Mohit Kumar

GaN p-channel field-effect transistors (p-FETs) are critical for enabling complementary integration of power and logic, while offering high breakdown capability. However, achieving high on-current in GaN p-FETs remains a significant challenge, primarily due to the low hole concentration, poor mobility, and challenges in forming stable, low-resistance ohmic contacts. Here, we present a novel GaN p-FET architecture that exhibits unconventional electron conduction, which helps enhance both thermal response and current modulation. We conduct a comprehensive investigation of heavily Mg-doped p⁺⁺-GaN layers, focusing on contact optimization for high-temperature operation. Structural and interfacial characterization confirms high crystal quality and a thermally robust Ni/Au contact stack stabilized by an interfacial Ni_xO_y layer. This strategic interfacial layer, combined with moderate-temperature annealing, promotes Mg activation and suppresses oxygen-related traps, resulting in a ~ 73% reduction in contact resistance. Temperature-dependent analysis further reveals non-monotonic Schottky barrier modulation driven by interface evolution. Integrated into the device, this contact strategy enables thermally enhanced operation, with a drastically increase in on-state current and threshold voltage shifting positively by ~ 69% with temperature. These findings highlight a model shift in GaN p-FET design, where interface study and transport-mode innovation enable high-performance, thermally resilient devices for next-generation power integration.

Caractérisations par microscopie Raman et autres microscopies de matériaux à base de béryllium dans le cadre d'ITER: Dans les tokamaks comme ITER, les composants face au plasma subissent de très forts flux de particules et de chaleur. Des phénomènes tels que l'endommagement ou la fusion des matériaux, la rétention de D et de T, et la formation de matériaux mixtes peuvent nuire gravement au fonctionnement de la machine. Le béryllium (Be) a été choisi pour la conception des parois d'ITER. Trois types d'échantillons de Be sont caractérisés ici par microscopies Raman, électronique, à force atomique et confocal. 1) Nous étudions la formation de cloques à la surface d'un échantillon de Be bombardé d'ions D de 2 keV. La morphologie des cloques de même que la qualité cristalline sont analysées en fonction de la fluence. Nous observons que les cloques se forment à partir d'une fracture à l'interface définie par l'implantation, et également qu'elles craquent elles-mêmes à partir d'une certaine taille, ne dépassant pas typiquement 1 micro-métre. 2) Nous étudions plusieurs films de Be, Be/D et Be/O/C/D synthétisés par pulvérisation magnétron et contenant différents taux de D. Nous montrons que D est piégé sous forme moléculaire (D2), ainsi que sous forme de liaisons C-D et O-D dans le cas de Be/O/C/D. Nous montrons à la fois que la qualité cristalline baisse avec le taux de D et que D2 est probablement piégé dans les joints de grain. 3) Nous étudions des échantillons de Be venant des parois de JET. Nous confirmons la présence d'oxyde de Be (BeO) et nouvelles phases correspondant à des deutéroxydes (Be/O/D). Nos résultats indiquent que si la mobilité est suffisante pour créer des oxydes, sous l'effet du bombardement plasma, des hydroxydes peuvent aussi être créés

The continuous evolution of high-power and high-frequency electronic devices demands advanced semiconductor technologies. The proposed GaN p-FET device architecture incorporates a p-GaN source region that enables the simultaneous formation of two-dimensional electron gas (2DEG) and two-dimensional hole gas (2DHG) channels. This dual-channel mechanism enhances carrier confinement and mobility, offering a pivotal pathway toward high-performance GaN-based electronics. This simulation study systematically examines key parameters to optimize device configurations: Mg²⁺ doping (0.05 to 50 × 10¹⁹ cm^− 3), contact metal work function (4.0 to 6.3 eV), AlGaN layer thickness (4 to 25 nm), and Al mole fraction (0.1 to 0.45) in relation to the performance of p-GaN source layer n-GaN/AlGaN/GaN double heterostructure FETs. Extensive analyses reveal that a GaN pFET with a 5 nm p-GaN layer doped with 1 × 10¹⁹ cm^− 3 Mg²⁺ and a 10 nm AlGaN layer with an Al mole fraction of 0.2, demonstrates superior performance metrics. Compared to state-of-the-art technologies, this specific device configuration achieves optimal threshold voltage (~ |4| V) control, high I_ON/I_OFF ratios (0.39 × 10¹²), and minimized leakage current, essential for reliable high-performance operations. Additionally, the study highlights the critical impact of the contact metal work function, with a work function of 5.15 eV significantly reducing contact resistivity and minimizing leakage current, enhancing device efficiency. These findings highlight that precise control over doping, material thickness, and composition is essential for optimizing GaN pFET performance and reliability for next-generation electronic applications.

This study investigated the low contact resistivity and Schottky barrier characteristics in p-GaN by modifying the thickness and doping levels of a p-InGaN cap layer. A comparative analysis with highly doped p-InGaN revealed the key mechanisms contributing to low-resistance contacts. Atomic force microscopy inspections showed that the surface roughness depends on the doping levels and cap layer thickness, with higher doping improving the surface quality. Notably, increasing the doping concentration in the p⁺⁺-InGaN cap layer significantly reduced the specific contact resistivity to 6.4 ± 0.8 × 10⁻⁶ Ω·cm², primarily through enhanced tunneling. Current–voltage (I–V) characteristics indicated that the cap layer’s surface properties and strain-induced polarization effects influenced the Schottky barrier height and reverse current. The reduction in barrier height by approximately 0.42 eV in the p⁺⁺-InGaN layer enhanced hole tunneling, further lowering the contact resistivity. Additionally, polarization-induced free charges at the metal–semiconductor interface reduced band bending, thereby enhancing carrier transport. A transition in current conduction mechanisms was also observed, shifting from recombination tunneling to space-charge-limited conduction across different voltage ranges. This research underscores the importance of doping, cap layer thickness, and polarization effects in achieving ultra-low contact resistivity, offering valuable insights for improving the performance of p-GaN-based power devices.