# Self-Heating of Annealed Ti/Al/Ni/Au Contacts to Two-Dimensional Electron Gas in AlGaN/GaN Heterostructures

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## Abstract

**:**

^{−5}) pulse regime.

## 1. Introduction

## 2. Samples and Measurement Techniques

## 3. Current-Dependent Contact Resistance

## 4. Noise Performance of ${\mathit{R}}_{\mathbf{c}}\left(\mathit{I}\right)$ and ${\mathit{R}}_{\mathbf{ch}}\left(\mathit{I}\right)$

## 5. Discussion

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Microscope image of the TLM samples of the AlGaN/GaN channel with electrodes (of width W and length D) (

**a**) and intersection illustration of the AlGaN/GaN heterostructure with the 2DEG channel, showing the active part of the epitaxial structure and involving only two electrodes (

**b**). Arrows illustrate the current flow. An illustration of the DUT connection in the electronic scheme is presented in (

**c**).

**Figure 2.**The dependence of the low-field total resistance R on the channel length L. Data for group of TLM samples 1, fabricated of AlGaN/GaN (bottom inset), are shown by rectangles, meanwhile, the triangles as well as circles demonstrate results for other two groups of TLM samples 2, made of AlGaN/AlN/GaN (top inset).

**Figure 3.**The dependence of the total resistance R on the current I for the different channel length L (

**a**) and on channel length for a different current (

**b**). L = 6 $\mathsf{\mu}$m (closed triangles), 12.5 $\mathsf{\mu}$m (open diamonds), 25 $\mathsf{\mu}$m (open triangles), 45 $\mathsf{\mu}$m (open circles) and 65 $\mathsf{\mu}$m (closed rectangles). The measurements are presented for the AlGaN/GaN channel. The resistance values at a given currents (represented by the vertical dashed lines) are obtained from a linear interpolation; for the particular current I = 126 mA those are indicated as crosses. The applied maximal voltage for each length channel is indicated in the right side of the figure. Interpolated values of different length channels are depicted in the (

**b**) for each current and are used for the estimation of the current dependent contact resistance ${R}_{\mathrm{c}}$ and ${L}_{\mathrm{x}}$ (see interception with abscissa and ordinate axis in (

**b**)). Solid lines are linearly fit with Equation (1) and arrows show the direction of the increase in ${R}_{\mathrm{c}}$ and ${L}_{\mathrm{x}}$. I = 24 mA, 74 mA, 100 mA, 126 mA, 153 mA, 178 mA, 203 mA, 220 mA, 236 mA, 257 mA, 271 mA and 282 mA.

**Figure 4.**The dependence of the contact resistance ${R}_{\mathrm{c}}$ on the current density $I/W$ (

**a**) and on the dissipated electric power density ${P}_{\mathrm{c}}$ in contacts (

**b**) for different samples; AlGaN/GaN (squares), AlGaN/AlN/GaN (triangles and circles). The dependence of the contact resistance change $\Delta {R}_{\mathrm{c}}={R}_{\mathrm{c}}-{R}_{\mathrm{c}0}$ relatively to its low-field value is also presented (right-side axis). Lines are $\Delta {R}_{\mathrm{c}}\propto {I}^{5}$ (

**a**) and $\Delta {R}_{\mathrm{c}}\propto {P}_{\mathrm{c}}$ (

**b**), respectively.

**Figure 5.**The dependence of ${L}_{\mathrm{x}}$ on the current density for different samples; AlGaN/GaN (squares), AlGaN/AlN/GaN (triangles and circles).

**Figure 6.**The dependence of the microwave excess noise temperature $\Delta {T}_{\mathrm{n}}$ on the current for the different channels length of the same TLM in the AlGaN/GaN sample (

**a**). L = 6 $\mathsf{\mu}$m (closed triangles), 12.5 $\mathsf{\mu}$m (open diamonds), 25 $\mathsf{\mu}$m (open triangles) and 45 $\mathsf{\mu}$m (open circles). Lines guide the eyes. Estimated $\Delta {T}_{\mathrm{n}}$ at the constant currents is plotted versus channel length (

**b**). I = 100 mA (circles), 150 mA (rectangles), 220 mA (triangles) and 270 mA (pentagons). Curves are the fit by the model (Equation (6)). Excess noise temperature $\Delta {T}_{\mathrm{nc}}$ of the contact resistance ${R}_{\mathrm{c}}$ is estimated as a fitting parameter and its current dependence is depicted by the open rectangles.

**Figure 7.**The dependence of the relative contact resistance change $({R}_{\mathrm{c}}-{R}_{\mathrm{c}0})/{R}_{\mathrm{c}0}$ on the dissipated electric power density ${P}_{\mathrm{c}}$ in contacts for different samples; AlGaN/GaN (squares), AlGaN/AlN/GaN (triangles and circles).

**Figure 8.**The dependence of channel resistance change $\Delta {R}_{2\mathrm{D}}={R}_{2\mathrm{D}}-{R}_{2\mathrm{D}0}$ on dissipated power density in channel; AlGaN/GaN (closed squares), AlGaN/AlN/GaN (closed triangles and circles). The inset shows the dependence of the excess noise temperature $\Delta {T}_{\mathrm{n}}$ on the dissipated power per electron ${P}_{\mathrm{e}}$ in the 45 $\mathsf{\mu}$m-long channel. The lines in the main panel and inset demonstrate the dependencies of $\Delta {R}_{2\mathrm{D}}\sim {P}_{2\mathrm{D}}$ and $\Delta {T}_{\mathrm{n}}\sim {P}_{\mathrm{e}}$, respectively.

**Figure 9.**The dependence of the contact resistance ${R}_{\mathrm{c}}$ on the channel sheet resistance ${R}_{2\mathrm{D}}$ for different samples; AlGaN/GaN (squares), AlGaN/AlN/GaN (triangles and circles). Lines illustrate the slopes of the dependencies. Starting at ${R}_{2\mathrm{D}}\sim $ 750 $\Omega $/sq., the increase in ${R}_{\mathrm{c}}$ becomes faster (dashed lines versus solid lines).

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**MDPI and ACS Style**

Šermukšnis, E.; Jorudas, J.; Šimukovič, A.; Kovalevskij, V.; Kašalynas, I.
Self-Heating of Annealed Ti/Al/Ni/Au Contacts to Two-Dimensional Electron Gas in AlGaN/GaN Heterostructures. *Appl. Sci.* **2022**, *12*, 11079.
https://doi.org/10.3390/app122111079

**AMA Style**

Šermukšnis E, Jorudas J, Šimukovič A, Kovalevskij V, Kašalynas I.
Self-Heating of Annealed Ti/Al/Ni/Au Contacts to Two-Dimensional Electron Gas in AlGaN/GaN Heterostructures. *Applied Sciences*. 2022; 12(21):11079.
https://doi.org/10.3390/app122111079

**Chicago/Turabian Style**

Šermukšnis, Emilis, Justinas Jorudas, Artūr Šimukovič, Vitalij Kovalevskij, and Irmantas Kašalynas.
2022. "Self-Heating of Annealed Ti/Al/Ni/Au Contacts to Two-Dimensional Electron Gas in AlGaN/GaN Heterostructures" *Applied Sciences* 12, no. 21: 11079.
https://doi.org/10.3390/app122111079