Influence of Thermal and Fast Neutron Irradiation on dc Electrical Performances of AlGaN/GaN Transistors
The influence of thermal neutron irradiation and fast neutron irradiation on the electrical properties of AlGaN/GaN HEMTs is investigated. An increase in the drain current and a decrease in the access resistances are observed when devices are irradiated with a thermalized neutrons fluence of 4.3 × 1010 neutrons.cm-2 while no evolution is observed with the same fluence of fast neutrons. However, the same phenomenon is observed when the fast neutron fluence is higher (1.8 × 1012 neutrons.cm-2). AlGaN/GaN heterojunctions are analyzed by gamma spectroscopy after thermalized or fast neutron irradiations to understand the physical mechanisms induced by irradiations. In fact, we have shown that the improvement of electrical properties of devices after thermal neutrons irradiation is linked to a Ga-Ge transmutation effect. Moreover, the evolution of the drain current and access resistance when the AlGaN/GaN heterojunctions are irradiated by fast neutrons can be induced by N vacancies creation and/or a change of the strain state of the layers and/or Ga-Ge transmutation effect.
Mechanism of high-fluence proton induced electrical degradation in AlGaN/GaN high-electron-mobility transistors
The effects of displacement damage induced by 3 and 6 MeV protons in AlGaN/GaN high-electron-mobility transistors (HEMTs) are investigated. For the 6 MeV protons at a dose of 5 × 1014 cm−2, a 12% decrease in saturation current, a 3.8% decrease in the peak transconductance, a 0.3 V positive shift of the threshold voltage, and a three-to fourfold decrease in reverse gate leakage current are observed compared with the pre-irradiation values. The main degradation mechanism is considered to be the generation of deep trap states in the band gap, which remove electrons and reduce the carrier mobility in a two-dimensional electron gas (2DEG). Both the carrier removal rate and negatively charged trap density can be extracted, which shows that about 3500 proton injections lead to one carrier removal. Proton fluence and energy are found to be two key parameters that affect the degradation characteristics of irradiated GaN HEMTs.
Evaluation of Impact of Yarn Count and Stitch Length on Pilling, Abrasion, Shrinkage and Tightness Factor of 1 ? 1 Rib Cotton Knitted Fabrics
This study investigates the impact of yarn count and stitch length of 100% cotton knitted fabrics. 1 × 1 ribs structured fabrics were used in this research work. The stitch length 2.50 mm, 2.52 mm, 2.60 mm, 2.70 mm, 2.80 mm and 2.96 mm were used of the yarn count of 26Ne, 28Ne and 36Ne. The areal densities of the grey fabrics were in various amounts. The impacts of yarn count and stitch length were measured concerning pilling resistance, abrasion resistance, and shrinkage and tightness factor. The result showed that the fabric pilling grade decreased while number of cycle increased. Abrasion resistance decreased but length wise shrinkage increased despite the fact that the stitch length increased. The results also exposed that the tightness factor of the fabric increased with the increase of the stitch length in both dyeing and washing state and finished state compared to grey state for the yarn count 26Ne and homogeneous result not found for yarn count 28Ne and 36 Ne. Evaluation of Impact of Yarn Count and Stitch Length on Pilling, Abrasion, Shrinkage and Tightness Factor of 1 × 1 Rib Cotton Knitted Fabrics