N-Polar GaN Cap MISHEMT With Record Power Density Exceeding 6.5 W/mm at 94 GHz

Unintentional impurity incorporation in N‐polar GaN films grown by metalorganic vapor phase epitaxy (MOVPE) was investigated. The influences of growth conditions on the impurity concentration, electrical properties, and optical properties were discussed. Secondary‐ion mass spectroscopy showed that both concentrations of carbon and oxygen were changed by growth conditions. With decreasing H2/(H2 + N2) ratio, the carbon concentration increased, while the oxygen concentration decreased. At higher V/III ratios, the oxygen concentration decreased. Nitrogen‐rich carrier gas and a high V/III ratio can decrease oxygen incorporation in the N‐polar GaN epitaxial layer. The growth parameters discussed in this study are concluded to affect the adsorption/desorption properties of impurities. Based on these results, the electrical properties of N‐polar III‐nitrides can also be controlled by choosing the appropriate MOVPE growth conditions. This technology will lead to improvements in N‐polar III‐nitride‐based device performance.

Section: Introductionmentioning

confidence: 99%

Control of impurity concentration in N‐polar () GaN grown by metalorganic vapor phase epitaxy

Tanikawa

Kuboya

Matsuoka

2017

“…To improve the performance of AlGaN/GaN HEMTs, an AlN interlayer is widely used between AlGaN and GaN because of the effect of low alloy scattering . The nitrogen‐polar (N‐polar) GaN/AlGaN structure is attracting interest because of the back‐barrier effect of AlGaN, and several promising results have been reported . A higher frequency operation requires a substrate with a high resistivity and high breakdown voltage .…”

Section: Introductionmentioning

confidence: 99%

Growth and Characterization of Nitrogen‐Polar AlGaN/AlN Heterostructure for High‐Electron‐Mobility Transistor

Ito

Sakamoto

Isono

et al. 2020

A nitrogen‐polar (N‐polar) AlGaN/AlN high‐electron‐mobility transistor (HEMT) is proposed, and the generation of a 2D electron gas (2DEG) is simulated. The band diagram of N‐polar (Al)GaN/AlN shows the generation of the 2DEG, whereas that of the conventional metal‐polar (Al)GaN/AlN structure shows the generation of a 2D hole gas. Furthermore, the concentration of the 2DEG is considerably high even when the (Al)GaN layer is as thin as a few nanometers. N‐polar AlGaN/AlN is grown on sapphire substrates with a misorientation angle of 2°; furthermore, atomic force microscope measurements in a range of 5 × 5 μm2 demonstrate that the root‐mean‐square value obtained from atomic force microscopy of N‐polar AlGaN is approximately 0.7 nm. N‐polar AlGaN layers with a thickness of approximately 40–60 nm with more than 50% Al content are almost coherently grown on the N‐polar AlN layer with a thickness of approximately 400 nm.

“…This helps reduce the gate–channel distance in HEMTs, and the back barrier provided by the AlGaN layer makes the carrier confinement stronger in comparison with Ga‐polar GaN HEMTs. Successful growth and device application of N‐polar GaN materials have been reported from different groups. In particular, the superior power performance of N‐polar GaN HEMTs compared with their Ga‐polar counterparts has been demonstrated in high frequencies over 90 GHz .…”

Section: Introductionmentioning

confidence: 99%

“…Successful growth and device application of N‐polar GaN materials have been reported from different groups. In particular, the superior power performance of N‐polar GaN HEMTs compared with their Ga‐polar counterparts has been demonstrated in high frequencies over 90 GHz . To exploit the full potential of N‐polar GaN, we need to clarify its material properties, particularly ones that are different from those obtained by Ga‐polar materials.…”

Section: Introductionmentioning

confidence: 99%

Effective Schottky Barrier Height Model for N‐Polar and Ga‐Polar GaN by Polarization‐Induced Surface Charges with Finite Thickness

Suemitsu

Makabe

2020

The nitrogen‐polar GaN material system is a promising candidate for high‐frequency applications, such as those in the millimeter‐wave range. Schottky barrier height is one of fundamental parameters necessary for device applications of N‐polar GaN. Herein, vertical Schottky diodes for both N‐polar and Ga‐polar GaN are prepared, and it is found through experiments that the barrier height of N‐polar GaN is smaller than that of Ga‐polar GaN by 0.21 V. This difference in the barrier height stems from the polarization‐induced surface charge layer of a few angstroms thickness under the surface. Numerical calculation of band profiles suggests that a significant band bending caused by the large amount of polarization charges pushes the conduction band energy downward (upward) in the N‐polar (Ga‐polar) surface depending on the sign of the polarization charges, which results in two different effective Schottky barrier heights. This difference is explained by assuming the polarization‐charge layer thickness of about 5 Å. A simple analytical model to estimate the difference in barrier heights between the two polarities is also proposed.