the AlGaN layer, and the hole barrier layer closer to the base region is thinner, so that more holes can be diffused into the periodic quantum structure, and the photoconductive gain effect is improved; and the hole barrier closer to the emitter is thicker, which is beneficial to preventing holes from diffusing into the emitter and maintaining higher electron injection ratio and transistor amplification factor.
Example 6
As shown in fig. 4, this embodiment shows a GaAs-based high-gain photodetector, which mainly includes an emitter layer 401, a periodic quantum structure layer 402, a base layer 403, an absorber layer 407, and a collector layer 404, which are sequentially disposed from bottom to top. Lower contact electrodes 405 are provided on both sides of the upper surface of the emitter layer 401, and upper contact electrodes 406 are provided on both sides of the upper surface of the absorber layer 405.
The emitter layer 401 is made of n-type AlGaAs, has an Al component of 20% and has an electron concentration of 2X 1018cm-3And the thickness is 300 nm.
The periodic quantum structure layer 402 is an AlGaAs/GaAs superlattice structure, in which the Al component is 20%, the period number is 20, the AlGaN layer thickness is 4nm, and the GaN layer thickness is 6nm in each period.
The base 403 is a p-type GaN layer with a hole concentration of 1 × 1018cm-3The thickness is 100 nm.
The collector 404 is n-type GaAs with an electron concentration of 5 × 1017cm-3And the thickness is 120 nm.
The lower contact electrode 405 and the upper contact electrode 406 are both Au/AuGeNi alloy.
The absorber layer 407 is unintentionally doped GaAs to a thickness of 200 nm.
Example 7
This example performed detector characterization on the photodetector prepared in example 1.
As shown in FIG. 5, which is the result of the dark current test of the photodetector described in example 1, the photocurrent gain of the detector is as high as 1.3 × 10 at a low bias voltage of 10V5. The gain of the photodetector without the AlGaN/GaN superlattice in example 1 was 6.5X 104It is clear that by introducing a periodic quantum structure, the photoelectric gain of the device is improved by about 20 times, which also roughly coincides with the calculation results in example 1.
As shown in fig. 6, which is a response speed test result of the device prepared in example 1, the measured rise time and fall time of the detector are 2.4ns and 500ns, respectively, which is much faster than the response speed of the conventional photoconductive detector in order of more than ms. Therefore, the scheme provided by the invention can improve the responsivity of the device and can obtain high response speed.
Similarly, in this embodiment, the photo-detector prepared in embodiments 2 to 6 is subjected to the dark current test and the corresponding speed test, and then the photo-detector has the same photoelectric gain improvement and high response speed as those of embodiment 1. Therefore, the photoelectric detector obtained by the invention has the effects of high photoelectric gain and high response speed.
It should be understood that the above-mentioned embodiments of the present invention are only examples for clearly illustrating the technical solutions of the present invention, and are not intended to limit the specific embodiments of the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention claims should be included in the protection scope of the present invention claims.
Claims (10)
1. The high-gain photoelectric detector is characterized by comprising an emitter, a base, an absorption layer and a collector which are sequentially arranged from bottom to top, and further comprising a periodic quantum structure layer, wherein the periodic quantum structure layer is arranged between the emitter and the collector, or is arranged in the base, or is arranged in the emitter;
the periodic quantum structure layer comprises a plurality of periodic repeating structures, and each period contains a semiconductor heterojunction.
2. A high gain photodetector as claimed in claim 1, wherein a series of hole well layers and hole barrier layers are present in the periodic quantum structure layer formed by heterojunction valence band steps.
3. The high-gain photoelectric detector as claimed in claim 2, wherein a series of electron well layers and electron barrier layers formed by heterojunction conduction band steps exist in the periodic quantum structure layer, and the probability of electrons escaping from the electron well layers is higher than the probability of holes escaping from the hole well layers.
4. A high gain photodetector according to claim 2, the depth of the hole well in the periodic quantum structure being higher than 3kT, where k is the boltzmann constant and T is the operating temperature; the thickness of the single hole barrier layer is not less than 0.5 nm.
5. The high-gain photodetector as claimed in claim 1, wherein the number of the periodic quantum structure layers is greater than or equal to 3.
6. A high gain photodetector according to claim 1, further comprising upper and lower contact electrodes;
ohmic contact is formed between the upper contact electrode and the collector, and between the lower contact electrode and the emitter, or the height of a contact potential barrier is lower than 0.5 eV.
7. A high gain photodetector according to claim 1, wherein said emitter and collector are of n-type conductivity semiconductor material with an electron concentration higher than 5 x 1016cm-3。
8. A high gain photodetector according to claim 1, wherein said substrate is a p-type conductivity semiconductor material and has a hole concentration higher than 1 x 1016cm-3。
9. A high gain photodetector according to claim 1, characterized in that said absorption layer is an intrinsic semiconductor or an unintentionally doped semiconductor, and the concentration of both electrons and holes is below 5 x 1017cm-3。
10. A high gain photodetector as claimed in claim 1, wherein said periodic quantum structure layer is a quantum well layer or a superlattice layer.
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Citations (6)
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| CN1773729A (en) * | 2005-09-23 | 2006-05-17 | 中国科学院上海技术物理研究所 | Self-amplifying infrared detector |
| CN102646703A (en) * | 2012-05-07 | 2012-08-22 | 中国电子科技集团公司第五十五研究所 | Epitaxial structure of single crystal indium phosphide (InP) group compound semiconductor film |
| US20140050242A1 (en) * | 2012-08-17 | 2014-02-20 | Geoff W. Taylor | Optoelectric Integrated Circuit |
| CN105206702A (en) * | 2014-06-27 | 2015-12-30 | 中国人民解放军军械工程学院 | Novel-structurally single-photon detector |
| CN109494275A (en) * | 2018-11-22 | 2019-03-19 | 中国科学院长春光学精密机械与物理研究所 | A kind of AlGaN base solar blind UV electric transistor detector and preparation method thereof |
| CN111477717A (en) * | 2020-04-26 | 2020-07-31 | 中国科学院半导体研究所 | Self-refrigerating antimonide superlattice infrared detector and preparation method thereof |
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| CN1773729A (en) * | 2005-09-23 | 2006-05-17 | 中国科学院上海技术物理研究所 | Self-amplifying infrared detector |
| CN102646703A (en) * | 2012-05-07 | 2012-08-22 | 中国电子科技集团公司第五十五研究所 | Epitaxial structure of single crystal indium phosphide (InP) group compound semiconductor film |
| US20140050242A1 (en) * | 2012-08-17 | 2014-02-20 | Geoff W. Taylor | Optoelectric Integrated Circuit |
| CN105206702A (en) * | 2014-06-27 | 2015-12-30 | 中国人民解放军军械工程学院 | Novel-structurally single-photon detector |
| CN109494275A (en) * | 2018-11-22 | 2019-03-19 | 中国科学院长春光学精密机械与物理研究所 | A kind of AlGaN base solar blind UV electric transistor detector and preparation method thereof |
| CN111477717A (en) * | 2020-04-26 | 2020-07-31 | 中国科学院半导体研究所 | Self-refrigerating antimonide superlattice infrared detector and preparation method thereof |
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