Epitaxial structure and preparation method of heterojunction photodetector

Abstract

The present invention relates to the field of semiconductor photodetectors, and provides an epitaxial structure of a heterojunction photodetector and a preparation method thereof, which comprises, from bottom to top, a substrate, an interface lower layer, an interface transition layer, an interface upper layer, a SiN x In-situ passivation layer and ohmic contact electrode; the anode and cathode of the ohmic contact electrode are deposited on SiN x The in-situ passivation layer surface, or the anode and cathode of the ohmic contact electrode are deposited on the pre-etched SiN x Advantages: The present invention utilizes high film quality and in-situ growth of thin SiN films without the introduction of impurity atoms in an air-free environment. x The film acts as a passivation layer, reducing surface defects in group III nitride photodetectors and thereby inhibiting the capture of photogenerated carriers by semiconductor surface defects. This approach not only effectively improves the severe persistent photoconductivity effect in detectors caused by surface defects and the resulting response speed limitations, but also significantly improves the detector's photoresponse stability and the uniformity of the on-chip device's dark current.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor photodetectors, and more particularly to an epitaxial structure and a preparation method of a heterojunction photodetector. Background Art

[0002] A photodetector is a device that converts an external optical signal into an internal electrical signal. It is now widely used in optical communications, environmental monitoring, biomedical imaging, and other fields. The basic operating principle of a semiconductor photodetector is that under external light, the semiconductor material absorbs photons and generates electron-hole pairs, which in turn affects the conductivity of the semiconductor material itself. In other words, the conductivity of the semiconductor in the light state and the dark state differ. Depending on the detector structure, photodetectors can be divided into two categories: non-gain type and gain type. Non-gain devices include Schottky barrier photodiodes, PIN photodiodes, and Schottky contact metal-semiconductor-metal (MSM) photodiodes. Gain-type devices include avalanche photodiodes, bipolar heterojunction phototransistors, field-effect heterojunction phototransistors, etc.

[0003] With the rapid development of information technology, numerous applications require photodetectors with high responsiveness and the ability to detect weak light. This necessitates high internal gain. Thanks to the strong spontaneous polarization and piezoelectric polarization effects in wurtzite-structured III-nitride semiconductors, heterojunctions composed of different III-nitride semiconductor components can generate a polarization electric field, causing the epitaxial thin film layers on both sides of the heterojunction to exhibit a high-resistance state. The electron-hole pairs generated by light weaken this electric field, restoring conductivity in the light-absorbing epitaxial thin film layer and enabling carrier transport (hence, this epitaxial layer is also called a light-absorbing and transporting layer). The polarization electric field acts as a light-controlled built-in gate, thus forming a heterojunction phototransistor with field-effect transistors. This unipolar heterojunction phototransistor exhibits photoconductive gain in addition to photogate-controlled gain, thus achieving high responsiveness.

[0004] While these III-nitride heterojunction polarization-based phototransistor detectors offer high gain and, consequently, high responsivity, they often exhibit a strong persistent photoconductivity (PPC) effect. This refers to the delay between the onset and removal of a light signal, in which the detector's response current takes a while to reach its steady-state peak before decaying to its steady-state dark current value. For devices with severe PPC, the response current may not recover to its initial dark current value until hours or even days after light is removed. This is because, under persistent illumination, deep-level defects and localized states in the epitaxial layer capture photogenerated minority carriers, inducing persistent majority carrier injection. These defects release charge carriers more slowly after light is removed, leading to severe PPC. PPC not only degrades the photodetector's response speed, limiting its applications in optical communications and optical logic computing, but also compromises its weak-light response characteristics and periodic photoresponse stability, severely impacting its practicality. For example, a response current that remains high in the dark state after illumination will affect the device's detection of subsequent weak light signals, while the gradual rise in the response peak will affect the detector's sequential light signals; at the same time, since defects are usually non-uniformly distributed, they will affect the on-chip uniformity of the detector.

[0005] For heterojunction photodetectors, the defects that cause PPC mainly come from the surface, interface and body of the epitaxial layer. Among them, the defects in the body and interface can be suppressed by improving the epitaxial growth, while the surface defects are unavoidable from the perspective of crystal structure and can only be reduced and controlled through process treatment. Among them, surface passivation is an effective way. x 、Al2O3、SiN x A commonly used method is to deposit a dielectric film passivation layer. This involves removing the epitaxial structure from the metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) chamber before subsequent passivation layer deposition. However, the epitaxial layer surface of the epitaxial wafer removed from the growth chamber will have pre-reacted with oxygen in the air or produced impurity adsorption, resulting in additional surface states. Furthermore, ex-situ passivation layers are typically deposited at relatively low temperatures, resulting in a high concentration of defects and impurity charges, resulting in poor passivation layer quality.

[0006] Therefore, developing an in-situ surface passivation method to suppress surface defects of semiconductor materials is of great significance for effectively alleviating the PPC effect of heterojunction photodetectors and improving the practical performance of detectors, including response speed, response stability and on-chip uniformity. Summary of the Invention

[0007] The present invention aims to reduce surface defects in the epitaxial layer of a heterojunction photodetector and provide an epitaxial structure and preparation method for a heterojunction photodetector, in order to effectively control surface defects without adding subsequent process steps, thereby alleviating the PPC effect of the device and improving the device's light response speed, light response stability and on-chip uniformity.

[0008] In order to achieve the above technical effects, the present invention provides an epitaxial structure of a heterojunction photodetector, which comprises, from bottom to top, a substrate, an interface lower layer, an interface transition layer, an interface upper layer, a SiN x In-situ passivation layer and ohmic contact electrode; the anode and cathode of the ohmic contact electrode are deposited on SiN x The in-situ passivation layer surface, or the anode and cathode of the ohmic contact electrode are deposited on the pre-etched SiN x The upper surface of the interface of the in-situ passivation layer can form an ohmic contact through conventional ohmic contact deposition and heat treatment alloy process. The upper layer of the interface is a light absorption and transport layer.

[0009] Furthermore, the SiN x The value of x in the in-situ passivation layer is 0.5-1.5.

[0010] The SiN x The in-situ passivation layer is prepared by metal organic chemical vapor deposition of SiH4 and NH3. It can be grown in-situ on the surface of the device after the epitaxial structure is grown, without the need to pre-etch the passivation layer under the electrode.

[0011] Furthermore, the lower interface layer, the interface transition layer and the upper interface layer of the detector epitaxial structure are all made of Group III nitride semiconductor materials, and the lower interface layer, the interface transition layer and the upper interface layer form a heterojunction with each other.

[0012] Furthermore, the interface transition layer is a group III nitride layer whose band gap gradually changes from the lower interface layer to the upper interface layer by adjusting its composition, and its thickness ranges from 0 to 50 nm; when the thickness is 0, a sudden heterojunction is formed between the lower interface layer and the upper interface layer; when the thickness is not 0, a gradual heterojunction is formed.

[0013] The upper interface layer and the lower interface layer are both Group III nitride materials, and the polarization strength of the two layers is different, so the polarization effect can be used to generate positive / negative polarization charges at the interface between the two layers; the Group III nitride semiconductor materials used are all grown on polar surfaces or semi-polar surfaces, where the polar surfaces are arranged in the direction of metal polarity, that is, they grow along the

[0001] crystal direction.

[0014] Furthermore, the interface upper layer is a single-layer interface upper layer, and the interface upper layer is an n-type doped layer. The doping methods of the n-type doped layer include: uniform doping, alternating doping and linear gradient doping. The equivalent electron concentration range of the n-type doped layer is 3×10 17 cm -3 to 8×10 18 cm -3 .

[0015] Furthermore, the interface upper layer is a double-layer interface upper layer, and the interface upper layer is composed of a non-doped barrier layer with a relatively wide bandgap width and a channel layer with a relatively narrow bandgap width.

[0016] If the upper layer of the interface is a single-layer n-type doped layer, taking AlGaN material as an example, the Al component of the lower layer of the interface AlGaN should be higher than that of the upper layer of the interface. Due to the existence of piezoelectricity and spontaneous polarization, negative polarization charges will be generated at the interface, which will raise the energy band at that location and generate a built-in electric field pointing to the interface, thereby depleting the electrons in the upper layer of the interface, making it in a high-resistance state in the absence of light and having a lower dark current. When in-band response light is applied, electron-hole pairs will be generated in the upper layer of the interface. Under the action of the electric field, photogenerated electrons drift to the surface to increase conductivity, while photogenerated holes drift to the interface to shield the effect of the negative polarization charge on the interface, thereby further reducing the conductivity of the epitaxial layer and making the device have a higher photocurrent.

[0017] If the upper layer of the interface is a double layer consisting of a barrier layer and a channel layer, taking AlGaN material as an example, the Al component of the barrier layer in the double layer is higher than that of the channel layer, then a two-dimensional electron gas (2DEG) will be induced between the double layers. Furthermore, if AlGaN with an Al component higher than that of the upper layer of the interface is selected as the lower layer of the interface, negative polarization charges will be generated at the interface between the upper and lower layers, thereby depleting the 2DEG in the dark state. Under light, photogenerated electrons will replenish the 2DEG under the action of the electric field, and photogenerated holes will weaken the effect of the negative polarization charges, restoring the conductivity of the channel layer in the upper layer of the interface.

[0018] In this technical solution, in-situ SiN x The tunneling passivation layer has the advantages of high film quality and no introduction of impurity atoms (such as oxygen atoms) in the air environment. It can effectively reduce the surface defects of heterojunction photodetectors and has the advantage of not increasing the complexity of the ohmic contact preparation process. The above two types of heterojunction photodetectors are surface devices, and their carrier transport is strongly affected by the surface state concentration. Under light, the photogenerated carriers will drift to the surface of the device under the action of the built-in polarization electric field. The trap-type energy levels in the surface defects will capture the drifted carriers and provide partial defect-related photoconductivity gain, but at the same time it will also reduce the response speed of the device, thereby causing the PPC effect and periodic light response instability in the device. Therefore, by in-situ preparation of thin SiN xBy tunneling through the passivation layer, the PPC of the high-gain heterojunction photodetector can be effectively alleviated, and the response speed, optical response stability, and on-chip uniformity can be significantly improved.

[0019] Preferably, the lattice structure of the group III nitride material is a wurtzite structure, and the material has piezoelectric polarization and spontaneous polarization effects, including GaN, AlN, Al x Ga 1-x N, In x Ga 1-x N, Al x In 1-x N, Al x In y Ga 1-x-y N materials, where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1.

[0020] Preferably, the upper and lower layers of the interface can be Al x Ga 1-x N / Al y Ga 1-y N, In y Ga 1-y N / In x Ga 1-x N, InGaN / AlGaN and other heterojunctions with polarization intensity differences. When 0 ≤ x < y ≤ 1, there are negative-polarized charges at the upper and lower interfaces; when 0 ≤ y < x ≤ 1, there are positive-polarized charges at the upper and lower interfaces.

[0021] Preferably, if the upper layer of the interface is an n-type doped layer, this layer can be composed of a uniformly doped layer and an unintentionally doped layer of the same composition, where the carrier concentration of the unintentionally doped layer is less than 5 × 10 17 cm -3 .

[0022] Preferably, when n-type doping is used for the upper layer of the interface, Si can be used for uniform doping, and the doping concentration is higher than 1 × 10 17 cm -3 、lower than 5 × 10 19 cm -3 , because a moderate doping concentration can not only maintain a high carrier concentration and mobility but also keep the device in a depleted state in the dark.

[0023] Preferably, in the 2DEG structure, the barrier layer / channel layer included in the upper layer of the double layer can be Al x Ga 1-x N / Al y Ga 1-y N, In y Ga 1-y N / In x Ga1-x N, where 0 ≤ y < x ≤ 1. Positive polarization charges will form at the interface between the barrier layer and the channel layer, thereby inducing the generation of 2DEG.

[0024] Preferably, in the 2DEG structure, AlN, GaN, or InN with a thickness of 1 - 2 nm can be inserted between the barrier layer and the channel layer in the upper layer of the bilayer interface as a spacer layer, which can reduce alloy scattering and increase the carrier concentration.

[0025] Preferably, in the 2DEG structure, a 10 - nm graded - composition AlGaN or InGaN layer can be inserted between the upper and lower layers of the interface as an interface transition layer to reduce the relaxation degree of the upper layer of the interface, so as to ensure that there are more negative polarization charges at the upper and lower layer interfaces, which can better deplete the channel in the upper layer of the interface.

[0026] Preferably, when the upper layer of the interface is n - type doped or unintentionally doped, SiN x The cathode and anode ohmic contact electrodes on the passivation layer are both metal stacks of Ti / Al / Ni / Au or V / Al / V / Au, with a thickness of 15 / 80 / 20 / 60 nm. Under illumination, due to the relatively thin thickness of the SiN x passivation layer, carriers can tunnel - transport to the metal electrode, so the electrode forms a good ohmic contact with the upper layer of the interface.

[0027] Preferably, when the upper layer of the interface is n - type doped, the thickness of the upper layer of the interface is set to ensure that the total amount of carriers in the upper layer of the interface is less than the total amount of negative polarization charges at the upper and lower layer interfaces, so as to ensure that the doped carriers are depleted.

[0028] Preferably, in the 2DEG structure, the total amount of positive - polarization charges at the interface between the barrier layer and the channel layer in the upper layer of the bilayer interface should be less than the total amount of negative - polarization charges at the upper and lower interfaces, so as to ensure that the 2DEG is depleted.

[0029] Another object of the present invention is to provide a method for preparing a heterojunction photodetector epitaxial structure:

[0030] After growing the specified epitaxial structure in the MOCVD chamber, close the metal source, open the Si source, and continue to grow the SiN x passivation layer in - situ on the original structure. The specific steps are as follows:

[0031] (1) Close the metal source, set the NH₃ flow rate (F1) and the Si source flow rate (F2) to specified values, keep the carrier gas atmosphere as hydrogen, and set the chamber temperature to T1 until the flow rate and temperature of the flowmeter are stable;

[0032] (2) Introduce NH₃ and the Si source into the MOCVD chamber to prepare in - situ SiN xThe passivation layer has a growth time of t1 and a corresponding thickness of d1;

[0033] (3) After the growth is completed, turn off the Si source while keeping the NH3 flow rate unchanged, and anneal the SiN x passivation layer while cooling down.

[0034] Preferably, for the growth of SiN x the NH3 flow rate used is 0.04 mol / min < F1 < 0.37 mol / min; for the growth of SiN x the Si source used is SiH4, and its flow rate is 0.02 μmol / min < F1 < 0.36 μmol / min, and the flow rate ratio of the group V source to the group IV source varies within the range of 10 5 - 10 7 range.

[0035] Preferably, the growth time is 455 s < t1 < 7000 s, and the corresponding thickness is 1 nm < d1 < 6 nm.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] (1) It provides an in-situ passivation method that significantly improves the PPC effect of heterojunction photodetectors. The thin SiN x tunneling passivation layer prepared in-situ by MOCVD has the advantages of high film formation quality and no impurity atoms in the air environment. Without affecting the subsequent device process steps, it reduces the surface defects of group III nitride photodetectors, thereby suppressing the capture of photo-generated carriers by semiconductor surface defects. This not only speeds up the device's response to light but also promotes the recombination of photo-generated carriers after the light is removed, thus effectively alleviating the PPC effect that limits the device's frequency characteristics and weak light response.

[0038] (2) The SiN x in-situ passivation layer significantly improves the stability of the detector's periodic light response process. Due to the reduction of surface defects after passivation, the light and dark currents of the device always remain stable during multiple on / off cycles of the light, and there is no continuous increase in the light and dark currents during the cycle, which helps to improve the stability of the device in actual application scenarios.

[0039] (3) The SiN x in-situ passivation layer significantly improves the uniformity of the dark currents of detectors at different positions on the chip. Because the surface defect concentrations at different positions on the chip before passivation are different, the dark current values of the corresponding devices also vary greatly. By preparing the SiN x in-situ passivation layer, the surface defects at each position on the chip are suppressed, and the dark current values of devices at different positions tend to be consistent, which is beneficial to improving the utilization rate of devices on the chip.

[0040] (4) In-situ preparation of SiN in MOCVD chamber x The passivation layer also offers the advantage of simple processing. It can be deposited directly after the epitaxial structure is grown, eliminating the need for subsequent wet processing or ex-situ passivation layer growth in a PECVE or LPCVD chamber. Furthermore, ohmic contact electrodes can be fabricated directly on the thin tunneling passivation layer, significantly reducing process complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the epitaxial structure of the heterojunction photodetector in Examples 1 and 2 of the present invention.

[0042] Figure 2 This is a curve showing the decay of the current of the heterojunction photodetector over time after the light is removed in Example 1 of the present invention.

[0043] Figure 3 This is the periodic light response curve of Example 1 of the present invention under different light intensities.

[0044] Figure 4 is the standard deviation of dark current at different on-chip locations in Example 1 of the present invention.

[0045] Figure 5 Schematic diagram of the epitaxial structure of the heterojunction photodetector in Example 3 and Example 5 of the present invention.

[0046] Figure 6 Schematic diagram of the epitaxial structure of the heterojunction photodetector in Example 4 of the present invention.

[0047] Figure 7 Schematic diagram of the epitaxial structure of the heterojunction photodetector in Example 6 of the present invention.

[0048] Reference numerals: substrate 101, interface lower layer 102, interface transition layer 103, first interface upper layer 104, second interface upper layer 105, interface upper layer 200, SiN x In-situ passivation layer 106 , anode contact electrode 107 , cathode contact electrode 108 . DETAILED DESCRIPTION

[0049] The accompanying drawings are for illustrative purposes only and are not to be construed as limiting the present invention. To better illustrate the following embodiments, some components in the accompanying drawings may be omitted, enlarged, or reduced in size, and do not represent actual product dimensions. Those skilled in the art will appreciate that some well-known structures and their descriptions may be omitted from the accompanying drawings.

[0050] In order to explain the application of the invention technology more clearly and easily, the present invention mainly provides embodiments by taking AlGaN and InGaN matrix semiconductors as examples, which does not mean that other Group III nitride semiconductor materials are not included.

[0051] Example 1

[0052] like Figure 1 As shown, this embodiment discloses a method for growing a thin SiN x The epitaxial structure of the device is as follows from bottom to top: a c-plane sapphire substrate layer 101; a uid-AlN buffer layer that also serves as an interface lower layer 102 with a thickness of 400 nm; a uid-AlGaN interface transition layer 103 with a thickness of 10 nm, where the Al content is reduced from 100% to 49%; an interface upper layer 200 consisting of a first interface upper layer 104 and a second interface upper layer 105; and a uid-AlGaN buffer layer 102 with a thickness of 400 nm. 0.49 Ga 0.51 N is used as the first interface upper layer 104, which is a channel layer with a thickness of 70 nm; uid-Al 0.56 Ga 0.44 N is used as the second interface upper layer 105, which is a barrier layer with a thickness of 15 nm; SiN x The in-situ passivation layer 106 has a thickness of 1 nm; the anode contact electrode 107 and the cathode contact electrode 108 are both Ti / Al / Ni / Au metal stacks, and the thickness of each metal layer is 15 / 80 / 20 / 60 nm respectively.

[0053] In the device structure disclosed in this embodiment, the SiN x The value of x in the in-situ passivation layer is 0.5-1.5; the grown III-nitride epitaxial layers are all

[0001] oriented, so there is a strong polarization effect in each nitride epitaxial layer, including spontaneous polarization and piezoelectric polarization. Since the thickness of the uid-AlN layer below the interface is 400 nm, the stress of the sapphire substrate has been relaxed in this layer, and only spontaneous polarization exists. The graded layer can make the uid-AlN layer above the interface 0.49 Ga 0.51 N maintains a relatively low relaxivity, thus 0.49 Ga 0.51 N / uid-AlN interface produces more polarized negative charges. 0.56 Ga 0.44 N / uid-Al 0.49 Ga 0.51 The N interface will produce polarized positive charges, which should induce the formation of 2DEG. However, 0.49 Ga 0.51N / uid-AlN interface and uid-Al 0.56 Ga 0.44 The polarized negative charge on the N surface will raise the energy band of the heterojunction as a whole, thereby depleting the 2DEG and making the uid-Al 0.49 Ga 0.51 The N-channel maintains high resistance in the dark state, meaning the device has a low dark current. Under illumination, photogenerated carriers generated in the upper layer of the double-layer interface are separated to the surface and interface by the polarization electric field, shielding the negatively polarized charges on the surface and interface, thereby restoring the device channel to a low resistance state, meaning the device has a high photocurrent.

[0054] Since the active layer involved in absorption in the device of this embodiment is located on the surface, the photogenerated carriers are easily affected by the surface state during the transport process, thereby affecting the performance of the device.

[0055] Therefore, based on the working principle of the device, this embodiment in situ grows a thin SiN x Passivation layer, which can effectively reduce surface defects and thus significantly improve device performance. It is worth mentioning that thanks to SiN x The thickness of the layer is only 1 nm, so the ohmic contact electrode Ti / Al / Ni / Au can be deposited directly on the surface of the passivation layer without pre-etching the SiN layer under the metal. x layer.

[0056] In addition, the ungrown SiN x The same structure device with in-situ passivation layer was used as a control, and relevant performance tests were performed on both non-passivated (W / O) and passivated (W) devices.

[0057] Figure 2 The current decay curves of the unpassivated (W / O) and passivated (W) devices after light is removed are as follows: the wavelength and intensity of the light are 260 nm and 700 μW / cm 2 It can be seen that the unpassivated device exhibits a severe PPC effect, with the current only decaying by one order of magnitude after 20 s; while the passivated device decays by more than four orders of magnitude, which indicates that the SiN x The passivation layer effectively reduces surface defects and promotes the recombination of photogenerated carriers after the light is removed, thus significantly alleviating PPC.

[0058] Figure 3 (a) and Figure 3(b) Reflects the cyclic response of the unpassivated (W / O) and passivated (W) devices under different light intensities, where the illumination on / off time in a single cycle is 20 / 20 s. The test results show that in each cycle, the photocurrent continues to increase with the increase of the on-time. After the illumination is turned on, the continuous increase in photocurrent is due to the continuous capture of holes by defects under weak light. Therefore, the relatively small increase in photocurrent reflects that the passivated device has a lower concentration of defects. In addition, under various light intensities, the passivated device shows excellent time-dependent stability of the photocurrent, while the current of the unpassivated device not only shows a significant periodic increase, but also fluctuates, which is related to the higher surface defect concentration of the unpassivated device.

[0059] Figure 4 is the standard deviation of dark current of unpassivated (W / O) and passivated (W) devices at different locations on the chip. At each voltage, the standard deviation of dark current of the passivated device is much smaller than that before passivation, which shows that passivation improves the uniformity of dark current at different locations on the chip. Because the surface defect concentration at different locations on the chip is different before passivation, the dark current values ​​of the devices at the corresponding locations are also quite different. By preparing SiN x With the in-situ passivation layer, surface defects at all locations on the chip are suppressed, and the dark current values ​​of devices at different locations tend to be consistent, which is beneficial to improving the utilization rate of on-chip devices.

[0060] Example 2

[0061] like Figure 1 As shown, this embodiment discloses a method for growing a thin SiN x In-situ passivation layer uid-InGaN-based double-layer interface upper layer heterojunction photodetector. The epitaxial structure of the device is, from bottom to top, a c-plane sapphire substrate layer 201; a uid-GaN buffer layer that also serves as an interface lower layer 102 with a thickness of 3 μm; a uid-InGaN interface transition layer 103 with an In content increasing from 0% to 20% with a thickness of 10 nm; an interface upper layer 200 consisting of a first interface upper layer 104 and a second interface upper layer 105; a uid-InGaN buffer layer 102 with a thickness of 3 μm; a uid-InGaN interface transition layer 103 with an In content increasing from 0% to 20% with a thickness of 10 nm; a uid-InGaN interface upper layer 200 consisting of a first interface upper layer 104 and a second interface upper layer 10 0.2 Ga 0.8 N is used as the first interface upper layer 104, which is a channel layer with a thickness of 80 nm; uid-GaN is used as the second interface upper layer 105, which is a barrier layer with a thickness of 15 nm; SiN x The in-situ passivation layer 206 has a thickness of 1 nm. The anode contact electrode 107 and the cathode contact electrode 108 are both Ti / Al / Ni / Au metal stacks, and the thickness of each metal layer is 15 / 80 / 20 / 60 nm respectively.

[0062] In the device structure disclosed in this embodiment, the SiN xThe value of x in the in-situ passivation layer is 0.5-1.5; the grown III-nitride epitaxial layers are all

[0001] oriented, so there is a strong polarization effect in each nitride epitaxial layer, including spontaneous polarization and piezoelectric polarization. Since the thickness of the lower interface uid-GaN layer is 3 μm, the stress of the sapphire substrate has been relaxed in this layer, and only spontaneous polarization exists. The graded layer can make the upper interface uid-In 0.2 Ga 0.8 N maintains a relatively low relaxation, thus 0.2 Ga 0.8 The N / uid-GaN interface generates more polarized negative charges. Similarly, the channel and barrier layers (uid-GaN / uid-In) in the upper layer of the interface 0.2 Ga 0.8 N) will produce polarized positive charges, which should induce the formation of 2DEG. However, 0.2 Ga 0.8 The polarized negative charge at the N / uid-GaN interface and the uid-GaN surface will raise the energy band of the heterojunction as a whole, thereby depleting the 2DEG and making the uid-In 0.2 Ga 0.8 The N-channel maintains high resistance in the dark state, meaning the device has a low dark current. Under illumination, photogenerated carriers generated in the upper layer of the double interface are separated to the surface and interface by the polarization electric field, shielding the negatively polarized charges on the surface and interface, thereby restoring the device channel to a low resistance state, meaning the device has a high photocurrent.

[0063] Since the active layer involved in absorption in the device of this embodiment is located on the surface, the photogenerated carriers are easily affected by the surface state during the transport process, thereby affecting the performance of the device.

[0064] Therefore, based on the working principle of the device, this embodiment in situ grows a thin SiN x Passivation layer, which can effectively reduce surface defects and thus significantly improve device performance. It is worth mentioning that thanks to SiN x The thickness of the layer is only 1 nm, so the ohmic contact electrode Ti / Al / Ni / Au can be deposited directly on the surface of the passivation layer without pre-etching the SiN layer under the metal. x layer.

[0065] Example 3

[0066] like Figure 5 As shown, this embodiment discloses a method for growing a thin SiN xn-AlGaN-based single-layer interface upper heterojunction photodetector with in-situ passivation layer. The epitaxial structure of the device is, from bottom to top, a c-plane sapphire substrate layer 101; a uid-AlN buffer layer that also serves as the interface lower layer 102 with a thickness of 400 nm; an Al2O3 uniformly doped with Si for n-type 0.49 Ga 0.51 N is used as the upper interface layer 200, with a thickness of 80 nm and a doping concentration of 1×10 18 cm -3 ;SiN x The in-situ passivation layer 106 has a thickness of 1 nm; the anode contact electrode 107 and the cathode contact electrode 108 are both Ti / Al / Ni / Au metal stacks, and the thickness of each metal layer is 15 / 80 / 20 / 60 nm respectively.

[0067] In the device structure disclosed in this embodiment, the SiN x The x value in the in-situ passivation layer ranges from 0.5 to 1.5. The resulting III-nitride epitaxial layers all have a

[0001] orientation, resulting in strong polarization effects within each nitride epitaxial layer, including spontaneous and piezoelectric polarization. Since the 400 nm thick uid-AlN layer below the interface has already relaxed the stress of the sapphire substrate, only spontaneous polarization exists. The 80 nm thick upper interface layer experiences greater compressive stress from the AlN layer below the interface, resulting in lower relaxation and spontaneous polarization and piezoelectric polarization in opposite directions. Consequently, negative polarization charges are generated at the interface between the upper and lower layers. In the dark state, this negative polarization charge raises the energy band of the heterojunction, depleting electrons in the upper interface layer. Under illumination, photogenerated electron-hole pairs are generated in the upper interface layer. The photogenerated electrons drift toward the surface under the action of the polarization electric field, participating in electrical conduction. The photogenerated holes are transported toward the interface, shielding the negative polarization charge and further enhancing the conductivity of the upper interface layer.

[0068] Since the active layer involved in absorption in the device of this embodiment is located on the surface, the photogenerated carriers are easily affected by the surface state during the transport process, thereby affecting the performance of the device.

[0069] Therefore, based on the working principle of the device, this embodiment in situ grows a thin SiN x Passivation layer, which can effectively reduce surface defects and thus significantly improve device performance. It is worth mentioning that thanks to SiN x The thickness of the layer is only 1 nm, so the ohmic contact electrode Ti / Al / Ni / Au can be deposited directly on the surface of the passivation layer without pre-etching the SiN layer under the metal. x layer.

[0070] Example 4

[0071] like Figure 6 As shown, this embodiment discloses a method for growing a thin SiN x In-situ passivation layer n-AlGaN-based double-layer interface upper layer heterojunction photodetector. The epitaxial structure of the device is, from bottom to top, a c-plane sapphire substrate layer 101; a uid-AlN buffer layer that also serves as the interface lower layer 102, with a thickness of 400 nm; and an interface upper layer 200 composed of a first interface upper layer 104 and a second interface upper layer 105. The uid-AlGaN with an Al component of 49% is the first interface upper layer 104, and the epitaxial layer with the same component and uniformly doped with Si for n-type is the second interface upper layer 105, with thicknesses of 10 nm and 80 nm, respectively, with an n-type doping concentration of 1×10 18 cm -3 ;SiN x The in-situ passivation layer 106 has a thickness of 1 nm; the anode contact electrode 107 and the cathode contact electrode 108 are both Ti / Al / Ni / Au metal stacks, and the thickness of each metal layer is 15 / 80 / 20 / 60 nm respectively.

[0072] In the device structure disclosed in this embodiment, the SiN x The x value in the in-situ passivation layer ranges from 0.5 to 1.5. The III-nitride epitaxial layers are all grown in a

[0001] orientation, resulting in strong polarization effects (including spontaneous and piezoelectric polarization) within each nitride epitaxial layer. Since the 400 nm thick uid-AlN layer below the interface has already relaxed the stress of the sapphire substrate, only spontaneous polarization exists. The upper interface layer, with the same composition and a total thickness of 90 nm, experiences greater compressive stress from the AlN layer below the interface, resulting in lower relaxation and spontaneous polarization with opposite piezoelectric polarization. Consequently, negative polarization charges are generated at the interface between the upper and lower layers. In the dark state, these negative polarization charges raise the energy band of the heterojunction, depleting electrons in the upper interface layer. Under illumination, photogenerated electron-hole pairs are generated in the upper interface layer. Under the action of the polarized electric field, the photogenerated electrons drift toward the surface and participate in electrical conduction. Photogenerated holes are transported toward the interface to shield the polarized negative charge, further enhancing the conductivity of the upper interface layer. It should be noted that the upper interface layer of this embodiment also includes an unintentionally doped layer with the same composition as the n-type layer. This layer is primarily intended to reduce the recombination of photogenerated holes caused by interface defects, thereby further promoting the recovery of the conductivity of the upper interface layer under illumination.

[0073] Since the active layer involved in absorption in the device of this embodiment is located on the surface, the photogenerated carriers are easily affected by the surface state during the transport process, thereby affecting the performance of the device.

[0074] Therefore, based on the working principle of the device, this embodiment in situ grows a thin SiN xPassivation layer, which can effectively reduce surface defects and thus significantly improve device performance. It is worth mentioning that thanks to SiN x The thickness of the layer is only 1 nm, so the ohmic contact electrode Ti / Al / Ni / Au can be deposited directly on the surface of the passivation layer without pre-etching the SiN layer under the metal. x layer.

[0075] Example 5

[0076] like Figure 5 As shown, this embodiment discloses a method for growing a thin SiN x In-situ passivation layer uid-InGaN-based single-layer interface upper heterojunction photodetector. The epitaxial structure of the device is from bottom to top: C-plane sapphire substrate layer 101; uid-GaN buffer layer also serves as the interface lower layer 102, with a thickness of 3 μm; uid-In 0.2 Ga 0.8 N is used as the upper interface layer 200 with a thickness of 120 nm; SiN x The in-situ passivation layer 106 has a thickness of 1 nm; the anode contact electrode 107 and the cathode contact electrode 108 are both Ti / Al / Ni / Au metal stacks, and the thickness of each metal layer is 15 / 80 / 20 / 60 nm respectively.

[0077] In the device structure disclosed in this embodiment, the SiN x The x value in the in-situ passivation layer ranges from 0.5 to 1.5. The III-nitride epitaxial layers are all grown in a

[0001] orientation, resulting in strong polarization effects in each nitride epitaxial layer, including spontaneous and piezoelectric polarization. Since the uid-GaN layer below the interface is 3 μm thick, it has already relaxed the stress of the sapphire substrate and exhibits only spontaneous polarization. The upper interface layer, 120 nm thick, is subject to greater compressive stress from the GaN layer below the interface, resulting in lower relaxation and exhibiting spontaneous polarization and piezoelectric polarization in opposite directions. Consequently, negative polarization charges are generated at the interface between the upper and lower layers. In the dark state, these negative polarization charges raise the energy band of the heterojunction, depleting electrons in the upper interface layer. Under illumination, photogenerated electron-hole pairs are generated in the upper interface layer. The photogenerated electrons drift toward the surface under the action of the polarization electric field, participating in electrical conduction. Photogenerated holes are transported toward the interface, shielding the negative polarization charges and further enhancing the conductivity of the upper interface layer.

[0078] Since the active layer involved in absorption in the device of this embodiment is located on the surface, the photogenerated carriers are easily affected by the surface state during the transport process, thereby affecting the performance of the device.

[0079] Therefore, based on the working principle of the device, this embodiment in situ grows a thin SiN xPassivation layer, which can effectively reduce surface defects and thus significantly improve device performance. It is worth mentioning that thanks to SiN x The thickness of the layer is only 1 nm, so the ohmic contact electrode Ti / Al / Ni / Au can be deposited directly on the surface of the passivation layer without pre-etching the SiN layer under the metal. x layer.

[0080] Example 6

[0081] like Figure 7 As shown, this embodiment discloses a method for growing a thin SiN x In-situ passivation layer uid-InGaN-based single-layer interface upper heterojunction photodetector. The epitaxial structure of the device is, from bottom to top, a c-plane sapphire substrate layer 101; a uid-GaN buffer layer that also serves as an interface lower layer 102 with a thickness of 3 μm; a uid-InGaN interface transition layer 103 with an In content increased from 0% to 20% and a thickness of 30 nm; and a uid-InGaN interface transition layer 104 with a thickness of 30 nm. 0.2 Ga 0.8 N is used as the upper interface layer 200 with a thickness of 120 nm; SiN x The in-situ passivation layer 106 has a thickness of 1 nm; the anode contact electrode 107 and the cathode contact electrode 108 are both Ti / Al / Ni / Au metal stacks, and the thickness of each metal layer is 15 / 80 / 20 / 60 nm respectively.

[0082] In the device structure disclosed in this embodiment, the SiN x The value of x in the in-situ passivation layer is 0.5-1.5; the III-nitride epitaxial layers are all grown in the

[0001] orientation, so there is a strong polarization effect in each nitride epitaxial layer, including spontaneous polarization and piezoelectric polarization. Since the thickness of the lower interface uid-GaN layer is 3 μm, the stress of the sapphire substrate has been relaxed in this layer, and only spontaneous polarization exists. The graded layer can make the upper interface uid-In 0.2 Ga 0.8 N maintains a relatively low relaxation and is subjected to a large compressive stress, thereby 0.2 Ga 0.8 The N / uid-GaN interface generates a large amount of polarized negative charge. In the dark state, this polarized negative charge raises the energy band of the heterojunction, depleting the electrons in the upper layer of the interface. Under illumination, photogenerated electron-hole pairs are generated in the upper layer of the interface. Under the action of the polarized electric field, the photogenerated electrons drift toward the surface and participate in conductivity. The photogenerated holes are transported to the interface to shield the polarized negative charge, further improving the conductivity of the upper layer of the interface.

[0083] Since the active layer participating in absorption in the device of this embodiment is located on the surface, the photo-generated carriers are easily affected by surface states during the transport process, thereby affecting the performance of the device.

[0084] Therefore, based on the working principle of the device, a thin SiN passivation layer is in-situ grown on the surface of the device in this embodiment. This layer can effectively reduce surface defects, thus significantly improving the device performance. It is worth mentioning that due to the thickness of the SiN layer being only 1 nm, the ohmic contact electrodes Ti / Al / Ni / Au can be directly deposited on the surface of the passivation layer without pre-etching the SiN layer under the metal. x 层的厚度仅为1 nm,所以欧姆接触电极Ti / Al / Ni / Au可直接沉积在钝化层表面,不用预先刻蚀金属下方的SiN x 层的厚度仅为1 nm,所以欧姆接触电极Ti / Al / Ni / Au可直接沉积在钝化层表面,不用预先刻蚀金属下方的SiN x 层。

[0085] Example 7

[0086] This embodiment provides a preparation method for the epitaxial structure of a heterojunction photodetector, which is characterized by including the following steps:

[0087] S1. Grow an interface lower layer, an interface transition layer, and an interface upper layer on a substrate by metalorganic chemical vapor deposition;

[0088] S2. Close the metal source, set the NH3 flow rate F1 and the Si source flow rate F2 to specified values, keep the carrier gas atmosphere as hydrogen, and set the chamber temperature to T1 until the flow rate and temperature of the flow meter are stable;

[0089] S3. Introduce NH3 and the Si source into the epitaxial chamber to prepare an in-situ SiN passivation layer with a growth time of t1 and a corresponding thickness of d1; x 钝化层,生长时间为t1,对应厚度为d1;

[0090] S4. After the growth is completed, close the Si source, keep the NH3 flow rate unchanged at the same time, and perform annealing treatment on the SiNx passivation layer while cooling down.

[0091] Furthermore, the NH3 flow rate F1 satisfies: 0.04 mol / min < F1 < 0.37 mol / min;

[0092] The Si source is SiH4, and the Si source flow rate F2 satisfies: 0.02 μmol / min < F2 < 0.36 μmol / min, and the flow rate ratio of the group V source to the group IV source varies within the range of 1 to 5 -10 7 范围内变化。

[0093] ]Furthermore, the growth time t1 satisfies: 455 s

Claims

1. A method for preparing a heterojunction photodetector epitaxial structure, characterized in that: The following steps are involved: S1. growing an interface lower layer, an interface transition layer, and an interface upper layer on a substrate by metal organic chemical vapor deposition; S2. Turn off the metal source, set the NH3 flow rate F1 and the Si source flow rate F2 to the specified values, keep the carrier gas atmosphere as hydrogen, set the cavity temperature to T1, and wait until the flow meter flow and temperature remain stable; S3, NH3, Si source into the epitaxial cavity, prepare in-situ SiN x Passivation layer, growth time is t1, corresponding thickness is d1; S4. After the growth is completed, turn off the Si source and keep the NH3 flow rate unchanged. x The passivation layer is annealed; The NH3 flow rate F1 satisfies: 0.04 mol / min <F1<0.37 mol / min; The Si source is SiH4, and the flow rate F2 of the Si source satisfies: 0.02 μmol / min < F2 < 0.36 μmol / min, and the flow rate ratio of the group V source to the group IV source varies within the range of 10 5 -10 7 ; The SiN x The value of x in the in-situ passivation layer is 0.5-1.

5.

2. The method for preparing a heterojunction photodetector epitaxial structure according to claim 1, wherein: The growth time t1 satisfies: 455 s < t1 < 7000 s, and the corresponding thickness d1 satisfies: 1 nm <d1<6 nm。 3. A heterojunction photodetector epitaxial structure prepared by the preparation method of claim 1, characterized in that: From bottom to top, it includes substrate, lower interface layer, interface transition layer, upper interface layer, SiN x In-situ passivation layer and ohmic contact electrode; The anode and cathode of the ohmic contact electrode are deposited on SiN x In-situ passivation layer surface, Or the anode and cathode of the ohmic contact electrode are deposited on the SiN x The upper surface of the interface of the in-situ passivation layer.

4. The heterojunction photodetector epitaxial structure according to claim 3, wherein: The lower interface layer, the interface transition layer and the upper interface layer of the detector epitaxial structure are all made of Group III nitride semiconductor materials, and the lower interface layer, the interface transition layer and the upper interface layer form a heterojunction with each other.

5. The heterojunction photodetector epitaxial structure according to claim 3, characterized in that: The interface transition layer is a group III nitride layer whose band gap gradually changes from the lower interface layer to the upper interface layer by adjusting its composition, and its thickness ranges from 0 to 50 nm. When the thickness is 0, a sudden heterojunction is formed between the lower interface layer and the upper interface layer; when the thickness is not 0, a gradual heterojunction is formed.

6. The heterojunction photodetector epitaxial structure according to claim 3, characterized in that: The interface upper layer is a single-layer interface upper layer, and the interface upper layer is an n-type doping layer.

7. The heterojunction photodetector epitaxial structure according to claim 3, wherein: The interface upper layer is a double-layer interface upper layer, and the interface upper layer is composed of a non-doped barrier layer with a relatively wide bandgap width and a channel layer with a relatively narrow bandgap width.

8. The heterojunction photodetector epitaxial structure according to claim 6, wherein: The doping methods of the n-type doping layer include uniform doping, alternating doping and linear gradient doping. The equivalent electron concentration in the n-type doping layer ranges from 3×10 17 cm -3 to 8×10 18 cm -3 .

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