Method for measuring electron drift rate of III-nitride heterostructure in multi-physical environment

Abstract

The invention discloses a method for measuring the electron drift rate of a group III nitride heterostructure in a multi-physical environment, and belongs to the technical field of semiconductors. The method comprises the following steps: firstly, forming an H-shaped channel by a group III nitride heterostructure, and symmetrically preparing rectangular test electrodes on two sides of the channel to obtain a sample to be tested; then a sample to be tested is placed in one or more physical environments and connected into a test circuit, voltage is applied to a test electrode, current passing through the H-shaped channel is measured, the electron drift rate v is obtained, and the change relation of the electron drift rate v along with an electric field E in the external physical environments such as a temperature field, a light field, a magnetic field and different gas atmospheres is obtained. Measurement of the 2DEG electron drift rate in the III nitride heterostructure under different physical fields is achieved, the method has important significance in comprehensive evaluation and optimization of the performance of III nitride devices, and guidance is provided for design and optimization of the devices.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology, and particularly relates to a method for measuring the electron drift rate of group III nitride heterostructures in a multi-physical environment, realizing the measurement of the electron drift rate in external physical environments such as temperature fields, light fields, magnetic fields, and different gas atmospheres, and studying the relationship between the electron drift rate and the change of the external field. Background Art

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

[0003] Compared with Si-based semiconductor materials, group III nitride materials have a large bandgap (except for InN), a high valley separation energy, a relatively large polar optical phonon (LO) energy, better thermal conductivity, and a lower dielectric constant. These characteristics ensure that group III nitride materials have better high-field transport properties than the Si-based material system. Taking GaN as an example, compared with Si, its most important electron high-field transport characteristics include:

[0004] 1) Since the longitudinal optical (LO) phonons in GaN materials have a relatively high energy (about 92 meV, about 30 meV for silicon materials), carriers can be sufficiently accelerated before reaching the phonon scattering threshold. Research data shows that the maximum migration rate of carriers in the GaN epitaxial layer can reach the order of 3×10 7 cm / s, which has an order-of-magnitude advantage compared with silicon materials (about 1×10 7 cm / s);

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

[0006] 3) Benefiting from its wide bandgap characteristic and excellent thermal conductivity, GaN-based devices have significantly better stability in high-temperature working environments than Si-based devices, which provides a physical basis for the thermal management of power electronic devices.

[0007] Based on the above advantages, the improvement of the saturated electron drift velocity in GaN-based HEMT electronic devices has several positive impacts on device performance. First, it significantly increases the operating frequency of the device, enabling GaN HEMT to perform excellently in high-frequency applications. For example, in 5G communication and radar systems, it can meet the high-frequency requirements and achieve high-speed data transmission. Second, this improvement also enhances the power characteristics of the device, increasing the amount of charge passed by electrons per unit time, thereby increasing the output current and output power. At the same time, it reduces the on-resistance, decreases the power loss, and improves the power conversion efficiency.

[0008] In addition, the increase in the saturated electron drift velocity speeds up the switching speed of the device, shortening the transmission time of electrons in the channel. This is very important for digital circuits and mixed-signal circuits that require fast switching, and can improve the overall performance and response speed of the system. At the same time, it helps to improve the thermal performance of the device, reduce the thermal loss, and increase the thermal conductivity. This is very important for the thermal management of high-power devices and can improve the reliability and lifespan of the device. Finally, this improvement also enhances the reliability of the device, reduces the hot electron effect and current collapse effect, and improves the stability and service life of the device.

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

[0010] In order to accurately measure the electron drift velocity of the 2DEG layer in group III nitride heterostructures and study the scattering mechanism of electron transport by introducing an external field at the same time, the present invention proposes a method for measuring the electron drift velocity of 2DEG in a heterostructure, and connects the circuit to a hot stage to realize the measurement of the electron drift velocity under a temperature field, a light field, etc.

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

[0012] A method for measuring the electron drift velocity of group III nitride heterostructures in a multi-physical environment, comprising the following steps:

[0013] 1) Form an H-shaped channel in the group III nitride heterostructure, and symmetrically prepare rectangular test electrodes on both sides of the channel to obtain a sample to be measured. Then, the current I passing 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 2DEG in the heterostructure, which can be measured by the Van der Pauw method; q is the elementary charge amount;

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

[0017]

[0018] See Figure 2 , where 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 implantation 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 a certain physical environment or multiple physical environments, connect it to the test circuit, apply a voltage to the test electrodes, measure the current passing through the H-shaped channel, obtain the electron drift velocity v according to formula (1), and combine with formula (2) to obtain the variation relationship of the electron drift velocity v with the electric field E.

[0020] Preferably, in step 1), the width W of the H-shaped channel is 1 - 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 prepare the H-shaped channel and test electrodes 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) Transfer the pattern of the H-shaped channel to the hard mask through photolithography, and then etch the group III nitride under the protection of the hard mask to obtain the heterostructure of the H-shaped channel;

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

[0025] Preferably, in step 1a), first remove the surface oxide layer of the heterostructure through inorganic cleaning, and then perform organic cleaning to remove organic contaminants.

[0026] Preferably, in step 1a), plasma-enhanced chemical vapor deposition is used to grow silicon dioxide (SiO 2 ) or silicon nitride (SiN x ) as the hard mask.

[0027] Preferably, in step 1c), deposit metal Ti / Al / Ni / Au by electron beam evaporation, then perform organic cleaning to strip the photoresist, and then perform rapid thermal annealing to form ohmic contacts.

[0028] Preferably, see Figure 3, in step 2), the test circuit 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 to be tested is connected to the short-pulse high-voltage power supply and is 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 is grounded through the resistor; the voltage difference shown by Ch1 - Ch2 of the oscilloscope is the voltage V applied to the sample to be tested, and the voltage shown by Ch2 divided by the resistance value of the resistor is the current I passing through the sample to be tested.

[0029] The physical environment described in step 2) can be a temperature field, a light field, a magnetic field, or different gas atmospheres, etc. Among them, the temperature field is regulated by placing the sample to be tested on a hot stage, the light field is realized by applying different intensities of light to the sample to be tested, the magnetic field can be obtained by applying 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, the temperature field, the light field, and the magnetic field are realized by using a hot stage device as Figure 4 described. It includes a housing, an electric heating stage, a cover plate, and probes. Among them, 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, and an air inlet and an air outlet are provided on the outer shell for air flow in and out, so that the variation relationship of the electron drift rate with the applied electric field can be measured at different temperatures and atmospheres; a light-transmitting window is provided on the cover plate at a position directly facing the electric heating stage, so that the electron drift rate can be measured under the condition of adding light in situ to study the transport properties of electrons.

[0031] Advantages of the present invention:

[0032] Measuring the electron drift rate of 2DEG in III-nitride heterostructures in different physical environments is of great significance. In the temperature field, measuring the electron drift rate helps to evaluate the thermal stability and performance changes of the device, providing a basis for optimizing the thermal management design. As the temperature increases, the electron scattering may increase, thus reducing the drift rate and affecting the high-frequency performance and switching speed of the device. In the light field, measuring the electron drift rate can study the photoelectric effect of the device, providing important information for the development of optoelectronic devices. Under the action of the light field, the generation and recombination of photo-generated carriers will affect the electron concentration and drift velocity of 2DEG, and further affect the photoelectric response characteristics of the device. In addition, in other physical environments such as electric fields and magnetic fields, measuring the electron drift rate also helps to deeply understand the electrical and magnetic properties of the device, providing guidance for the design and optimization of the device. In short, measuring the electron drift rate of 2DEG in different physical environments plays a key role in comprehensively evaluating and optimizing the performance of GaN-based HEMT devices. Description of the Drawings

[0033] Figure 1 Schematic diagram of the H-shaped channel and test electrodes of the group-III nitride heterostructure sample after processing in the embodiment.

[0034] Figure 2 Top view of the group-III nitride heterostructure sample in the embodiment and parameter description.

[0035] Figure 3 Schematic diagram of connecting the test sample to the measurement circuit in the embodiment.

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

[0037] Figure 5 Variation curve of the electron drift velocity v of the GaN heterostructure measured in the embodiment with the applied electric field E.

[0038] Figure 6 Variation curve of the electron drift velocity v of the GaN heterostructure measured in the embodiment with the applied electric field E at different temperatures.

[0039] In the above-mentioned drawings, the meanings of the reference numerals are as follows:

[0040] 1. Test electrode; 2. Group-III nitride heterostructure sample processed into an H-shaped channel; 3. Short-pulse high-voltage power supply; 4. Position of the sample in the 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. Hot stage cover plate; 14. Transparent window pane. Detailed Description of the Invention

[0041] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further describes the present invention in detail through embodiments with reference to the drawings.

[0042] The basic idea of the present invention is: processing the group-III nitride heterostructure sample into an H-shaped channel through a process. Such a test sample structure can ensure avoiding the influence of possible electric field spikes near the electrodes on the channel electric field uniformity, reducing the influence of contact resistance and controlling the electrode injection effect of carriers. Utilizing the property of v = I / nWq, the electron drift velocity is obtained, and the electric field strength of the H-shaped channel is calculated to obtain the relationship between the electron drift velocity and the applied electric field. Combining the sample with the hot stage and building a test circuit can in-situ study the transport properties of electrons in a multi-physical environment (temperature field, light field).

[0043] In this embodiment, the GaN heterostructure is taken as an example, and the heterostructure sample is grown in the following manner:

[0044] 1) MOCVD epitaxially grow a 200 nm AlN nucleation layer on the SiC substrate;

[0045] 2) After the growth of the AlN nucleation layer, MOCVD epitaxially grow a 0.42 μm GaN buffer layer;

[0046] 3) Further MOCVD epitaxially grow a 1 nm AlN spacer layer;

[0047] 4) Further MOCVD epitaxially grow a 15.4 nm Al x Ga 1-x N barrier layer, where x is preferably 0.25 - 0.30;

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

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

[0050] To form an H-shaped channel for testing in the heterostructure sample, the following process steps are required:

[0051] 1) Cleaning: Remove the surface oxide layer of the heterostructure by inorganic cleaning, and then perform organic cleaning to remove organic contaminants;

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

[0053] 2) Use plasma-enhanced chemical vapor deposition (PECVD) to grow SiO 2 on the heterostructure as a mask for etching the GaN-based material;

[0054] The thickness of the grown SiO 2 layer is determined according to the GaN thickness and the ICP etching ratio in the next step, so that the GaN covered by SiO 2 is exactly protected from being etched, but too thick SiO 2 is not conducive to the pattern integrity of the etching.

[0055] 3) Mesa etching: First, coat a positive photoresist AZ6130 with a thickness of 4 μm, then perform photolithography, and ICP etch SiO 2 to transfer the photolithography pattern to the SiO 2 layer. After etching, use organic cleaning to wash off the photoresist, and then use SiO 2 as a mask to perform the second ICP etching to the substrate to form an H-shaped channel. After etching, use hydrofluoric acid to wash off the remaining SiO2 Mask layer;

[0056] The ICP etching parameters can be that the etching gas is CH 3 F, the RF power is 250 W, and the ICP power is 100 W.

[0057] 4) Fabricate test electrodes: Use negative photoresist (the thickness can be 1.5 μm) for the second lithography, electron beam evaporation deposit metal Ti / Al / Ni / Au (the thickness can be 20 / 175 / 50 / 200 nm), use organic cleaning to strip the photoresist, and then perform rapid thermal annealing (anneal at 850 °C for 35 s in an N 2 atmosphere) to form an n-type ohmic contact, and obtain the test sample as Figure 1 shown.

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

[0059] I = nqWv (1)

[0060] We can get v = I / nWq, where v is the electron drift rate, W is the channel width, I is the current passing through the H-shaped channel, n is the surface density of the heterostructure 2DEG, which can be measured by the Van der Pauw method; q is the elementary charge quantity. To calculate the electric field strength in the channel region, strictly speaking, it is necessary to simulate the electric field at the channel, but for simplicity, the electric field strength E in the channel can be estimated using the 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 ( Figure 3 ), in this embodiment, T = 500 μm, L′ = 100 μm, L = 15 μm, and W = 5 μm.

[0063] Figure 3It is a schematic diagram of the measurement circuit structure. To reduce the Joule heat 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 8 ns, a pulse period of 1 s, and an adjustable voltage of 0 - 450 V. 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 40 dB attenuator; the other electrode is connected to the Ch2 channel of the oscilloscope 7 through a BNC connector and a 20 dB attenuator, and is grounded through a 50-ohm resistor 5 at the same time. Turn on the switch of the short-pulse high-voltage power supply 3. The voltage difference shown by Ch1 - Ch2 of the oscilloscope 7 is the voltage V applied to the sample, and I = Ch2 / 50Ω is the current passing through the sample. By changing the voltage V, the electric field in the channel can be regulated. Based on v = I / nqW and Equation (2), the curve of the electron drift velocity v varying with the applied electric field E can be plotted. As Figure 5 shown, in this embodiment, the relationship between the electron drift velocity of the GaN-based heterostructure 2DEG and the applied external field strength under a high electric field is measured. It can be seen that when the signal frequency generated by the short-pulse high-voltage power supply 3 is 1 Hz, as the external field increases, the electron drift velocity increases. When E > 15 kV / cm, it can be considered that the electron drift velocity has saturated. By changing the signal frequency generated by the short-pulse high-voltage power supply 3 and conducting tests, it can be seen that as the frequency increases, the electron drift velocity decreases. And when E > 15 kV / cm, due to the significant Joule heat effect leading to an enhanced carrier scattering effect, the electron drift velocity becomes lower.

[0064] Figure 4 It is a schematic diagram of the in-situ measurement structure of the multi-physical environment built by combining the sample with the 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. Place the sample to be measured on the hot stage. The two test electrodes 1 of the test sample 10 are respectively connected to the corresponding two probes 12 of the electric heating stage 11, and then connected to the Figure 3 test circuit shown. By changing the sample temperature through the hot stage, the electron drift velocity of the GaN heterostructure at different temperatures is measured, as Figure 6 shown. It can be seen that as the ambient temperature increases, the carrier scattering enhances, and under the action of the electric field, the electron drift velocity becomes lower.

[0065] By installing a light source on the hot stage, the relationship between the electron drift velocity and the applied electric field can also be measured under the light field. Seal the hot stage, leaving only the air inlet 8 and the air outlet 9 for air flow in and out. By introducing different atmospheres, the relationship between the electron drift velocity and the applied electric field can be measured at different temperatures and atmospheres. In addition, since there is a light-transmitting window 14 on the hot stage cover 13, the electron drift velocity can also be measured under the condition of adding light in-situ to study the transport properties of electrons.

[0066] The specific implementation of this technical solution has been elaborated in detail in terms of design objectives, technical means, and implementation effects. It should be noted that the specific examples listed are only used to assist in explaining the core content of the present invention and do not constitute a limitation on the application scope of the technical solution. According to the technical principles and design requirements proposed by the present invention, any derivative implementation methods such as adaptive adjustments, technical equivalent replacements, or optimization improvements based on this technical solution all fall within the protection scope of the present invention.

Claims

1. A method for measuring electron drift rate of a III-nitride heterostructure in a multi-physical environment, comprising the following steps: 1) Form an H-shaped channel in the III-nitride heterostructure, and prepare rectangular test electrodes symmetrically on both sides of the channel to obtain a sample to be tested. The current I passing through the H-shaped channel is obtained according to formula (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 basic charge; The electric field strength E in the channel is estimated according to formula (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) placing the sample to be tested prepared in step 1) in one or more physical environments and connecting it to a test circuit, applying voltage to the test electrode, measuring the current passing through the H-shaped channel, and obtaining the electron drift velocity v according to formula (1). Combining formula (2) to obtain the relationship between the electron drift velocity v and the electric field E.

2. The measuring method according to claim 1, characterized in that: Step 1) Prepare an H-shaped channel and a test electrode according to the following steps: 1a) cleaning the surface of the III-nitride heterostructure and then growing a hard mask thereon; 1b) transferring the H-shaped channel pattern to a hard mask by photolithography, and then etching the III-nitride under the protection of the hard mask to obtain an H-shaped channel heterostructure; 1c) removing the hard mask, coating a negative photoresist and performing photolithography to obtain a pattern of a test electrode, and then depositing a metal and annealing to form an ohmic contact test electrode.

3. The measuring method according to claim 2, characterized in that: In step 1a), the surface oxide layer of the heterostructure is first removed by inorganic cleaning, and then organic cleaning is performed to remove organic contamination.

4. The measuring method according to claim 2, characterized in that: In step 1a), plasma enhanced chemical vapor deposition is used to grow silicon dioxide or silicon nitride as a hard mask.

5. The measuring method according to claim 2, characterized in that: Step 1c) depositing metal Ti / Al / Ni / Au by electron beam evaporation, followed by organic cleaning to strip the photoresist, and then rapid thermal annealing to form an ohmic contact.

6. The measuring method according to claim 1, characterized in that: The width W of the H-shaped channel in step 1) is 1-10 μm.

7. The measuring method according to claim 1, characterized in that: The test circuit in step 2) includes a short pulse high voltage power supply, a first attenuator, an oscilloscope, a second attenuator and a resistor, wherein one test electrode of the sample to be tested is connected to the short pulse high voltage power supply and is 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 is grounded through a resistor; the voltage difference shown in Ch1-Ch2 of the oscilloscope is the voltage V applied to the sample to be tested, and the voltage shown in Ch2 divided by the resistance value of the resistor is the current I passing through the sample to be tested.

8. The measuring method according to claim 1, characterized in that: The physical environment in step 2) includes a temperature field, a light field, a magnetic field and different gas atmospheres, wherein the temperature field is regulated 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, and the gas atmosphere is obtained by introducing gas into the space where the sample to be tested is located.

9. The measuring method according to claim 8, characterized in that: Step 2) placing the sample to be tested in a hot stage device, the hot stage device comprising a shell, an electric heating stage, a cover plate and a probe, wherein the electric heating stage is located in the shell, and the sample to be tested is placed on the electric heating stage; two probes are provided, which are respectively connected to two test electrodes of the sample to be tested, and then connected to an external electric field through a joint; the cover plate is covered on the shell to form a closed internal space, and an air inlet and an air outlet are provided on the shell for air flow in and out; a light-transmitting window is provided on the cover plate at a position directly facing the electric heating stage.

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

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