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In this work, we demonstrate enhancement-mode regrown p-GaN gate devices with high threshold voltage as well as a robust forward time-dependent gate breakdown (TDGB) stability. The regrown p-GaN gate HEMTs are fabricated with two different AlGaN barriers. Devices with 16nm Al0.235 Ga0.765 N yield a $\text{V}_{\text {TH}}$ of 1.5V and a high threshold voltage ($\text{V}_{\text {TH}}$) of 2.7V is observed for 7nm AlGaN along with a gate breakdown voltage of more than 10V. Lastly, the regrown p-GaN gate HEMTs with 7nm AlGaN barrier demonstrate an operating $\text{V}_{\text {G}}$ of 7.46V and 7V for 1% failure rate of 10-year lifetime at 150°C and 25°C, which is amongst the highest values compared to the reported literature for regrown p-GaN gate HEMTs. [ABSTRACT FROM AUTHOR]

In this article, a physics-based analytical model which considers the channel charge (Qch) for enhancement-mode p-GaN power high-electron-mobility transistors (HEMTs) is developed. First, by considering the same dynamic channel charge (dQch) for the Schottky/p-GaN junction capacitance (Cj,Sch) and the p-i-n-junction capacitance (Cp-i-n), due to the p-GaN/AlGaN junction and two-dimensional electron gas (2DEG) charge, the analytical formula to calculate the voltage drop in the p-GaN layer (VpGaN) is presented. Second, by implementing the analytical formulae in the advanced SPICE model (ASM) GaN model, the proposed physics-based model reliably fits the measured C – V and I – D – V – G characteristics of the samples under different processing conditions. This provides significant insight regarding the Mg concentration, the voltage drop at the Schottky metal/p-GaN junction (Vj,Sch), and the voltage drop at the p-GaN/AlGaN junction (Vp-i-n). Finally, the I – D – V – G and I – D – V – D characteristics of enhancement-mode p-GaN power HEMTs are modeled, displaying good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

In this letter, a fully transparent AlGaN/GaN HEMT (FT-HEMT) using indium-tin-oxide (ITO) as a transparent electrode is fabricated. The n-ohmic contacts are formed based on a Si-implant process using a deposited ITO rather than the conventional alloyed metal stacks. Following a post-annealing process at 600°C, the field-effect mobility and the maximum current density for an FT-HEMT were 1004 cm2/ $\text{V}{\cdot }\text{s}$ and 179 mA/mm, respectively. Furthermore, the measured transmittance for a fabricated chip in the visible range of 400 - 700 nm was greater than 70%, which is almost the same as an as-grown GaN-on-sapphire substrate. These results show that, by using this approach, an FT-HEMT that has superior electronic properties, such as high mobility and high output current, can be realized, and show great promise for applications in transparent and/or flexible electronics, as well as other optoelectronic devices. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate the use of a machine learning (ML)-based statistical approach to model and analyze the impact of the fabrication processes on the threshold voltage in recessed gate AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors. First, we employ a ML-based Tikhonov regularization approach using the input of 19 different processing splits to generate a multivariable analytical equation that considers four critical processing parameters, such as the remaining AlGaN depth, ex-situ wet clean, in-situ plasma, and gate dielectric. Furthermore, the artificial neural network-based approach, which cannot be used to further analyze the impact of the process, is implemented for the comparison. Second, the results from this analytical equation show a nice agreement with the measured threshold voltage, indicating a successful correlation between the processing parameters and the threshold voltage. Finally, the impact of each process on the threshold voltage can be analyzed through the coefficient value related to each process, which can be a useful guidance for the device optimization toward the targeted performance. [ABSTRACT FROM AUTHOR]

In this letter, we analyzed the gate capacitance characteristics in p-GaN gate/AlGaN/GaN heterostructures by using a two-junction capacitor model. First, we have observed that the C – V behavior depends on the different processing conditions of the p-GaN gate. Second, a two-junction capacitor model considering a series connection of the Schottky metal/p-GaN junction capacitor and the AlGaN barrier capacitor is proposed to explain this C – V behavior. Based on this model, the junction capacitance has an influence on the total capacitance value under a high gate bias due to the Schottky metal/p-GaN junction. Furthermore, the Mg-concentration and hole density can be extracted. The extracted hole density is consistent with the results obtained by Hall measurements. [ABSTRACT FROM AUTHOR]

We focus on slow de-trapping phenomena in AlGaN/GaN MIS-HEMTs with a bilayer dielectric ( in-situ Si 3 N 4 /Al 2 O 3 ) with two different thicknesses of in-situ Si 3 N 4 (10 nm and 5 nm). By using a “filling pulse” at a positive gate voltage, a trap with activation energy of 0.69–0.7 eV was identified to be responsible for the V TH shift. Based on literature, filling conditions, and the simulated band diagrams, this trap is most probably located at the interface between the dielectrics and AlGaN barrier. A physical model is proposed to explain the V TH shift due to the trapping/de-trapping phenomena based on the occupation dynamics of donor traps at the interface between the in-situ Si 3 N 4 /Al 2 O 3 and the AlGaN barrier. [ABSTRACT FROM AUTHOR]

The reliability of Au-free Ohmic contacts has been evaluated under a constant current stress (500 mA/mm) in a high temperature environment (150 °C, 175 °C, and 200 °C). Two Ohmic contact schemes with different Ti/Al thicknesses (5 nm/100 nm and 10 nm/100 nm) have been tested. The results showed that the degradation of the resistance ( R increase ) is accelerated at a higher temperature condition. Moreover, R increase has a square root dependence with the time. This indicates that a diffusion process could be responsible for the observed degradation. This has been confirmed by means of physical failure analyses (FIB/TEM) performed on a highly degraded device: an apparent roughness of the interface between TiN and the Ohmic metal layer was observed. On top of this, Nitrogen out-diffusion into the Ohmic metal was observed in the EDS/EELS analyses, suggesting that a material diffusion phenomenon might play a role. In addition, we observed that the devices with a lower initial contact resistance ( R c ) showed lower degradation with respect to devices with a larger initial R c . This suggests that obtaining lower R c is beneficial not only for the performance but also for the reliability. [ABSTRACT FROM AUTHOR]

In this paper, we review and add additional data and understandings on our findings on the two most common failure modes of GaN-based HEMTs: 1) permanent gate leakage current increase and 2) output current drop. We suggested that they have different origins and one is not necessarily correlated to the other. Yet, they can both concur to the device degradation. First, we demonstrate that the phenomenon of gate leakage current increase has a voltage-accelerated degradation kinetic. Therefore, the identification of the critical voltage for leakage increase is meaningless. We demonstrate that the time-to-breakdown tBD data are Weibull distributed and we prove that they represent intrinsic failures. According to our data, this phenomenon is not related to the inverse piezoelectric effect. Finally, a new degradation model for the gate leakage current increase based on the percolation path theory is proposed. Second, we show that the permanent output current drop is a consequence of the relaxation of AlGaN layer. This occurs by means of formation of crystallographic defects as described by the inverse piezoelectric degradation model. Finally, we show an excellent stability of devices with reduced Al content in the AlGaN barrier, proving the crucial role of strain in the reliability of AlGaN/GaN HEMTs. [ABSTRACT FROM AUTHOR]

In this letter, we studied the forward bias gate breakdown mechanism on enhancement-mode p-GaN gate AlGaN/GaN high-electron mobility transistors. To the best of our knowledge, it is the first time that the temperature dependence of the forward gate breakdown has been characterized. We report for the first time on the observation of a positive temperature dependence, i.e., a higher temperature leads to a higher gate breakdown voltage. Such unexpected behavior is explained by avalanche breakdown mechanism: at a high positive gate bias, electron/hole pairs are generated in the depletion region at the Schottky metal/p-GaN junction. Furthermore, at a high gate bias but before the catastrophic gate breakdown, a light emission was detected by a emission microscopy measurement. This effect indicates an avalanche luminescence, which is mainly due to the recombination of the generated electron/hole pairs. [ABSTRACT FROM PUBLISHER]

This paper reports an extensive analysis of the trapping and reliability issues in AlGaN/GaN metal insulator semiconductor (MIS) high electron mobility transistors (HEMTs). The study was carried out on three sets of devices with different gate insulators, namely PEALD SiN, RTCVD SiN and ALD Al 2 O 3 . Based on combined dc, pulsed and transient measurements we demonstrate the following: (i) the material/deposition technique used for the gate dielectric can significantly influence the main dc parameters (threshold current, subthreshold slope, gate leakage) and the current collapse; and (ii) current collapse is mainly due to a threshold voltage shift, which is ascribed to the trapping of electrons at the gate insulator and/or at the AlGaN/insulator interface. The threshold voltage shift (induced by a given quiescent bias) is directly correlated to the leakage current injected from the gate; this demonstrates the importance of reducing gate leakage for improving the dynamic performance of the devices. (iii) Frequency-dependent capacitance–voltage (C–V) measurements demonstrate that optimized dielectric allow to lower the threshold-voltage hysteresis, the frequency dependent capacitance dispersion, and the conductive losses under forward-bias. (iv) The material/deposition technique has a significant impact on device robustness against gate positive bias stress. Time to failure is Weibull-distributed with a beta factor not significantly influenced by the properties of the gate insulator. The results presented within this paper provide an up-to-date overview of the main advantages and limitations of GaN-based MIS HEMTs for power applications, on the related characterization techniques and on the possible strategies for improving device performance and reliability. [ABSTRACT FROM AUTHOR]