Improved oxide passivation of AlGaN∕GaN high electron mobility transistors

Abstract

MgO has proven effective in the past as a surface passivation layer to minimize current collapse in AlGaN∕GaN high electron mobility transistors (HEMTs). However, MgO is not environmentally stable and more stable oxides need to be developed. MgCaO can be produced that is lattice matched to the GaN. Three samples were grown with 0%, 50% and 75% of Ca, which had respective lattice mismatches of −6.5% for MgO, −1% for Mg0.50Ca0.50O and +4% for Mg0.25Ca0.75O. Drain saturation current in HENTs had increases of 4.5% and 1%, respectively, for Mg0.5Ca0.5O and Mg0.25Ca0.75O passivated devices. However, there was a 10% decrease for the device passivated with pure MgO. This was due to strain applied on the nitride HEMT by the oxide, which is consistent with the piezoelectric effect in the nitride HEMT by the oxide, which is consistent with the piezoelectric effect in the nitride form the lattice mismatch between AlGaN and GaN. From pulsed measurements, HEMTs passivated with Mg0.5Ca0.5O and Mg0.25Ca0.75O showed higher passivation effectiveness (90% of dc current) then the MgO passivated HEMTs (83% dc current). This is due to the closer lattice matching of these calcium containing oxides and the reduction in interface traps associated with lattice mismatch.

Role of Gate Oxide in AlGaN/GaN High-Electron-Mobility Transistor pH Sensors

“…The Sc 2 O 3 was deposited by radiofrequency (RF) plasma-activated molecular beam epitaxy (MBE) at 100°C using elemental Sc evaporated from a standard effusion all at 1130°C and O 2 derived from an Oxford RF plasma source. [22][23][24] For comparison, we also fabricated devices with just the native oxide present in the gate region and also with a UV-ozone-induced oxide. The latter was produced by exposing the sample to UVozone at room temperature for 5 min.…”

Band Offsets in the Mg0.5Ca0.5O/GaN Heterostructure System

“…Therefore, all of the binding energies are accurate on an absolute scale within 0.02-0.03 eV, over the binding energy range of 0-100 eV. 28 The bottom part of the figure shows a lattice image of the crystalline MgCaO. These types of films have shown excellent passivation properties on AlGaN/ GaN HEMTs.…”

“…These types of films have shown excellent passivation properties on AlGaN/ GaN HEMTs. 28 The digital samples all showed a uniform depth profile, as determined by Auger electron spectroscopy, especially near the surface, as shown in Fig. 2.…”

“…Crystalline films of Mg 0.5 Ca 0.5 O are lattice matched to GaN and produce superior surface passivation on HEMT structures than MgO. 28 The HEMTs passivated with Mg 0.5 Ca 0.5 O and Mg 0.25 Ca 0.75 O showed higher passivation effectiveness (90% of dc current) than the MgO passivated HEMTs (83% of dc current). This is due to the closer lattice matching of these calcium containing oxides and the reduction in interface traps associated with lattice mismatch.…”

“…This is due to the closer lattice matching of these calcium containing oxides and the reduction in interface traps associated with lattice mismatch. 28 In addition, while pure MgO degrades over time in atmosphere due to reaction with water vapor to form magnesium hydroxide, Mg(OH) 2 , uncapped MgCaO shows much less degradation and, when capped with 5 nm of Sc 2 O 3 , showed no detectable changes.…”