Methods for measuring electron drift rates of group III nitride heterostructures in multi-physics environments

Abstract

This invention discloses a method for measuring the electron drift velocity of a group III nitride heterostructure in multiple physical environments, belonging to the field of semiconductor technology. The method first forms an H-shaped channel in the group III nitride heterostructure and symmetrically prepares rectangular test electrodes on both sides of the channel to obtain the sample to be tested. Then, the sample is placed in one or more physical environments and connected to a test circuit. A voltage is applied to the test electrodes, and the current flowing through the H-shaped channel is measured to obtain the electron drift velocity v. The variation of the electron drift velocity v with the electric field E under external physical environments such as temperature field, light field, magnetic field, and different gas atmospheres is obtained. Measuring the 2DEG electron drift velocity in a group III nitride heterostructure under different physical fields is of great significance for comprehensively evaluating and optimizing the performance of group III nitride devices, providing guidance for device design and optimization.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically relating to a method for measuring the electron drift rate of a group III nitride heterostructure in a multi-physical environment. It realizes the measurement of electron drift rate in external physical environments such as temperature field, light field, magnetic field, and different gas atmospheres, and studies the relationship between electron drift rate and external field. Background Technology

[0002] Currently, with the continuous development of semiconductor devices, the size of nitride microwave power devices has reached the sub-micrometer level. The typical electric field strength in the active channel of these devices far exceeds the electric field value to which Ohm's law applies. Therefore, the performance of the devices is no longer solely determined by the low-field transport characteristics of charge carriers in the material, but is increasingly influenced by the hot electron transport behavior under high electric fields. To better understand and improve device performance, it is crucial to study the carrier transport characteristics of nitride materials and electronic devices under high electric fields.

[0003] Compared to Si-based semiconductors, group III nitrides (except InN) possess large band gaps, high valley separation energies, large polar optical phonon (LO) energies, better thermal conductivity, and lower dielectric constants. These properties ensure that group III nitrides exhibit superior high-field transport properties compared to Si-based systems. Taking GaN as an example, its most important high-field electron transport characteristics compared to Si include:

[0004] 1) Due to the high energy of longitudinal optical (LO) phonons in GaN (approximately 92 meV, compared to approximately 30 meV in silicon), charge carriers can be sufficiently accelerated before reaching the phonon scattering threshold. Research data shows that the maximum carrier mobility in GaN epitaxial layers can reach 3 × 10⁻⁶. 7 The speed is on the order of cm / s, compared to silicon (approximately 1×10⁻⁶). 7 (cm / s) has a magnitude advantage;

[0005] 2) Under strong field conditions, the critical field strength required for the GaN system to achieve the maximum carrier migration rate exceeds 200 kV / cm, which is nearly an order of magnitude higher than the threshold field strength of silicon materials (about 30 kV / cm). This characteristic is due to the wide bandgap characteristics and large valley spacing of the material itself.

[0006] 3) Thanks to its wide bandgap characteristics and excellent thermal conductivity, GaN-based devices are significantly more stable than silicon-based devices in high-temperature operating environments, which provides a physical basis for the thermal management of power electronic devices.

[0007] Based on the above advantages, the improvement in the saturated electron drift velocity in GaN-based HEMT electronic devices has several positive impacts on device performance. First, it significantly increases the device's operating frequency, enabling GaN HEMTs to perform exceptionally well in high-frequency applications, such as 5G communication and radar systems, meeting high-frequency requirements and achieving high-speed data transmission. Second, this improvement also enhances the device's power characteristics, increasing the amount of charge passing through the device per unit time, thereby increasing output current and output power, while simultaneously reducing on-resistance, decreasing power loss, and improving power conversion efficiency.

[0008] Furthermore, the increased saturated electron drift velocity accelerates the switching speed of the device, shortening the electron transport time in the channel. This is crucial for digital and mixed-signal circuits requiring rapid switching, improving overall system performance and response speed. Simultaneously, it helps improve the device's thermal performance, reducing heat loss and increasing thermal conductivity. This is essential for thermal management of high-power devices, enhancing reliability and lifespan. Finally, this improvement also enhances device reliability, reducing thermionic effects and current collapse, thus improving device stability and lifespan.

[0009] Therefore, a testing method is needed to study the electron drift rate of 2DEG in group III nitride heterostructures, and to simultaneously introduce different external physical environments to study the electron transport properties. Summary of the Invention

[0010] To achieve accurate measurement of the electron drift rate of the 2DEG layer in group III nitride heterostructures, and to study the scattering mechanism of electron transport by introducing an external field, this invention proposes a method for measuring the electron drift rate of the 2DEG in heterostructures. The circuit is connected to a hot stage to realize the measurement of the electron drift rate under temperature field, light field, etc.

[0011] The present invention adopts the following technical solution:

[0012] A method for measuring the electron drift rate of a group III nitride heterostructure in a multi-physics environment includes the following steps:

[0013] 1) Form an H-shaped channel by creating a heterostructure of group III nitrides, and symmetrically fabricate rectangular test electrodes on both sides of the channel to obtain the sample to be tested. Then, the current I through the H-shaped channel can be obtained according to equation (1):

[0014] I=nqWv (1)

[0015] Where v is the electron drift velocity; W is the channel width; n is the surface density of the heterostructure 2DEG, which can be measured by the van der Berg method; and q is the elementary charge.

[0016] The electric field strength E in the channel can be estimated using an approximate formula:

[0017]

[0018] See Figure 2 W and L are the width and length of the channel region, respectively; T is the length of the test electrode in the direction perpendicular to the channel; L′ is the length of the injection region along the current direction; and V is the voltage difference between the two test electrodes.

[0019] 2) Place the sample to be tested prepared in step 1) in one or more physical environments and connect it to the test circuit. Apply voltage to the test electrode and measure the current through the H-shaped channel. Obtain the electron drift rate v according to equation (1) and obtain the relationship between the electron drift rate v and the electric field E by combining equation (2).

[0020] Preferably, the width W of the H-shaped channel in step 1) is 1 to 10 μm, for example, about 2 μm. To make the electric field strength in the channel more accurate, W should be much smaller than L, and L should be much smaller than L'.

[0021] Furthermore, the above measurement method can be used to prepare the H-shaped channel and test electrode according to the following steps:

[0022] 1a) Clean the surface of the group III nitride heterostructure and then grow a hard mask on it;

[0023] 1b) The pattern of the H-shaped channel is transferred onto a hard mask by photolithography, and then the group III nitride is etched under the protection of the hard mask to obtain the heterostructure of the H-shaped channel;

[0024] 1c) Remove the hard mask, coat with negative photoresist and perform photolithography to obtain the pattern of the test electrode, then deposit metal and anneal to form the test electrode with ohmic contact.

[0025] Preferably, in step 1a), the surface oxide layer of the heterogeneous structure is first removed by inorganic cleaning, and then organic cleaning is performed to remove organic contaminants.

[0026] Preferably, in step 1a), silicon dioxide (SiO2) or silicon nitride (SiN) is grown by plasma-enhanced chemical vapor deposition. x () as a hard mask.

[0027] Preferably, in step 1c), metal Ti / Al / Ni / Au is deposited by electron beam evaporation, followed by organic cleaning to remove the photoresist, and then rapid thermal annealing to form an ohmic contact.

[0028] Preferably, see Figure 3The test circuit described in step 2) includes a short-pulse high-voltage power supply, a first attenuator, an oscilloscope, a second attenuator, and a resistor. One test electrode of the sample under test is connected to the short-pulse high-voltage power supply and simultaneously connected to the Ch1 channel of the oscilloscope through the first attenuator. The other test electrode is connected to the Ch2 channel of the oscilloscope through the second attenuator and simultaneously grounded through the resistor. The voltage difference shown by Ch1-Ch2 on the oscilloscope is the voltage V applied to the sample under test, and the voltage shown by Ch2 divided by the resistance value is the current I passing through the sample under test.

[0029] The physical environment mentioned in step 2) can be a temperature field, a light field, a magnetic field, or different gas atmospheres, etc. The temperature field is controlled by placing the sample to be tested on a hot stage, the light field is achieved by applying light of different intensities to the sample to be tested, the magnetic field can be obtained by adding a magnet to the sample to be tested, and the gas atmosphere is obtained by introducing gas into the space where the sample to be tested is located.

[0030] In some embodiments of the present invention, using, for example Figure 4 The aforementioned hot stage device realizes temperature, light, and magnetic fields. It includes a housing, an electric heating stage, a cover plate, and probes. The electric heating stage is located inside the housing, and the sample to be tested is placed on the electric heating stage. There are two probes, which are respectively connected to the two test electrodes of the sample to be tested, and then connected to an external electric field through connectors. The cover plate covers the housing to form a sealed internal space. The outer shell has an air inlet and an air outlet for airflow, so as to realize the measurement of the relationship between electron drift rate and external electric field under different temperatures and atmospheres. The cover plate has a light-transmitting window at the position directly opposite the electric heating stage, so as to measure electron drift rate under in-situ light conditions and study electron transport properties.

[0031] The beneficial effects of this invention are:

[0032] Measuring the electron drift velocity of 2DEGs in group III nitride heterostructures under different physical environments is of great significance. In a temperature field, measuring the electron drift velocity helps assess the thermal stability and performance changes of the device, providing a basis for optimizing thermal management design. Increased temperature may lead to increased electron scattering, thereby reducing the drift velocity and affecting the high-frequency performance and switching speed of the device. In an optical field, measuring the electron drift velocity allows for the study of the photoelectric effect of the device, providing important information for the development of optoelectronic devices. Under the influence of an optical field, the generation and recombination of photogenerated carriers affect the electron concentration and drift velocity of the 2DEG, thus affecting the photoelectric response characteristics of the device. Furthermore, measuring the electron drift velocity in other physical environments, such as electric and magnetic fields, also helps to gain a deeper understanding of the electrical and magnetic properties of the device, providing guidance for device design and optimization. In summary, measuring the 2DEG electron drift velocity in different physical environments plays a crucial role in comprehensively evaluating and optimizing the performance of GaN-based HEMT devices. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the H-shaped channel and test electrode of the group III nitride heterostructure sample after processing in the example.

[0034] Figure 2 This is a top view and parameter description of the group III nitride heterostructure sample in the examples.

[0035] Figure 3 This is a schematic diagram showing the test sample connected to the measurement circuit in an embodiment.

[0036] Figure 4 This is a schematic diagram of the multi-physical environment in-situ measurement structure built by combining the sample with a hot stage in the embodiment.

[0037] Figure 5 The figure shows the curve of electron drift velocity v of GaN heterostructure as a function of applied electric field E, as measured in the example.

[0038] Figure 6 The figure shows the curves of electron drift velocity v of GaN heterostructure measured in the example as a function of applied electric field E at different temperatures.

[0039] In the above figures, the meanings of the reference numerals are as follows:

[0040] 1. Test electrode; 2. Sample of group III nitride heterostructure fabricated into H-channel; 3. Short pulse high voltage power supply; 4. Position of sample in circuit diagram; 5. 50 ohm resistor; 6. Attenuator; 7. Oscilloscope; 8. Air inlet; 9. Air outlet; 10. Test sample; 11. Electric heating stage; 12. Probe; 13. Heated stage cover; 14. Transparent window. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0042] The basic idea of ​​this invention is to process a group III nitride heterostructure sample into an H-shaped channel using a specific process. This test sample structure ensures that potential electric field spikes near the electrodes do not affect the channel electric field uniformity, reduces the influence of contact resistance, and controls the electrode injection effect of charge carriers. Using the property v = I / nWq, the electron drift velocity is obtained, and the electric field strength of the H-shaped channel is calculated to derive the relationship between the electron drift velocity and the applied electric field. By combining the sample with a hot stage and constructing a test circuit, the electron transport properties can be studied in situ in multiple physical environments (temperature field, light field).

[0043] This embodiment uses a GaN heterostructure as an example. The heterostructure sample is grown in the following manner:

[0044] 1) A 200 nm AlN nucleation layer was epitaxially grown by MOCVD on a SiC substrate;

[0045] 2) After the AlN nucleation layer was grown, a 0.42 μm GaN buffer layer was grown by MOCVD epitaxy;

[0046] 3) Further MOCVD epitaxy of a 1nm AlN spacer layer;

[0047] 4) Further MOCVD epitaxy of 15.4nm Al x Ga 1-x For N-type barrier layers, x values ​​of 0.25–0.30 are preferred.

[0048] 5) Finally, a 1.5nm GaN cap layer is epitaxially grown using MOCVD;

[0049] The heterostructure sample used for electron drift rate testing must meet the condition that the sample forms a two-dimensional electron gas (2DEG).

[0050] To form an H-shaped channel in a heterostructured sample that can be tested, the following process steps are required:

[0051] 1) Cleaning: The surface oxide layer of the heterogeneous structure is removed by inorganic cleaning, followed by organic cleaning to remove organic contaminants;

[0052] The inorganic cleaning can be done by soaking in hydrochloric acid for 5 minutes, and the organic cleaning can be done by sonicating acetone, ethanol, and deionized water for 5 minutes each.

[0053] 2) SiO2 was grown on the heterostructure using plasma-enhanced chemical vapor deposition (PECVD) as a mask for etching GaN-based materials;

[0054] The thickness of the grown SiO2 layer is determined based on the GaN thickness and the ICP etching ratio in the next step, so that it can just protect the GaN under the SiO2 layer from being etched. However, if the SiO2 is too thick, it will be detrimental to the integrity of the etched pattern.

[0055] 3) Mesa etching: First, positive photoresist AZ6130 is coated with a thickness of 4μm. Then, photolithography is performed, and SiO2 is etched by ICP to transfer the photolithographic pattern onto the SiO2 layer. After etching, the photoresist is washed away by organic cleaning. Then, using SiO2 as a mask, a second ICP etching is performed to the substrate to form an H-shaped channel. After etching, the remaining SiO2 mask layer is washed away with hydrofluoric acid.

[0056] ICP etching parameters can be: etching gas CH3F, RF power 250W, ICP power 100W.

[0057] 4) Fabrication of test electrodes: A second photolithography is performed using negative photoresist (thickness can be 1.5 μm). Electron beam evaporation is used to deposit metal Ti / Al / Ni / Au (thickness can be 20 / 175 / 50 / 200 nm). The photoresist is stripped using organic cleaning, followed by rapid thermal annealing (annealing at 850℃ for 35 s in a N2 atmosphere) to form an n-type ohmic contact, resulting in the following: Figure 1 The test sample shown.

[0058] like Figure 2 As shown, to prevent the Joule heating generated during sample measurement from affecting the electron drift rate and to increase the electric field in the channel region, the channel width W should be relatively narrow (around 2 μm). According to the definition of current:

[0059] I=nqWv (1)

[0060] We can obtain v = I / nWq, where v is the electron drift velocity, W is the channel width, I is the current through the H-shaped channel, n is the surface density of the heterostructure 2DEG, which can be measured using the van der Berg method, and q is the elementary charge. To calculate the electric field strength in the channel region, strictly speaking, it is necessary to simulate the electric field at the channel. However, for simplicity, the electric field strength E in the channel can be estimated using an approximate formula:

[0061]

[0062] Where V is the voltage difference between the two test electrodes 1 of the sample, T is the length of the test electrode in the direction perpendicular to the channel, L′ is the length of the injection region along the current direction, and L and W are the length and width of the channel region, respectively. Figure 3 In this embodiment, T = 500 μm, L′ = 100 μm, L = 15 μm, and W = 5 μm.

[0063] Figure 3 For the circuit structure diagram, to reduce the Joule heating effect of the device, the power supply connected to the sample is a short-pulse high-voltage power supply 3 with a pulse time of 8ns, a pulse period of 1s, and an adjustable voltage of 0-450V. One of the sample test electrodes 1 is connected to the short-pulse high-voltage power supply 3 through a BNC connector, and simultaneously connected to the Ch1 channel of the oscilloscope 7 through a 40dB attenuator; the other electrode is connected to the Ch2 channel of the oscilloscope 7 through a BNC connector and a 20dB attenuator, and simultaneously grounded through a 50-ohm resistor 5. When the short-pulse high-voltage power supply 3 is turned on, the voltage difference shown by Ch1-Ch2 on the oscilloscope 7 is the voltage V applied to the sample, and I = Ch2 / 50Ω is the current flowing through the sample. By changing the voltage V, the electric field in the channel can be controlled, and the curve of the electron drift velocity v changing with the applied electric field E can be plotted based on v = I / nqW and equation (2). Figure 5As shown, this embodiment measures the relationship between the electron drift velocity of the GaN-based heterostructure 2DEG and the applied external field strength under a high electric field. It can be seen that when the signal frequency generated by the short-pulse high-voltage power supply 3 is 1Hz, the electron drift velocity increases with the increase of the external field. When E>15kV / cm, the electron drift velocity can be considered saturated. Changing the signal frequency generated by the short-pulse high-voltage power supply 3 and conducting tests shows that the electron drift velocity decreases with increasing frequency. Furthermore, when E>15kV / cm, the electron drift velocity decreases further due to the enhanced carrier scattering effect caused by the significant Joule heating effect.

[0064] Figure 4 This is a schematic diagram of a multi-physics environment in-situ measurement structure built by combining the sample with a hot stage. By changing the temperature of the hot stage, the relationship between the electron drift velocity and the applied electric field can be measured at different temperatures. The sample to be tested is placed on the hot stage, and the two test electrodes 1 of the test sample 10 are respectively connected to the two probes 12 corresponding to the electric heating stage 11, and then connected to the probes 12. Figure 3 In the test circuit shown, the sample temperature is changed by a hot stage, and the electron drift rate of the GaN heterostructure at different temperatures is measured, such as... Figure 6 As shown, it can be seen that as the ambient temperature increases, carrier scattering intensifies, and the electron drift velocity decreases under the influence of the electric field.

[0065] By adding a light source to the hot stage, the relationship between electron drift velocity and an applied electric field can be measured under a light field. By sealing the hot stage, leaving only the air inlet 8 and outlet 9 for airflow, and introducing different atmospheres, the relationship between electron drift velocity and an applied electric field can be measured under different temperatures and atmospheres. Furthermore, since the hot stage cover plate 13 has a light-transmitting window 14, electron drift velocity can also be measured under in-situ light conditions to study electron transport properties.

[0066] The specific implementation methods of this technical solution have been described in detail regarding the design objectives, technical means, and implementation effects. It should be noted that the specific examples listed are only used to assist in illustrating the core content of the present invention and do not constitute a limitation on the application scope of the technical solution. Based on the technical principles and design requirements proposed in this invention, any derivative implementation methods, such as adaptive adjustments, equivalent technical substitutions, or optimizations based on this technical solution, are all within the protection scope of this invention.

Claims

1. A method for measuring the electron drift rate of a group III nitride heterostructure in a multi-physics environment, comprising the following steps: 1) Form an H-shaped channel by creating a heterostructure of group III nitrides, and symmetrically prepare rectangular test electrodes on both sides of the channel to obtain the sample to be tested. The current I through the H-shaped channel is then obtained according to equation (1): I=nqWv (1) Where v is the electron drift velocity, W is the channel width, n is the surface density of the heterostructure 2DEG, and q is the elementary charge. The electric field strength E in the channel is estimated according to equation (2): Where W and L are the width and length of the channel region, respectively, and T is the length of the test electrode in the direction perpendicular to the channel. L′ is the length of the injection region along the current direction, and V is the voltage difference between the two test electrodes; 2) Place the sample to be tested prepared in step 1) in one or more physical environments and connect it to the test circuit. Apply voltage to the test electrode and measure the current through the H-shaped channel. Obtain the electron drift rate v according to equation (1) and obtain the relationship between the electron drift rate v and the electric field E by combining equation (2).

2. The measurement method as described in claim 1, characterized in that, Step 1) Prepare the H-shaped channel and test electrode according to the following steps: 1a) Clean the surface of the group III nitride heterostructure and then grow a hard mask on it; 1b) The pattern of the H-shaped channel is transferred onto a hard mask by photolithography, and then the group III nitride is etched under the protection of the hard mask to obtain the heterostructure of the H-shaped channel; 1c) Remove the hard mask, coat with negative photoresist and perform photolithography to obtain the pattern of the test electrode, then deposit metal and anneal to form the test electrode with ohmic contact.

3. The measurement method as described in claim 2, characterized in that, In step 1a), the surface oxide layer of the heterogeneous structure is first removed by inorganic cleaning, and then organic cleaning is performed to remove organic contaminants.

4. The measurement method as described in claim 2, characterized in that, In step 1a), silicon dioxide or silicon nitride is grown using plasma-enhanced chemical vapor deposition as a hard mask.

5. The measurement method as described in claim 2, characterized in that, Step 1c) Deposit metal Ti / Al / Ni / Au by electron beam evaporation, followed by organic cleaning to remove the photoresist, and then rapid thermal annealing to form ohmic contacts.

6. The measurement method as described in claim 1, characterized in that, The width W of the H-shaped channel mentioned in step 1) is 1 to 10 μm.

7. The measurement method as described in claim 1, characterized in that, The test circuit described in step 2) includes a short-pulse high-voltage power supply, a first attenuator, an oscilloscope, a second attenuator, and a resistor. One test electrode of the sample under test is connected to the short-pulse high-voltage power supply and simultaneously connected to channel Ch1 of the oscilloscope through the first attenuator. The other test electrode is connected to channel Ch2 of the oscilloscope through the second attenuator and simultaneously grounded through the resistor. The voltage difference shown by Ch1-Ch2 on the oscilloscope is the voltage V applied to the sample under test, and the voltage shown by Ch2 divided by the resistance value is the current I passing through the sample under test.

8. The measurement method as described in claim 1, characterized in that, The physical environment described in step 2) includes a temperature field, a light field, a magnetic field, and different gas atmospheres. The temperature field is controlled by placing the sample to be tested on a hot stage. The light field is achieved by applying light of different intensities to the sample to be tested. The magnetic field is obtained by applying a magnet to the sample to be tested. The gas atmosphere is obtained by introducing gas into the space where the sample to be tested is located.

9. The measurement method as described in claim 8, characterized in that, Step 2) Place the sample to be tested in the hot stage device, which includes a housing, an electric heating stage, a cover plate, and probes. The electric heating stage is located inside the housing, and the sample to be tested is placed on the electric heating stage. There are two probes, which are respectively connected to the two test electrodes of the sample to be tested, and then connected to an external electric field through connectors. The cover plate covers the housing to form a sealed internal space. The housing has an air inlet and an air outlet for airflow to enter and exit. The cover plate has a light-transmitting window at the position facing the electric heating stage.

10. The measurement method according to any one of claims 1 to 9, characterized in that, The group III nitride heterostructure is a GaN-based heterostructure.

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