ultra-wide Bandgaps for futuRE high power electronic ApPlications – BREAkuP

- Growth optimization of Al-rich heterostructures grown on native bulk AlN substrates yielding low dislocation density (TDD < 105/cm2) as well as on AlN templates on silicon and SiC substrates.
- In-depth investigation and understanding of the Al-rich heterostructures on AlN films growth mechanisms and heterostructure behavior. This task will strongly support the optimization of the layers’ quality throughout an iterative collaboration around the growth within a large structural (X-Ray Diffraction, cathodoluminescence, AFM, HRTEM, EBIC) and electrical characterizations of the epi-layers (2DEG and buffer properties, high voltage, high temperature, pulsed IV).
- Development of innovative high performance lateral AlN-based HEMTs with larger 2DEG confinement, low buffer trap density and reduced thermal impedance.
- Development of HEMTs with AlN barrier layer towards the ultimate all-binary AlN/GaN/AlN heterostructure to maximize the 2DEG density (Ns > 2x1013/cm2) and device performance (sheet resistance < 300 O/sq, substrate grounded vertical breakdown voltage > 3 kV).
- Growth demonstration of the optimum AlN-based heterostructure on large wafer diameter by the French start-up EasyGaN.

• Electron injection into the silicon substrate for GaN-on-Si thin HEMTs.
• Buffer breakdown characteristics confirm the superiority of UWBG AlN.
• Superior breakdown voltage is observed for AlGaN/GaN-on-AlN with thinner GaN channel depicting the interplay between electric field distribution extending to AlN and defect density inside the channel, showing the promise of this structure.
• Scaling of breakdown field strength with Al mole fraction into the channel is experimentally verified.
• Buffer breakdown > 2.5 MV/cm has been observed for sub-micron MIS-HEMT structures on silicon.
• High Al% content AlGaN channel gives excellent electrical performance at high temperatures.
Significant reduction of the contact resistances by means of regrown ohmic contacts.
Several advanced techniques have been employed to investigate these novel heterostructures: A mean threading dislocation density in the range of fewer than 108 cm2 was estimated in AlN buffer by XDR analysis. More visible with the TEM pictures, along the [11-20] zone axis, some of them can extend until the thin GaN channel. Without any evident correlation, steps are detected at the AlGaN/GaN and GaN/AlN interfaces leading to an unambiguous roughness. Device simulations and static characterizations were used to determine four operation regimes: accumulation (V > 2 V), impoverishment below the gate (-5.7 V < V < 2 V), depletion below the gate (-7 V < V < -5.7 V) and depletion beyond the gate (V < -7 V). The management of the DLTS technique in these different regimes allowed five traps to be identified. Investigation of electrically active defects by EBIC (electron beam induced current) and cathodoluminescence has been also performed enabling to experimentally observe the space charge region prior to the breakdown.

• Thinner GaN channel structures using the same epi-design in order to explicate the impact of GaN channel thickness on the overall breakdown of device.
• Optimization of device fabrication process with the aim of achieving better on-state electrical characteristics for AlGaN/GaN-on-AlN HEMTs.
• Tuning the Al content into the barrier as well as the channel may give rise to a better version of power HEMTs.
• AlGaN channel HEMTs on silicon with thicker buffer layers to exploit the electrical field behavior inside the structure with different Al mole fraction in the channel.
• High Al% composition AlGaN channel HEMTs-on-AlN can be grown to critically boost the breakdown voltage of devices, making them capable to perform switching at multiple kilovolts and high temperatures for next-generation of UWBG power electronics.

Based on these preliminary promising results, more work is required on improving the material quality and epi design on both bulk AlN and silicon substrates in order to establish a novel class of high-power switching transistors.

The project Breakup enabled generating 4 articles published in international journals and 11 international conferences from which 8 were invited talks:

S. Rennesson,et al, “Ultrathin AlN-based HEMTs grown on silicon substrate by NH3-MBE”, Phys. Status Solidi A, 2018

Abid I., Kabouche R., Medjdoub F., GaN integration on silicon for high power devices, Invited talk, European Materials Research Society Meeting, E-MRS Fall 2019, Warsaw, Poland, September 16-19, 2019

Medjdoub F., Towards higher voltage in III-nitride devices, Invited talk, 13th International Conference on Nitride Semiconductors 2019, ICNS-13, Bellevue, WA, USA, July 7-12, 2019

Medjdoub F., High voltage GaN-based electron devices, Invited talk, 55th Annual Workshop on Compound Semiconductor Materials and Devices, WOCSEMMAD 2019, Jacksonville, FL, USA, February 18-20, 2019

Medjdoub F., Invited talk, Increasing the blocking voltage of GaN HEMTs, 9th Compound Semiconductor International Conference, Brussels, Belgium, March 26-27, 2019

Medjdoub F., Next generation of GaN-on-silicon power devices, Invited talk, 4th International Conference on Emerging Electronics, ICEE 2018, Bangalore, India, December 17-19, 2018

I. Abid, et al, « AlGaN/GaN High Electron Mobility Transistors with Ultra -Wide Bandgap AlN buffer », WOCSDICE, Cabourg, France, 2019

I. Abid, et al, Remarkable Lateral Breakdown Voltage in thin channel AlGaN/GaN High Electron Mobility Transistors on thick AlN/Sapphire Templates, 13th International Conference on Nitride Semiconductors 2019, ICNS-13, Bellevue, WA, USA, July 7-12, 2019

I. Abid, et al, “High Lateral Breakdown Voltage in Thin Channel AlGaN/GaN High Electron Mobility Transistors on AlN/Sapphire Templates”, Micromachines 2019, 10, 690; doi:10.3390/mi10100690

I. Abid, et al, Remarkable Breakdown Voltage on AlN/AlGaN/AlN double heterostructure, Proc. of the 2020 32nd International Symposium on Power Semiconductor Devices and ICs (ISPSD) Sept. 2020, Vienna, Austria

I. Abid, et al, AlN-based power devices, Invited talk, 56th Annual Workshop on Compound Semiconductor Materials and Devices, WOCSEMMAD 2020, February 16 -19, 2020, Saguaro Palm Springs, Palm Springs CA

I Abid, et al, “AlGaN channel High Electron Mobility Transistors with re-grown ohmic contacts”, Electronics 2021, 10, 635

Medjdoub F., Invited talk, GaN RF and power research at IEMN, C3NiT center day, Linkoping, Sweden, Nov. 2021

J. Mehta, et al, Prospects of Ultrawide Bandgap Materials and Devices, Invited talk, The 22nd international union of Materials Research Societies – International conference in Asia, IUMRS - ICA 2021, Jeju, Korea, Oct. 2021

J. Mehta,et al, «AlGaN/GaN HEMTs on AlN substrate for power electronics », 44th Workshop on Compound Semiconductor Devices and Integrated Circuits held in Europe, WOCSDICE, Bristol, UK, 2021

J. Bassaler,et al, « Detailed study of Al0.9Ga0.1N/GaN heterostructures with thin GaN on AlN/Sapphire templates », submitted to J. of Applied Phys., 2022

The aim of this project is to explore and to develop radically new material systems based on AlN ultra-wide bandgaps for future power devices providing higher robustness and superior temperature operation towards the ultimate all-binary AlN/GaN/AlN heterostructure. The AlN material will enable high efficiency operation beyond 1200 V as well as higher power performances in the millimeter-wave range, which is not currently reachable by GaN devices. This project will push the boundaries of power devices by studying AlN-based technology, which compared to any other semiconductor has even better material properties (including the relatively mature GaN and SiC materials). AlN-based structures represent the logical step further towards a breakthrough solution for the significant reduction of the vertical leakage currents, higher breakdown voltage, higher frequency of operation and enhanced thermal conductivity.
The consortium consisting in three academic laboratories (IEMN, CRHEA and Institut Néel) offers a perfect complementarity by bringing a unique expertise at the cutting edge for this ambitious development of novel power devices. It can be pointed out that each partner collaborates extensively with national industrials developing power devices such as ExaGaN, OMMIC, UMS and the start-up EasyGaN. This reflects the favorable environment to bring this basic research work on innovative material and architectures to real demonstrators within a rather short period of time.