Fabrication of high reliability AlGaN / GaN HEMTs on high quality GaN free-standing substrate

Le nitrure de gallium (GaN) constitue le meilleur candidat pour la réalisation de transistors de type HEMT de puissance fonctionnant à haute fréquence. A l’heure actuelle, en raison de la faible disponibilité de substrats GaN, la plupart des dispositifs sont fabriqués par hétéro-épitaxie sur des substrats Si, SiC, ou saphir. Jusqu'à présent, aucun de ces substrats n’a permis la croissance directe de GaN de haute qualité cristalline. Par conséquent, le développement de ces technologies doit faire face à de nombreux défauts (densités de dislocations de l’ordre de 108-1010cm-2) et à des contraintes mécaniques notables (plusieurs centaines de MPa) apparaissant dans le matériau entrainant de nombreuses questions quant à la fiabilité des dispositifs. Le but de cette thèse est de qualifier de nouveaux dispositifs électroniques de type HEMT pour les applications RF à partir d'une nouvelle stratégie de substrat GaN présentant une haute qualité cristalline. A partir de substrats GaN free-standing, le CRHEA a fait croitre une couche tampon de GaN suffisamment épaisse et résistive pour limiter le couplage du substrat avec l’hétérostructure AlGaN / GaN et ainsi minimiser les courants de fuite et les pertes de propagation RF. La technique de croissance MOVPE permettra d’obtenir des films de GaN épais tout en contrôlant la résistivité par auto-compensation de carbone. La croissance de l’hétérostructure AlGaN/GaN a été ensuite développée sur ces substrats. Le procédé technologique de fabrication des composants HEMTs AlGaN/GaN sur substrat GaN pour des applications RF a été développé à l’IEMN. La lithographie électronique a permis de réaliser des composants avec des longueurs de grilles en T ultra-courtes (jusqu’à 70 nm). Les caractéristiques I-V en régimes DC et Pulsé et des mesures de paramètres S ont été effectuées pour déterminer les fréquences de coupure des transistors. Les mesures de puissance hyperfréquence à 18 GHz et à 40 GHz ont démontré un résultat représentant l’état de l’art des HEMTs sur substrats GaN.Gallium nitride is the best candidate for the fabrication of High Electron Mobility Transistors for high power/high frequency applications. Due to the lack of availability of GaN substrates, most of devices are currently fabricated by hetero-epitaxy on Si, SiC or sapphire substrates. None of these substrates allows the direct growth of high quality GaN crystal. Therefore, many defects (TDD 108-1010 cm-2) and significant mechanical stress appear in the material leading many questions about the reliability of the devices. The aim of this subject is to overcome these limitations and qualify new electronic devices for RF applications using GaN substrate with a high crystalline quality. Thick and resistive GaN buffer layer was grown at CHREA in order to limit leakage current and RF losses. MOVPE growth technique will permit thick GaN layer while controlling the resistivity by using carbon self-compensation or iron incorporation. Heterostructures will be grown from these substrates.Technological process was developed at IEMN to fabricate AlGaN/GaN devices on GaN substrate for RF applications. E-beam lithography-based process was used to fabricate transistors with short gate-length ranging down to 70 nm. DC, pulsed characteristics and S-parameters measurements were performed to determine cut-off frequency of the transistors. 18 GHz and 40 GHz microwave power measurements have shown a state-of-the-art result for HEMTs on GaN substrates

Fabrication de transistors HEMTs AlGaN/GaN de haute fiabilité sur substrat free-standing GaN de haute qualité

Gallium nitride is the best candidate for the fabrication of High Electron Mobility Transistors for high power/high frequency applications. Due to the lack of availability of GaN substrates, most of devices are currently fabricated by hetero-epitaxy on Si, SiC or sapphire substrates. None of these substrates allows the direct growth of high quality GaN crystal. Therefore, many defects (TDD 108-1010 cm-2) and significant mechanical stress appear in the material leading many questions about the reliability of the devices. The aim of this subject is to overcome these limitations and qualify new electronic devices for RF applications using GaN substrate with a high crystalline quality. Thick and resistive GaN buffer layer was grown at CHREA in order to limit leakage current and RF losses. MOVPE growth technique will permit thick GaN layer while controlling the resistivity by using carbon self-compensation or iron incorporation. Heterostructures will be grown from these substrates.Technological process was developed at IEMN to fabricate AlGaN/GaN devices on GaN substrate for RF applications. E-beam lithography-based process was used to fabricate transistors with short gate-length ranging down to 70 nm. DC, pulsed characteristics and S-parameters measurements were performed to determine cut-off frequency of the transistors. 18 GHz and 40 GHz microwave power measurements have shown a state-of-the-art result for HEMTs on GaN substrates.Le nitrure de gallium (GaN) constitue le meilleur candidat pour la réalisation de transistors de type HEMT de puissance fonctionnant à haute fréquence. A l’heure actuelle, en raison de la faible disponibilité de substrats GaN, la plupart des dispositifs sont fabriqués par hétéro-épitaxie sur des substrats Si, SiC, ou saphir. Jusqu'à présent, aucun de ces substrats n’a permis la croissance directe de GaN de haute qualité cristalline. Par conséquent, le développement de ces technologies doit faire face à de nombreux défauts (densités de dislocations de l’ordre de 108-1010cm-2) et à des contraintes mécaniques notables (plusieurs centaines de MPa) apparaissant dans le matériau entrainant de nombreuses questions quant à la fiabilité des dispositifs. Le but de cette thèse est de qualifier de nouveaux dispositifs électroniques de type HEMT pour les applications RF à partir d'une nouvelle stratégie de substrat GaN présentant une haute qualité cristalline. A partir de substrats GaN free-standing, le CRHEA a fait croitre une couche tampon de GaN suffisamment épaisse et résistive pour limiter le couplage du substrat avec l’hétérostructure AlGaN / GaN et ainsi minimiser les courants de fuite et les pertes de propagation RF. La technique de croissance MOVPE permettra d’obtenir des films de GaN épais tout en contrôlant la résistivité par auto-compensation de carbone. La croissance de l’hétérostructure AlGaN/GaN a été ensuite développée sur ces substrats. Le procédé technologique de fabrication des composants HEMTs AlGaN/GaN sur substrat GaN pour des applications RF a été développé à l’IEMN. La lithographie électronique a permis de réaliser des composants avec des longueurs de grilles en T ultra-courtes (jusqu’à 70 nm). Les caractéristiques I-V en régimes DC et Pulsé et des mesures de paramètres S ont été effectuées pour déterminer les fréquences de coupure des transistors. Les mesures de puissance hyperfréquence à 18 GHz et à 40 GHz ont démontré un résultat représentant l’état de l’art des HEMTs sur substrats GaN

Influence of Fluorine implantation on the electrical characteristics of GaN-on-GaN vertical Schottky and P-N diodes

International audienceGaN-based power devices have been gaining popularity in recent years thanks to GaN properties such as wide bandgap, high electron mobility, and high breakdown field strength, allowing low Ron, and high-frequency operation. Lateral GaN devices, which are grown on a foreign substrate like Si and sapphire [1], have already been commercialized and have been able to achieve much better performance compared to their silicon counterparts. However, these devices are unable to achieve sufficiently high breakdown voltage (BV>1kV). One alternative to boost the breakdown voltage and lower Ron is to have vertical devices grown on a native GaN substrate. These devices still suffers from premature breakdown and high reverse leakage due to electric field crowding at the junction edge. This issue can be resolved by creating an effective edge termination either by using Mg implantation [2] to create a p-doped region or by alternate species implantation by Nitrogen [3] or Argon [4] to create a resistive region at the junction edge. However, due to the difficulty in creating p-GaN by ion implantation due to compensation by Hydrogen and large activation energy of ~170 meV, alternate species of implantation is preferred. Fluorine ion implantation [5] is an attractive alternative as it can form a negative fixed charge owning to its highest electronegativity thus spread the electric field away from the contact and can also modulate the free charge carrier in GaN.In this study, P-N and Schottky structures are fabricated using multi energy Fluorine implantation as an edge termination. The influence of the implant on the electrical characteristics is studied by varying the implant overlap beneath the contact. µ-Raman scanning of the device suggests a reduction in free charge concentration in the implanted region, and an increase in the built-in potential obtained through C-V measurements compared to the device with no implantation. The influence of implantation on the electrical characteristics (B-V, I-V, and C-V) is analyzed and TCAD simulations using Synopsys® SentaurusTM are performed to help interpret the results

Influence of Fluorine implantation on the electrical characteristics of GaN-on-GaN vertical Schottky and P-N diodes

International audienceGaN-based power devices have been gaining popularity in recent years thanks to GaN properties such as wide bandgap, high electron mobility, and high breakdown field strength, allowing low Ron, and high-frequency operation. Lateral GaN devices, which are grown on a foreign substrate like Si and sapphire [1], have already been commercialized and have been able to achieve much better performance compared to their silicon counterparts. However, these devices are unable to achieve sufficiently high breakdown voltage (BV>1kV). One alternative to boost the breakdown voltage and lower Ron is to have vertical devices grown on a native GaN substrate. These devices still suffers from premature breakdown and high reverse leakage due to electric field crowding at the junction edge. This issue can be resolved by creating an effective edge termination either by using Mg implantation [2] to create a p-doped region or by alternate species implantation by Nitrogen [3] or Argon [4] to create a resistive region at the junction edge. However, due to the difficulty in creating p-GaN by ion implantation due to compensation by Hydrogen and large activation energy of ~170 meV, alternate species of implantation is preferred. Fluorine ion implantation [5] is an attractive alternative as it can form a negative fixed charge owning to its highest electronegativity thus spread the electric field away from the contact and can also modulate the free charge carrier in GaN.In this study, P-N and Schottky structures are fabricated using multi energy Fluorine implantation as an edge termination. The influence of the implant on the electrical characteristics is studied by varying the implant overlap beneath the contact. µ-Raman scanning of the device suggests a reduction in free charge concentration in the implanted region, and an increase in the built-in potential obtained through C-V measurements compared to the device with no implantation. The influence of implantation on the electrical characteristics (B-V, I-V, and C-V) is analyzed and TCAD simulations using Synopsys® SentaurusTM are performed to help interpret the results

Electrical Transport Characteristics of Vertical GaN Schottky-Barrier Diode in Reverse Bias and Its Numerical Simulation

We investigated the temperature-dependent reverse characteristics (JR-VR-T) of vertical GaN Schottky-barrier diodes with and without a fluorine-implanted edge termination (ET). To understand the device leakage mechanism, temperature-dependent characterizations were performed, and the observed reverse current was modeled through technology computer-aided design. Different levels of current were observed in both forward and reverse biases for the ET and non-ET devices, which suggested a change in the conduction mechanism for the observed leakages. The measured JR-VR-T characteristics of the non-edge-terminated device were successfully fitted in the entire temperature range with the phonon-assisted tunneling model, whereas for the edge-terminated device, the reverse characteristics were modeled by taking into account the emission of trapped electrons at a high temperature and field caused by Poole–Frenkel emission

Influence of fluorine implantation on the physical and electrical characteristics of GaN-on-GaN vertical Schottky diode

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